Surface Reconstruction of Quaternary Deep Eutectic Solvent-Directed Co-Cu Nanosheets for Efficient Oxygen Evolution Electrocatalysis

Developing cost-effective electrocatalysts with accelerated kinetics is pivotal for sustainable hydrogen production via water electrolysis. In this study, we propose a quaternary deep eutectic solvent (DES) system to directly fabricate Co-Cu alloy nanosheets on a NiMo foam substrate via one-step electrodeposition. Comprehensive characterizations reveal that the catalyst undergoes a dynamic surface reconstruction during electrochemical activation, evolving from initial nanosheets into a hierarchical rod-shaped architecture. This process generates a synergistic crystalline/amorphous heterojunction composed of CoOOH and Cu(OH) 2, which profoundly optimizes the electronic structure. Consequently, the activated Co-Cu/NiMo catalyst delivers superior oxygen evolution reaction performance, requiring a low overpotential of 241 mV to reach 10 mA cm −2 . Microkinetic and practical evaluations further highlight an impressive turnover frequency of 27 s −1 at 250 mV and a near-quantitative Faradaic efficiency of 98.4%. These metrics confirm that the bimetallic synergy fundamentally accelerates the intrinsic per-site reaction kinetics and ensures highly selective charge utilization. Coupled with robust durability exceeding 60 h, this work validates the efficacy of quaternary DESs in materials synthesis and provides valuable insights into reconstruction-induced activity enhancements in transition metal alloys.