Robust CuCl Nanocatalyst with Stable Cu ⁺ for Promoting CO ₂ Electrochemical Reduction to Ethylene

The electrochemical CO 2 reduction reaction (CO 2 RR) to produce multicarbon products represents a promising route for sustainable carbon utilization. Copper-based catalysts are unique in catalyzing C–C coupling, but the active Cu + species, which favor ethylene formation, are prone to reduction during reaction. In this work, we demonstrate that halogen doping, combined with a nanoconfinement strategy, effectively stabilizes Cu + within a nanoporous carbon matrix. Two model catalysts supported on porous carbon spheres (Cu@C-1 derived from CuCl 2 and Cu@C-2 from CuSO 4 ) were synthesized. After calcination, Cu@C-1 predominantly comprises CuCl while Cu@C-2 mainly consists of Cu 2 O with trace sulfur doping. They both have a similar average copper oxidation state. During the CO 2 RR at −1.3 V versus the RHE, the Cu@C-1 nanocatalyst achieves selective ethylene production with a Faradaic efficiency (FE) of 41.5% and a partial current density of 110.7 mA cm –2 whereas the Cu@C-2 nanocatalyst primarily generates methane (FE of 49.5% and partial current density of 124.4 mA cm –2 ). In situ and postreaction characterizations reveal that nanoscale confinement in Cu@C-1 maintains its CuCl phase under the reaction conditions, which promotes the *COCHO intermediate and facilitates C–C coupling toward ethylene. Conversely, Cu@C-2 nanoparticles are reduced to metallic Cu 0, favoring the methane pathway. This work highlights that tailoring the precursor anion offers a precise level of control over the initial copper phase and its dynamic state under electrolysis, thereby steering the CO 2 RR selectivity toward the desired products.