74 µm PEEK‐Reinforced Sulfonated Poly(phenylene sulfone)‐Membrane for Stable Water Electrolysis with Lower Gas Crossover and Lower Resistance than Nafion N115

Polymer electrolyte membrane (PEM) water electrolysis is a crucial technology for green hydrogen production. Hydrocarbon membranes are drawing a lot of attention due to potentially superior properties and the fact that common fluorinated polymers might face a potential ban. This study introduces a sulfonated poly(phenylene sulfone) (sPPS) membrane, reinforced with a poly(ether‐ether‐ketone) (PEEK) mesh. The reinforced membrane induces a drastic increase in dimensional stability, enabling direct anode casting—an essential step toward industrial manufacturing. It further exhibits a significant reduction in water uptake (115% vs 294% for pure sPPS) and a 40% lower H2‐crossover (0.18 mA cm−2) compared to the industry standard N115 (0.31 mA cm−2). Due to the lower thickness (74 vs 127 µm) and higher ion exchange capacity (IEC)(1.92 vs 0.89 mmol g−1), the PEEK‐sPPS membrane displays a substantially lower resistance (70 vs 159 mΩ cm2 for N115). This directly translates into a voltage reduction of ≈90 mV at 1 A cm−2 or ≈180 mV at 2 A cm−2, both typical operating current densities. Finally, PEEK‐sPPS exhibits the longest lifetime shown for hydrocarbon membranes with almost 650 h at 1 A cm−2 and a low degradation rate (80 µV h−1). In the light of potential regulatory constraints on polyfluoroalkyl substances and thus Nafion membranes, hydrocarbon polymers become increasingly interesting for polymer electrolysis membranes. In this study, the authors present a poly(ether‐ether‐ketone)–reinforced hydrocarbon membrane that exhibits lower gas cross over and lower resistance than Nafion and is long‐term stable.