Surface modifications of gasketless carbon composite bipolar plates for gas tightness

The bipolar plate is one of the most important components for proton exchange membrane fuel cell (PEMFC) systems. The bipolar plate provides many functions, such as establishing electrical connections between cells in series, providing separation between gases in adjacent cells, supplying structural support for the stack and creating flow channels for water and gases. Although carbon fiber composite bipolar plates have high strength and stiffness with corrosion resistance in acid environment, it requires high gas tightness of the fuel cell stack for proper performance, which compromises commercialization of PEMFC. Conventional bipolar plates use extra rubber gaskets to seal the stack, which requires additional curing process in high temperature that might damage the bipolar plate. In this study, in order to secure the gas tightness without using extra gaskets and curing cycle for them, surface modifications are applied to the composite bipolar plate, and their surface morphologies are investigated. To obtain high gas tightness without rubber gaskets, several materials such as graphite foil, PI film and PET films are coated on the surface of the bipolar plate to evaluate coating effects on the gas tightness, which depends on surface hardness and morphology. The coating layer is co-cured during the curing of the bipolar plate by the compression molding method without extra curing cycle. Additionally, plasma surface treatment and mechanical abrasion are used to evaluate the influence of surface morphologies on the gas tightness of the stack.