Breaking the Activity‐Stability Trade‐Off in Oxygen Evolution Catalysis via Self‐Limiting Atomic‐Spacing Engineering

Electrochemical water splitting demands efficient catalysts circumventing the persistent compromise between activity and stability in conventional oxygen evolution reaction (OER) pathways. While the oxygen pathway mechanism (OPM) offers a promising solution by enabling direct O-O coupling free from scaling relations, its implementation requires atomic-level control over intermetallic distances. Herein, self-limiting atomic-spacing engineering is reported through grafting an "active skin" onto CoMoO₄ (AS@CMO), harnessing intrinsic metal leaching for precision regulation of Co-Co distance. The in situ formed metal-coordination polymer layer simultaneously suppresses metal dissolution and optimizes the Co-Co spacing. This atomic-spacing control triggers distinct OER pathway switching: pristine CMO (3.34 Å) follows the adsorbate evolution mechanism (AEM); defect-overloaded systems (2.59 Å) undergo lattice oxygen mechanism (LOM); while defect-controlled AS@CMO (2.83 Å) achieves the coveted OPM pathway. The resulting catalyst delivers a low OER overpotential (η₁₀ = 1.48 V) with 400-h stability and enhanced hydrogen evolution activity (η₁₀ = 78 mV). As a bifunctional electrode (AS@CMO-2 || AS@CMO-2), it drives overall water splitting at 1.45 V-outperforming noble-metal benchmarks (RuO₂ || Pt/C, η₁₀ = 1.60 V). This work establishes a paradigm of OER pathway control via self-limiting atomic-spacing engineering, breaking the activity-stability trade-off in non-precious catalysts.