Fuel cell stack

A fuel cell stack, comprising:

• unit cells stacked one above another, wherein
• each of the unit cells includes
• an electric power generator including a membrane electrode assembly, and
• two separators sandwiching the electric power generator,
• each of the two separators includes a first surface facing the electric power generator, and a second surface opposite the first surface,
• one of the two separators of one of the unit cells is in contact with one of the two separators of an adjacent one of the unit cells in a stacking direction of the unit cells to allow cooling medium to flow therebetween,
• a direction orthogonal to the stacking direction is referred to as a first direction, and a direction orthogonal to both the stacking direction and the first direction is referred to as a second direction,
• the first surface of each of the two separators includes a gas passage meandering back and forth in the first direction while extending in the second direction, in which reactant gas flows through the gas passage,
• the gas passage of each of the two separators in each of the unit cells is formed so that the reactant gas in the gas passage of one of the two separators flows in a direction opposite to a direction in which the reactant gas in the gas passage of the other one of the two separators flows,
• the second surface of each of the two separators includes a cooling passage meandering back and forth in the first direction while extending in the second direction, in which the cooling medium flows through the cooling passage,
• the cooling passage includes
• undulating portions extending in an undulating manner in the first direction and arranged in the second direction, in which each of the undulating portions includes a first end and a second end in the first direction, and
• a connecting portion that connects the first end of one of the undulating portions to the second end of an adjacent one of the undulating portions in the second direction,
• each of the unit cells includes a cooling medium supply manifold configured to supply the cooling medium to the cooling passage, and a cooling medium discharge manifold configured to discharge the cooling medium from the cooling passage,
• the cooling medium supply manifold and the cooling medium discharge manifold are located at opposite sides of the cooling passage in the first direction,
• the undulating portions include at least a first undulating portion and a second undulating portion located upstream of the first undulating portion with respect to a flow direction of the reactant gas, and
• the cooling medium flowing through the first undulating portion has a greater pressure loss than the cooling medium flowing through the second undulating portion.