Gas diffusion layer for fuel cell, method for manufacturing said layer, membrane-electrode assembly, and fuel cell

A gas-diffusion layer, used for fuel cells, the gas-diffusion layer comprising:

• a porous material that includes as main ingredients conductive particles and a polymer resin, wherein the gas-diffusion layer internally possesses pores with a size from 0.01 μm to 0.05 μm, and hollows with a size from about 1 μm to about 200 μm,
• wherein a fluid flow channel is formed on one side of the gas-diffusion layer,
• wherein the hollows are present only in ribs forming the fluid flow channel, and
• wherein the distribution of the pores is the same at a bottom of the fluid flow channel and at the ribs.

A method for producing a gas-diffusion layer used for fuel cells, the method comprising:

• (i) kneading conductive particles, a polymer resin, a pore-forming agent, a surfactant, and a dispersion solvent into a mixture;
• (ii) rolling the mixture obtained in Step (i) to shape the mixture into a sheet;
• (iii) baking the sheet-shaped mixture to sublime the pore-forming agent, thereby forming hollows therein, and to remove the surfactant and the dispersion solvent;
• (iv) further rolling the baked mixture to adjust a thickness of the baked mixture;
• and
• (v) pressing the sheet-shaped mixture rolled in Step (iv) against a mold having a patterned indented surface to form a fluid flow channel thereon,
• wherein, in Step (v), the hollows present in a part of the sheet-shaped mixture corresponding to a projecting part of the mold are crushed by the projecting part of the mold, such that a proportion of the hollows present in ribs forming the fluid flow channel is larger than a proportion of the hollows present in a bottom of the fluid flow channel, and
• wherein the distribution of pores is the same at the bottom and at the ribs.

A method for producing a gas-diffusion layer used for fuel cells, the method comprising:

• (i) kneading conductive particles, a polymer resin, a pore-forming agent, a surfactant, and a dispersion solvent into a mixture;
• (ii) rolling the mixture obtained in Step (i) to shape the mixture into a sheet;
• (iii) baking the sheet-shaped mixture to sublime the pore-forming agent, thereby forming hollows therein, and to remove the surfactant and the dispersion solvent;
• (iv) further rolling the baked mixture to adjust a thickness of the baked mixture;
• and
• (v) pressing the sheet-shaped mixture rolled in Step (iv) against a mold having a patterned indented surface to form a fluid flow channel thereon,
• wherein, in Step (v), the hollows present in a part of the sheet-shaped mixture corresponding to a projecting part of the mold are crushed by the projecting part of the mold, such that there are no hollows in a bottom of the fluid flow channel, and the hollows are present only in ribs forming the fluid flow channel, and
• wherein the distribution of pores is the same at the bottom and at the ribs.