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

ABSTRACT 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 cm 2 membrane electrode assemblies (MEAs). This design offers a scalable, efficient solution for high‐purity hydrogen production through electrochemical WGSR.