Manipulating Cu Nanoparticle Surface Oxidation States Tunes Catalytic Selectivity toward CH4 or C2+ Products in CO2 Electroreduction

Abstract Herein, a facile seed‐assisted strategy for preparing Cu nanoparticles (NPs) with polyvinyl pyrrolidone (PVP) capping is presented. Compared to the Cu NPs with deficient PVP protection, the Cu NPs capped with a sufficient amount of PVP remain almost completely as Cu 0 species. In contrast, the Cu NPs that are considered PVP deficient form an oxide structure in which the inner layer is face‐centered cubic Cu and the outer layer is, at least in part, made up of Cu 2 O species. Furthermore, to eliminate CO 2 molecule diffusion and simultaneously obtain significant current density (200 mA cm −2 ) for industrial applications, a flow cell configuration is used for carbon dioxide electro reduction reaction (CO 2 RR) testing in 0.5 m potassium hydroxide solution. The Cu NPs with zero valence deliver Faradaic efficiencies (FEs) for the CO 2 reduction to CH 4 of over 70%, with a current density exceeding 200 mA cm −2 , outstripping the performances of the majority of the reported CO 2 electrocatalysts. Interestingly, the distribution of products catalyzed by the Cu NPs with + 1 valence includes multicarbon products (C 2+ ) such as C 2 H 4 , C 2 H 5 OH, CH 3 COOH, and C 3 H 7 OH with combined FEs of > 80%, with current densities of up to 300 mA cm −2 . The above results unambiguously establish that surface oxidation of Cu species plays a crucial role in the CO 2 RR.