A Mg-3%Al-1%Zn alloy (AZ31) magnesium alloy plate having a thickness of 0.8 mm (manufactured by Osaka Fuji Corp.) was used as the anode. The chemical composition is shown in **Table 1**. The surface was polished with #600 SiC paper, rinsed with water, and wiped with ethanol. As a cathode material, a part of commercially available WAMB (Aqumo Holdings "Aqumo candle®") [9] was used. Although details are not clarified, it seems to consist of pulp-

thickness of 0.6 mm was used as the current collector of the cathode. As the separator, pulp/ polypropylene nonwoven fabric having a thickness of 0.25 mm was used. These electrodes were piled in the order of current collector/cathode/separator/anode to construct the unit cell, shown in **Figure 3**. The electrode size was 25 × 50 mm except for the separator which had 10 mm longer than others for absorbing water. A Pt wire of ϕ 0.6 mm was sandwiched

**AZ31B** 3.03 0.78 0.29 0.021 <0.006 Bal.

**Al Zn Mn Si Fe + Cu + Ni Mg**

, catalyst, graphite, and NaCl [8]. A Cu foil having a

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95

approaches to improve performance are also proposed.

**2. Materials and methods**

based nonwoven fabric containing MnO2

**Table 1.** Chemical composition of the Mg anode.

**Figure 1.** Appearance and structure of type II WAMB. (a) Commercial product (handy LED lamp). (b) Structure.

**Figure 2.** Illuminance of WAMB (stacked cell). Illuminance was measured at 30 cm distance from LED [9].

In this chapter, the discharge performance of WAMB is presented based on our recent research [11–13]. We first describe the discharge behavior of unit cells, following the studies of cell stacking. Factors that affect discharge performance are identified and analyzed. Several approaches to improve performance are also proposed.

#### **2. Materials and methods**

Unlike other primary batteries, Mg batteries can be activated with neutral electrolyte when in use. This ensures a long shelf life, easy-to-use operation, and safe disposal of used batteries. Conventional sea water-activated Mg batteries use metal chloride cathodes [1, 3]. Recent water-activated Mg batteries follow the same principle, with incorporating modern electric and battery technologies. There are roughly two kinds of water-activated batteries. Type I battery consists of Mg anode, air-diffusion cathode, and electrolyte container. An appropriate amount of neutral electrolyte, usually NaCl solution, is injected in use. It is also called Mg-air battery [1, 6, 7]. Type II battery is a stacked structure of unit cells, and a small amount of water (1~2 ml) is injected in use [8]. Type I batteries can generate current densities of around tens

and can be served as small-middle sized generators. Although the capacity of the

cells, suitable for power saving devices like LED. There are several articles about type I battery [1, 6, 7], but technical information is limited for type II battery. Hereafter, type II battery

**Figure 1** shows several WAMB-operated LED lamps and their structure [9]. It is the size of a cigarette lighter, weighs about 20 g. A WAMB contains 3–4 unit cells stacked in a plastic casing. One or two LEDs are connected to the battery terminals. Details of the unit cell will be discussed later. Small amount of water is injected to the bottom of the casing to illuminate LED [10]. In the absence of water, juice and saliva can be used. As water is gradually lost during discharge, its intermittent supply is necessary. **Figure 2** shows the change in LED illuminance with water injection [9]. Comparisons with other illumination sources are mentioned. Each water injection restores illuminance while the intensity gradually disappears. After 6–7 injections, the WAMB cannot generate enough power for the LED and goes out. One WAMB can provide light in about a week, which is sufficient as an emergency illumination source. In addition to its compactness, it does not contain any hazardous substances, which enables safe

is called as water-activated magnesium battery (WAMB) and described in this article.

**Figure 1.** Appearance and structure of type II WAMB. (a) Commercial product (handy LED lamp). (b) Structure.

), it is compact and boosts up easily by stacking unit

of mA/cm2

94 Magnesium Alloys - Selected Issue

type II battery is limited (about 1 mA/cm2

operation and disposal of the used WAMB [8, 9].

A Mg-3%Al-1%Zn alloy (AZ31) magnesium alloy plate having a thickness of 0.8 mm (manufactured by Osaka Fuji Corp.) was used as the anode. The chemical composition is shown in **Table 1**. The surface was polished with #600 SiC paper, rinsed with water, and wiped with ethanol. As a cathode material, a part of commercially available WAMB (Aqumo Holdings "Aqumo candle®") [9] was used. Although details are not clarified, it seems to consist of pulpbased nonwoven fabric containing MnO2 , catalyst, graphite, and NaCl [8]. A Cu foil having a thickness of 0.6 mm was used as the current collector of the cathode. As the separator, pulp/ polypropylene nonwoven fabric having a thickness of 0.25 mm was used. These electrodes were piled in the order of current collector/cathode/separator/anode to construct the unit cell, shown in **Figure 3**. The electrode size was 25 × 50 mm except for the separator which had 10 mm longer than others for absorbing water. A Pt wire of ϕ 0.6 mm was sandwiched

**Table 1.** Chemical composition of the Mg anode.

scanned frequency was changed from 100 kHz to 1 Hz using an electrochemical apparatus (Solartron Analytical, Modulab Xm). The obtained spectrum was analyzed by curve fitting software (Scribner ZView). When *V*cell fell below the terminal voltage of 0.7 V in the unit cell and 2.5 V in the stacked cell, the discharge test was interrupted. After that, the same amount of water was injected, and the test was restarted. When *V*cell decreased to the terminal voltage within 1 h after water injection, the discharge test was terminated, and cumulative discharge

*d* × *S* × *t*

cell weight (g), and *L* is the total amount of injecting water (g). *M* does not include the weight of the casing. For the calculation of Eq. (1), *L* is fixed as 1.5 g for a unit cell and 6 g for a stacked

After the test, the discharged cells were disassembled, and the appearance of the electrodes was examined. The consumption of Mg anode *ΔW* (g) was measured after removing the dis-

*d* × *S*/*I*

(mA) was calculated with *ΔW*, assuming Mg is dissolved with the ionic valency of 2.

**Figure 4** shows the polarization curve of the unit cell with a water injection of 0.8 ml [13].

was about 1.4 to 1.5 V. By stacking four cells in series, *V*cell reaches 5.6 ~ 6 V, which is sufficient

**Figure 5(a)** shows the discharge curve of WAMB unit cell at the initial injection of water [11]. The amount of water was changed from 0.4 to 0.8 ml. The unit cell did not hold more than 1 ml of water. *V*cell was kept at about 1.4 V for a certain period and declined rapidly. The larger the amount of water, the longer the discharge time was obtained. **Figure 5(b)** shows the dependence of the discharge time on the amount of water. A relationship expressed by a quadratic

with *i*

*total*/24.31 = 2206 *W*/*t*

d of 15 mA/cm2

(Wh/kg).

*total* (3)

. As described later, the

(<10 mA), and *V*cell

), *M* is the

97

*total*/(*M* + *L*) (1)

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*grav*. × 100 (2)

The discharge capacity was evaluated by the gravimetric energy density *E*g

cell, referring the result of the weight increase after the discharge test.

*grav*. = 2 × 96,500 × *W*/*t*

current range used in the constant discharge test was less than 1 mA/cm2

function can be seen. Hereafter, the injection of water was fixed to 0.8 ml.

to illuminate a small LED with a forward voltage of 2.5–3.5 V.

**3.2. Discharge behavior of unit cell with water injection**

*V*cell.avg is the average of the monitored *V*cell, *S* is the area of the electrode (= 12.5 cm2

charged product by a wire brush. Current efficiency *CE* (%) was calculated by Eq. (2).

time *t*

*Igrav*.

**3. Results**

*I*

total (h) was calculated.

*Eg* = *Vcell*.*avg* × *i*

*CE* = *i*

**3.1. Initial discharge capacity of unit cell**

The power density reached about 10 mW/cm2

**Figure 3.** Experimental setup of WAMB discharge study. (a) Structure of the unit cell. (b) Setup of the unit cell. (c) Setup of the stacked cell.

between the separator and the anode and used as a reference electrode. To avoid direct contact with the Pt wire, a small piece of the separator was attached to the anode side. Two Cu sheets were attached to the outside of the unit cell and used as terminals. The assembly was further cramped with two acrylic plates under a pressure of 6 N. Stacked cells were prepared by superimposing four unit cells in series and inserted into a commercial WAMB casing. Tap water (Sagami river system, Samukawa water purifying plant) was used to activate WAMB by injecting them into the bottom of the separator. The amount of water was varied from 0.4 to 0.8 ml in a unit cell and 2 ml in a stacked cell.

The initial discharge capacity of WAMB was analyzed with a unit cell by measuring a potentiodynamic polarization curve. After 20 min of water injection, the cell voltage *V*cell and the discharge current density *i* d were monitored at a scanning rate of 1 mV/s.

A constant current discharge test of 0.24 mA/cm2 in the unit cell and 0.08–0.80 mA/cm2 in the stacked cell was performed. The anode potential *E*a , the cathode potential *E*c , *V*cell, and electrochemical impedance spectroscopy (EIS) of the anode, cathode, and cell were independently measured in the unit cell. In the stacked cell, *V*cell and the cell impedance were monitored. The EIS was performed in a current-controlled mode with an amplitude of 1% of *i* d, and the scanned frequency was changed from 100 kHz to 1 Hz using an electrochemical apparatus (Solartron Analytical, Modulab Xm). The obtained spectrum was analyzed by curve fitting software (Scribner ZView). When *V*cell fell below the terminal voltage of 0.7 V in the unit cell and 2.5 V in the stacked cell, the discharge test was interrupted. After that, the same amount of water was injected, and the test was restarted. When *V*cell decreased to the terminal voltage within 1 h after water injection, the discharge test was terminated, and cumulative discharge time *t* total (h) was calculated.

The discharge capacity was evaluated by the gravimetric energy density *E*g (Wh/kg).

$$E\_g = V\_{cell,avg} \times i\_d \times \mathbb{S} \times t\_{total} / (\text{M} + \text{L}) \tag{1}$$

*V*cell.avg is the average of the monitored *V*cell, *S* is the area of the electrode (= 12.5 cm2 ), *M* is the cell weight (g), and *L* is the total amount of injecting water (g). *M* does not include the weight of the casing. For the calculation of Eq. (1), *L* is fixed as 1.5 g for a unit cell and 6 g for a stacked cell, referring the result of the weight increase after the discharge test.

After the test, the discharged cells were disassembled, and the appearance of the electrodes was examined. The consumption of Mg anode *ΔW* (g) was measured after removing the discharged product by a wire brush. Current efficiency *CE* (%) was calculated by Eq. (2).

$$\text{CE} = i\_d \times \text{S} / I\_{gum} \times 100 \tag{2}$$

*Igrav*. (mA) was calculated with *ΔW*, assuming Mg is dissolved with the ionic valency of 2.

 *I grav*. = 2 × 96,500 × *W*/*t total*/24.31 = 2206 *W*/*t total* (3)

#### **3. Results**

between the separator and the anode and used as a reference electrode. To avoid direct contact with the Pt wire, a small piece of the separator was attached to the anode side. Two Cu sheets were attached to the outside of the unit cell and used as terminals. The assembly was further cramped with two acrylic plates under a pressure of 6 N. Stacked cells were prepared by superimposing four unit cells in series and inserted into a commercial WAMB casing. Tap water (Sagami river system, Samukawa water purifying plant) was used to activate WAMB by injecting them into the bottom of the separator. The amount of water was varied from 0.4

**Figure 3.** Experimental setup of WAMB discharge study. (a) Structure of the unit cell. (b) Setup of the unit cell. (c) Setup

The initial discharge capacity of WAMB was analyzed with a unit cell by measuring a potentiodynamic polarization curve. After 20 min of water injection, the cell voltage *V*cell and the

chemical impedance spectroscopy (EIS) of the anode, cathode, and cell were independently measured in the unit cell. In the stacked cell, *V*cell and the cell impedance were monitored.

The EIS was performed in a current-controlled mode with an amplitude of 1% of *i*

d were monitored at a scanning rate of 1 mV/s.

in the unit cell and 0.08–0.80 mA/cm2

, the cathode potential *E*c

in the

d, and the

, *V*cell, and electro-

to 0.8 ml in a unit cell and 2 ml in a stacked cell.

A constant current discharge test of 0.24 mA/cm2

stacked cell was performed. The anode potential *E*a

discharge current density *i*

of the stacked cell.

