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

Abstract

High temperature proton exchange membrane fuel cells (HT-PEMFCs) typically employ either acid-absorbing or hydrophobic electrode binders in their catalyst layers (CLs). A recently introduced alternative is the ionomeric binder PWN, poly(2,3,5,6-tetrafluorostyrene-4-phosphonic acid). In literature, PWN with a phosphonation degree of 70% was shown to remarkably improve HT-PEMFC performance. Here, we investigate the influence of the phosphonation degree (40–95%) of this ionomeric binder on HT-PEMFC performance. PWN is employed in the cathode CL and compared to the commonly used polytetrafluoroethylene (PTFE) binder. The electrochemical behavior 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-in regarding peak power density (PPD), activation overpotential (as studied by Tafel analysis), and reproducibility in the 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 impact on 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 improvements in performance, but a precise adjustment of the phosphonation degree is required to obtain optimal results.