Adsorption energy difference dictates selective ethanol electrooxidation.

Replacing the sluggish oxygen evolution reaction (OER) with the ethanol oxidation reaction (EOR) reduces energy consumption while enabling the upgrading of biomass-derived feedstocks for green hydrogen production. However, the design of efficient non-noble-metal catalysts is restricted by a lack of fundamental understanding of the electronic descriptors that govern multi-reactant organic oxidations. Here, we show that the activities of the OER and EOR are fundamentally decoupled in a series of Ni-based spinel oxides (NiM2O4, M = Fe, Co, Al, and Mn). Unlike the OER, the EOR requires the cooperative activation of ethanol and hydroxyl species. By integrating electrochemical analysis with the density functional theory, we identified the adsorption energy difference between OH and CH3CH2OH as a reaction-specific descriptor that dictates both catalytic activity and product selectivity for the EOR. Accordingly, NiCo2O4, possessing the optimal balance in adsorption energetics, achieved a superior acetate faradaic efficiency of 89.3% in a three-electrode system. Under practical membrane electrode assembly operation, NiCo2O4 maintained high acetate selectivity over a current density range of 50 to 300 mA cm-2, delivering the highest faradaic efficiency of 81.8% at 100 mA cm-2. These findings transcend conventional single-intermediate descriptor approaches and provide a framework for the rational design of selective electrocatalysts for complex multi-reactant systems.