Boosting CO2 Electroreduction to Multicarbon Products via Tuning of the Copper Surface Charge

Abstract

Electrochemical CO2 reduction (ECR) to multicarbon compounds holds great potential but remains plagued with large overpotential, low Faradaic efficiency (FE), and debilitating competition from the evolution of hydrogen and the C1 product. The design and development of advanced catalytic systems is required to overcome these problems. Here, we demonstrate the selective cathodic CO2 conversion to C2+ chemicals (C2H4, C2H5OH, and n-C3H7OH) by optimizing the surface charge of Cu via fine-tuned annealing of CuSiO3@SiO2. Stabilization of Cu+ by forming Cu–O–Si bonds is attained, as predicted by density functional theory (DFT) calculations and evidenced by multiple experiments. The C2+ selectivity is readily regulated by adjusting the surface content of Cu+, underpinning its significance during the ECR. The resulting Cuδ+@SiO2 with a Cu0-to-Cu+ surface ratio of ∼0.5 achieves a remarkable C2+ FE as high as ∼70%, C2+ partial geometric current density of about 9 mA cm–2, and large C2+-to-C1 ratio of ∼10, using an H-type cell in aqueous CsBr electrolytes at mild overpotentials. The high C2+ FE and current density persist over 12 h of continuous CO2 electrolysis. In addition, a respectable C2+ FE of ∼52% can still be attained even at a large current density (500 mA cm–2) in a flow reactor system. DFT computations reveal that the oxidized copper species Cu+ boosts C–C coupling by lessening the formation energy of the critical *OCCOH intermediate. This work underscores the prominent role of the support–catalyst interaction and the modulation of Cu oxidation states in steering the ECR selectivity.