Optimizing Surface ^* H Coverage over Cu ₂ O/Co ₃ O ₄ Heterojunction Enables Efficient Neutral Electrocatalytic Hydrogenation of 5‐hydroxymethylfurfural to 2,5‐dihydroxymethylfuran

Electrochemical hydrogenation (ECH) of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-dihydroxymethylfuran (DHMF) offers a sustainable route for biomass valorization. Recent studies have underscored the importance of reactive hydrogen species (^*H) on the catalyst surface in determining reaction selectivity, particularly under neutral conditions. However, the mechanistic understanding of how ^*H coverage governs the reaction pathway remains poorly understood, and effective strategies for optimizing surface ^*H coverage are still lacking. Herein, density functional theory (DFT) calculations first reveal that an optimum ^*H coverage on the Cu₂O surface effectively suppresses ketyl intermediate coupling and thermodynamically favors DHMF formation. Inspired by this insight, a Cu₂O/Co₃O₄ heterojunction catalyst is constructed, in which Co₃O₄ serves as a redox-active cocatalyst to stabilize Cu⁺ sites and modulate the electronic structure of Cu₂O, thereby enhancing H₂O activation and enabling precise tuning of ^*H coverage. The Cu₂O/Co₃O₄ heterojunction catalyst delivers an excellent HMF conversion (97%) and DHMF selectivity (97%), significantly outperforming the pristine Cu₂O (71% DHMF selectivity, 62% HMF conversion). This work uncovers the mechanistic role of ^*H coverage in pathway regulation and highlights heterointerface engineering as a powerful strategy for designing efficient electrocatalysts for selective biomass upgrading under neutral conditions.