Poly(phenylene sulfide) Graphite Composites with Graphite Nanoplatelets as a Secondary Filler for Bipolar Plates in Fuel Cell Applications

Graphite nanoplatelets (GNPs) have been used as a secondary filler to improve the electrical conductivity of poly(phenylene sulfide) (PPS)/graphite composites for use as bipolar plates in fuel cells, and the effects of adding small quantities of GNPs on the electrical, thermal, and mechanical properties of PPS/GNP/graphite composites have been extensively studied. The GNPs were compounded with PPS to produce master batch (MB) chips that were further ground to fine MB powder (MB_g). PPS/MB_g/graphite powders were compressed to fabricate 10-mm thick square samples. Composites containing a large quantity of graphite (~80 wt%) were then tested for use as a bipolar plate in phosphoric acid fuel cells. When 5 wt% GNP was added to the PPS/graphite composite, the in-plane electrical conductivity increased almost twofold from 643 to 1340 S·cm⁻¹, the through-plane electrical conductivity increased from 19 to 54 S·cm⁻¹, the through-plane thermal conductivity increased approximately two-fold from 60 to 129 W·(mK)⁻¹, and the flexural strength decreased slightly from 32 to 26 MPa. The fractured surface of the compressed MB_g sample revealed well-dispersed GNPs in the PPS matrix, which created electrical pathways and improved the electrical conductivity of the non-conducting PPS matrix material. Thus, the PPS/GNP/graphite composite is a promising system for bipolar plate applications because a higher amount of graphite (~93 wt%) is needed in PPS/graphite composites to reach the same level of electrical conductivity as the PPS/MB_g(5 wt%)/graphite (75 wt%) composite, and such a large quantity of graphite is difficult to process and leads to weaker mechanical properties. [Figure not available: see fulltext.]