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Although copper is widely used as an electrocatalyst for the CO2 reduction reaction, often little emphasis is placed on identifying exactly the facet distribution of the copper surface. Furthermore, because of differing surface preparation methodologies, reported characaterization voltammograms (where applicable) often vary significantly between laboratories, even for surfaces of supposedly the same orientation. In this work, we describe a surface preparation methodology involving the combination of induction annealing and well-documented electrochemical steps, by which reproducible voltammetry for copper surfaces of different orientations can be obtained. Specifically, we investigated copper surfaces of the three principal orientations: {111}, {100} and {110}, and a representative polycrystalline surface. We compared these surfaces to surfaces reported in the literature prepared via either electropolishing or UHV-standard methodologies, where we find induction preparation to yield improvements in surface quality with respect to electropolished surfaces, though not quite as good as those obtained by UHV-preparation.

The electrocatalytic CO2 reduction reaction (CO2RR) is a promising strategy for producing multi-carbon compounds using only CO2 and H2O at room temperature. Significant advances have already been achieved in understanding how some characteristics of copper electrodes, the current state-of-the-art catalyst for multi-carbon formation via CO2RR, affect the product spectrum. Advances and insights have been reported for, among others, the effect of crystallographic orientation, active surface area, and composition of M-copper (M = Au, Ag, Zn, etc.) materials, and how these alter the distribution of CO2RR products. However, a systematic study evaluating the significance of these variables in the CO2RR to C2+ products is still lacking in the literature and represents an important step in the development of new materials with optimized properties that can be more selective to C2+ compounds. In this paper, we have systematically investigated the effect of the roughness factor, chemical composition, and surface morphology of CuxZny electrocatalysts on the product distribution during CO2RR. Firstly, Cu, Cu90Zn10, and Cu75Zn25 electrodes were exposed to oxidation-reduction cycles to produce Cu and CuxZny electrodes with different morphologies, roughness factors, and chemical composition. Our results show that an increase in the roughness factor and Zn content lead to higher faradaic efficiency (FE) to C2+ products. Furthermore, the influence of the nanoscale morphology is imperative for the production of C2+ compounds. Specifically, nanocubes of Cu and CuxZny presented the highest FE to C2+ products among the different surface morphologies studied in this work (polished flat surface, nanosheres, nanocubes, nanodendrites, and nanocauliflowers), showing that CC coupling during CO2RR is mainly shape dependent.