among the various types of fuel cells , polymer electrolyte fuel 
 cells ( pefcs ) have attracted the most attention for transportation 
 and portable applications .
advantages include the following : rapid 
 start - up and shut down , low temperature operation ( 80 c ) , 
 high power density , and fully solid state components .
current state - of - the - art 
 technology uses platinum ( pt ) or platinum alloys supported on carbon 
 for both anode and cathode electrodes .
it is estimated that the catalyst 
 layers contribute to as much as 39% of the total fuel cell stack cost , making it one of the major challenges for pefc 
 commercialization . in order to meet the u.s .
department of energy 
 ( doe ) targets for 2015 , it is necessary to reduce the amount of pt 
 catalyst used by three - quarters , while ensuring the same performance .
another major challenge is insufficient durability ; 
 current state - of - the art performance under realistic operating conditions 
 is just half of the target set by the doe .
it is generally accepted that catalyst activity and durability depends 
 on pt particle size and dispersion ( which can be affected by the support 
 material ) , as well as the interaction between the catalyst particle 
 and the support .
the most widely used 
 catalyst support is carbon black vulcan xc-72r , which has high surface 
 area and good electrical conductivity . however
, pt particles can get 
  buried  inside the pores and hence reduce the active 
 triple - phase boundary accessible for electrochemical reaction .
furthermore , 
 vulcan xc-72r is electrochemically unstable at high potential , leading 
 to corrosion after extended operation in acidic media and varying 
 potentials . as the carbon corrodes , pt nanoparticles agglomerate into 
 larger particles and/or detach from the support material , consequently 
 reducing the electrochemical surface area ( ecsa ) and catalytic activity . to solve this issue ,
much effort has been directed toward 
 the development 
 of alternative , chemically stable catalyst supports . in recent years , 
 numerous conductive ceramics or oxide containing composites have been 
 studied ; these include ito , wo3 , tio2 , ceo2 and ceo2zro2 , wc , ti4o7 , nbo2 or nb2o5 , tin , 
 tib2 , and sic .
various graphitized carbon support materials with special pore structures 
 have also been explored , such as carbon nanotubes ( cnts ) , nanofibers 
 ( cnfs ) , nanohorns ( cnhs ) , and nanocoils ( cncs ) . despite having promising performance and durability , there are concerns 
 over their costly and complex synthesis methods .
the graphitic structure has been shown to be effective at increasing 
 durability ; however , its inert surface has a limited amount of active 
 sites where the pt nanoparticle can stably anchor .
these are often 
 associated with structural electronic defects that yield higher interaction 
 energy with the metal nanoparticle . a reasonable balance between catalyst 
 dispersion and catalyst  support interaction is necessary to 
 meet the fuel cell performance requirement .
an emerging trend 
 is to dope the carbon support materials with 
 oxygen or nitrogen , which act as 
tethers  or  anchors  
 by increasing the interaction of the catalyst with the supporting 
 materials , which leads to increased pt nanoparticle dispersions .
unfortunately , surface oxygen functional groups on carbon are known 
 to reduce the durability of fuel cell catalysts by promoting carbon 
 corrosion . on the other hand ,
a growing 
 body of literature suggests that the presence of nitrogen in carbon 
 supports improves durability , as well as enhancing the intrinsic catalytic 
 activity for both oxygen reduction reaction ( orr ) and methanol oxidation 
 reaction ( mor ) .
the incorporation of nitrogen into carbon leads to a reduction in 
 detrimental surface oxygen groups and thus provides enhanced tolerance 
 toward oxidation .
the role of the n - surface 
 species in catalytic enhancement is less studied and has only been 
 hypothesized based on experimental observation and physicochemical 
 reasoning .
n defects near 
 the catalyst  particle interface adsorb oxygen containing intermediates 
 that would otherwise block catalyst active sites , and thereby facilitate 
 their removal and increase the rate of electrochemical reaction .
it has been shown that the n - dopant alters the catalyst electronic 
 structure , resulting in a higher binding energy , which may decrease 
 the specific interaction between the pt nanoparticles and poisoning 
 intermediates .
this is further supported 
 by an x - ray photoelectron spectroscopy ( xps ) study and theoretical 
 calculations , where it was observed that pt nanoparticles nucleate 
 strongly and experience a strong  tethering
n - doped carbon materials also 
 have higher specific capacitance , suggesting the presence of additional 
 charged species within the helmholtz layer , which might provide sites 
 for surface groups to participate in the removal of strongly adsorbed 
 poisoning intermediates . given 
 the potential of n - doped carbon materials ,
graphitic carbon 
 nitride material was chosen as a suitable candidate for a catalyst 
 support in this study .
polymeric solids with high n : c ratios formed 
 by reactions of nitrogen - rich molecules were first reported by berzelius 
 and later studied by liebig , franklin , pauling , and others .
a fully condensed end member has the composition c3n4 with a planar structure related to graphite or graphene . 

