High-Purity Hydrogen Production From Water-Gas Shift Reaction in a High-Temperature Polymer Electrolyte Membrane Electrolyzer.

The water-gas shift reaction (WGSR) is a critical pathway for hydrogen production, yet current methods face trade-offs between purity and scale. Thermocatalytic WGSR achieves high product purity but requires energy-intensive gas separation, while room-temperature electrocatalysis is limited by low current densities due to mass transfer constraints. Here, we report a high-temperature polymer electrolyte membrane electrolyzer (HT-PEME) operating at 120°C-200°C that combines the advantages of both approaches. The HT-PEME utilizes a RuIr/C catalyst, with Ir sites enhancing the balance of *OH- and CO-adsorption on Ru, accelerating WGSR kinetics and lowering overpotential. Operating above the boiling point of water, the system shifts to a gas-solid reaction interface, overcoming mass transfer limitations. This setup delivers a steady-state current density of 1179 mA cm-2 at 0.6 V, producing hydrogen at ≥ 99.99% purity without external separation processes. Furthermore, this high performance has been successfully scaled up to an electrolyzer stack comprising five 45 cm2 membrane electrode assemblies (MEAs). This design offers a scalable, efficient solution for high-purity hydrogen production through electrochemical WGSR.