The influence of intrinsically proton conductive electrode binder materials on HT-PEMFC performance

High temperature proton exchange membrane fuel cells (HT-PEMFCs) typically employ either acid-absorbing orhydrophobic electrode binders in their catalyst layers (CLs). A recently introduced alternative is the ionomericbinder PWN, poly(2,3,5,6-tetrafluorostyrene-4-phosphonic acid). In literature, PWN with a phosphonation degreeof 70% was shown to remarkably improve HT-PEMFC performance. Here, we investigate the influence of thephosphonation degree (40–95%) of this ionomeric binder on HT-PEMFC performance. PWN is employed in thecathode CL and compared to the commonly used polytetrafluoroethylene (PTFE) binder. The electrochemicalbehavior is tested at 180 ◦C at ambient pressure under H2/air conditions using a commercial phosphoric acid (PA)-doped PBI-membrane. HT-PEMFCs with PWN generally outperform fuel cells (FCs) with PTFE after a full break-inregarding peak power density (PPD), activation overpotential (as studied by Tafel analysis), and reproducibility inthe mass transport region. Further, PWN-electrodes show higher electrochemically active surface areas (ECSAs)than PTFE-electrodes after completing the break-in. We find that the phosphonation degree has a substantial impacton the PPD, with PWNs with lower phosphonation degrees (40–60%) outperforming highly phosphonated PWNs(70–95%). Taken together, PWN as an ionomeric electrode binder in HT-PEMFCs shows remarkable improvementsin performance, but a precise adjustment of the phosphonation degree is required to obtain optimal results