however , most graphitic carbon nitrides are composed of c and n , along 
 with residual amounts of h , and they are attracting new interest due 
 to their unique structural and optoelectronic properties .
the structures are based on triazine ( c3n3 ) or heptazine ( c6n7 ) ring units linked by 
 n = or nh bridges to form sheets or zigzag 
 chains of monomer units linked by hydrogen bonds to give a 2d array . 

typical examples include liebig s melon , melem , or highly condensed 
 cxnyhz graphitic structures formed by continued 
 elimination of nh3 component ( figure 1a  c ) .
recent discussions of graphitic carbon nitride structures 
 and their properties have been based mainly on polymerized heptazine 
 models that are shown to more thermodynamically stable , but structures based on condensation of s - triazine rings can also 
 be produced under different synthesis conditions , and both structure 
 types may be present .
structural motifs found in graphitic carbon nitrides : 
 ( a ) liebig s 
 melon ( [ c6n7(nh2)(nh)]n ) contains zigzag chains of heptazine ( tri - s - triazine ) 
 units linked by bridging nh groups and decorated on 
 their edges by n 
h groups , ( b ) fully condensed c3n4 layer based on heptazine units , and ( c ) graphitic carbon 
 nitride based on triazine ring units .
graphitic carbon nitrides are semiconductors with an intrinsic 
 band gap near 2.7 ev and optical absorption extending into the visible 
 range .
these materials exhibit catalytic and photocatalytic 
 activity and are also of interest for their intercalation , ion exchange , 
 and redox properties .
because of their high nitrogen content , tunability reminiscent of 
 polymer chemistry , and facile synthesis procedure , they may provide 
 a good balance between activity , durability , and cost in pefc operation . 

 carbon composites 
 could provide comparable orr catalytic activity to that achieved by 
 commercial pt / c in alkaline electrolyte with enhanced durability and 
 high carbon monoxide ( co ) tolerance .
although 
 nitrogen in n - doped graphite / graphene introduces a charge carrier 
 ( n - type polaron ) , this charge is not necessarily localized on the 
 nitrogen . in the case of graphitic carbon nitride materials , they 
 are stoichiometric materials and contain abundant lewis acid and base 
 sites ( terminal and bridging nh groups and lone pairs of n 
 in triazine / heptazine rings , respectively ) that are potential anchoring 
 sites for pt as well as adsorption sites for co. to our knowledge , 
 the first application of graphitic carbon nitride as a catalyst support 
 can be attributed to yu et al . in 2007 for the direct methanol fuel 
 cell ( dmfc ) operation .
it was shown that 
 ptru supported on graphitic carbon nitride in dmfc exhibits 7883% 
 higher power density than on vulcan xc-72 .
previously , it was 
 shown that pt deposited on graphitic carbon 
 nitride is more stable than commercial pt / vulcan under acidic accelerated 
 carbon corrosion protocol ( after 1000 scans ) and has higher methanol 
 oxidation activity per electrochemical surface area .
in this study , three different graphitic carbon nitride 
 materials ( polymeric carbon nitride , crystalline poly(triazine ) amide , 
 and boron - doped graphitic carbon nitride ) were prepared , and their 
 electrochemical durability was investigated in comparison to conventional 
 carbon black , vulcan xc-72 .
pt nanoparticles were deposited on each 
 material , and their electrochemical properties and potential applications 
 in pefc were investigated .
polymeric 
 carbon nitride ( gcnm ) was prepared by thermolysis and 
 condensation reactions of a 1:1 molar ratio mixture of dicyandiamide 
 ( dcda , c2n4h4 ) and melamine ( c3n6h9 ) at 550 c .
a finely ground 
 sample was loaded in an alumina boat into a quartz tube in a tubular 
 furnace under nitrogen flow .
the temperature was raised to 550 c 
 at 5 c / min for 15 h. crystalline poly(triazine)imide ( pti / licl ) was synthesized from dcda in molten 
 eutectic licl / kcl ( 45:55 wt % ) mixtures heated at 400 c under 
 n2 ( g ) for 6 h and then sealed under vacuum and heated 
 to 600 c for 12 h. b - doped graphitic carbon nitride ( b - gcnm ) 
 was prepared by using 
 ionic liquids . in a typical synthesis , 1-butyl-3-methylimidazolium 
 tetrafluoroborate ( bmimbf4 ) was dissolved in water and 
 stirred for 5 min
. then dcda was added , and the mixture was heated 
 at 100 c in an oil bath until the water completely evaporated . 

