Catalyst electro-redeposition controls morphology and oxidation state for selective carbon dioxide reduction

The reduction of carbon dioxide to renewable fuels and feedstocks offers opportunities for large-scale, long-term energy storage. The synthesis of efficient CO 2 reduction electrocatalysts with high C2:C1 selectivity remains a field of intense interest. Here we present electro-redeposition, the dissolution and redeposition of copper from a sol–gel, to enhance copper catalysts in terms of their morphology, oxidation state and consequent performance. We utilized in situ soft X-ray absorption spectroscopy to track the oxidation state of copper under CO 2 reduction conditions with time resolution. The sol–gel material slows the electrochemical reduction of copper, enabling control over nanoscale morphology and the stabilization of Cu + at negative potentials. CO 2 reduction experiments, in situ X-ray spectroscopy and density functional theory simulations revealed the beneficial interplay between sharp morphologies and Cu + oxidation state. The catalyst exhibits a partial ethylene current density of 160 mA cm –2 (−1.0 V versus reversible hydrogen electrode) and an ethylene/methane ratio of 200. Catalysts that can selectively reduce carbon dioxide to C2+ products are attractive for the generation of more complex and useful chemicals. Here, an electro-redeposited copper catalyst is shown to provide excellent selectivity and high current density for ethylene formation. Detailed characterization and theory link the performance to the catalyst morphology.