Development of the sandwich end plate and composite bipolar plate for PEMFC stack

Abstract

A conventional PEMFC (Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell) stack is composed of various components such as endplates, bipolar plates, MEAs (membrane electrode assem-bly), and GDLs (gas diffusion layers). Among these, conventional endplates and bipolar plates have been made of massive metallic materials or graphite increasing weight and thermal inertia. The large mass deteriorates the fuel economy especially for passenger vehicles while the large thermal inertia prevents a fuel cell stack from a prompt cold start due to ice-blocking below sub-zero temperature. Fiber reinforced composites have high potential for the fuel cell applications due to their high specific stiffness and low volumetric heat capacity. This study presents the applications of composite materials both for the endplate and the bipolar plate. Since the endplates should have high flexural stiffness to maintain flatness offering even contact pres-sure inside the stack when large bending moment is exerted by clamping devices, a design concept of a composite sandwich endplate with pre-curvature was proposed by the Axiomatic Design. The newly designed endplates were fabricated and evaluated both by experiments and finite element analyses. Also the prototype composite endplates were incorporated in a PEMFC stack to verify their effect on cold-start characteristics im-provement. The developed endplates exhibited light-weight and excellent cold start performance. The bipolar plates made of continuous carbon fiber composite was investigated in order to overcome the obstacles of high cost and low durability reside in conventional graphite or metallic ones. In this study, the curing process and the mold design for the fine channel formability of composite bipolar plates were investigated. In order to decrease the interfacial electrical resistance between a GDL and a bipolar plate, the plasma surface treatment and the hybrid composite bipolar plate with graphite foil surface embedded were investigated. Then the prototype composite bipolar plates were manufactured and employed in a PEMFC stack. The characteristics of the composite bipolar plates were compared with those of conventional bipolar plates made of stainless steel.