MEMBRANE-ELECTRODE ASSEMBLY, FUEL CELL STACK, FUEL CELL SYSTEM AND OPERATION METHOD THEREOF
A membrane-electrode assembly includes: a polymer electrolyte membrane; catalyst layers disposed on the polymer electrolyte membrane; and gas diffusion layers respectively disposed on the catalyst layers. Each of the gas diffusion layers is constituted by a porous member containing electrically-conductive particles and polymer resin as major components, and a ratio (y/x) of a tensile strength y (N/cm) of the gas diffusion layer to a dry-wet size change rate x (%) of the polymer electrolyte membrane is 0.10 or higher.
1 . A membrane-electrode assembly comprising:
a polymer electrolyte membrane;
catalyst layers disposed on the polymer electrolyte membrane; and
gas diffusion layers respectively disposed on the catalyst layers, wherein:
each of the gas diffusion layers is constituted by a porous member containing electrically-conductive particles and polymer resin as major components; and
a ratio y/x of a tensile strength y (N/cm) of the gas diffusion layer to a dry-wet size change rate x (%) of the polymer electrolyte membrane is 0.10 or higher.
2 . The membrane-electrode assembly according to claim 1 , wherein the tensile strength y of the gas diffusion layer is 4.2 N/cm or lower.
3 . The membrane-electrode assembly according to claim 1 , wherein each of the dry-wet size change rate in a length direction that is a flow direction of the polymer electrolyte membrane when producing the polymer electrolyte membrane and the dry-wet size change rate in a width direction perpendicular to the length direction is 20% or lower.
4 . The membrane-electrode assembly according to claim 1 , wherein an adhesive strength between the catalyst layer and the gas diffusion layer is 0.1 MPa or higher.
5 . A fuel cell stack comprising
a plurality of cells, each including the membrane-electrode assembly according to claim 1 and a pair of plate-shaped separators sandwiching the membrane-electrode assembly, wherein
a width of a groove that is a reactant gas channel formed on a main surface of each of the separators is 1.1 mm or shorter, the main surface being opposed to the gas diffusion layer of the membrane-electrode assembly.
6 . A fuel cell system comprising:
a fuel cell stack including a plurality of cells, each including the membrane-electrode assembly according to claim 1 and a pair of plate-shaped separators sandwiching the membrane-electrode assembly, reactant gas channels being respectively formed on main surfaces of the separators, the main surfaces being respectively opposed to the pair of gas diffusion layers of the membrane-electrode assembly; and
a reactant gas supply device configured to respectively supply a fuel gas and an oxidizing gas as reactant gases to the reactant gas channels of the pair of separators.
7 . A method of operating a fuel cell system,
the fuel cell system comprising:
a fuel cell stack including a plurality of cells, each including the membrane-electrode assembly according to claim 1 and a pair of plate-shaped separators sandwiching the membrane-electrode assembly, reactant gas channels being respectively formed on main surfaces of the separators, the main surfaces being respectively opposed to the pair of gas diffusion layers of the membrane-electrode assembly; and
a reactant gas supply device, wherein
the fuel cell stack generates electric power in such a manner that the reactant gas supply device respectively supplies a fuel gas and an oxidizing gas as reactant gases to the reactant gas channels of the pair of separators of the fuel cell stack.
8 . The method according to claim 7 , wherein the fuel cell stack generates the electric power under conditions that a temperature inside the fuel cell stack is not lower than 5° C. and not higher than 90° C.
9 . The method according to claim 7 , wherein the fuel cell stack generates the electric power under conditions that a relative humidity inside the membrane-electrode assembly is not lower than 0% and not higher than 100%.