Thin Reinforced Sulfonated Poly(phenylene sulfone) Membranes for Durable Water Electrolysis: Suppressed Swelling and Enhanced Stability Over 2000 Hours

Hydrocarbon (HC) membranes have the potential to significantly enhance the efficiency of water electrolyzers. However, their low mechanical integrity under electrolysis conditions, due to severe swelling, poses a challenge for industrial‐scale applications. Here, we present a 12 µm‐thick sulfonated poly(phenylene sulfone) (sPPS) membrane reinforced with a porous polyethylene (PE) substrate. The PE substrate reduces in‐plane swelling by a factor of 7 (10% vs 69%) and improves mechanical stability (440 MPa vs 50 MPa) in water at 60°C. Under electrolysis conditions, a 24 µm thick sandwich of two reinforced membranes shows stable operation over more than 2000 h in a constant current hold at 1 A cm −2 conducted at 60°C (first 1000 h) and 80°C (remaining 1000 h) with only 6 µV h −1 of voltage deviation within the last 500 h. With a potential of 1.67 V and a hydrogen in oxygen content of 1 vol% at 3 A cm −2 , the PFAS‐free membrane clearly outperforms a state‐of‐the‐art reference (Nafion‐N211: 1.73 V and 1.5 vol% at 3 A cm −2 ).