Recombination Catalyst Embedded Separators Enable a Wide Operating Window for High Pressure Alkaline Water Electrolysis

Recent advances in alkaline water electrolyzers (AWEs) have focused on pressurized operation and reduced ohmic resistance, enabled by the adoption of thinner porous separators. However, despite these improvements, H₂ crossover remains a critical limitation that restricts the pressure range and the operational window. Herein, we introduce a separator architecture that incorporates a Pt-based recombination catalyst at the separator mid-plane by spray-coating a Pt/Nafion ink (80 µg·cm⁻² Pt) onto a reinforcing open mesh and embedding it within a polysulfone/zirconia composite matrix. The resulting 200 µm-thick separator reduces hydrogen crossover by 60% relative to Zirfon 220 and achieves a lower cell voltage (1.0 A cm⁻² at 1.78 V) compared to the Zirfon 220 cell (1.84 V at 1 A cm⁻²). Although partial catalyst-layer loss was observed under severe dynamic load cycling, stable operation demonstrates the validity of the internal recombination strategy. By integrating recombination functionality directly within a thin, mechanically reinforced separator, this work provides a practical and scalable route to safer and more operationally flexible pressurized AWEs.