Sulfur form regulation and dual-interface effect: catalytic mechanism of nickel-based catalyst in ethanol...

Electrocatalytic organic oxidation emerge as energy-efficient alternatives to conventional oxygen evolution reactions (OER) for sustainable hydrogen coproduction. The design of efficient catalysts and the understanding of the underlying mechanisms of anodic nucleophilic reagent electrooxidation constitute the core of electrochemistry-driven technological advances. Herein, this paper reports a nickel sulfide heterostructure embedded in biomass carbon (NiS-NiS₂/CC), which exhibits great ethanol oxidation reaction (EOR) activity with a current density of 50 mA·cm^-2 at 1.45 V and excellent stability with 98 % current retention for 12 h owing to the unique heterogeneous structure regulated by different forms of sulfur (S^2- and S₂^2-). Redistribution of electrons at the NiS-NiS₂-CC interface induces an electrophilic/nucleophilic region, forming a contact potential difference that becomes a driving force for the polarization of ethanol to occur. Based on experimental results, we propose that ethanol electrooxidation on NiS-NiS₂/CC follows a cyclic mechanism involving reversible Ni^II/Ni^III redox transitions. (electrochemical and non-electrochemical, EC and non-EC) and an accompanying EOR. The activity source of the EOR is Ni(OH)O with electrophilic adsorbed oxygen, and the existence of ethanol can inhibit the phase transition of the electrocatalyst to the high-valent electrooxidation product. This mechanism well illustrates not only the transient presence of Ni^III-OOH but also the formation of highly selective acetate. Our work elucidates the ethanol oxidation mechanism on sulfur-regulated nickel sulfide heterostructures, providing fundamental insights for designing high-performance nickel-based sulfide electrocatalysts.