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.