All‐Hydrocarbon MEA for PEM Water Electrolysis Combining Low Hydrogen Crossover and High Efficiency

Abstract Hydrocarbon ionomers bear the potential to significantly lower the material cost and increase the efficiency of proton‐exchange membrane water electrolyzers (PEMWE). However, no fully hydrocarbon membrane electrode assembly (MEA) with a performance comparable to Nafion‐MEAs has been reported. PEMWE‐MEAs are presented comprising sPPS as membrane and electrode binder reaching 3.5 A cm −2 at 1.8 V and thus clearly outperforming state‐of‐the‐art Nafion‐MEAs (N115 as membrane, 1.5 A cm −2 at 1.8 V) due to a significantly lower high frequency resistance (57 ± 4 mΩ cm² vs 161 ± 7 mΩ cm²). Additionally, pure sPPS‐membranes show a three times lower gas crossover (<0.3 mA cm −2 ) than Nafion N115‐membranes (>1.1 mA cm −2 ) in a fully humidified surrogate test. Furthermore, more than 80 h of continuous operation is shown for sPPS‐MEAs in a preliminary durability test (constant current hold at 1 A cm −2 at 80 °C). These results rely on the unique transport properties of sulfonated poly(phenylene sulfone) (sPPS) that combines high proton conductivity with low gas crossover.