(A) study on composite bipolar plates for high temperature PEMFC

Abstract

The primary components of proton exchange membrane fuel cell (PEMFC) systems are bipolar plate, end plate, membrane electrode assembly (MEA), gas diffusion layer (GDL), and gasket. The PEMFC, which is composed of many components, induces a sealing problem in the stack that affects the fuel efficiency, reliability, and maintenance costs of the system. Conventional PEMFCs are sealed with numerous elastomeric gaskets to seal the stack, which increases the manufacturing and assembly costs. To reduce the assembly time and to increase the sealing reliability without using gaskets, a gasket-integrated carbon/silicone elastomer composite bipolar plate has been developed. The silicone elastomer is used rather than conventional glassy thermoset or thermoplastic polymers for the matrix of the composite bipolar plate, where the silicone elastomer serves not only as a matrix material of composite but also as a gasket material due to its resilience. The mechanical and electrical properties of the developed carbon/silicone elastomer composite were investigated at both room temperature and the operating temperature of high temperature PEMFC (HT-PEMFC). The sealability of the gasket-integrated composite bipolar plate was tested. To reduce the electrical contact resistance of the carbon composite bipolar plate, the “soft layer method” was developed, which is an innovative manufacturing method that exposes carbon fibers on the surface of the composite bipolar plate. Soft release films were inserted between the compression mold and the composite to prevent the formation of a resin-rich area and to expose carbon fibers on the surface of the bipolar plate. The developed method significantly decreased the contact resistance, which satisfied the target established by the Department of Energy (DOE) of the United States by a great margin. The effects of the curing method with the soft layer method on the mechanical and electrical properties of the composite bipolar plate were investigated. Additionally, the soft layer method was applied for fabrication of the fabric-type composites whose surface morphology is more complicated than that of the unidirectional continuous fiber composites. The thickness of the soft layer was varied, and a purging process was introduced for development of the high performance composite bipolar plate. Finally, by combining the gasket-integration concept and the soft layer method, a composite bipolar plate for HT-PEMFC was developed. The bipolar plate showed excellent electrical and thermomechanical properties. Compared with the conventional graphite bipolar plate, the newly developed composite bipolar plate displayed better performance in the unit cell test.