Patent ID: 7700216

Claim:
A stack for a fuel cell system comprising: an electricity generating unit including a membrane-electrode assembly (MEA) and a separator disposed on either surface of the MEA; an end plate at either side of the electricity generating unit, the end plate comprising an inner surface facing the electricity generating unit and an outer surface opposite the inner surface; a restraint portion joined with the end plate and fastening the end plate and the electricity generating unit together, wherein the restraint portion includes a restraint rod in the end plate and a nut screw-joined with the restraint rod for fastening the restraint rod to the end plate; and an element for reducing stress concentration coupled to the outer surface of the end plate to reduce a stress force generated by the nut from concentrating at a portion where the restraint portion is joined with the end plate, wherein a perimeter size of the end plate is larger than a perimeter size of the electricity generating unit, and the end plate comprises an inner portion having a size corresponding to the perimeter size of the electricity generating unit and an edge portion located outside of the inner portion, and wherein a portion of the edge portion proximate to where the restraint rod and the nut are screw-joined with each other is bent at an angle toward the electricity generating unit relative to the inner portion.