the resulting solid was then heated in an alumina crucible for 2 h 
 at 350 c and kept at this temperature for 4 h. then , the temperature 
 was raised to 550 c for another 4 h and finally cooled to room 
 temperature .
the pt 
 catalyst was deposited onto gcnm using the ethylene glycol reduction 
 method .
ground gcnm ( 0.09 g ) was dispersed in 200 ml of ethylene glycol 
 ( fisher scientific ) , and chloroplatinic acid ( 39.82% pt basis , 0.1507 
 g , sigma aldrich ) was added to the suspension .
the mixture was stirred 
 for 4 h under inert atmosphere and then heated to 140 c for 
 3 h , resulting in a dark brown mixture .
the solid product was collected 
 via vacuum filtration and dried at 60 c in a vacuum oven .
the 
 pt loading was 40 wt % for pt / gcnm and 20 wt % for pt / pti - licl and pt / b - gcnm .
c , n , h analyses for gcnms were performed 
 using a carlo - erba ea1108 system .
sem was performed with a jeol jsm-6301f 
 field emission imaging system at 5 kv .
tem images were taken using 
 a jeol tem1010 instrument operating at 80 kv and hrtem images were 
 taken using a jeol tem2010 instrument operating at 200 kv .
the x - ray 
 diffraction data were obtained using a bruker - axs d4 system for the 
 support materials and stoe powder diffractometer for the supported 
 catalyst materials .
bet measurements were carried out using a micrometrics 
 asap 2420 surface area / porosity analyzer .
the electrochemical measurements were carried 
 out in a conventional 
 three - electrode cell connected to an autolab pgstat32 potentiostat . 

