Electrochemical restructuring of H₂O₂ activated copper selenide for CO₂ reduction

Copper chalcogenides such as Cu_2-xSe, acknowledged as efficient CO₂ 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 Cu_2-xSe to steer structural evolution under catalytic conditions and facilitate the generation of the active phases. As-prepared Cu_2-xSe nanowires were reconstructed through H₂O₂ 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 H₂O₂ further accelerates this process by inducing a structural loosening and partial oxidation of the Cu_2-xSe phase. Supported by in situ Raman spectroscopy, quasi-in situ 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 CO₂ electroreduction. The as-prepared Cu_2-xSe nanowires, with diameters of about 300 nm, exhibit a 23% methanol selectivity and a low CO₂ selectivity of only 4% at -1.4 V versus the reversible hydrogen electrode. In contrast, 50-90 nm Cu₂O cubes obtained after H₂O₂ 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 Cu₂Se (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 CO₂ conversion catalysts.