the following description is of the best - contemplated mode of carrying out the invention . this description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense . the scope of the invention is best determined by reference to the appended claims . fig2 is an exploded view of a fuel cell 100 of a first embodiment of the invention . fig3 a is a sectional view of the fuel cell along i - i direction of fig2 . fig3 b is an assembly view of the first embodiment of the invention . with reference to fig2 , 3 a and 3 b , the fuel cell 100 of the first embodiment of the invention comprises a substrate layer 110 , a first electrode 111 , a second electrode 112 , a first chamber layer 120 and a second chamber layer 130 . the substrate layer 110 comprises a first surface 113 and a second surface 114 . the first surface 113 is opposite to the second surface 114 . the first electrode 111 is formed on the first surface 113 . the second electrode 112 is formed on the second surface 114 . the first chamber layer 120 is disposed on the first electrode 111 . the first chamber layer 120 comprises a first flow passage 121 and a first fuel chamber 122 . the first flow passage 121 is connected to the first fuel chamber 122 . a first gas ( oxygen ) 101 passes the first flow passage 121 entering the first fuel chamber 122 to contact the first electrode 111 . the second chamber layer 130 is disposed on the second electrode 112 . the second chamber layer 130 comprises a second flow passage 131 and a second fuel chamber 132 . the second flow passage 131 is connected to the second fuel chamber 132 . a second gas ( hydrogen ) 102 passes the second flow passage 131 entering the second fuel chamber 132 to contact the second electrode 121 . the substrate layer 110 , the first electrode 111 , the second electrode 112 , the first chamber layer 120 and the second chamber layer 130 are combined by co - firing . in the first embodiment , the first fuel chamber 122 and the second fuel chamber 132 are through holes . the first gas ( oxygen ) 101 is ionized into oxygen ions . the oxygen ions enter the substrate layer 110 , moving to the second electrode 112 , and react with the second gas ( hydrogen ) 102 to generate water , heat and electricity . in the fuel cell 100 of the first embodiment , the first chamber layer 120 is disposed on the first surface 113 , and the second chamber layer 130 is disposed on the second surface 114 . the first chamber layer 120 further comprises a third flow passage 123 . the second chamber 130 further comprises a fourth flow passage 133 . the substrate 110 further comprises a fifth flow passage 115 and a sixth flow passage 116 . the fifth flow passage 115 is connected to the first flow passage 121 and the fourth flow passage 133 . the sixth flow passage 116 is connected to the second flow passage 131 and the third flow passage 123 . fig3 c is a sectional view along ii - ii direction of fig2 . with reference to fig2 and fig3 c , the substrate layer 110 comprises wire holes 117 , the first chamber layer comprises wire holes 124 , and the second chamber layer 130 comprises wire holes 134 . the wire holes 117 , 124 and 134 contain wires 1171 , 1241 and 1341 to conduct the electricity generated by the fuel cell . with reference to fig3 a , the first electrode 111 comprises a first collecting film 1111 , the first collecting film 1111 is formed on a surface of the first electrode 111 , the second electrode 112 comprises a second collecting film 1121 , and the second collecting film 1121 is formed on a surface of the second electrode 112 . the substrate layers comprises : ( a ) cerium oxide or zirconium oxide single -/ co - doped with positive ion with + 2 or + 3 charges ; ( b ) lamo 2 o 9 ; or ( c ) perovskite . the first and second electrodes comprise : ( a ) pt , au , pd , rh , ir , ru , os , ni , co and fe ; ( b ) lasrmno 3 or lasrcofeo 3 ; or ( c ) a compound of cerium oxide and lasrmno 3 , or a compound of cerium oxide and lasrcofeo 3 . in a modified embodiment , the first and second electrodes further comprise a second phase material for resisting carbonization , poisoning or vulcanization , such as copper or cerium oxide . the first and second chamber layer comprise : ( a ) cerium oxide or zirconium oxide mixed with positive ion with + 2 or + 3 charges ; ( b ) lamo 2 o 9 ; ( c ) perovskite ; ( d ) magnesium aluminate spinel ; ( e ) lanthanum aluminum oxide ; or ( f ) aluminum oxide the substrate layer , the first electrode , the second electrode , the first chamber layer and the second chamber layer are co - fired by electric furnace , atmosphere furnace , microwave sintering furnace , laser annealing or heat press . the co - firing temperature is between 600 ° c . and 800 ° c . ( thin film process ) or between 1300 ° c . and 1600 ° c . ( thick film process ). the first and second electrodes are formed by screen print , inject print , spread or lift - off process . the thickness of the first and second electrodes is about 0 . 