Restricting Copper Reconstruction with Ultrathin Polydopamine for Selective and Stable Electrochemical CO₂ Reduction Reaction to C₂ Products

A strategy is presented to mitigate copper surface reconstruction during electrochemical CO₂ reduction reaction (EC-CO₂RR) by conformally coating copper microcubes (CuMCs) with an ultrathin (≈2 nm) polydopamine (PDA) layer. The formation of nanocubes (30–50 nm in size) at the surface of microcubes at the early stages of the EC-CO₂RR contributes to suppressed surface reconstruction and sustained Faradaic efficiency (FE) for C₂ products. Furthermore, PDA coating effectively stabilizes adsorbed CO_atop and CO_bridge intermediates and promotes C.C coupling. As a result, the FE for C₂ products increases from 52.0 ± 4.0% for unmodified CuMCs to 81.6 ± 2.8% for PDA-coated CuMCs at −1.18 V versus reversible hydrogen electrode (V_RHE). The PDA coating effectively slows down the surface evolution process of the catalyst during electrolysis. After 18 h of continuous operation at −0.88 V_RHE, the CuMCs retain their original framework owing to a tightly adhered PDA layer that effectively stabilizes the surface and enhances catalyst durability. In situ surface-enhanced infrared absorption spectroscopy confirms the presence of adsorbed CO_atop, CO_bridge, and OCCOH intermediates on PDA/CuMCs surface, which are believed to boost C.C coupling. This work highlights the potential of polymer film to stabilize the catalyst surface and steer product distribution in CO₂ electroreduction.