a glassy carbon ( gc ) electrode with a surface area of 0.196 cm was employed as a working electrode , a pt mesh was used as 
 a counter electrode , and a hydrogen reference electrode ( gaskatel ) , 
 joined to the main chamber via a luggin capillary , was used as a reference 
 electrode .
a catalyst ink of 1.4 mg ml was obtained 
 by dispersing the catalyst in a mixture of acetone , isopropyl alocohol , 
 and nafion ultrasonically for 1 h. the ink was deposited on the gc 
 and dried at room temperature , resulting in a loading of 35 g 
 cm .
the working electrode was electrochemically 
 cleaned prior to each measurement via potential cycling between 0 
 and 1.2 v for 10 cycles , or until a steady state was reached , at a 
 scan rate of 20 mv s. all electrochemical measurements 
 were carried out at 25 c in 0.1 m hclo4 , except for 
 mor which was carried out in 1 m ch3oh + 0.1 m hclo4 .
all chemicals used were analytical 
 grade , and solutions were prepared with deionized water ( millipore , 
 18.2 mcm ) an accelerated start  stop 
 cycling protocol was used for the carbon corrosion test .
one cycle 
 involves applying a voltage hold at 1.0 v for 30 s followed by two 
 sequences of voltage cycling between 1.0 and 1.5 at 0.5 v s. the change in cyclic voltammogram ( capacitance and electrochemical 
 surface area ) was monitored after 1 , 10 , 20 , 50 , 100 , 200 , 500 , 1000 , 
 and 2000 cycles .
in this study , 
 different graphitic carbon nitride phases were prepared 
 with the aim to address the effect of catalyst support properties 
 such as crystallinity , porosity , and composition on the electrochemical performance in pefc .
polymeric carbon nitride 
 was prepared using a typical method of thermolysis and condensation . 
 electronically modified graphitic carbon nitride with high porosity 
 was prepared using ionic liquid under the same conditions , whereas 
 highly crystalline graphitic carbon nitride was prepared via ionothermal 
 method .
layered carbon nitride was 
 prepared by thermolysis and condensation reactions of 1:1 molar ratio 
 mixtures of dicyandiamide ( c2n4h4 ) and melamine ( c3n6h9 ) at 550 c 
 for 15 h. finely ground samples were 
 heated in a tubular furnace under n2 flow at 5 c / min 
 and allowed to cool to room temperature before being removed . upon 
 heating
, the condensation process takes place by removal of nh3 species leading to materials with different c : n : h stoichiometry 
 depending on the synthesis temperature .
x - ray diffraction pattern 
 ( a ) and sem image ( b ) of a typical layered 
 carbon nitride prepared by thermal condensation of dcda / melamine 1:1 
 molar ratio . a typical x - ray diffraction 
 pattern ( xrd ) is shown in figure 2a .
the strong 
 peak at 27.5 2 
 corresponds to a repeat distance of 0.32 nm that correlates 
 with the 002 reflection usually observed for graphitic materials . 

the feature around 12.5 2 corresponds to an in - plane 
 repeat distance of 0.70 nm that matches with the dimensions of polyheptazine 
 or polytriazine structures within the layers .
scanning electron 
 microscope ( sem ) examination ( figure 2b ) indicated 
 that gcnm exhibits a latticework of 
 interlocking planar microstructures with individual layer thicknesses 
 on the order of 23 nm that give rise to porous aggregates 
 with pore sizes on the order of a few nanometers .
this material is 
 not highly condensed , and its structure is believed to be close to 
 that of liebig s melon .
the aggregates are fused together to 
 give rise to much larger pores ( 12 m ) in the resulting 
 solid .
the bet measurements showed a surface area of 28 m g. poly(triazine ) imide carbon nitride ( pti - licl ) was prepared using an ionothermal route . 

this method allowed us 
 to obtain a highly crystalline carbon nitride using relatively mild 
 conditions . in a typical synthesis ,
dcda was mixed with a eutectic 
 mixture of licl / kcl ( 45:55 wt % ) and heated at 400 c for 6 h 
 under n2 ( g ) followed by a thermal treatment under high 
 vacuum at 600 c for 12 h. the pti - licl compound exhibits a sharp series of peaks in the x - ray diffraction 
 pattern consistent with a p63 cm unit cell ( figure 3a ) .
the hexagonal symmetry of the pti - licl can be clearly seen in the sem images 
 of the hexagonal - shaped crystallites ( figure 3b ) .
this material is a triazine - based ( c3n3)2(nh)3.licl structure with li and 
 cl intercalated both within and between the graphitic 
 layers .
x - ray diffraction pattern ( a ) and sem 
 image ( b ) of a poly(triazine)imide 
 carbon nitride prepared by ionothermal route .
1-butyl-3-methylimidazolium 
 tetrafluoroborate ( bmimbf4 ) ionic liquid was used to modify 
 the electronic structure of gcnm by substituting c ( [ he]2s2p ) by b ( [ he]2s2p ) .
the x - ray diffraction pattern 
 ( figure 4a ) is dominated by the ( 002 ) interlayer - stacking 
 reflection usually observed in gcnms .
the higher porosity of b - gcnm 
 compared to gcnm and pti - licl is clearly 
 seen in the sem images ( figure 4b ) . a homogeneous 
 porosity with pores of about 5075 nm were detected .
x - ray diffraction 
 pattern ( a ) and sem image ( b ) of b - gcnm doped 
 with 10 wt % b. platinum was deposited onto the supports 
 via the ethylene glycol 
 method .
the xrd patterns ( figure 5a  d ) confirm the presence of platinum in each sample 
 as characterized by the peaks at 39.8 2 and 46.5 
 2 corresponding to pt 111 and 200 reflections , respectively . 