96 Magnesium Alloys - Selected Issue

#### **3.1. Initial discharge capacity of unit cell**

**Figure 4** shows the polarization curve of the unit cell with a water injection of 0.8 ml [13]. The power density reached about 10 mW/cm2 with *i* d of 15 mA/cm2 . As described later, the current range used in the constant discharge test was less than 1 mA/cm2 (<10 mA), and *V*cell was about 1.4 to 1.5 V. By stacking four cells in series, *V*cell reaches 5.6 ~ 6 V, which is sufficient to illuminate a small LED with a forward voltage of 2.5–3.5 V.

#### **3.2. Discharge behavior of unit cell with water injection**

**Figure 5(a)** shows the discharge curve of WAMB unit cell at the initial injection of water [11]. The amount of water was changed from 0.4 to 0.8 ml. The unit cell did not hold more than 1 ml of water. *V*cell was kept at about 1.4 V for a certain period and declined rapidly. The larger the amount of water, the longer the discharge time was obtained. **Figure 5(b)** shows the dependence of the discharge time on the amount of water. A relationship expressed by a quadratic function can be seen. Hereafter, the injection of water was fixed to 0.8 ml.

**Figure 7** exhibits the change of Nyquist diagram of the anode, cathode, and unit cell with different injection cycles. The Mg anode drew a depressed capacitive semicircle, followed by an inductive loop in the low frequency region. In general, the size of trajectory increased with injection cycles. The impedance of the cathode was negligible in the first cycle but increased thereafter. Furthermore, a Warburg impedance was recognized in the low frequency region. There are several EIS studies on the corrosion of Mg or Mg alloys [14–16], but the application to neither Mg battery nor Mg anodized in NaCl solution is rare. Then, referring the equivalent electric circuit of pure Mg corroding in NaCl solution [14], a circuit for the WAMB anode is

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proposed in **Figure 8(a)** [13].

*L*a

MnO2

*CPE*c

*R*s.a: Solution resistance at the anode.

electrode of Zn-MnO2

*R*s.c: Solution resistance at the cathode.

*R*1a, *R*2a: Resistance associated with the dissolution of the anode.

: Inductance associated with the dissolution of the anode.

*R*ct.c: Resistance associated with the reduction of MnO2

*R*3a: Resistance associated with the hydrogen gas evolution on the anode.

battery [17, 18].

**Figure 6.** Discharge behavior of WAMB (unit cell) at a current density of 0.24 mA/cm2

with time under different discharge cycle. (b) Change of discharge time and power with the discharge cycle.

*CPE*1a: Constant phase element associated with the discharge product on the anode.

*CPE*2a: Constant phase element associated with the electrochemical double layer of the anode.

As for the WAMB cathode, an equivalent circuit was expressed in **Figure 8(b)**, referring the

: Constant phase element associated with the electrochemical double layer of the cathode.

.

[13]. (a) Change of *E*a

, *E*c , and *V*cell

**Figure 4.** Initial discharge performance of WAMB (unit cell) [13].

**Figure 5.** Discharge behavior of WAMB (unit cell) at the first injection of water at a current density of 0.24 mA/cm2 [11]. (a) Discharge curves of WAMB. (b) Dependence of discharged period on the water content.

**Figure 6** presents the discharge behavior of WAMB with different discharge cycles [13]. *E*a kept constant about −1.6 V regardless of discharge time and cycles, and *E*c changed every discharge cycle. *V*cell followed the change in *E*c . The discharge time was gradually shortened by injection cycles shown in **Figure 6(b)**. It was possible to regenerate WAMB up to 8 times of water injection. *t* total was calculated to be 51.7 h.

**Figure 7** exhibits the change of Nyquist diagram of the anode, cathode, and unit cell with different injection cycles. The Mg anode drew a depressed capacitive semicircle, followed by an inductive loop in the low frequency region. In general, the size of trajectory increased with injection cycles. The impedance of the cathode was negligible in the first cycle but increased thereafter. Furthermore, a Warburg impedance was recognized in the low frequency region.

There are several EIS studies on the corrosion of Mg or Mg alloys [14–16], but the application to neither Mg battery nor Mg anodized in NaCl solution is rare. Then, referring the equivalent electric circuit of pure Mg corroding in NaCl solution [14], a circuit for the WAMB anode is proposed in **Figure 8(a)** [13].

*R*s.a: Solution resistance at the anode.

*R*1a, *R*2a: Resistance associated with the dissolution of the anode.

*R*3a: Resistance associated with the hydrogen gas evolution on the anode.

*CPE*1a: Constant phase element associated with the discharge product on the anode.

*CPE*2a: Constant phase element associated with the electrochemical double layer of the anode.

*L*a : Inductance associated with the dissolution of the anode.

As for the WAMB cathode, an equivalent circuit was expressed in **Figure 8(b)**, referring the MnO2 electrode of Zn-MnO2 battery [17, 18].

*R*s.c: Solution resistance at the cathode.

**Figure 6** presents the discharge behavior of WAMB with different discharge cycles [13]. *E*a

**Figure 5.** Discharge behavior of WAMB (unit cell) at the first injection of water at a current density of 0.24 mA/cm2

by injection cycles shown in **Figure 6(b)**. It was possible to regenerate WAMB up to 8 times of

changed every

[11].

. The discharge time was gradually shortened

kept constant about −1.6 V regardless of discharge time and cycles, and *E*c

(a) Discharge curves of WAMB. (b) Dependence of discharged period on the water content.

total was calculated to be 51.7 h.

discharge cycle. *V*cell followed the change in *E*c

**Figure 4.** Initial discharge performance of WAMB (unit cell) [13].

98 Magnesium Alloys - Selected Issue

water injection. *t*

*R*ct.c: Resistance associated with the reduction of MnO2 .

*CPE*c : Constant phase element associated with the electrochemical double layer of the cathode.

**Figure 6.** Discharge behavior of WAMB (unit cell) at a current density of 0.24 mA/cm2 [13]. (a) Change of *E*a , *E*c , and *V*cell with time under different discharge cycle. (b) Change of discharge time and power with the discharge cycle.

*W*c : Warburg impedance of the cathode (open).

Here, constant phase element (CPE) [19] such as *CPE*1a, *CPE*2a, and *CPE*c was employed instead of capacitance to reflect the inhomogeneity of the electrode surface.

The curve fitting of the experimental data of each electrode was performed using simulation software. The results are shown in **Table 2** and superimposed on the experimental data in **Figure 9**. The proposed circuit approximated the impedance spectrum, showing the depressed capacitive semicircle, the presence of the inductive loop at the anode, and the Warburg impedance at the cathode. Curioni et al. [15] reported that the reciprocal of (*R*1a + *R*2a) shows a good correlation with the corrosion rate of pure Mg obtained from the hydrogen evolution reaction. Then, the parameter (*R*1a + *R*2a) is replaced with *R*ct.a, the sum of *R*ct.a and *R*ct.c. is replaced with

**Table 2.** Parameters of equivalent circuit shown in **Figure 8** to simulate the response of WAMB discharged at 0.24 mA/cm2

**Figure 8.** Electrical equivalent circuits for the WAMB anode and the WAMB cathode. (a) Anode. (b) Cathode.

First 4.47 3E-07 23.3 27.2 3.74E-03 0.284 2.01E-04 0.84 4.17 Second 11.3 0.13 36.1 34.8 1.93E-03 0.424 9.13E-06 1.14 6.96 Sixth 3.05 3.72 36.5 58.7 4.01E-04 0.733 2.85E-06 1.25 12.9

Rs.c (Ω) Rct.c (Ω) CPEc-T (-) CPEc-P (-) Wc-R (-) Wc-T (-) Wc-P (-)

First 12.3 1.71 8.99E-06 0.956 9.7 0.702 0.608 Second 11.6 10.3 2.90E-05 0.744 17.6 1.053 0.744 Sixth 2.24 25.7 4.49E-04 0.628 10.8 0.393 0.628

Rs.a (Ω) R1a (Ω) R2a(Ω) R3a (Ω) CPE1a-T (-) CPE1a-(-) CPE2a-T (-) CPE2a-P (-) La

water content in the cell. However, at the sixth water injection, *V*cell reached the terminal volt-

stage than the anode. After that, both values increased with the number of water injections. In

**Figure 11** presents the potentiodynamic polarization curves of the cathode before and after the discharge test. The cathode current decreased significantly after the test, suggesting a decrease in discharge capacity. In case of the anode, a white-gray discharge product was observed. After removing them, the thickness of the Mg plate was partly diminished, but the shape remained.

started to increase. In case of *R*ct, the cathode took a smaller value at the initial

at each electrode can be obtained

(Ωs)

101

.

and *R*ct of the anode, cathode, and cell at different

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increases with the discharge time, suggesting a decrease in the

*R*ct.cell, and discussed herewith. These parameters and *R*s

the sixth water injection, *R*ct.a and *R*ct.c reached the same level.

roughly from the trajectory shown in **Figure 9** [14].

**Figure 10** plots the time dependence of *R*s

injection cycles. In general, *R*s

age before *R*s

**Anode**

**Cathode**

**Figure 7.** Nyquist diagrams of the anode, cathode, and cell of WAMB unit cell after (a) first, (b) second, and (c) sixth cycles of water injection [13].

**Figure 8.** Electrical equivalent circuits for the WAMB anode and the WAMB cathode. (a) Anode. (b) Cathode.

*W*c

100 Magnesium Alloys - Selected Issue

: Warburg impedance of the cathode (open).

Here, constant phase element (CPE) [19] such as *CPE*1a, *CPE*2a, and *CPE*c

**Figure 7.** Nyquist diagrams of the anode, cathode, and cell of WAMB unit cell after (a) first, (b) second, and (c) sixth

cycles of water injection [13].

of capacitance to reflect the inhomogeneity of the electrode surface.

was employed instead

**Table 2.** Parameters of equivalent circuit shown in **Figure 8** to simulate the response of WAMB discharged at 0.24 mA/cm2 .

The curve fitting of the experimental data of each electrode was performed using simulation software. The results are shown in **Table 2** and superimposed on the experimental data in **Figure 9**. The proposed circuit approximated the impedance spectrum, showing the depressed capacitive semicircle, the presence of the inductive loop at the anode, and the Warburg impedance at the cathode. Curioni et al. [15] reported that the reciprocal of (*R*1a + *R*2a) shows a good correlation with the corrosion rate of pure Mg obtained from the hydrogen evolution reaction. Then, the parameter (*R*1a + *R*2a) is replaced with *R*ct.a, the sum of *R*ct.a and *R*ct.c. is replaced with *R*ct.cell, and discussed herewith. These parameters and *R*s at each electrode can be obtained roughly from the trajectory shown in **Figure 9** [14].

**Figure 10** plots the time dependence of *R*s and *R*ct of the anode, cathode, and cell at different injection cycles. In general, *R*s increases with the discharge time, suggesting a decrease in the water content in the cell. However, at the sixth water injection, *V*cell reached the terminal voltage before *R*s started to increase. In case of *R*ct, the cathode took a smaller value at the initial stage than the anode. After that, both values increased with the number of water injections. In the sixth water injection, *R*ct.a and *R*ct.c reached the same level.

**Figure 11** presents the potentiodynamic polarization curves of the cathode before and after the discharge test. The cathode current decreased significantly after the test, suggesting a decrease in discharge capacity. In case of the anode, a white-gray discharge product was observed. After removing them, the thickness of the Mg plate was partly diminished, but the shape remained.

**Figure 9.** Comparison between the calculated and the measured impedance spectra of WAMB. (a) Anode after 6th cycle. (b) Cathode after 6th cycle.

**Figure 10.** Time dependence of *R*s and *R*ct of the WAMB cathode and the WAMB anode and their combined cell (unit cell) at a current density of 0.24 mA/cm2 .

#### **3.3. Discharge behavior of stacked cell with water injection**

Time variation of *V*cell of the stacked WAMB at a current density of 0.24 mA/cm2 was presented in **Figure 12**. As expected, *V*cell has quadrupled by stacking four unit cells. The behavior of *V*cell was basically the same as that of the unit cell. Total discharge time reached 95.6 h, which was about twice that of the unit cell. **Figure 13** shows the Nyquist diagram of the stacked cell after the first, third, and fifth water injections. The spectra drew depressed capacitive semicircles up to the fourth water injection. The diameter (= *R*ct.cell) was initially large, but gradually became smaller. In the fifth water injection, a Warburg impedance appeared in the low frequency region. *R*s. cell and *R*ct.cell at the terminal voltage were 24 and 288 Ω, respectively,

. (a) Discharge curves. (b)

**Figure 12.** Discharge behavior of the WAMB stacked cell at a current density of 0.24 mA/cm2

**Figure 11.** Potentiodynamic polarization curves of the WAMB cathode (unit cell) before discharging and after six cycles

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103

which were about four times the value in the unit cell.

