Electrical and mechanical properties of polypropylene/epoxy blend-graphite/carbon black composite for proton exchange membrane fuel cell bipolar plate

Abstract

Conductive polymer composites (CPCs) exhibit favorable density and corrosion resistance for application as bipolar plate (BP) in proton exchange membrane fuel cell (PEMFC). However, achieving CPCs that combine the required level of electrical conductivity and mechanical strength is a challenge that has limited their application in PEMFC BPs. This study explored the potential of achieving CPC BPs with high electrical and mechanical performance by using carbon black (CB) as a secondary filler in graphite-polymer composites. Polypropylene (PP)/epoxy blend was selected as the matrix due to its good combination of strength and toughness as well as its potential to form a co-continuous morphology, which promotes the formation of more continuous conducting networks within the composite, leading to enhanced electrical performance. The PP/epoxy/graphite/CB composites were prepared by melt mixing in a Rheomixer at 190 °C and 60 rpm for 10 min, followed by compression molding at 200 °C and 6 metric tonnes for 10 min. The electrical conductivity of the composites increased from 49.26 Scm−1 to 90.34 Scm−1 (in-plane) and from 0.37 Scm−1 to 9.34 Scm−1 (through-plane) as the total filler content increased from 50 to 85 wt%. The flexural strength initially increased from 45.57 MPa at 50 wt% to 51.84 MPa at 60 wt% total filler content. Further increase in total filler content led to a decrease in flexural strength. The nanosize CB particles, used as a minor filler, filled the voids between the graphite particles, leading to the formation of more conducting pathways and higher electrical conductivities compared to the PP/epoxy/graphite composites without CB fillers. The PP/epoxy/graphite/CB composite with 80 wt% total filler content exhibited the most promising in-plane conductivity (88.5 Scm−1), through-plane conductivity (8.52 Scm−1), and flexural strength (28.53 MPa) for BP application.