the tem images shown in figure 6a  d 
 indicate varying extents of pt nanoparticle dispersion in each sample , 
 with large agglomeration seen in all samples except for the commercial 
 catalyst .
x - ray diffraction pattern of supported pt electrocatalysts : ( a ) 
 pt / vulcan , ( b ) pt / gcnm , ( c ) pt / pti - licl , and ( d ) pt / b - gcnm .
the average pt crystallite sizes calculated using the scherrer 
 equation and the particle size estimated from tem images are summarized 
 in table 1 .
all pt on graphitic carbon nitride 
 materials have larger particle sizes ( 4.28.0 nm ) compared 
 to commercial pt / vulcan ( 3.5 nm ) .
this is due to the agglomeration 
 in all the samples , indicating that the method used for catalyst deposition 
 is not optimized .
tem images of ( a ) pt / vulcan , ( b ) pt / gcnm , ( c ) pt / pti - licl , and ( d ) pt / b - gcnm . estimated from tem image based on 
 the average of 100 particles . calculated from 111 signal widths 
 of xrd using the scherrer equation .
the stability 
 of the carbon nitrides was determined by observing the change in double - capacitance 
 in the cyclic voltammetry measurements while performing the carbon 
 corrosion test .
capacitance increases with the number of scans due 
 to an increase in surface area and concentration of hydrophilic carbon 
 corrosion products with oxygen functionalities at the surface of the 
 carbon support .
the presence of oxygen functionalities 
 reduces the durability of pefc catalysts by promoting carbon corrosion . 

in addition , a more hydrophilic surface may affect water management 
 in fuel cells and potentially contribute to performance instability 
 and variability .
figure 7 displays the degree 
 of corrosion behavior / surface modification of graphitic carbon nitride 
 materials , in comparison to a commercial vulcan carbon support .
after 
 2000 cycles , all materials exhibit a higher degree of tolerance to 
 cycling , compared to commercial carbon black ( vulcan ) , with b - gcnm 
 showing the best tolerance at only a 6% increase in capacitance at 
 the end of the cycle .
change in double - layer capacitance ( calculated at 0.40 
 v ) of the 
 support materials as a result of accelerated carbon corrosion cycling .
all carbon nitride supported pt 
 catalysts have lower initial electrochemical 
 surface area ( ecsa ) compared to commercial pt catalyst .
this is due to higher degree of agglomeration 
 and larger particle size , as shown in figure 6 .
this also indicates that each graphitic carbon nitride material 
 has a different ability to accommodate catalyst particles .
in addition , 
 carbon nitride materials have 1 order of magnitude less bet surface 
 area compared to vulcan carbon , and hence the same mass percentage 
 loading of pt nanoparticles on vulcan carbon would result in higher 
 pt particle density on graphitic carbon nitride .
change in ecsa ( calculated 
 from hydrogen adsorption / desorption ) 
 of the supported pt electrocatalsysts as a result of accelerated carbon 
 corrosion cycling .
the durability of the 
 materials in the presence of pt nanoparticles 
 was evaluated using the same accelerated protocol , with cv and ecsa 
 recorded at regular intervals as part of the diagnostic ( figure 8) .
the decrease in ecsa is believed to be due to 
 platinum agglomeration and dissolution as a result of substrate corrosion . at the end of the 2000 cycles ,
commercial pt / vulcan exhibits a 36.3% 
 decrease in ecsa ( table 2 ) .
pt / gcnm and pt / b - gcnm 
 show higher ecsa loss at 81.0% and 100% loss , respectively , despite 
 each support having higher degree of corrosion tolerance , as displayed 
 in figure 7 .
in addition , 
 it is also observed that graphitic carbon nitride supported pt catalysts 
 with higher initial ecsa exhibit higher electrochemical durability , 
 indicating there is a link between good metal 
support material that provides strong adsorption and 
 anchoring sites for the pt nanoparticles will increase particle dispersion 
 and limit leaching and agglomeration processes during the accelerated 
 test .
the catalytic 
 activities of graphitic carbon nitride supported pt catalysts were 
 investigated in 1 m methanol + 0.1 m hclo4 solution at 
 25 c .
it is generally accepted 
 that low overpotential and high peak current density are an indication 
 of good methanol oxidation reaction ( mor ) activity .
the current density 
 is normalized to the ecsa of each respective material due to the inherent 
 differences in ecsa .
all graphitic carbon nitride supported catalysts 
 exhibit lower overpotential and higher peak current density compared 
 to pt / vulcan .
in addition , pt / pti - licl exhibits the lowest overpotential whereas pt / b - gcnm has the highest 
 peak current density .
mor overpotential may be influenced by particle 
 size effects : smaller pt nanoparticles enhance the oxidation of poisoning 
 intermediates and , hence , decrease the overpotential .
given the difference in pt particle size in all materials with pt / vulcan 
 having the smallest particle size , particle size effect can be eliminated 
 from this observation .
this suggests that the presence of nitrogen 
 on / within the support material could lead to intrinsic mor catalytic 
 enhancement .
furthermore , each of the graphitic carbon nitride 
 materials has different structural properties and therefore would 
 require a different synthesis approach . methanol oxidation reaction 
 of supported pt electrocatalysts in 
 1 m ch3oh + 0.1 m hclo4 at 25 c with a 
 scan rate of 2 mv s.
for the first time , three different graphitic carbon nitride materials 
 ( polymeric gcnm , pti - licl , and b - doped 
 gcnm ) were prepared and tested as catalyst support materials for pefcs . 