Change of discharge time and power with discharge cycle.

of discharging.

**Figure 11.** Potentiodynamic polarization curves of the WAMB cathode (unit cell) before discharging and after six cycles of discharging.

**Figure 12.** Discharge behavior of the WAMB stacked cell at a current density of 0.24 mA/cm2 . (a) Discharge curves. (b) Change of discharge time and power with discharge cycle.

**3.3. Discharge behavior of stacked cell with water injection**

.

(b) Cathode after 6th cycle.

102 Magnesium Alloys - Selected Issue

**Figure 10.** Time dependence of *R*s

at a current density of 0.24 mA/cm2

Time variation of *V*cell of the stacked WAMB at a current density of 0.24 mA/cm2

in **Figure 12**. As expected, *V*cell has quadrupled by stacking four unit cells. The behavior of *V*cell was basically the same as that of the unit cell. Total discharge time reached 95.6 h, which was about twice that of the unit cell. **Figure 13** shows the Nyquist diagram of the stacked

and *R*ct of the WAMB cathode and the WAMB anode and their combined cell (unit cell)

**Figure 9.** Comparison between the calculated and the measured impedance spectra of WAMB. (a) Anode after 6th cycle.

was presented

cell after the first, third, and fifth water injections. The spectra drew depressed capacitive semicircles up to the fourth water injection. The diameter (= *R*ct.cell) was initially large, but gradually became smaller. In the fifth water injection, a Warburg impedance appeared in the low frequency region. *R*s. cell and *R*ct.cell at the terminal voltage were 24 and 288 Ω, respectively, which were about four times the value in the unit cell.

**Figure 13.** Impedance spectra of WAMB (stacked cell) at the termination voltage after different discharging cycles.

was disappeared except for the *d4*, which was located on the outermost side of the stacked

Discharging of WAMB begins with feeding water to the cathodes via separators. Water dissolves NaCl in the cathode material and creates an ionic path between the electrodes. The cell

Anode:Mg Mg2+ + 2e (4)

O + 2e Mn2

O Mn2

O3 + Mg (OH)

and the current efficiency *CE* of the unit, and the

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. It is noticeable that *CE*

O3 + 2OH− (5)

2 (6)

d of 0.48 mA/cm2

cell. The surface of the Cu current collector attached to the Mg anodes was blackened.

reached its maximum of 71 Wh/kg at *i*

**Figure 15** illustrates the energy density *E*g

was greatly decreased by stacking the unit cells.

**Figure 15.** Specific energy and current efficiency of WAMB [13].

**4.1. Discharge behavior of WAMB unit cell**

Cathode:2MnO2 + H2

Total:Mg + 2MnO2 + H2

stacked cell. *E*g

**4. Discussions**

reactions are expressed as:

**Figure 14.** Appearance of WAMB (stacked cell) at a current density of 0.24 mA/cm2 after six cycles of discharge [13].

#### **3.4. Discharge capacity and current efficiency**

The appearance of the electrode after the discharge test was shown in **Figure 14**. They are: (1) current collector, (2) cathode, (3) separator, and (4) anode before/after the removal of the discharge product. The alphabetical suffix indicates the layer of the stacked cell. Thus, the first unit cell was stacked in the order of *[a1/a2/a3/b4]*, following the second cell as *[b1/b2/b3/ b4]*, the third as *[c1/c2/c3/c4]*, and the fourth as *[d1/d2/d3/d4]*. At the anode, a white and gray discharge product was visible. After the removal of the product, more than half of the anode

**Figure 15.** Specific energy and current efficiency of WAMB [13].

was disappeared except for the *d4*, which was located on the outermost side of the stacked cell. The surface of the Cu current collector attached to the Mg anodes was blackened.

**Figure 15** illustrates the energy density *E*g and the current efficiency *CE* of the unit, and the stacked cell. *E*g reached its maximum of 71 Wh/kg at *i* d of 0.48 mA/cm2 . It is noticeable that *CE* was greatly decreased by stacking the unit cells.

#### **4. Discussions**

**3.4. Discharge capacity and current efficiency**

104 Magnesium Alloys - Selected Issue

**Figure 14.** Appearance of WAMB (stacked cell) at a current density of 0.24 mA/cm2

The appearance of the electrode after the discharge test was shown in **Figure 14**. They are: (1) current collector, (2) cathode, (3) separator, and (4) anode before/after the removal of the discharge product. The alphabetical suffix indicates the layer of the stacked cell. Thus, the first unit cell was stacked in the order of *[a1/a2/a3/b4]*, following the second cell as *[b1/b2/b3/ b4]*, the third as *[c1/c2/c3/c4]*, and the fourth as *[d1/d2/d3/d4]*. At the anode, a white and gray discharge product was visible. After the removal of the product, more than half of the anode

after six cycles of discharge [13].

**Figure 13.** Impedance spectra of WAMB (stacked cell) at the termination voltage after different discharging cycles.

#### **4.1. Discharge behavior of WAMB unit cell**

Discharging of WAMB begins with feeding water to the cathodes via separators. Water dissolves NaCl in the cathode material and creates an ionic path between the electrodes. The cell reactions are expressed as:

$$\text{Anode:}\,\text{Mg}\xrightarrow{\Delta}\text{Mg}^{2+}+\text{2e}\tag{4}$$

$$\text{Cathode:}\,2\text{MnO}\_2 + \text{H}\_2\text{O} + 2\text{e} \xrightarrow{\Delta} \text{Mn}\_2\text{O}\_3 + 2\text{OH}^-\tag{5}$$

$$\text{Total:}\,\text{Mg} + 2\,\text{MnO}\_2 + \text{H}\_2\text{O} \xrightarrow{} \text{Mn}\_2\text{O}\_3 + \text{Mg}\,\text{(OH)}\_2\tag{6}$$

Eq. (6) is an exothermic reaction. Enthalpy change −*ΔH* was calculated to be 484 kJ/mol [20]. Since WAMB is an open structure, the injected water evaporates gradually due to heat. Water was also consumed by Eq. (5) to form Mg(OH)2 . Therefore, intermittent water injection is indispensable. The discharge behavior of WAMB depends on the dissolution of the Mg anode and the reduction of MnO2 in the cathode. As shown in **Figure 6**, *E*a was stable regardless of the discharge time and the cycle of water injection. In contrast, *E*c varied with discharge conditions that affected *V*cell. All these facts suggest that WAMB is the cathode-controlled system. The decline in the cathode capacity after the discharge shown in **Figure 11** confirms such an assumption.

is illustrated in **Figure 17** [13]. During water injection, most of the water penetrates from the separator into the cathode material osmotically. However, some of them may penetrate small gaps between the Cu collector and the Mg anode. As a result, a galvanic cell having Mg as anode and Cu as cathode is formed, and the former is corroded preferentially. In this case, the anode reaction is represented by Eq. (4) and the cathode reaction is by Eq. (7). In

shown in Section (a) of **Figure 17**. However, the portion where the galvanic corrosion is being occurred forms the closed circuit shown in section (b), and the Mg anode does not contribute to the discharge performance and is wasted by corrosion. The fact that the Mg anode *d4* in **Figure 14** is less susceptible to corrosion than other anodes corroborates the absence of such galvanic corrosion. In addition, galvanic corrosion results in forming the corrosion products between the anode and the Cu collector, causing IR drop and reducing *V*cell. Cu collectors are also oxidized (see **Figure 14**—(1)) to increase the contact resistance. To reduce the loss due to galvanic corrosion and maximize the discharge capacity of WAMB, the choice of higher *i*

is less than 100 Wh/kg [25], dramatic improvement of WAMB may not be feasible. Still,

) and generates electricity as

Discharge Behavior of Water-Activated Magnesium Battery

http://dx.doi.org/10.5772/intechopen.79789

of WAMB is 71 kWh/kg, which

battery (154 Wh/kg) or Zn-air battery (415 Wh/kg) [25]. Since

battery or the reserved battery technologies [2, 3], of which

d up

107

principle, WAMB establishes the flows of electron and ions (OH−

is recommended.

**4.3. Technical challenge and future applications of WAMB**

Based on current research, the gravimetric energy density *E*g

there are several rooms to enhance the capabilities of WAMB. **A.** Design to eliminate galvanic corrosion in the stacked cell. **B.** Catalyst for enhancing the ability of the cathode [26–30].

**Figure 16.** Schematic diagram of the time variation of electrochemical parameters in WAMB [13].

**C.** Mg alloy for improving discharge capacity [31–33].

**D.** Selection of electrolyte and additive [34–37].

to around 0.5 mA/cm2

*E*g

is inferior to Zn-alkaline MnO2

WAMB inherits the dry Mg-MnO2

Based on the EIS result shown in **Figure 10**, the anode and cathode behaviors during the discharge can be schematically interpreted as **Figure 16**. At the initial stage, *R*ct.c is smaller than *R*ct.a and does not affect the discharge behavior. As time elapses, *R*s.cell gradually increases due to the depletion of water and stops the discharge reaction. After repeated water injection, the initial *R*ct.c and *R*ct.a tend to show larger values than the preceding cycle. This suggests a decrease in the conductive MnO2 in the cathode and a decrease in the reaction area of the anode due to the accumulation of Mg(OH)2 . In addition, a decrease in *E*c lowers *V*cell. At the end of the period, even if the water amount is sufficient (small *R*s.cell), the gap between *V*cell and the terminal voltage becomes small, so the discharge ends in a short time.

At the terminal stage, the Warburg impedance appeared in the cathode of **Figure 7(b)** and **(c)**. Qu [18] discussed the existence of Warburg impedance appearing at the MnO2 cathode of an alkaline Mn battery system, in terms of the volume expansion of the cathode during discharge. Such expansion prevents the proton diffusion of the entire lattice of MnO2 , which is an important rate-determining step. When the discharge exceeds 50%, the localized Jahn-Teller deformation begins to occur and the proton diffusion coefficient decreases. Though such volume expansion was not recognizable in the present system, structural analysis of the cathode using XRD would provide detailed mechanism of the degradation of WAMB.

#### **4.2. Discharge behavior of WAMB stacked cell**

In general, the discharge behavior of the stacked cell follows that of the unit cell. It is worth noting that *t* total almost doubled by stacking. The exact cause is not clear, but it may be related to the generation of the voluminous Mg(OH)2 which is 73.5% more molar volume than Mg metal [21]. Such expansion compresses the electrodes in the casing, improves mutual contact, and would lead to the prolongation of the discharge time.

On the other hand, *CE* was sharply decreased in the stacked cell. *CE* of 64% obtained at the unit cell is within the range of 55–66%, which is reported in the corrosion of Mg [22]. The reason that the *CE* of Mg is less than 100% in Mg is closely related to the hydrogen gas evolution reaction that occurs simultaneously even if Mg is anodically polarized [23, 24].

$$2\mathrm{H\_2O} + 2\mathrm{e^-} \to \mathrm{H\_2} + 2\mathrm{OH^-} \tag{7}$$

However, the fact is that *CE* as low as 20% in the stacked cell cannot be explained in this context. The reason for this is interpreted by galvanic corrosion by the Cu current collector, which is illustrated in **Figure 17** [13]. During water injection, most of the water penetrates from the separator into the cathode material osmotically. However, some of them may penetrate small gaps between the Cu collector and the Mg anode. As a result, a galvanic cell having Mg as anode and Cu as cathode is formed, and the former is corroded preferentially. In this case, the anode reaction is represented by Eq. (4) and the cathode reaction is by Eq. (7). In principle, WAMB establishes the flows of electron and ions (OH− ) and generates electricity as shown in Section (a) of **Figure 17**. However, the portion where the galvanic corrosion is being occurred forms the closed circuit shown in section (b), and the Mg anode does not contribute to the discharge performance and is wasted by corrosion. The fact that the Mg anode *d4* in **Figure 14** is less susceptible to corrosion than other anodes corroborates the absence of such galvanic corrosion. In addition, galvanic corrosion results in forming the corrosion products between the anode and the Cu collector, causing IR drop and reducing *V*cell. Cu collectors are also oxidized (see **Figure 14**—(1)) to increase the contact resistance. To reduce the loss due to galvanic corrosion and maximize the discharge capacity of WAMB, the choice of higher *i* d up to around 0.5 mA/cm2 is recommended.

