Current state of facet characterisation on copper

Copper is a promising catalyst for several electrocatalytic processes, such as the hydrogenation of carbon dioxide and unsaturated bonds in organic molecules. Significant efforts have been devoted to developing synthetic strategies for rational engineering of surface site geometries on copper, aiming to enhance activity and product selectivity. This current opinion summarises recent advances in electrochemically induced surface refaceting and nanostructuring of copper, as well as techniques employed to address the facet distribution on modified electrodes. Special focus is placed on discussing the strengths and limitations of three groups of characterisation techniques: probe and electron microscopies to elucidate the atomic structure of surface active sites; x-ray and electron backscattered diffraction techniques for determining crystallographic grain orientations; and the cyclic voltammetry technique for investigating the electrochemical behaviour of well-defined electrified interfaces. A multi-approach that combines electrochemical methods with operando surface characterisation is crucial for guiding the rational design of copper electrocatalysts.