Fuel cell stack and manufacturing method therefor

1. A fuel cell stack comprising:

a plurality of unit cells stacked together; and

a tightening member configured to tighten the plurality of unit cells along a stacking direction of the plurality of unit cells, wherein

each of the unit cells includes:

a MEGA (Membrane-Electrode Gas-diffusion-layer Assembly) plate having a MEGA and a frame member bonded around the MEGA; and

two separators for holding the MEGA plate therebetween,

at least one separator of the two separators is formed of a press-formed plate having recesses and protrusions,

among portions of the recesses and protrusions, a portion coming toward the MEGA plate is designated as recessed portion, and a portion going apart from the MEGA plate is designated as protruded portion,

the one separator has a first recessed portion bonded to the frame member, a first protruded portion contiguous to the first recessed portion, and a second recessed portion formed on one side of the first protruded portion opposed to the first recessed portion,

the fuel cell stack is capable to take a tightened state in which a tightening load is imparted to the plurality of unit cells by the tightening member, and a non-tightened state in which no tightening load is imparted by the tightening member while the plurality of unit cells are maintained to be stacked together, and

the second recessed portion is in contact with the frame member in the tightened state, and the second recessed portion is out of contact with the frame member in the non-tightened state.

2. The fuel cell stack in accordance with claim 1 , wherein

the first protruded portion is formed at a position inside the first recessed portion while the second recessed portion is formed inside the first protruded portion.

3. The fuel cell stack in accordance with claim 1 , wherein

an other separator of the two separators has a first recessed portion bonded to the frame member, a first protruded portion contiguous to the first recessed portion, and a second recessed portion formed on one side of the first protruded portion opposed to the first recessed portion at positions opposed to the first recessed portion, the first protruded portion, and the second recessed portion of the one separator, respectively, and

the second recessed portion of the one separator and the second recessed portion of the other separator are in contact with the frame member in the tightened state, and the second recessed portion of the one separator and the second recessed portion of the other separator are out of contact with the frame member in the non-tightened state.

4. A method of manufacturing a fuel cell stack comprising the steps of:

(a) preparing a plurality of unit cells, and a tightening member configured to tighten the plurality of unit cells; and

(b) stacking the plurality of unit cells together and tightening the plurality of unit cells along a stacking direction of the plurality of unit cells by the tightening member, wherein

each of the unit cells includes:

a MEGA (Membrane-Electrode Gas-diffusion-layer Assembly) plate having a MEGA and a frame member bonded around the MEGA; and

two separators for holding the MEGA plate therebetween,

at least one separator of the two separators is formed of a press-formed plate having recesses and protrusions,

among portions of the recesses and protrusions, a portion coming toward the MEGA plate is designated as recessed portion, and a portion going apart from the MEGA plate is designated as protruded portion,

the one separator has a first recessed portion bonded to the frame member, a first protruded portion contiguous to the first recessed portion, and a second recessed portion formed on one side of the first protruded portion opposed to the first recessed portion so as to be out of contact with the frame member,

the step (b) includes imparting a tightening load to the plurality of unit cells by the tightening member so as to put the second recessed portion of the one separator into contact with the frame member,

the fuel cell stack is capable to take a tightened state in which the tightening load is imparted to the plurality of unit cells by the tightening member, and a non-tightened state in which no tightening load is imparted by the tightening member while the plurality of unit cells are maintained to be stacked together, and

the second recessed portion is in contact with the frame member in the tightened state, and the second recessed portion is out of contact with the frame member in the non-tightened state.

5. The method in accordance with claim 4 , wherein

the first protruded portion is formed at a position inside the first recessed portion while the second recessed portion is formed inside the first protruded portion.

6. The method in accordance with claim 4 , wherein

an other separator of the two separators has a first recessed portion bonded to the frame member, a first protruded portion contiguous to the first recessed portion, and a second recessed portion formed on one side of the first protruded portion opposed to the first recessed portion at positions opposed to the first recessed portion, the first protruded portion, and the second recessed portion of the one separator, respectively, and

the second recessed portion of the one separator and the second recessed portion of the other separator are in contact with the frame member in the tightened state, and the second recessed portion of the one separator and the second recessed portion of the other separator are out of contact with the frame member in the non-tightened state.