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

Abstract

The electrochemical CO2 reduction (eCO2RR) over copper offers a promising method to convert captured CO2 to valuable chemicals (C2+), like ethylene and ethanol. This study examines Cu and Ag as co-catalysts, deposited on gas diffusion electrodes (GDE) 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 the hydrogen evolution. To mitigate this pulsed eCO2RR, with intermittent oxidative pulses, was successfully applied. The as-prepared bimetallic Cu99Ag1 – CD, achieved a maximum total FEC2+ of 75% at 150 mA cm-2, which is amongst the highest reported in literature for these catalysts.