An in situ near-ambient pressure X-ray photoelectron spectroscopy study of CO2 reduction at Cu in a SOE cell

The cathodic behavior of a model solid oxide electrolysis cell (SOEC) has been studied by means of near-ambient pressure (NAP) X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS), aiming at shedding light on the specific role of the metallic component in a class of cermets used as electrodes. The focus is on the surface chemistry and catalytic role of Cu, the increasingly popular metallic component in electrodes used in CO2 electrolysis and CO2/H2O co-electrolysis. The NAP-XPS and NEXAFS results, obtained in situ and operando conditions and under electrochemical control, have provided important insights about the evolution of the chemical composition of the Cu surface. We have found that in dry CO2 ambient carbon deposits are scavenged at low cathodic potential by the oxidising action of nascent O, while at high cathodic polarisations C grows due to activation of CO reduction. Instead, in CO2/H2O mixtures, surface deposit of C is steady over the whole investigated potential range. The presence of adsorbed CO has also been detected during electrolysis of CO2/H2O mixtures, while no CO is found in pure CO2 ambient.