Effect of perfluorosulfonic acid ionomer in anode catalyst layer on proton exchange membrane water electrolyzer performance

The equivalent weight (EW) and side-chain length of perfluorosulfonic acid (PFSA) ionomers have been found to significantly influence the performance of different proton exchange membrane (PEM)-based electrochemical devices. However, few reports have investigated their influence on PEM water electrolyzers (PEMWE). In this study, we investigate the influence of EW and side-chain length on PEMWE's membrane electrode assemblies (MEAs) which are fabricated by four different PFSA ionomers. It is found that the change in PFSA ionomer EWs barely influences the microstructure of the anode catalyst layer (ACL) but affects its surface wettability and MEA performance. Different from that in PEM fuel cells, MEA in PEMWEs prepared by PFSA ionomers with higher EWs shows better cell performance. The voltage difference comes from the change in the mass transport overpotential which is up to 113 mV with the comparison between PFSA ionomers with the highest EW and the lowest EW, which attributes to the changed wettability and water-oxygen transport of the ACLs. The influence of PFSA ionomer side-chain lengths on cell performance is not observed. This work provides insight into the effect of PFSA ionomers and offers information on how to design high-performance PFSA ionomers for PEMWE applications.