Even if reaction gas flows into a substantially rectangular anode-side and cathode-side gaps formed between an annular main body portion and a membrane electrode assembly in an anode side and a cathode side of a fuel cell, the reaction gas is prevented from flowing out from an outlet without passing through an electrode to cause degradation of power generation efficiency. At least one of anode-side gasket and cathode-side gasket in the fuel cell is provided with an extra sealing portion connected to an annular main body portion in such a manner that, among two pairs of gap portions opposing to each other in the anode-side gap and the cathode-side gap, the extra sealing portion intersects with one pair of gap portions having a larger pressure gradient of fuel gas and oxidant gas in a direction from an upstream side to a downstream side of a fuel gas flow channel and an oxidant gas flow channel.
1. A fuel cell including a unit cell comprising:
a membrane electrode assembly including a polymer electrolyte membrane with hydrogen ion conductivity, and an anode and a cathode sandwiching said polymer electrolyte membrane;
an anode-side separator with electric conductivity including a fuel gas flow channel for supplying and discharging a fuel gas to and from said anode;
a cathode-side separator with electric conductivity including an oxidant gas flow channel for supplying and discharging an oxidant gas to and from said cathode; and
an anode-side gasket disposed on a circumference portion of said membrane electrode assembly in a face of said anode-side separator and a cathode-side gasket disposed on a circumference portion of said membrane electrode assembly in a face of said cathode-side separator, for sealing said fuel gas and said oxidant gas, respectively, wherein
an anode-side gap of a substantially rectangular shape is formed between said anode-side gasket and said membrane electrode assembly in the side of said anode and a cathode-side gap of a substantially rectangular shape is formed between said cathode-side gasket and said membrane electrode assembly in the side of said cathode, and
at least one of said anode-side gasket and said cathode-side gasket has: an annular main body portion disposed along the circumference portion of said membrane electrode assembly; and an extra sealing portion being integrated with said main body portion and bridging two points on opposite sides of said main body portion such that, among two pairs of gap portions opposing to each other in said anode-side gap and said cathode-side gap, said extra sealing portion partially intersects with one pair of said gap portions having a larger pressure gradient of said fuel gas and said oxidant gas in a direction from an upstream side to a downstream side of said fuel gas flow channel and said oxidant gas flow channel.
2. The fuel cell in accordance with claim 1 , wherein at least one of said fuel gas flow channel and said oxidant gas flow channel has a serpentine shape including a plurality of straight line portions and a curved portion connecting said straight line portions adjacent to each other.
3. The fuel cell in accordance with claim 2 , wherein said extra sealing portion is placed on a rib between said plurality of straight line portions.
4. The fuel cell in accordance with claim 1 , wherein at least one of said anode-side gap and said cathode-side gap has a width of more than 0.3 mm and less than 1.5 mm.
5. The fuel cell in accordance with claim 1 , wherein said extra sealing portion is placed closer to an inlet side than an outlet side of said fuel gas flow channel and said oxidant gas flow channel.