Vacancy‐Suppressed RuO 2 Assemblies Promote the Adsorbate Evolution Mechanism for Efficient and Durable Acidic Oxygen Evolution Reaction

ABSTRACT Overcoming the sluggish acidic oxygen evolution reaction (OER) is critical for advancing proton exchange membrane water electrolysis (PEMWE) toward large‐scale green hydrogen production, yet its development is hindered by the intrinsic trade‐off between activity and stability. Herein, we introduce a controllable synthesis strategy to engineer RuO 2 assemblies from ultrasmall Ru nanocrystals supported on carbon via air annealing for efficient acidic OER. This process concurrently induces a Ru‐to‐RuO 2 crystal transformation and facilitates carbon thermal decomposition, yielding a catalyst (Ru‐nano/C‐300) with markedly enhanced electrochemically active surface area (ECSA) and superior OER performance, requiring only 218 mV at 10 mA cm −2 , and exhibiting a Tafel slope of 43.8 mV dec −1 and a mass activity 21‐fold higher than commercial RuO 2 (c‐RuO 2 ) at 1.5 V vs. reversible hydrogen electrode (RHE). Tetramethylammonium cation (TMA + ) poisoning experiments combined with in‐situ spectroscopic analyses verify that the catalysts predominantly operate via the adsorbate evolution mechanism (AEM) pathway, while electron paramagnetic resonance (EPR) results indicate that suppressing oxygen vacancy formation is crucial for the reaction mechanism. These results demonstrate vacancy suppression coupled with morphology engineering as a powerful strategy to develop both efficient and durable catalysts for acidic OER.