Cerium Dioxide as an Electron Buffer to Stabilize Iridium for Efficient Water Electrolysis

Abstract Sustaining the steady state for highly active non‐stoichiometric iridium (Ir)‐based oxide (IrO x ) at low Ir loading remains challenging primarily due to the continuous oxidation and sequent dissolution of Ir active sites during the oxygen evolution reaction (OER). In this context, a new iridium–cerium (Ce) substitution solid solution oxide (SSO) has been developed, featuring uniformly dispersed Ir atoms within Ce dioxide (CeO 2 ) matrix as electron buffer, which delivers remarkable acidic OER catalytic activity and enhanced stability. The electron‐buffering capacity of CeO 2 facilitates the charge transfer toward Ir atoms, leading to abundant active low‐valence Ir sites and effectively prevent their oxidation and dissolution. As a result, Ir─Ce SSO demonstrates an overpotential of merely 238 mV@10 mA cm −2 . Proton exchange membrane water electrolyzer employing Ir─Ce SSO at a low Ir loading of 396 µg Ir cm −2 operates consistently for over 100 h@500 mA cm −2 . Density functional theory (DFT) calculations corroborate that the electron‐buffering effect of CeO 2 enriches the density of Ir III and substantially increases the dissolution energy barrier of Ir atoms. This study presents a viable approach to addressing the issues of instability and low efficiency in Ir‐based OER electrocatalysts for acidic water electrolysis.