#### **4.3. Technical challenge and future applications of WAMB**

Eq. (6) is an exothermic reaction. Enthalpy change −*ΔH* was calculated to be 484 kJ/mol [20]. Since WAMB is an open structure, the injected water evaporates gradually due to heat. Water

indispensable. The discharge behavior of WAMB depends on the dissolution of the Mg anode

tions that affected *V*cell. All these facts suggest that WAMB is the cathode-controlled system. The decline in the cathode capacity after the discharge shown in **Figure 11** confirms such an

Based on the EIS result shown in **Figure 10**, the anode and cathode behaviors during the discharge can be schematically interpreted as **Figure 16**. At the initial stage, *R*ct.c is smaller than *R*ct.a and does not affect the discharge behavior. As time elapses, *R*s.cell gradually increases due to the depletion of water and stops the discharge reaction. After repeated water injection, the initial *R*ct.c and *R*ct.a tend to show larger values than the preceding cycle. This suggests a

end of the period, even if the water amount is sufficient (small *R*s.cell), the gap between *V*cell and

At the terminal stage, the Warburg impedance appeared in the cathode of **Figure 7(b)** and

of an alkaline Mn battery system, in terms of the volume expansion of the cathode during

is an important rate-determining step. When the discharge exceeds 50%, the localized Jahn-Teller deformation begins to occur and the proton diffusion coefficient decreases. Though such volume expansion was not recognizable in the present system, structural analysis of the

In general, the discharge behavior of the stacked cell follows that of the unit cell. It is worth

metal [21]. Such expansion compresses the electrodes in the casing, improves mutual contact,

On the other hand, *CE* was sharply decreased in the stacked cell. *CE* of 64% obtained at the unit cell is within the range of 55–66%, which is reported in the corrosion of Mg [22]. The reason that the *CE* of Mg is less than 100% in Mg is closely related to the hydrogen gas evolution

However, the fact is that *CE* as low as 20% in the stacked cell cannot be explained in this context. The reason for this is interpreted by galvanic corrosion by the Cu current collector, which

reaction that occurs simultaneously even if Mg is anodically polarized [23, 24].

total almost doubled by stacking. The exact cause is not clear, but it may be related

**(c)**. Qu [18] discussed the existence of Warburg impedance appearing at the MnO2

discharge. Such expansion prevents the proton diffusion of the entire lattice of MnO2

cathode using XRD would provide detailed mechanism of the degradation of WAMB.

the terminal voltage becomes small, so the discharge ends in a short time.

in the cathode. As shown in **Figure 6**, *E*a

. Therefore, intermittent water injection is

in the cathode and a decrease in the reaction area of the

which is 73.5% more molar volume than Mg

O + 2e H2 + 2OH− (7)

. In addition, a decrease in *E*c

was stable regardless of

lowers *V*cell. At the

cathode

, which

varied with discharge condi-

was also consumed by Eq. (5) to form Mg(OH)2

the discharge time and the cycle of water injection. In contrast, *E*c

and the reduction of MnO2

106 Magnesium Alloys - Selected Issue

decrease in the conductive MnO2

anode due to the accumulation of Mg(OH)2

**4.2. Discharge behavior of WAMB stacked cell**

to the generation of the voluminous Mg(OH)2

2H2

and would lead to the prolongation of the discharge time.

assumption.

noting that *t*

Based on current research, the gravimetric energy density *E*g of WAMB is 71 kWh/kg, which is inferior to Zn-alkaline MnO2 battery (154 Wh/kg) or Zn-air battery (415 Wh/kg) [25]. Since WAMB inherits the dry Mg-MnO2 battery or the reserved battery technologies [2, 3], of which *E*g is less than 100 Wh/kg [25], dramatic improvement of WAMB may not be feasible. Still, there are several rooms to enhance the capabilities of WAMB.

**Figure 16.** Schematic diagram of the time variation of electrochemical parameters in WAMB [13].

They are briefly commented as follows. Several studies conducted in type I water-activated Mg battery are also useful for type II WAMB. In addition, we performed some experimental trials that are summarized in **Table 3**. The relative increase in *t*total compared to the standard condition was used as an index of improvement.

#### *4.3.1. Design for eliminating galvanic corrosion in the stacked cell*

The galvanic corrosion occurs in the condition of stacking unit cells, and it seems that the penetration water in the gap between the anode and the Cu collector is the main cause. It is conceivable to separate the unit cells and connect them outside the casing to avoid the galvanic contact. Although it is technically possible, the structure becomes complicated. A solution is to bond the electrodes using conductive tape to seal the gap. Although it induces contact resistance to decrease *V*cell, it is effective to eliminate the galvanic corrosion and improve the *CE*. With this configuration, a 150% increase in *t* total was possible in our preliminary trials.

by adding specific alloying elements such as Li [31], Ca [32], Pb [33] to Mg-Al alloys. As shown in **Table 3**, it was found that Mg-14Li-1Al alloy demonstrated excellent performance as the anode. The presence of lithium hydroxide in the discharge product seems to maintain *R*s.a low even after multiple water injections. Similar effects are expected for Mg-Al alloys

**Method Modification Cell t**

A Cu plated conductive tape bet. Mg/Cu Stack 146 B Add Cu powder in cathode mix Stack 82

C Use Mg-Li-Al alloy as anode Unit 208 D Add LiCl in cathode mix Stack 163 — None — 100

**Table 3.** Technical proposals to improve the discharge performance of WAMB.

Add Ni powder in cathode mix Stack 135 Add Fe powder in cathode mix Stack 105

NaCl is the standard electrolyte for type I and II water-activated batteries. It results in a larger *V*cell compared to a phosphate- or nitrate-based electrolyte but lowers *CE* [34]. Magnesium forms a soluble compound with organic acids such as acetic acid and citric acid [35]. Addition of citric acid did not improve the discharge performance of type I battery [36]. Some additives form chelates with Mg which raise *V*cell [37]. We found that the use of LiCl instead of NaCl

Finally, we consider that the recent attention of WAMB comes from aspects other than poweroriented issues, that is, the convenience and safe handling, or expectations of Mg as an energy carrier for a sustainable society [38]. Apart from LED lamps, water sensors from diapers [39] to underground pipelines [40], biodegradable batteries for medical implants or home appli-

total. Although the reason is uncertain, there is a possibility that the same effect as

cathode and magnesium

**total (%)**

http://dx.doi.org/10.5772/intechopen.79789

109

Discharge Behavior of Water-Activated Magnesium Battery

was 1.4–1.5 V over 50 h

at 15 mA/cm2

.

containing Ca [32].

increased *t*

**5. Conclusions**

*4.3.4. Selection of electrolyte and additive*

the Mg-Li-Al alloy anode described above may have occurred.

ances [41, 42] can be expected as new applications of WAMB.

A water-activated magnesium battery (WAMB) consisting of MnO2

**1.** The initial power density of WAMB showed the maximum of 10 mW/cm2

cathode. The injection of water regenerated the WAMB unit cell up to 8 times.

at the unit cell. Changes in the cell voltage were closely related to the performance of the

The cell voltage under a constant current discharge of 0.24 mA/cm2

anode was evaluated. The obtained results are as follows:

#### *4.3.2. Catalyst for enhancing the ability of the cathode*

Eq. (5) can be considered as a kind of oxygen reduction reaction. Therefore, the addition of oxygen catalyst shifts *E*c more noble. Apart from Pt group catalysts, several organic [26, 27], inorganic [28], or complex [29, 30] catalysts are promising. We studied the effect of Ni, Cu, and Fe powder in the MnO2 containing cathode mix. The addition of Ni powder gave the best performance among them.

#### *4.3.3. Mg alloy for improving discharge capacity*

In this study, a versatile AZ31 alloy was used as the anode. There are several Mg alloys developed for type I water-activated Mg batteries. It is effective to improve the discharge capacity

**Figure 17.** Schematic diagram of electron and ionic flows of WAMB (stacked cell): Section (a) indicates the normal discharge behavior, and section (b) indicates the abnormal behavior caused by the occurrence of a galvanic corrosion between the Cu current collector and the Mg anode.

**Table 3.** Technical proposals to improve the discharge performance of WAMB.

by adding specific alloying elements such as Li [31], Ca [32], Pb [33] to Mg-Al alloys. As shown in **Table 3**, it was found that Mg-14Li-1Al alloy demonstrated excellent performance as the anode. The presence of lithium hydroxide in the discharge product seems to maintain *R*s.a low even after multiple water injections. Similar effects are expected for Mg-Al alloys containing Ca [32].

#### *4.3.4. Selection of electrolyte and additive*

They are briefly commented as follows. Several studies conducted in type I water-activated Mg battery are also useful for type II WAMB. In addition, we performed some experimental trials that are summarized in **Table 3**. The relative increase in *t*total compared to the standard

The galvanic corrosion occurs in the condition of stacking unit cells, and it seems that the penetration water in the gap between the anode and the Cu collector is the main cause. It is conceivable to separate the unit cells and connect them outside the casing to avoid the galvanic contact. Although it is technically possible, the structure becomes complicated. A solution is to bond the electrodes using conductive tape to seal the gap. Although it induces contact resistance to decrease *V*cell, it is effective to eliminate the galvanic corrosion and improve the

Eq. (5) can be considered as a kind of oxygen reduction reaction. Therefore, the addition of

inorganic [28], or complex [29, 30] catalysts are promising. We studied the effect of Ni, Cu,

In this study, a versatile AZ31 alloy was used as the anode. There are several Mg alloys developed for type I water-activated Mg batteries. It is effective to improve the discharge capacity

**Figure 17.** Schematic diagram of electron and ionic flows of WAMB (stacked cell): Section (a) indicates the normal discharge behavior, and section (b) indicates the abnormal behavior caused by the occurrence of a galvanic corrosion

total was possible in our preliminary trials.

more noble. Apart from Pt group catalysts, several organic [26, 27],

containing cathode mix. The addition of Ni powder gave the best

condition was used as an index of improvement.

*CE*. With this configuration, a 150% increase in *t*

*4.3.2. Catalyst for enhancing the ability of the cathode*

*4.3.3. Mg alloy for improving discharge capacity*

between the Cu current collector and the Mg anode.

oxygen catalyst shifts *E*c

108 Magnesium Alloys - Selected Issue

and Fe powder in the MnO2

performance among them.

*4.3.1. Design for eliminating galvanic corrosion in the stacked cell*

NaCl is the standard electrolyte for type I and II water-activated batteries. It results in a larger *V*cell compared to a phosphate- or nitrate-based electrolyte but lowers *CE* [34]. Magnesium forms a soluble compound with organic acids such as acetic acid and citric acid [35]. Addition of citric acid did not improve the discharge performance of type I battery [36]. Some additives form chelates with Mg which raise *V*cell [37]. We found that the use of LiCl instead of NaCl increased *t* total. Although the reason is uncertain, there is a possibility that the same effect as the Mg-Li-Al alloy anode described above may have occurred.

Finally, we consider that the recent attention of WAMB comes from aspects other than poweroriented issues, that is, the convenience and safe handling, or expectations of Mg as an energy carrier for a sustainable society [38]. Apart from LED lamps, water sensors from diapers [39] to underground pipelines [40], biodegradable batteries for medical implants or home appliances [41, 42] can be expected as new applications of WAMB.

#### **5. Conclusions**

A water-activated magnesium battery (WAMB) consisting of MnO2 cathode and magnesium anode was evaluated. The obtained results are as follows:

**1.** The initial power density of WAMB showed the maximum of 10 mW/cm2 at 15 mA/cm2 . The cell voltage under a constant current discharge of 0.24 mA/cm2 was 1.4–1.5 V over 50 h at the unit cell. Changes in the cell voltage were closely related to the performance of the cathode. The injection of water regenerated the WAMB unit cell up to 8 times.

**2.** Electrochemical impedance spectroscopy was applied to monitor the discharge performance of WAMB. An electrical equivalent circuit of the anode and the cathode was proposed from the frequency spectra. They consisted of solution resistance, charge transfer resistance, constant phase element, inductance for the anode, and Warburg impedance for the cathode. Curve fitting using simulation software agreed well the experimental data.

