Sodium Persulfate Pre‐treatment of Copper Foils Enabling Homogenous Growth of Cu(OH)(2) Nanoneedle Films for Electrochemical CO(2) Reduction

Oxide‐derived copper (OD−Cu) catalysts have received widespread attention for their ability to produce energy‐dense multicarbon products. Within this class of materials, nanostructured copper hydroxide (Cu(OH)(2)) has shown excellent catalytic properties, but its synthesis requires complex pre‐treatment steps of the Cu surface. In this study, we have developed a simple two‐step synthesis method for homogenous Cu(OH)(2) nanoneedle films using a sodium persulfate pre‐treatment step prior to anodization. The Cu(OH)(2) nanoneedle films show drastically enhanced uniformity after the pre‐treatment due to improved current distribution and can be grown over large surface areas (63 cm(2)). As a catalyst for CO(2) reduction, the Cu(OH)(2) favours ethylene formation, with a near total suppression of methane production. A peak faradaic efficiency (FE) of 36.5 % is found at −1.0 V vs. the reversible hydrogen electrode (RHE), and the catalyst remains stable while providing an ethylene to methane ratio of 27.8 after 6 h of reaction.