Deactivation of copper electrocatalysts during CO2 reduction occurs via dissolution and selective redeposition mechanism†

As electrochemical CO₂ reduction (ECR) nears industrialisation levels, addressing the uncontrolled stability, restructuring, and deactivation of copper (Cu) catalysts during operation becomes as crucial as achieving high activity and selectivity for a single product. This study used a high-surface area Cu catalyst that exhibited changes in ECR product selectivity over prolonged operation. The detection of dissolved Cu species during electrolysis confirmed an intermediates-mediated Cu dissolution mechanism at ECR potentials (−0.8 to −1.1 V vs. reversible hydrogen electrode). The findings suggest that the electrodeposition of dissolved Cu species is biased towards Cu catalyst sites with lower reaction intermediates coverage, e.g. adsorbed CO (*CO). A dynamic equilibrium between dissolution and subsequent selective redeposition gradually led to morphological restructuring, resulting in a shift in selectivity away from ECR and towards hydrogen production. With the obtained extensive experimental results, theoretical modelling, and literature data, four interconnected parameters governing restructuring and selectivity shifts were recognised: (i) size and (ii) crystallographic orientation of facets of the nanoparticles, (iii) *CO coverage and (iv) CO_bridgevs. CO_atop ratio.