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Discharge Behavior of Water-Activated Magnesium Battery

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### **Author details**

Isao Nakatsugawa1 \*, Yasumasa Chino1 and Hideki Nakano2

\*Address all correspondence to<EMAIL_ADDRESS>
1 Structural Materials Research Institute, National Institute of Advanced Industrial Science and Technology, Nagoya, Japan

2 CLT Ltd., Nagoya, Japan

#### **References**

**2.** Electrochemical impedance spectroscopy was applied to monitor the discharge performance of WAMB. An electrical equivalent circuit of the anode and the cathode was proposed from the frequency spectra. They consisted of solution resistance, charge transfer resistance, constant phase element, inductance for the anode, and Warburg impedance for the cathode. Curve fitting using simulation software agreed well the experimental data.

**3.** By monitoring solution resistance and charge transfer resistance, the degradation behavior of WAMB was analyzed. At the initial stage, an increase of solution resistance due to the depletion of water determined the discharge time. When water was repeatedly injected to regenerate WAMB, the increase in the charge transfer resistance of the anode and the cathode controlled the discharge time and the cell voltage, respectively. At the final stage, the Warburg impedance appeared in the cathode frequency spectrum. These data suggest that WAMB is the cathode-controlled system. The loss of discharge capacity and the volume

**4.** Stacking the unit cells in series was effective for increasing the cell voltage and extending the discharge time. On the other hand, the current efficiency decreased from 64 to 10–20%. The reason was interpreted in terms of a galvanic corrosion occurring at the Mg anode

**5.** The power density of WAMB was 71 Wh/kg, which was lower than the current Zn batteries. Several approaches to improve performance were proposed. Promising applications of

and Hideki Nakano2

1 Structural Materials Research Institute, National Institute of Advanced Industrial Science

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of Batteries. 4th ed. New York: McGraw-Hill Education; 2011. pp. 10.1-10.13

expansion of MnO2

110 Magnesium Alloys - Selected Issue

**Author details**

Isao Nakatsugawa1

**References**

and Technology, Nagoya, Japan

2 CLT Ltd., Nagoya, Japan

and the Cu current collector.

was considered.

WAMB including biodegradable batteries were also mentioned.

\*, Yasumasa Chino1

\*Address all correspondence to<EMAIL_ADDRESS>

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**Chapter 7**

**Provisional chapter**

**Clinical Applications of Magnesium Hydride**

sis on-demand because its antioxidant activity cannot store.

hydrogen-saturated saline injection, reversible osmosis

hydrolysis, oral hydrogen-dissolving water, hydrogen gas inhalation,

**Clinical Applications of Magnesium Hydride**

DOI: 10.5772/intechopen.79507

Oxygen sustains the lives of human a unique element. However, oxygen is unwanted and harmful when it is over tension to introduce oxygen-derived free radicals in the cells. Hydrogen and oxygen are both involved in the genesis of life that exists on Earth and metabolism in vivo, so it is not strange to exert a biological effect. Recently, scientists have found that hydrogen is an essential physiological regulatory function with antioxidant, anti-inflammatory, and antiapoptotic protective effects on cells. Using therapeutic hydrogen includes different delivery methods, such as inhalation of hydrogen gas, oral hydrogen water, and injection of hydrogen-saturated saline. In clinical applications, magnesium hydride hydrolysis instead of traditional metallic magnesium is effective in increasing the theoretical hydrogen storage capacity by two times. The hydrogen-water comes across as being an excellent choice to produce from magnesium hydride hydroly-

**Keywords:** hydrogen, method, metallic magnesium hydrolysis, magnesium hydride

In 2007, Oshawa et al. [1] have the first reported that inhalation of only 2% hydrogen gas could selectively reduce oxygen-derived free radicals and improve cerebral ischemiareperfusion injuries. However, the underlying mechanism is still not precise; the protective effects of the small amount of hydrogen on oxidative stress draw much attention for developing the hydrogen biology. Since that, hydrogen biology becomes a hotspot in the medical research, more than 500 papers related to almost all diseases. Lots of evidence shows molecular hydrogen in cells, and organisms exerting the antioxidant, anti-inflammatory, and

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79507

Chung-Hsing Chao

Chung-Hsing Chao

**Abstract**

**1. Introduction**

#### **Chapter 7 Provisional chapter**

#### **Clinical Applications of Magnesium Hydride Clinical Applications of Magnesium Hydride**

DOI: 10.5772/intechopen.79507

#### Chung-Hsing Chao Chung-Hsing Chao

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79507

**Abstract**

Oxygen sustains the lives of human a unique element. However, oxygen is unwanted and harmful when it is over tension to introduce oxygen-derived free radicals in the cells. Hydrogen and oxygen are both involved in the genesis of life that exists on Earth and metabolism in vivo, so it is not strange to exert a biological effect. Recently, scientists have found that hydrogen is an essential physiological regulatory function with antioxidant, anti-inflammatory, and antiapoptotic protective effects on cells. Using therapeutic hydrogen includes different delivery methods, such as inhalation of hydrogen gas, oral hydrogen water, and injection of hydrogen-saturated saline. In clinical applications, magnesium hydride hydrolysis instead of traditional metallic magnesium is effective in increasing the theoretical hydrogen storage capacity by two times. The hydrogen-water comes across as being an excellent choice to produce from magnesium hydride hydrolysis on-demand because its antioxidant activity cannot store.

 Introduction**

In 2007, Oshawa et al. [1] have the first reported that inhalation of only 2% hydrogen gas could selectively reduce oxygen-derived free radicals and improve cerebral ischemiareperfusion injuries. However, the underlying mechanism is still not precise; the protective effects of the small amount of hydrogen on oxidative stress draw much attention for developing the hydrogen biology. Since that, hydrogen biology becomes a hotspot in the medical research, more than 500 papers related to almost all diseases. Lots of evidence shows molecular hydrogen in cells, and organisms exerting the antioxidant, anti-inflammatory, and

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

antiapoptotic for oxidative stress on some types of infections. Why is this discovery significant? Inhalation of hydrogen below the flammability limit of 4.6%, drinking containing saturated hydrogen water, and injection of containing saturated hydrogen saline could exert therapeutic biological effects for selectively eliminating the toxic free radicals, such as hydroxyl free radicals, superoxide radical in vivo. We can treat the reactive oxygen species-caused oxidative stress disease by administrating reductive drugs, such as vitamins. However, it would eliminate all reactive oxygen species [2]. Cells maintain metabolism through oxidizing food into energy species in vivo. Therefore, cells produce reactive oxygen free radicals to help to absorb nutritious substances, which is a unique phenomenon for biological organisms. But over the tension of free radicals can seriously affect the physiological functions, and even lead to death. Oxidative stress damage likes a peeled apple will turn brown with an injury.

electrolysis by polymer membrane method is too high. The magnesium hydride hydrolysis belongs to alkaline water efficiently enhances the saturated hydrogen dissolving in water, and the smallest hydrogen molecule passes nanometer-filter of reversible osmosis transformed

At room temperature, the concentration of hydrogen molecule dissolving in tap water is only 8.65 × 10−7 mg/L. At such a low level of hydrogen, there is no therapeutic effect in clinical applications. The saturation-hydrogen of 1.6 milligram/Liter [20–22] in water is more than million times of hydrogen concentration in tap water. This value is considered the hydrogen dissolved in water at room temperature to its maximum state. The amount of hydrogen will reduce if hydrogen escapes from the water surface equaling to the pressure at sea level, which is 101.325 kilopascal (one-atmosphere pressure). Hydrogen, under saturation condition, has been found to be able to exert its protective effects in the biological system [1–19]. Hydrogen is the minimum mass gas molecule with relatively steady reducibility, a valuable chemical property of redox reaction in metabolism. It has been accepted that hydrogen cannot directly interact with substances in the biological body, and that is why, we get hydrogen dissolving in water by oral or injection with saturated hydrogen saline. Since 2007, plenty of trials have been done using hydrogen inhalation medicine in treating ischemia-reperfusion injury at 1 or 2% hydrogen concentration for 35 min. Subsequently, a lot of researchers have shown that a small level of hydrogen has therapeutic effects on a variety of diseases. Even in pure oxygen gas environment, it is not flammable or explosive when the hydrogen concentration is less than 4% or over 95%. **Table 1** shows several delivery methods for hydrogen administration in vivo. In the following section, we introduce the means of producing hydrogen molecules, such as hydrogen from metallic magnesium rod hydrolysis [20], sodium chloride ionic water-electrolyzed hydrogen [21], and pure water through polymer membrane-electrolyzed hydrogen [22]. Later, we will explain and compare

into fresh high-content hydrogen water.

them with a specific mention as below.

Hydrogen water Oral intake H2

Increased intestinal hydrogen

**Table 1.** Hydrogen delivery methods.

amount

Hydrogen saline Intravenous injection by saturated H2 saline

**Administration Delivery methods Characteristics**

Hydrogen gas Inhalation gas mixture of H2 < 4% Rapid, unsafe, acute oxidative

Hydrogen solution Eye drop, bath immersion Low cost, safe, convenient

damage

Accurate dosage

Clinical Applications of Magnesium Hydride http://dx.doi.org/10.5772/intechopen.79507 117

water <1.6 mg/L Low cost, safe, convenient

Drug low cost, convenient

**2. Materials and methods**

What are free radicals? Free radicals are molecules and atomic groups with "unpaired" electrons. Owing to unpaired electrons, they will snatch free electrons of other molecules in vivo to match with them. After snatching electrons, they will turn molecules of the robbed electrons into newly free radicals. Finally, it will induce the "chain reaction of free radicals" so the unbalance of free radicals will cause the cells crisis. Hydrogen has the lightest weight with one proton and one electron, and the molecular hydrogen a nonradical, nonreactive, nonpolar, highly diffusible neutral gas, which can arbitrarily penetrate the cell membrane into nucleus and mitochondria to neutralize the highly reactive oxygen species in vivo. At a low concentration, hydrogen does not react with the characterized as large in number, low in activity, and beneficial reactive oxygen species, such as hydrogen peroxide, nitric oxide. This phenomenon is called the selectively neutralizing highly reactive free radicals. It means that low concentration hydrogen can be limited to deal with high reactive cytotoxic oxygen species and not to kill all the free radicals. Till now, hydrogen has been shown to have a therapeutic effect on over 170 different human diseases and animal models, including in antioxidant activity [1, 3–9], ischemia-reperfusion injury [2, 10–14], Parkinson's disease [15, 16], cancer [17], retina [12], chondrocytes [7], diabetes disease [18], irradiation-induced lung damage [8], mitochondrial disease [9], and cardiac disease [13, 19].

When hydrogen was focused on its biological effects in multiple diseases by scientists in recent years, the method of hydrogen applications is that we have to resolve it for adequately applying its antioxidant, anti-inflammatory, and antiapoptotic function for oxidative stress [1–19]. This antioxidant effect of molecular hydrogen has been proved. However, molecular hydrogen is not the same as hydrogen gas. Hydrogen water contains both atomic and molecular hydrogen. It is essential continuously to study the medical effects in vivo for hydrogen bioresearch. Producing high-quality hydrogen water method for clinical applications is one of the critical points in the study. Although, many scientists have studied hydrogen-associated techniques including magnesium rod hydrolysis, electrolytic water containing sodium chloride, and electrolyzed water by polymer membrane patents [20–22]. We found that the related methods of producing hydrogen dissolving in water were still limited. This chapter shows a new way of magnesium hydride hydrolysis by reacting with tap water. It is provided to increasing the theoretical hydrogen production amount by more than two times, solving the drawbacks that the rate of metallic magnesium rod hydrolysis is too low, the risk of internal explosion of the hydrogen-oxygen electrolysis process itself, and the cost of pure water electrolysis by polymer membrane method is too high. The magnesium hydride hydrolysis belongs to alkaline water efficiently enhances the saturated hydrogen dissolving in water, and the smallest hydrogen molecule passes nanometer-filter of reversible osmosis transformed into fresh high-content hydrogen water.

#### **2. Materials and methods**

antiapoptotic for oxidative stress on some types of infections. Why is this discovery significant? Inhalation of hydrogen below the flammability limit of 4.6%, drinking containing saturated hydrogen water, and injection of containing saturated hydrogen saline could exert therapeutic biological effects for selectively eliminating the toxic free radicals, such as hydroxyl free radicals, superoxide radical in vivo. We can treat the reactive oxygen species-caused oxidative stress disease by administrating reductive drugs, such as vitamins. However, it would eliminate all reactive oxygen species [2]. Cells maintain metabolism through oxidizing food into energy species in vivo. Therefore, cells produce reactive oxygen free radicals to help to absorb nutritious substances, which is a unique phenomenon for biological organisms. But over the tension of free radicals can seriously affect the physiological functions, and even lead

to death. Oxidative stress damage likes a peeled apple will turn brown with an injury.

mitochondrial disease [9], and cardiac disease [13, 19].

