Design and engineering of copper-based catalysts for the electrochemical co₂ reduction

Abstract

Since the industrial revolution, carbon dioxide (CO2) emissions have rapidly been increasing, up to a record of 430 ppm. This unbalanced CO2 concentration contributes to global warming, leading to harsher and unpredictable weather events. As a result, global markets are moving away from fossil fuels, and implementing green and sustainable alternatives. Carbon capture and utilisation has emerged as a viable technology to convert it into valuable chemicals. Among these techniques, the electrochemical CO2 reduction (eCO2R) is a highly promising pathway for producing carbon – neutral chemicals and fuels. Ethylene and ethanol (C2+) stand out for their high market value. Cu – based electrocatalysts emerge as a suitable material for producing these chemicals. Controlling morphology, composition, facets, and co metals is expected to profoundly affect reaction selectivity and product distribution. Therefore, the interplay between Cu facets, and compositional control is essential to enhance the selectivity for C2+ products. In the first chapter, we fabricated various morphologies of Cu2O. The influence of the morphology and exposed crystal facet on the eCO2R was studied. Nanocubes, and the Cu100 facet was most active for C2+ formation as confirmed through physicochemical characterisations. The second chapter touches upon the addition of Ag as co catalysts leading to a higher local CO concentration to alter C2+ as the C – C coupling step becomes more favoured. Different configurations of the CuAg bimetallic thin film heavily influenced the product selectivity. The alloyed CuAg catalysts was optimised for the CO2 reduction, and the C2+ production was maximised at low Ag%. Stability was improved by employing oxidative pulsing to partially restore the catalyst structure. The third chapter focused on the addition of N2 to the sputtering process to synthesise Cu1-xNx thin – films, which were shown to operate at higher energy efficiency. The presence of nitrogen in the bulk leads to nitrogen vacancies enabling more efficient stabilisation of key intermediates. Eventually this N2 sputtering was performed to form specific Cu3N nanocubes with hollow features, this showed that the vacancies induced by the Kirkendall effect can improve C2+ selectivity to 80%. Across these experimental studies, we have shown that controlling the composition and morphology of Cu – based catalysts is of fundamental importance to improve C2+ selectivity. The addition of a second element to Cu catalysts can alter electronic properties that affect product distributions. This dissertation thus provides insights into how catalyst design effect product selectivity, activity and stability, providing future design parameters for electrochemical catalysts.