Surface modification of a natural graphite/phenol formaldehyde composite plate with expanded graphite

Natural graphite/phenol formaldehyde (NG/PF) resin composite plates modified with thin layers of expanded graphite (EG) are fabricated by mold compression to lower the contact resistance between the plates and gas diffusion layers (GDLs). The modification considerably reduces contact resistance versus bare NG/PF plates. The extent of the decrease in contact resistance is influenced by the expanded volume of EG used. A low contact resistance of 1.42 mΩ cm2 persists for the EG (150 ml g−1)-modified NG/PF plates despite the PF content, whereas that of bare plates increases from 3.62 to 17.01 mΩ cm2 as PF content changes from 5 wt% to 30 wt%. With increasing EG thickness on the surface of NG/PF plates, contact resistance at first decreases and then approaches a constant value when the NG layer exceeds 40 μm. More importantly, the total electrical resistance, as expressed by volume resistance, can be reduced by applying EG layers to NG/PF composite plates. The reduction of total resistance is more remarkable for the composite plates with high PF content because the bulk resistance of the EG layer can be well compensated by the decrease of contact resistance at a proper range of EG layer thickness.