Fuel cell stack having improved joining strength between separators

A fuel cell stack comprising:

• a membrane electrode assembly;
• and
• first and second separators joined to each other,
• wherein
• the membrane electrode assembly and the first and second separators are stacked,
• the first separator includes:
• a first coolant groove portion along which coolant flows on a side of the second separator facing the first separator;
• and
• first and second fluid groove portions along which a first reaction fluid flows on a side opposite to the second separator facing the first separator, the first and second fluid groove portions being adjacent to each other through the first coolant groove portion and extending along the first coolant groove portion,
• the second separator includes:
• a second coolant groove portion along which the coolant flows on a side of the first separator facing the second separator;
• and
• third and fourth fluid groove portions along which a second reaction fluid flows on a side opposite to the first separator facing the second separator, and the third and fourth fluid groove portions being adjacent to each other through the second coolant groove portion and extending along the second coolant groove portion,
• the first and third fluid groove portions face each other in a stacking direction in which the membrane electrode assembly and the first and second separators are stacked,
• the second and fourth fluid groove portions face each other in the stacking direction,
• the first and second coolant groove portions face each other in the stacking direction and define a common coolant flow path,
• the first fluid groove portion includes a wide portion in which a groove width of the first fluid groove portion is partially increased,
• the second fluid groove portion includes a narrow portion in which a groove width of the second fluid groove portion is partially decreased,
• the wide portion of the first fluid groove portion is joined to the third fluid groove portion,
• a groove width of a part of the third fluid groove portion joined to the wide portion of the first fluid groove portion is greater than a groove width of a part of the first fluid groove portion other than the wide portion of the first fluid groove portion, and
• the wide portion of the first fluid groove portion is adjacent to the narrow portion of the second fluid groove portion through the first coolant groove portion.