Phase‐Engineered Bi‐RuO ₂ Single‐Atom Alloy Oxide Boosting Oxygen Evolution Electrocatalysis in Proton Exchange Membrane Water Electrolyzer

Abstract Engineering nanomaterials at single‐atomic sites can enable unprecedented catalytic properties for broad applications, yet it remains challenging to do so on RuO ₂ ‐based electrocatalysts for proton exchange membrane water electrolyzer (PEMWE). Herein, the rational design and construction of Bi‐RuO ₂ single‐atom alloy oxide (SAAO) are presented to boost acidic oxygen evolution reaction (OER), via phase engineering a novel hexagonal close packed ( hcp ) RuBi single‐atom alloy. This Bi‐RuO ₂ SAAO electrocatalyst exhibits a low overpotential of 192 mV and superb stability over 650 h at 10 mA cm ⁻² , enabling a practical PEMWE that needs only 1.59 V to reach 1.0 A cm ⁻² under industrial conditions. Operando differential electrochemical mass spectroscopy analysis, coupled with density functional theory studies, confirmed the adsorbate‐evolving mechanism on Bi‐RuO ₂ SAAO and that the incorporation of Bi ₁ improves the activity by electronic density optimization and the stability by hindering surface Ru demetallation. This work not only introduces a new strategy to fabricate high‐performance electrocatalysts at atomic‐level, but also demonstrates their potential use in industrial electrolyzers.