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 CO₂ 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 CO₂ 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. CO₂ 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.