116 Magnesium Alloys - Selected Issue

What are free radicals? Free radicals are molecules and atomic groups with "unpaired" electrons. Owing to unpaired electrons, they will snatch free electrons of other molecules in vivo to match with them. After snatching electrons, they will turn molecules of the robbed electrons into newly free radicals. Finally, it will induce the "chain reaction of free radicals" so the unbalance of free radicals will cause the cells crisis. Hydrogen has the lightest weight with one proton and one electron, and the molecular hydrogen a nonradical, nonreactive, nonpolar, highly diffusible neutral gas, which can arbitrarily penetrate the cell membrane into nucleus and mitochondria to neutralize the highly reactive oxygen species in vivo. At a low concentration, hydrogen does not react with the characterized as large in number, low in activity, and beneficial reactive oxygen species, such as hydrogen peroxide, nitric oxide. This phenomenon is called the selectively neutralizing highly reactive free radicals. It means that low concentration hydrogen can be limited to deal with high reactive cytotoxic oxygen species and not to kill all the free radicals. Till now, hydrogen has been shown to have a therapeutic effect on over 170 different human diseases and animal models, including in antioxidant activity [1, 3–9], ischemia-reperfusion injury [2, 10–14], Parkinson's disease [15, 16], cancer [17], retina [12], chondrocytes [7], diabetes disease [18], irradiation-induced lung damage [8],

When hydrogen was focused on its biological effects in multiple diseases by scientists in recent years, the method of hydrogen applications is that we have to resolve it for adequately applying its antioxidant, anti-inflammatory, and antiapoptotic function for oxidative stress [1–19]. This antioxidant effect of molecular hydrogen has been proved. However, molecular hydrogen is not the same as hydrogen gas. Hydrogen water contains both atomic and molecular hydrogen. It is essential continuously to study the medical effects in vivo for hydrogen bioresearch. Producing high-quality hydrogen water method for clinical applications is one of the critical points in the study. Although, many scientists have studied hydrogen-associated techniques including magnesium rod hydrolysis, electrolytic water containing sodium chloride, and electrolyzed water by polymer membrane patents [20–22]. We found that the related methods of producing hydrogen dissolving in water were still limited. This chapter shows a new way of magnesium hydride hydrolysis by reacting with tap water. It is provided to increasing the theoretical hydrogen production amount by more than two times, solving the drawbacks that the rate of metallic magnesium rod hydrolysis is too low, the risk of internal explosion of the hydrogen-oxygen electrolysis process itself, and the cost of pure water At room temperature, the concentration of hydrogen molecule dissolving in tap water is only 8.65 × 10−7 mg/L. At such a low level of hydrogen, there is no therapeutic effect in clinical applications. The saturation-hydrogen of 1.6 milligram/Liter [20–22] in water is more than million times of hydrogen concentration in tap water. This value is considered the hydrogen dissolved in water at room temperature to its maximum state. The amount of hydrogen will reduce if hydrogen escapes from the water surface equaling to the pressure at sea level, which is 101.325 kilopascal (one-atmosphere pressure). Hydrogen, under saturation condition, has been found to be able to exert its protective effects in the biological system [1–19]. Hydrogen is the minimum mass gas molecule with relatively steady reducibility, a valuable chemical property of redox reaction in metabolism. It has been accepted that hydrogen cannot directly interact with substances in the biological body, and that is why, we get hydrogen dissolving in water by oral or injection with saturated hydrogen saline. Since 2007, plenty of trials have been done using hydrogen inhalation medicine in treating ischemia-reperfusion injury at 1 or 2% hydrogen concentration for 35 min. Subsequently, a lot of researchers have shown that a small level of hydrogen has therapeutic effects on a variety of diseases. Even in pure oxygen gas environment, it is not flammable or explosive when the hydrogen concentration is less than 4% or over 95%. **Table 1** shows several delivery methods for hydrogen administration in vivo. In the following section, we introduce the means of producing hydrogen molecules, such as hydrogen from metallic magnesium rod hydrolysis [20], sodium chloride ionic water-electrolyzed hydrogen [21], and pure water through polymer membrane-electrolyzed hydrogen [22]. Later, we will explain and compare them with a specific mention as below.

**Table 1.** Hydrogen delivery methods.

#### **2.1. Magnesium hydrolysis**

Metallic magnesium is one of the soluble materials in our body, such as bone material and blood vessel stents. It is safe to use as a medical therapy. However, magnesium reacts violently with steam at high temperatures, such as burning or explosion with water vapor. It is active as a reductant agent for oxidizing water into hydrogen with a standard oxidation potential of +2.356 V. If we throw a small piece of magnesium into cold water, it reacts very slightly. Hydrogen gas is slowly released, because magnesium hydroxide is coated on its surface in the reaction. White-colored magnesium hydroxide mixed with water is called emulsion of magnesium milk which is used to neutralize excess stomach acid in treating constipation disease. Magnesium hydroxide is a base hardly soluble in cold water, while it can react with acid to generate a salt and water in a neutralization reaction. We expressed the chemical response according to the standard reduction potential of magnesium [23].

$$\text{Mg}\_{(s)} \rightarrow \text{Mg}^{+2}\_{(aq)} + 2\text{e}^-\text{E}^0 = -2.372\text{ V} \tag{1}$$

reduction at the cathode,

2H+

H2 O(l) → 0.5O2(aq)

and the overall redox reaction.

**2.3. Electrolysis of pure water**

cal reaction is as below.

(aq)

body's pH value by alkaline electrolytic water is lack of scientific basis.

+ 2e− → H2(aq) E0 = 0 V (5)

. (6)

Clinical Applications of Magnesium Hydride http://dx.doi.org/10.5772/intechopen.79507 119

+ H2(aq)

Electrolysis of water would be not spontaneous due to E0 = −1.23 V < 0. Therefore, it needs electrical power to drive electrolyzed water reaction. Electrolysis of water has advantages of simple, low cost, and convenient use. However, if it connects to the tap water, the water may contain part of chlorine or salt residues. The residual chlorine content of electrolysis of water will be 15–20% higher than the original tap water. Apart from chlorine, there is ozone in the water at the anode, and ozone has a pungent odor, a harmful effect on human health. Ozone is a strong oxidant which can also damage the lung causing lung bleeding and death. Therefore, the potential crisis in electrolyzed water generator may originate in improper design or use. For example, many manufacturers to reduce costs will not take the initiative to use gas-tight devices to separate the hydrogen and oxygen further, resulting in hydrogen and oxygen confluence, so that the machine is under explosive risk. Also, the hydrogen gas is generated at the cathode, so the solutions become more and more alkaline. The human body is not suitable for drinking too high-pH-value water. When the alkaline electrolytic water enters the stomach, it will be in a neutralization reaction with acidic gastric acid. Therefore, adjusting the human

Recently, the green energy market has sprung up, and a new technology called "polymer proton conducting membrane" of electrolytic production of hydrogen from pure water has emerged. Such electrolyzed pure water is the reverse reaction of "hydrogen fuel cell of power generation," which fuel cell directly transforms the chemical energy of hydrogen and oxygen into electricity. The only by-product is pure water. Japan has spared no effects to promote hydrogen fuel cell technology, TOYOTA, and Honda automotive company have also developed hydrogen fuel cell-powered electric vehicles. It uses pure water and electricity to produce hydrogen and oxygen. Due to high hydrogen production efficiency and high safety factor, the purity of hydrogen can reach over 99.999%. The polymer proton-conducting membrane is manufactured by DuPont Inc. as a solid electrolyte, which does not require dissolved ions in water. Instead, the higher the purity of water, the better can protect the core device of membrane electrode assembly without accompanying other by-products. The electrochemi-

H2 O(l) → 2H+ + 2e− + 0.5O2(g) at the anode (7)

2H+ + 2e− → H2(g) at the cathode (8)

$$2\text{H}\_{2}\text{O}\_{0} + 2\text{e}^{-} \rightarrow \text{H}\_{2\text{(aq)}} + 2\text{OH}^{-}\\E^{0} = -0.828\text{ V} \times 2\tag{2}$$

Magnesium hydrolysis in redox reaction would be spontaneous (E > 0). However, the rate of magnesium hydrolysis is gradually slow down because Mg(OH)2 is highly insoluble in water. Therefore, the total reaction of magnesium hydrolysis is as below.

$$\text{Mg}\_{\text{(s)}} + 2\text{H}\_{2}\text{O}\_{\text{(l)}} \rightarrow \text{H}\_{2\text{(aq)}} + \text{Mg}\text{ (OH)}\_{2\text{(s)}}\tag{3}$$

In the solution, two hydroxide ions combine with one magnesium ion to form magnesium hydroxide while leaving insufficient hydroxide ions to conduct the electrons. So, it cannot complete all the hydrolysis reaction despite the escaping hydrogen gas.

Magnesium hydrolysis producing hydrogen-rich water [20] is the most simple and cheap method for oral hydrogen. While drinking hydrogen water, magnesium hydroxide may also take in. There is no potential harm to the human body as a gastric acid inhibitor. If in a day we drink 2 liters of hydrogen water, the intake is 18 mg and will not exceed the limit of 300 mg per day.

#### **2.2. Electrolysis of ionic water**

Drinking electrolytic water has used for health care in Japan more than half a century. Commercially available electrolytic water generator [21] is called ion water electrolyzed. The core device of electrolytic water generator includes a pair of anode/cathode electrodes and ionic membrane. The electrolytic reaction has a standard electrode potential of −1.23 V. It means that it at least requires a potential difference of 1.23 V between anode and cathode to split water. The electrochemical reaction includes oxidation at the anode,

$$\mathrm{H\_2O\_{(l)}} \rightarrow 0.5\mathrm{O\_{2(aq)}} + 2\mathrm{H^+\_{(aq)}} + 2\mathrm{e^-} \\ \mathrm{E^0} = -1.23\,\mathrm{V} \tag{4}$$

reduction at the cathode,

**2.1. Magnesium hydrolysis**

118 Magnesium Alloys - Selected Issue

Metallic magnesium is one of the soluble materials in our body, such as bone material and blood vessel stents. It is safe to use as a medical therapy. However, magnesium reacts violently with steam at high temperatures, such as burning or explosion with water vapor. It is active as a reductant agent for oxidizing water into hydrogen with a standard oxidation potential of +2.356 V. If we throw a small piece of magnesium into cold water, it reacts very slightly. Hydrogen gas is slowly released, because magnesium hydroxide is coated on its surface in the reaction. White-colored magnesium hydroxide mixed with water is called emulsion of magnesium milk which is used to neutralize excess stomach acid in treating constipation disease. Magnesium hydroxide is a base hardly soluble in cold water, while it can react with acid to generate a salt and water in a neutralization reaction. We expressed the chemical response

(aq)

Magnesium hydrolysis in redox reaction would be spontaneous (E > 0). However, the rate of

In the solution, two hydroxide ions combine with one magnesium ion to form magnesium hydroxide while leaving insufficient hydroxide ions to conduct the electrons. So, it cannot

Magnesium hydrolysis producing hydrogen-rich water [20] is the most simple and cheap method for oral hydrogen. While drinking hydrogen water, magnesium hydroxide may also take in. There is no potential harm to the human body as a gastric acid inhibitor. If in a day we drink 2 liters of hydrogen water, the intake is 18 mg and will not exceed the limit of 300 mg

Drinking electrolytic water has used for health care in Japan more than half a century. Commercially available electrolytic water generator [21] is called ion water electrolyzed. The core device of electrolytic water generator includes a pair of anode/cathode electrodes and ionic membrane. The electrolytic reaction has a standard electrode potential of −1.23 V. It means that it at least requires a potential difference of 1.23 V between anode and cathode to

> + 2H+ (aq)

+ Mg (OH)

+ 2e− E0 = −2.372 V (1)

+ 2OH− E0 = −0.828 V × 2 (2)

is highly insoluble in water.

2(s) (3)

+ 2e− E0 = −1.23 V (4)

according to the standard reduction potential of magnesium [23].

magnesium hydrolysis is gradually slow down because Mg(OH)2

Therefore, the total reaction of magnesium hydrolysis is as below.

complete all the hydrolysis reaction despite the escaping hydrogen gas.

split water. The electrochemical reaction includes oxidation at the anode,

Mg(s) → Mg+2

2H2 O(l) + 2e− → H2(aq)

Mg(s) + 2H2 O(l) → H2(aq)

per day.

