Nanograin-Boundary-Abundant Cu 2 O-Cu Nanocubes with High C 2+ Selectivity and Good Stability during Electrochemical CO 2 Reduction at a Current Density of 500 mA/cm 2 .

Surface and interface engineering, especially the creation of abundant Cu 0 /Cu + interfaces and nanograin boundaries, is known to facilitate C 2+ production during electrochemical CO 2 reductions over copper-based catalysts. However, precisely controlling the favorable nanograin boundaries with surface structures (e.g., Cu(100) facets and Cu[ n (100)×(110)] step sites) and simultaneously stabilizing Cu 0 /Cu + interfaces is challenging, since Cu + species are highly susceptible to be reduced into bulk metallic Cu at high current densities. Thus, an in-depth understanding of the structure evolution of the Cu-based catalysts under realistic CO 2 RR conditions is imperative, including the formation and stabilization of nanograin boundaries and Cu 0 /Cu + interfaces. Herein we demonstrate that the well-controlled thermal reduction of Cu 2 O nanocubes under a CO atmosphere yields a remarkably stable Cu 2 O-Cu nanocube hybrid catalyst (Cu 2 O(CO)) possessing a high density of Cu 0 /Cu + interfaces, abundant nanograin boundaries with Cu(100) facets, and Cu[ n (100)×(110)] step sites. The Cu 2 O(CO) electrocatalyst delivered a high C 2+ Faradaic efficiency of 77.4% (56.6% for ethylene) during the CO 2 RR under an industrial current density of 500 mA/cm 2 . Spectroscopic characterizations and morphological evolution studies, together with in situ time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies, established that the morphology and Cu 0 /Cu + interfacial sites in the as-prepared Cu 2 O(CO) catalyst were preserved under high polarization and high current densities due to the nanograin-boundary-abundant structure. Furthermore, the abundant Cu 0 /Cu + interfacial sites on the Cu 2 O(CO) catalyst acted to increase the *CO adsorption density, thereby increasing the opportunity for C-C coupling reactions, leading to a high C 2+ selectivity.