01 mm ( thick film process ) or between 10 μm and 20 nm ( thin film process ). in the embodiment of the invention , materials of the substrate layer , the first chamber layer and the second chamber layer are selected to be matched . additionally , the substrate layer , the first chamber layer and the second chamber layer are co - fired to be integrally formed . the structure strength and reliability of the fuel cell is improved . as well , the fuel cell is easier assembled , and a sealing problem is prevented . with reference to fig4 a , a plurality of fuel cells can be stringed up as a cell stack 100 ′. in the cell stack 100 ′, the first gas ( oxygen ) 101 travels in the fifth flow passage , the first flow passage and the fourth flow passage . the second gas ( hydrogen ) 102 travels in the sixth flow passage , the second flow passage and the third flow passage . a cover layer 141 is disposed on the top of the cell stack 100 ′, and a cover layer 142 is disposed on the bottom of the cell stack 100 ′. the cover layer 141 and the cover layer 142 limit flow paths of the first gas ( oxygen ) 101 and the second gas ( hydrogen ) 102 . the cell stack 100 ′ of the embodiment provides more electricity with a simplified structure and reduced dimension . as shown in fig4 b , the fuel cells of fig4 a are parallelly connected to provide increased voltage . fig4 c shows a modified embodiment of the invention , wherein the fuel cells are serially connected to provide increased voltage . fig5 shows a fuel cell 200 of a second embodiment of the invention comprising a substrate layer 210 , a first electrode 211 , a second electrode 212 , a first chamber layer 220 , a second chamber layer 230 , a first cover layer 251 and a second cover layer 252 . the substrate layer 210 comprises a first surface 213 and a second surface 214 . the first surface 213 is opposite to the second surface 214 . the first electrode 211 is formed on the first surface 213 . the second electrode 212 is formed on the second surface 214 . the first chamber layer 220 is disposed on the first electrode 211 . the first chamber layer 220 comprises a first flow passage 221 and a first fuel chamber 222 . the first flow passage 221 is connected to the first fuel chamber 222 . a first gas ( oxygen ) 101 passes the first flow passage 221 entering the first fuel chamber 222 to contact the first electrode 211 . the second chamber layer 230 is disposed on the second electrode 212 . the second chamber layer 230 comprises a second flow passage 231 and a second fuel chamber 232 . the second flow passage 231 is connected to the second fuel chamber 232 . a second gas ( hydrogen ) 102 passes the second flow passage 231 entering the second fuel chamber 232 to contact the second electrode 221 . the substrate layer 210 , the first electrode 211 , the second electrode 212 , the first chamber layer 220 and the second chamber layer 230 are combined by co - firing . the first electrode 211 comprises a first collecting film 2111 , the first collecting film 2111 is formed on a surface of the first electrode 211 , the second electrode 212 comprises a second collecting film 2121 , and the second collecting film 2121 is formed on a surface of the second electrode 212 . in the fuel cell 200 of the second embodiment , the material of the elements and co - firing process are similar to the first embodiment . fig6 shows a fuel cell 200 ′ of a modified embodiment of the second embodiment of the invention , wherein the fuel cell 200 ′ comprise a first wire hole 241 and a second wire hole 242 . the first wire hole 241 is connected to the first fuel chamber 222 via a connection passage 223 allowing the first gas 101 to travel from the first fuel chamber 222 to the first wire hole 241 . the second wire hole 242 is connected to the second fuel chamber 232 via a connection passage 233 allowing the second gas 102 to travel from the second fuel chamber 232 to the second wire hole 242 . fig7 shows another embodiment of the invention , wherein a plurality of cell stacks 100 ′ are integrated in a cell unit 300 . the cell unit 300 comprises a first unit chamber 310 and a second unit chamber 320 . the cell stacks 100 ′ are parallelly arranged between the first unit chamber 310 and the second unit chamber 320 . each cell stacks 100 ′ comprises a first connection hole 103 ′ and a second connection hole 104 ′. the first gas ( oxygen ) 101 travels in the first unit chamber 310 . the second gas ( hydrogen ) 102 travels in the second unit chamber 320 . the first gas ( oxygen ) 101 and the second gas ( hydrogen ) 102 enter each cell stacks 100 ′ via the first connection hole 103 ′ and second connection hole 104 ′. in the embodiment of fig7 , the cell unit 300 can be serially connected or parallelly connected to provide increased electricity . while the invention has been described by way of example and in terms of the preferred embodiments , it is to be understood that the invention is not limited to the disclosed embodiments . to the contrary , it is intended to cover various modifications and similar arrangements ( as would be apparent to those skilled in the art ). therefore , the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements .