An innovative filler manipulation approach for low-cost composite coatings on metallic PEMFC bipolar plates

• Coatings of conductive particles in epoxy have been fabricated & tested in a PEM FC. • Alignment of the particles into chains led to significantly improved conductivity. • The coatings showed good ex-situ stability, and a low ICR of 20 mΩ cm 2. • Performance improved after 192 h in-situ due to enhanced interparticle contact. • Competitive coating cost with potential for savings due to low-cost manufacturing. A polymer composite coating for metallic bipolar plates (BPPs) in electrochemical devices was developed by combining an epoxy resin stable in the PEMFC environment with conductive particles. A novel filler alignment technique was used to produce high conductivity at lower particle loadings, optimizing the cost and performance of the BPP coating. This technique is suitable for high-throughput manufacturing and has already been demonstrated in roll-to-roll systems. The coated BPPs were evaluated under standard ex-situ and in-situ testing conditions, with a good ex-situ stability and a low interfacial contact resistance of 20 mΩ cm 2 reported. The alignment process had a positive impact on coating properties, with the alignment technique allowing a 20 % reduction in particle loading and a simultaneous 67 % reduction in ICR. In-situ results show that coatings are a feasible option for protection of BPPs in PEMFCs, but there is room for further optimisation. Finally, a simple cost model is developed to estimate the coating material costs and allow for a proper comparison with other standard coatings.