**2.2. Electrolysis of ionic water**

H2 O(l) → 0.5O2(aq)

$$2\text{H}^{\*}\_{\text{(aq)}} + 2\text{e}^{-} \rightarrow \text{H}\_{\text{(aq)}}\text{E}^{\text{o}} = \text{0 V} \tag{5}$$

and the overall redox reaction.

$$\text{H}\_{2}\text{O}\_{(l)} \rightarrow \text{ 0.5O}\_{2\text{(aq)}} + \text{H}\_{2\text{(aq)}}.\tag{6}$$

Electrolysis of water would be not spontaneous due to E0 = −1.23 V < 0. Therefore, it needs electrical power to drive electrolyzed water reaction. Electrolysis of water has advantages of simple, low cost, and convenient use. However, if it connects to the tap water, the water may contain part of chlorine or salt residues. The residual chlorine content of electrolysis of water will be 15–20% higher than the original tap water. Apart from chlorine, there is ozone in the water at the anode, and ozone has a pungent odor, a harmful effect on human health. Ozone is a strong oxidant which can also damage the lung causing lung bleeding and death. Therefore, the potential crisis in electrolyzed water generator may originate in improper design or use. For example, many manufacturers to reduce costs will not take the initiative to use gas-tight devices to separate the hydrogen and oxygen further, resulting in hydrogen and oxygen confluence, so that the machine is under explosive risk. Also, the hydrogen gas is generated at the cathode, so the solutions become more and more alkaline. The human body is not suitable for drinking too high-pH-value water. When the alkaline electrolytic water enters the stomach, it will be in a neutralization reaction with acidic gastric acid. Therefore, adjusting the human body's pH value by alkaline electrolytic water is lack of scientific basis.

#### **2.3. Electrolysis of pure water**

Recently, the green energy market has sprung up, and a new technology called "polymer proton conducting membrane" of electrolytic production of hydrogen from pure water has emerged. Such electrolyzed pure water is the reverse reaction of "hydrogen fuel cell of power generation," which fuel cell directly transforms the chemical energy of hydrogen and oxygen into electricity. The only by-product is pure water. Japan has spared no effects to promote hydrogen fuel cell technology, TOYOTA, and Honda automotive company have also developed hydrogen fuel cell-powered electric vehicles. It uses pure water and electricity to produce hydrogen and oxygen. Due to high hydrogen production efficiency and high safety factor, the purity of hydrogen can reach over 99.999%. The polymer proton-conducting membrane is manufactured by DuPont Inc. as a solid electrolyte, which does not require dissolved ions in water. Instead, the higher the purity of water, the better can protect the core device of membrane electrode assembly without accompanying other by-products. The electrochemical reaction is as below.

$$\text{H}\_{2}\text{O}\_{(l)} \rightarrow 2\text{H}^{+} + 2\text{e}^{-} + 0.5\text{O}\_{2(l)} \text{ at the anode} \tag{7}$$

$$2\text{H}^{+} \star 2\text{e}^{-} \rightarrow \text{H}\_{2\text{(0)}} \text{at the cathode} \tag{8}$$

Water molecule splits at the anode to form two positively charged hydrogen ions (H+ ), two electrons (e− ), and a half oxygen molecule (O2 ). The two electrons flow through an external circuit and the two hydrogen ions selectively move across the polymer electrolyte membrane to the cathode. At the cathode, the two hydrogen ions combine with the two electrons from the external circuit to form one hydrogen molecule (H2 ). The gas-tight polymer of proton exchange membrane prevents the oxygen at the anode from passing through the layer to the cathode, completely isolating the oxygen from the hydrogen gas, avoiding the internal explosion of the electrolysis process. Electrolytic water maintains at a neutral state of pH equal to 7 during the process of electrolysis. Furthermore, the amount of hydrogen production at a 3 Ampere/cm2 of current density is five times higher than that of the ion-electrolyzed water. The volume of pure water electrolyzed system can be smaller and lighter. Although the polymer electrolyte membrane has many advantages mentioned above, it is still costly to use. Also, it cannot use tap water to be another problem because metal ion, chlorine, carbon monoxide in the solution will poison the platinum catalyst, and its price cannot compete with the other products.

#### **2.4. Comparison of methods**

The method of magnesium hydrolysis of producing hydrogen water was invented by Dr. Hidemitsu Hayashi, who was the heart surgeon being responsible for clinical medicine. He began to study the medical benefits of hydrogen water in 1985 and published a report on hydrogen water treatment 10 years later. The magnesium rod consists of magnesium powders packed in a porous polyethylene resin (see **Figure 1**). The mild chemical reaction between magnesium and water lead to the generation of hydrogen bubbles and the formation of magnesium hydroxide on the surface of magnesium. This simple and effective process produces hydrogen antioxidant solution, which is more alkaline than that of pure water [20].

The ion-electrolyzed water system for producing hydrogen water was Akiyama Hiroyuki's invention [21], and the commercial product of both of acidic water and alkaline water has completed. The electrolytic water system includes an electrolysis generating unit, a reading display, and a control unit. It selectively makes and takes out a plurality of acidic-oxidation water and hydrogen-reduction water with a given pH value which is based on a series of operation modes. The reading unit reads the information stored in the external touch panel carried by the user. The control unit determines the operation mode; the ion electrolysis system is operated to improve the usability by a plurality of people [21].

Wang Dong invented the electrolyzed water system based on the polymer electrolyte membrane [22] as shown in **Figure 2**. The electrolyzed water-generating device provides high-purity hydrogen and oxygen for the fuel cell, including the front end plate, diffusion plate, conductive plate, special plate, flow field plate, membrane electrode, rear special plate, buffer plate, rear end plate, and other units, each unit is pressure-resistant. Water and gas flow field plates and conductive plates made of titanium alloy and other corrosion resistant alloys. The carbon fiber paper is used as the membrane electrode diffusion layer.  The working medium of the invention is pure water, has no pollution to the environment, can recycle, and the generated hydrogen water is high in purity and does not need complicated purification

Clinical Applications of Magnesium Hydride http://dx.doi.org/10.5772/intechopen.79507 121

**Figure 1.** Method of magnesium hydrolysis for producing hydrogen-rich water [20].

and treatment.

**Figure 2.** Polymer electrolyte membrane electrolyzer [22].

**Figure 1.** Method of magnesium hydrolysis for producing hydrogen-rich water [20].

Water molecule splits at the anode to form two positively charged hydrogen ions (H+

circuit and the two hydrogen ions selectively move across the polymer electrolyte membrane to the cathode. At the cathode, the two hydrogen ions combine with the two electrons from

exchange membrane prevents the oxygen at the anode from passing through the layer to the cathode, completely isolating the oxygen from the hydrogen gas, avoiding the internal explosion of the electrolysis process. Electrolytic water maintains at a neutral state of pH equal to 7 during the process of electrolysis. Furthermore, the amount of hydrogen production at a 3

volume of pure water electrolyzed system can be smaller and lighter. Although the polymer electrolyte membrane has many advantages mentioned above, it is still costly to use. Also, it cannot use tap water to be another problem because metal ion, chlorine, carbon monoxide in the solution will poison the platinum catalyst, and its price cannot compete with the other

The method of magnesium hydrolysis of producing hydrogen water was invented by Dr. Hidemitsu Hayashi, who was the heart surgeon being responsible for clinical medicine. He began to study the medical benefits of hydrogen water in 1985 and published a report on hydrogen water treatment 10 years later. The magnesium rod consists of magnesium powders packed in a porous polyethylene resin (see **Figure 1**). The mild chemical reaction between magnesium and water lead to the generation of hydrogen bubbles and the formation of magnesium hydroxide on the surface of magnesium. This simple and effective process produces

The ion-electrolyzed water system for producing hydrogen water was Akiyama Hiroyuki's invention [21], and the commercial product of both of acidic water and alkaline water has completed. The electrolytic water system includes an electrolysis generating unit, a reading display, and a control unit. It selectively makes and takes out a plurality of acidic-oxidation water and hydrogen-reduction water with a given pH value which is based on a series of operation modes. The reading unit reads the information stored in the external touch panel carried by the user. The control unit determines the operation mode; the ion electrolysis sys-

Wang Dong invented the electrolyzed water system based on the polymer electrolyte membrane [22] as shown in **Figure 2**. The electrolyzed water-generating device provides high-purity hydrogen and oxygen for the fuel cell, including the front end plate, diffusion plate, conductive plate, special plate, flow field plate, membrane electrode, rear special plate, buffer plate, rear end plate, and other units, each unit is pressure-resistant. Water and gas flow field plates and conductive plates made of titanium alloy and other corrosion resistant alloys. The carbon fiber paper is used as the membrane electrode diffusion layer. The membrane electrode is a high-activity electrode prepared by proton exchange

hydrogen antioxidant solution, which is more alkaline than that of pure water [20].

tem is operated to improve the usability by a plurality of people [21].

of current density is five times higher than that of the ion-electrolyzed water. The

), and a half oxygen molecule (O2

the external circuit to form one hydrogen molecule (H2

electrons (e−

120 Magnesium Alloys - Selected Issue

Ampere/cm2

products.

**2.4. Comparison of methods**

), two

). The two electrons flow through an external

). The gas-tight polymer of proton

**Figure 2.** Polymer electrolyte membrane electrolyzer [22].

membrane and composite platinum metal catalyst and carbon black. The working medium of the invention is pure water, has no pollution to the environment, can recycle, and the generated hydrogen water is high in purity and does not need complicated purification and treatment.

course of the reaction, which is the limiting step of magnesium hydride hydrolysis. These effects are advantageous. The by-product, citrate magnesium, also is a vital component of

The system of producing hydrogen-water, as shown in **Figure 3**, includes a reactor, reverse osmosis unit, valve, pump, control unit, digital display, water input, hydrogen-water output, hydrogen-water for therapeutic use, magnesium hydride block, and tap water input. **Figure 4** shows the porous structure of magnesium hydride of 35 × 35 × 17 in millimeters which was manufactured by direct hydrogenation processes using a low-cost combustion synthesis [24, 25]. The block of magnesium hydride is made by a light gray crystalline powder (99.9% in purity by mass) under high pressure and temperature of 200 bars and 500°C with magnesium iodide catalysts. The porous structure facilitates the water molecules to enter into magnesium hydride

(aq)

The magnesium hydride hydrolysis reaction shows a similar qualitative process. At the beginning of the response, water molecule reacts with magnesium hydride to release magnesium ions and negative hydrogen ions. And then, the negative hydrogen ions continuously split water molecules releasing hydrogen gas and hydroxide ions. Therefore, we can observe a

While the reaction reached the observed equilibrium of pH 11.0, more and more magnesium hydroxide precipitated on the outer surface of the magnesium hydride from the initially supersaturated solutions state. It is in excellent agreement with the observed pH of saturated

+ 2OH−− → Mg (OH)

+ 2H− (9)

Clinical Applications of Magnesium Hydride http://dx.doi.org/10.5772/intechopen.79507 123

+ 2OH−− (10)

2(s) (11)

bone in the human body.

inside to generate hydrogen.

steep increase in pH value.

Mg+2

The chemical reaction is expressed below.

MgH2(s) → Mg+2

2H− + 2H2 O(l) → H2(aq)

solutions of magnesium hydroxide in the literature [23, 25].

(aq)

**Figure 3.** The method of magnesium hydride hydrolysis producing hydrogen-water.

**Table 2.** Three primary producing hydrogen water methods [20–22].

**Table 2** listed the comparison between three primary producing hydrogen-water methods. This seemingly theoretical capacity of hydrogen, purity, reaction rate, etc. indeed relevant for real clinical application scenarios. As in many cases, the water of various sources whether or not is readily on site or therefore needs to transport the necessary amount of pure water or distilled water for use. We attempt to improve the conventional methods of producing hydrogen-water by using magnesium hydride hydrolysis. The double capacity of hydrogen sources of magnesium hydride hydrolysis originates as half from the hydride ions and half of the water protons. Thermodynamically, magnesium hydride on contacting with water to produce hydrogen-water is favorable and the by-product of magnesium hydroxide. However, in practice, not only the reaction kinetics is extremely slow but also the insoluble passivation layer of magnesium hydroxide soon coated on the outer surface to impede water entering. For example, the reaction yield of magnesium hydride hydrolysis at room temperature is below 1% after half an hour.

