Surface modifications of gasketless carbon composite bipolar plates for gas tightness of PEM fuel cells

•Surface modifications are applied to the gasketless carbon composite bipolar plate.•Gas sealing behavior of the gasketless bipolar plate is studied by FE analysis.•Corrosion resistivity of the surface modified bipolar plates is investigated.•Sealability test verifies the effectiveness of the surface modifications.•Graphite coating produced the perfect gas tightness of multi-tasking conditions.

A carbon fiber composite gasketless bipolar plate for proton exchange membrane (PEM) fuel cells was developed using the groove of a trapezoidal shape, which develops large contact stresses due to a wedge mechanism. The surface of the composite groove was modified to increase gas tightness without using rubber gaskets. Graphite, polyimide (PI) and polyethylene terephthalate (PET) film were co-cure bonded on the surface of the bipolar plate during the compression molding process to change its surface hardness, which could affect the gas tightness. Additionally, plasma surface treatment and mechanical abrasion were used to modify the surface morphologies. Corrosion and gas tightness tests on the surface modified bipolar plates were performed to verify the reliability of the gasketless sealing method.