Unraveling the Role of the Subsurface Sulfide in a CuS@CuO Core–Shell Nanosheet Array toward Electrochemical Reforming of Ethanol

Partial electrocatalytic oxidative upgrade of biomass-derived organic molecules such as ethanol is a way forward to achieve sustainable production of H2 at the cathode with net zero carbon emission. However, it is challenging to develop a suitable low-cost electrocatalyst with both high activity and product selectivity for the electrochemical reforming of ethanol. Here, we report that the subsurface sulfide in a CuS@CuO core–shell nanosheet array attenuates the oxidative power and optimizes the coordination environment of the active Cu sites, which enhances the electrocatalytic activity and selectivity. First-principles calculations confirm that the subsurface sulfide in CuS@CuO improves the adsorption energy of ethanol on the active Cu sites. As an outcome, CuS@CuO achieves >99% selectivity for ethanol-to-acetate conversion (147 mA cm–2 at 1.59 V vs RHE) and enhances the generation of H2 in a hybrid electrolyzer. This strategy can be generalized to the electrochemical reforming of diverse biomass-derived feedstock.