#### **3. Results and discussion**

In this section, we give a systematic study on the method of magnesium hydride hydrolysis for producing hydrogen-water. At first, this method provided to an increasing the theoretical hydrogen amount by two times than that of the technique of magnesium hydrolysis. The hydrogen-water produced from this method belongs to alkaline water. At room temperature, the reaction is prolonged because the low reaction kinetics and the surface are gradually covered with an insoluble layer of hydroxide on the outer to hinder response continuously. However, it can activate by using citric acid as a chelating agent. Like, citric acid can dissolve metal oxides by making them dissoluble. Citric acid belongs to a weak organic acid that has the chemical formula C6 H8 O7 . In biochemistry, the citric acid acts as an intermediate in the citric acid cycle occurred in the metabolism of all aerobic organisms. The chemical reaction of the citric acid cycle is the source of two-thirds of the food-derived energy in higher living creatures. Hans Adolf Krebs also received the 1953 Nobel Prize in Physiology Medicine for the discovery. In this study, citric acid acts as both of a catalyst to activate reaction kinetics and a chelating agent to inhibit the magnesium hydroxide formation over the complete course of the reaction, which is the limiting step of magnesium hydride hydrolysis. These effects are advantageous. The by-product, citrate magnesium, also is a vital component of bone in the human body.

The system of producing hydrogen-water, as shown in **Figure 3**, includes a reactor, reverse osmosis unit, valve, pump, control unit, digital display, water input, hydrogen-water output, hydrogen-water for therapeutic use, magnesium hydride block, and tap water input. **Figure 4** shows the porous structure of magnesium hydride of 35 × 35 × 17 in millimeters which was manufactured by direct hydrogenation processes using a low-cost combustion synthesis [24, 25]. The block of magnesium hydride is made by a light gray crystalline powder (99.9% in purity by mass) under high pressure and temperature of 200 bars and 500°C with magnesium iodide catalysts. The porous structure facilitates the water molecules to enter into magnesium hydride inside to generate hydrogen.

The chemical reaction is expressed below.

**Table 2** listed the comparison between three primary producing hydrogen-water methods. This seemingly theoretical capacity of hydrogen, purity, reaction rate, etc. indeed relevant for real clinical application scenarios. As in many cases, the water of various sources whether or not is readily on site or therefore needs to transport the necessary amount of pure water or distilled water for use. We attempt to improve the conventional methods of producing hydrogen-water by using magnesium hydride hydrolysis. The double capacity of hydrogen sources of magnesium hydride hydrolysis originates as half from the hydride ions and half of the water protons. Thermodynamically, magnesium hydride on contacting with water to produce hydrogen-water is favorable and the by-product of magnesium hydroxide. However, in practice, not only the reaction kinetics is extremely slow but also the insoluble passivation layer of magnesium hydroxide soon coated on the outer surface to impede water entering. For example, the reaction yield of magnesium hydride hydrolysis at room temperature is below

**Methods Magnesium hydrolysis [20] Ion-water electrolysis [21] Pure-water electrolysis [22]**

, HClO, O2

, O3 None

Theory Magnesium hydrolysis Electrolyzed water Electrolyzed water

Purity 100% 70–98% 100% Reaction rate Low Medium Medium Water Tap water Ion water Pure water

Safety High Explosion, toxicity may be possible High Cost Low Medium High

, Mg(OH)2 Cl2

**Table 2.** Three primary producing hydrogen water methods [20–22].

In this section, we give a systematic study on the method of magnesium hydride hydrolysis for producing hydrogen-water. At first, this method provided to an increasing the theoretical hydrogen amount by two times than that of the technique of magnesium hydrolysis. The hydrogen-water produced from this method belongs to alkaline water. At room temperature, the reaction is prolonged because the low reaction kinetics and the surface are gradually covered with an insoluble layer of hydroxide on the outer to hinder response continuously. However, it can activate by using citric acid as a chelating agent. Like, citric acid can dissolve metal oxides by making them dissoluble. Citric acid belongs to a weak organic acid that has

citric acid cycle occurred in the metabolism of all aerobic organisms. The chemical reaction of the citric acid cycle is the source of two-thirds of the food-derived energy in higher living creatures. Hans Adolf Krebs also received the 1953 Nobel Prize in Physiology Medicine for the discovery. In this study, citric acid acts as both of a catalyst to activate reaction kinetics and a chelating agent to inhibit the magnesium hydroxide formation over the complete

. In biochemistry, the citric acid acts as an intermediate in the

1% after half an hour.

By-product Mg+2, OH−

122 Magnesium Alloys - Selected Issue

the chemical formula C6

H8 O7

**3. Results and discussion**

$$\mathrm{MgH\_{2(s)}} \rightarrow \mathrm{Mg^{+2}\_{(aq)}} + 2\mathrm{H^{-}} \tag{9}$$

The magnesium hydride hydrolysis reaction shows a similar qualitative process. At the beginning of the response, water molecule reacts with magnesium hydride to release magnesium ions and negative hydrogen ions. And then, the negative hydrogen ions continuously split water molecules releasing hydrogen gas and hydroxide ions. Therefore, we can observe a steep increase in pH value.

$$2\mathrm{H}^{\cdot} + 2\mathrm{H}\_{2}\mathrm{O}\_{(0)} \rightarrow \mathrm{H}\_{2\mathrm{aq}} + 2\mathrm{OH}^{-} \tag{10}$$

While the reaction reached the observed equilibrium of pH 11.0, more and more magnesium hydroxide precipitated on the outer surface of the magnesium hydride from the initially supersaturated solutions state. It is in excellent agreement with the observed pH of saturated solutions of magnesium hydroxide in the literature [23, 25].

$$\text{Mg}^{\ast 2} \underset{\text{(aq)}}{\text{+2OH}^-} \text{+2OH}^- \rightarrow \text{Mg(OH)}\_{2\text{(s)}} \tag{11}$$

**Figure 3.** The method of magnesium hydride hydrolysis producing hydrogen-water.

The reaction percentage was calculated by:

/H2

 in theoretical value in Eq. (12).(13) The above behavior has also confirmed in our experiments with a stoichiometric amount of citric acid. For applications, the system injects a small amount of citric acid solution by a sequence of multiple separate times of various steps. To overcome the insoluble passivation layer, the mole ratio of citric acid to magnesium hydride is 2:3. About five times the mass of citric acid compared to magnesium hydride is necessary. **Figure 5** shows the measured reaction degree of magnesium hydride hydrolysis for 0.02, 0.05, and 0.1 moles of citric acid per one-liter-pure water. This data also compared with the literature of Hiraki et al. [26]. The time of dissolving molecular hydrogen as shown in the figure was sufficient for continuous use of 30 min for clinical applications. Finally, citric acid can completely prevent the insoluble passivation layers of magnesium hydroxide and thus significantly increase the reaction kinetics

Clinical Applications of Magnesium Hydride http://dx.doi.org/10.5772/intechopen.79507 125

The magnesium hydride hydrolysis is a very promising method to generate saturated hydrogen water since it is cheap, nontoxic, with a very long shelf life to give a two-times storage capacity of hydrogen than that of metallic magnesium. However, pure magnesium hydride hydrolysis reacts extremely slow and incompletely with water. At room temperature, the yield of hydrogen is less than 1% after half an hour. The addition of a small amount of citric acid solution highly increases the reaction kinetics and hydrogen yield. The kinetics and yield strongly depend on the pH in the solution, which can be adjusted by acids. This technology can serve as a superior replacement for magnesium hydrolysis, avoiding the danger of magnesium burning in oxygen. It is also a significant weight reduction in clinical applications while comparing with other methods of generating hydrogen-water. However, a small amount of molecular hydrogen on oxidative stress by efficiently neutralizing reactive oxygen species only explains part of the phenomena. Now, it is challenged by increasingly accumulated evidence. The future needs to prove the clinical effectiveness, and the evidence in the hydrogen molecular mechanism, medical,

Reaction degree in % = H2

and yield.

**4. Conclusions**

and biological effects.

**Author details**

Chung-Hsing Chao

Address all correspondence to<EMAIL_ADDRESS>
Ta Hwa University of Science and Technology, Hsinchu County, Taiwan R.O.C

**Figure 4.** Magnesium hydride (the external size of 35 × 35 × 17 millimeter, Bio-Coke Ltd. Japan).

That is to say, if we carefully control the pH in the hydrolysis reaction less than 11 with magnesium ions concentration less than 0.007 mol per liter, the supersaturated solution state in the solution will not occur. The insoluble magnesium hydroxide layer will not form on the surface to impede hydrolysis reaction. Magnesium hydride is split extremely slow to the hydrogen-saturated state (0.8 mM). The pH-dependence of the hydrolysis behavior of magnesium hydride seems reasonable. Furthermore, we repeatedly inject a small amount of citric acid solution before supersaturation state. The citric acid as a chelating agent can effectively reduce the concentration of magnesium ions and hydroxide ions to generate the soluble magnesium citrate.

$$\text{3MgH}\_{2(s)} \star \text{2C}\_3\text{H}\_4\text{(OH)}\text{(COOH)}\_{3\text{aq}} \rightarrow \text{6H}\_{2(aq)} \star \text{Mg}\_3\text{[C}\_3\text{H}\_4\text{(OH)}\text{(COO)}\_3\text{]}\_{2(aq)} \tag{12}$$

**Figure 5.** Reaction degree measured in the present result, which also compared with the data of [26].

The reaction percentage was calculated by:

Reaction degree in % = H2 /H2 in theoretical value in Eq. (12).(13)

The above behavior has also confirmed in our experiments with a stoichiometric amount of citric acid. For applications, the system injects a small amount of citric acid solution by a sequence of multiple separate times of various steps. To overcome the insoluble passivation layer, the mole ratio of citric acid to magnesium hydride is 2:3. About five times the mass of citric acid compared to magnesium hydride is necessary. **Figure 5** shows the measured reaction degree of magnesium hydride hydrolysis for 0.02, 0.05, and 0.1 moles of citric acid per one-liter-pure water. This data also compared with the literature of Hiraki et al. [26]. The time of dissolving molecular hydrogen as shown in the figure was sufficient for continuous use of 30 min for clinical applications. Finally, citric acid can completely prevent the insoluble passivation layers of magnesium hydroxide and thus significantly increase the reaction kinetics and yield.

#### **4. Conclusions**

That is to say, if we carefully control the pH in the hydrolysis reaction less than 11 with magnesium ions concentration less than 0.007 mol per liter, the supersaturated solution state in the solution will not occur. The insoluble magnesium hydroxide layer will not form on the surface to impede hydrolysis reaction. Magnesium hydride is split extremely slow to the hydrogen-saturated state (0.8 mM). The pH-dependence of the hydrolysis behavior of magnesium hydride seems reasonable. Furthermore, we repeatedly inject a small amount of citric acid solution before supersaturation state. The citric acid as a chelating agent can effectively reduce the concentration of magnesium ions and hydroxide ions to generate the soluble mag-

**Figure 4.** Magnesium hydride (the external size of 35 × 35 × 17 millimeter, Bio-Coke Ltd. Japan).

3(aq) → 6H2(aq)

+ Mg3 [C3 H4

(OH) (COO)

3]2(aq)

(12)

(OH) (COOH)

**Figure 5.** Reaction degree measured in the present result, which also compared with the data of [26].

nesium citrate.

124 Magnesium Alloys - Selected Issue

3MgH2(s) + 2 C3 H4

The magnesium hydride hydrolysis is a very promising method to generate saturated hydrogen water since it is cheap, nontoxic, with a very long shelf life to give a two-times storage capacity of hydrogen than that of metallic magnesium. However, pure magnesium hydride hydrolysis reacts extremely slow and incompletely with water. At room temperature, the yield of hydrogen is less than 1% after half an hour. The addition of a small amount of citric acid solution highly increases the reaction kinetics and hydrogen yield. The kinetics and yield strongly depend on the pH in the solution, which can be adjusted by acids. This technology can serve as a superior replacement for magnesium hydrolysis, avoiding the danger of magnesium burning in oxygen. It is also a significant weight reduction in clinical applications while comparing with other methods of generating hydrogen-water. However, a small amount of molecular hydrogen on oxidative stress by efficiently neutralizing reactive oxygen species only explains part of the phenomena. Now, it is challenged by increasingly accumulated evidence. The future needs to prove the clinical effectiveness, and the evidence in the hydrogen molecular mechanism, medical, and biological effects.

#### **Author details**

Chung-Hsing Chao

Address all correspondence to<EMAIL_ADDRESS>
Ta Hwa University of Science and Technology, Hsinchu County, Taiwan R.O.C

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