Electrochemical restructuring of HO activated copper selenide for CO reduction.

Copper chalcogenides such as CuSe, acknowledged as efficient CO reduction catalysts, do not represent the active phases but rather are precursors or pre-catalysts as they undergo significant transformations under reaction conditions. In this work we have tailored the initial structure of CuSe to steer structural evolution under catalytic conditions and facilitate the generation of the active phases. As-prepared CuSe nanowires were reconstructed through HO and electrochemical treatments, yielding distinct pre-catalysts. Their electrochemical reduction was found to be an effective strategy to enhance the formation of active metallic Cu nanoparticles. Chemical pretreatment with HO further accelerates this process by inducing a structural loosening and partial oxidation of the CuSe phase. Supported by Raman spectroscopy, quasi- X-ray diffraction, X-ray absorption fine structure spectroscopy and high-angle annular dark-field scanning transmission electron microscopy analysis, it is suggested that structural transformation is a common feature of many copper-based catalysts during CO electroreduction. The as-prepared CuSe nanowires, with diameters of about 300 nm, exhibit a 23% methanol selectivity and a low CO selectivity of only 4% at -1.4 V the reversible hydrogen electrode. In contrast, 50-90 nm CuO cubes obtained after HO oxidation and electro-activation treatments, also acting as pre-catalysts, have a CO selectivity up to 82%. Density functional theory computations demonstrate lower binding energy of reaction intermediates, including *CO, on metallic Cu (110) than on CuSe (220), which may account for the enhanced CO production of the electro-activated catalyst. Our work sheds light on the dependence of the catalytic performance of copper selenide on its initial restructuration and provides guidance for the development of efficient and selective CO conversion catalysts.