Electrochemical CO2 reduction reaction (CO2RR) to diverse high-value chemicals represents a promising carbon mitigation strategy, yet precisely controlling product selectivity remains a considerable challenge. Herein, we report a size-dependent Cu/CN catalyst for modulating the selectivity of CO2RR. Specifically, small Cu NPs on CN (∼5 nm, S–Cu/CN) achieved a 76.2% C2+ product selectivity at 0.6 A cm–2, while the large one (∼50 nm, L-Cu/CN) reached a 67.5% CH4 selectivity at 0.6 A cm–2. Physical characterizations revealed that S–Cu/CN displays partial Cu+ sites, whereas L-Cu/CN higher Cu+ content. Mechanism analysis revealed a balanced Cu0/Cu+ ratio in S–Cu/CN promotes C–C coupling at Cu+ sites to form C2+ products. Conversely, higher Cu+ content in L-Cu/CN decreased the *CO coverage and improved H2O dissociation, steering continuous hydrogenation toward CH4 generation. This work offers a novel strategy to design high-efficiency CO2RR electrocatalysts toward desired products.
Zhou et al. (2026) studied this question.