the results show that all graphitic carbon nitride materials prepared 
 in this study exhibit significantly improved durability compared to 
 commercial carbon black ( vulcan xc-72r ) and , therefore , are promising 
 catalyst support materials for pefc applications .
interestingly , b - gcnm 
 and pti / licl exhibit the highest stability . 
 as shown on the x - ray diffraction patterns , b - gcnm and pti / licl are more crystalline than vulcan and 
 gcnm , suggesting that crystallinity may play an important role in 
 the stability of the material against carbon corrosion .
this also 
 suggests that the presence of dopants such as boron in b - gcnm , and 
 li and cl in pti / licl , may enhance the stability of the support materials .
the durability of graphitic carbon nitride supported pt electrocatalysts 
 is highly dependent on the initial ecsa .
the pt / b - gcnm , with the lowest 
 ecsa of all carbon nitride supported catalyst , exhibits the lowest 
 durability with a loss of 100% after 2000 cycles .
the pt - pti / licl has the best durability of all pt - supported 
 catalyst with an ecsa loss of only 19% after 2000 scans .
this value 
 is even lower than pt / vulcan with an ecsa loss of 36% . in addition , 
 all graphitic carbon nitride supported pt electrocatalysts have higher 
 methanol oxidation activity per ecsa , compared to pt / vulcan .
this work shows that graphitic carbon nitrides are promising catalyst 
 supports that can potentially replace conventional carbon support . 

the performance of pti / licl is highly encouraging , and further research 
 is already being developed to optimize catalyst particle dispersion 
 and utilization .
 graphitic 
 carbon nitrides are investigated for developing highly 
 durable pt electrocatalyst supports for polymer electrolyte fuel cells 
 ( pefcs ) . 
 three different graphitic carbon nitride materials were synthesized 
 with the aim to address the effect of crystallinity , porosity , and 
 composition on the catalyst support properties : polymeric carbon nitride 
 ( gcnm ) , poly(triazine ) imide carbon nitride ( pti / li+cl ) , and boron - doped graphitic carbon nitride ( b - gcnm ) . 
 
 following accelerated corrosion testing , all graphitic carbon nitride 
 materials are found to be more electrochemically stable compared to 
 conventional carbon black ( vulcan xc-72r ) with b - gcnm support showing 
 the best stability . 
 for the supported catalysts , pt / pti - li+cl catalyst exhibits better durability with only 
 19% electrochemical surface area ( ecsa ) loss versus 36% for pt / vulcan 
 after 2000 scans . 
 superior methanol oxidation activity is observed 
 for all graphitic carbon nitride supported pt catalysts on the basis 
 of the catalyst ecsa . 
Introduction
Experimental Section
Results
Conclusion