Polymer electrolyte fuel cell and fuel cell system including the same

A polymer electrolyte fuel cell comprising:

• an electrolyte layer-electrode assembly including an electrolyte layer and a pair of electrodes sandwiching the electrolyte layer;
• a plate-shaped electrically conductive first separator disposed so as to be in contact with one electrode of the pair of electrodes of the electrolyte layer-electrode assembly, wherein one main surface of the first separator is in contact with the one electrode, the one main surface having a first reaction gas flowing region which is formed in a winding shape and through which a first reaction gas flows, the first reaction gas flowing region including a plurality of groove-shaped first straight line portions and one or more first turn portions;
• and
• a plate-shaped electrically conductive second separator disposed so as to be in contact with another electrode of the pair of electrodes of the electrolyte layer-electrode assembly, wherein one main surface of the second separator is in contact with the other electrode, the one main surface being provided with a second reaction gas flowing region which is formed in a winding shape and through which a second reaction gas flows, the second reaction gas flowing region including a plurality of groove-shaped second straight line portions and one or more second turn portions, wherein:
• in the first separator, among the one or more first turn portions, at least a most upstream first turn portion has a first recess and a plurality of first projections rising from a bottom surface of the first recess,
• in the second separator, among the one or more second turn portions, at least one second turn portion has a second recess and a plurality of second projections rising from a bottom surface of the second recess, and
• when seen in a thickness direction of the first separator, the first and second recesses overlap with each other, and an overlap area is more than 0% and less than or equal to 5% of a gross area, the overlap area being a total overlap area between the first and second recesses and second separators, the gross area being a total of the following areas:
• an area of all the first recesses of the first separator;
• and an area of all the second recesses of the second separator.