Enhancing selectivity and stability in electrochemical CO2 reduction using tailored sputtered CuAg electrodes

Abstract

Electrochemical CO₂ reduction (eCO₂RR) over copper offers a promising method to convert captured CO₂ to valuable chemicals (C₂₊), such as ethylene and ethanol. This study examines Cu and Ag as co-catalysts deposited on gas diffusion electrodes (GDEs) via magnetron sputtering to improve C₂₊ selectivity, and evaluates different configurations: CuAg-layered (L), AgCu-layered (L), CuAgCu-layered (L), and CuAg-co-deposited (CD). A 400 nm Cu layer achieved the highest C₂₊ selectivity (73%), outperforming 50 nm and 800 nm layers (61% and 62%), at a current density of 150 mA cm⁻². Among CuAg compositions, Cu₉₉Ag₁-CD exhibited the highest C₂₊ selectivity (75%), with ethylene and ethanol selectivities reaching 42% and 24%, respectively. Layered configurations showed lower selectivity due to limited CO spill-over from Ag to Cu, reducing C–C coupling. Co-deposited CuAg alloys enhanced CO transfer, whilst slightly favouring oxygenates over hydrocarbons. Electrode stability measurements at 150 mA cm⁻² revealed that surface reconstruction and electrode flooding trigger hydrogen evolution. To mitigate this pulsed eCO₂RR, intermittent oxidative pulses were successfully applied. The as-prepared bimetallic Cu₉₉Ag₁-CD achieved a maximum total FE_C2+ of 75% at 150 mA cm⁻², which is amongst the highest reported in the literature for these catalysts.