s-PIM as binder in Proton Exchange Membrane Water Electrolyzers: performance evaluation in a single-cell setup

Water electrolysis will have a crucial role in the coming years, as efficient hydrogen production is essential for advancing the integration of green hydrogen into the energy transition landscape. Proton exchange membrane water electrolyzers (PEMWE) are one of the most promising technologies, though they raise certain environmental concerns. The most diffused polymer in this technology is Nafion, a perfluorosulfonic acid (PFSA) polymer that finds use in the form of membrane and binder for catalysts. PFSAs carry some environmental issues, their production and disposal can be linked to the release in the atmosphere of very harmful fluorinated gases. Due to this, European Union plans to limit their production and use in the near future. The catalyst layer of the Membrane Electrode Assembly (MEA) is composed of the catalyst and an ionomer which serves as a binder. The binder has a very important role as it ensures better mechanical stability of the catalyst layer, but it also grants the correct transport of reactants and products of the reaction to/from the catalyst surface. This study presents an investigation of the performance of sulfonated Polymers of Intrinsic Microporosity (s-PIM), an innovative polymer which represents an alternative to Nafion. This study will offer an investigation of the performances of s-PIM as binder for the Oxygen Evolution Reaction (OER), the half-reaction occurring at the anode of PEMWEs. The research focuses on the testing of this polymer as anodic binder in a single-cell electrolyzer setup to fully comprehend its potential in future full-scale applications. The study was carried out by preparing multiple MEAs sharing the same loading of platinum and Nafion binder at the cathode and by varying the weight percentage of the binder at the anode, while maintaining the same loading of the catalyst for OER, iridium oxide. The MEAs were then tested in a single-cell PEMWE setup and were subjected to Linear Sweep Voltammetry (LSV) and Chronoamperometry (CA) tests to assess the electrochemical activity and the stability of the different anodic catalyst layer compositions. The results demonstrated that s-PIM holds significant potential as binder for the OER catalyst, with performances close to those developed by the MEA using the Nafion binder, both in terms of activity and stability. These results indicate that s-PIM is a promising binder material for anodic OER in PEMWE. Nonetheless, further research is needed to fully comprehend the potential of this polymer and its possible industrial applications.