Water-Hydroxide Trapping in Hollandite-Type Iridium Oxide Enables Efficient Proton Exchange Membrane Water Electrolysis

Abstract

The development of highly active iridium oxides with excellent stability in acidic environments and significantly reduced Ir content is crucial for advancing competitive proton exchange membrane water electrolyzer (PEMWE) technologies. In this study, an intrinsically active acid-stable low-iridium (Ir/IrO_x(OH)_y·(H₂O)_n) OER electrocatalyst via an alkali-assisted ethylene glycol reduction method is designed. The Ir/IrO_x(OH)_y·(H₂O)_n shows a hollandite-like structure with abundant edge-sharing IrO₆ octahedra that accommodates structural water and OH ligands in its tunnels. In situ/operando spectroscopies demonstrate that lattice water (or OH ligands)–mediated oxygen exchange bypasses key rate-limiting steps in the OER process, including oxygen–oxygen bond formation in the adsorbate evolution mechanism (AEM) and deprotonation in the lattice oxygen mechanism (LOM), which typically hinder OER efficiency. Moreover, the interfacial OH ligands are shown to accelerate the deprotonation of OER intermediates, thereby enhancing the kinetics of the hydrogen evolution reaction (HER). The resulting Ir/IrO_x(OH)_y·(H₂O)_n catalyst achieves a lower overpotential of 1.79 V and exhibits high durability, sustaining 1200 h at 1 A cm⁻² under industrial conditions. These findings highlight the potential of this catalyst for high-performance, durable PEMWE systems.