Electrochemical carbon deposition from CO2 on nickel and ceria electrodes studied by operando XPS

The solid oxide electrochemical cell (SOC) is a promising candidate for large-scale renewable energy storage. By electrolysis of CO2 and H2O, synthesis gas can be produced with high efficiency and subsequently upgraded to green hydrocarbon fuels for use in existing fuel infrastructure and vehicles. However, in state-of-the-art SOCs, electrolysis of CO2 or CO2/H2O mixtures can lead to carbon deposition in the Ni-based fuel-electrode, eventually destroying the electrode. It is known that alternative electrocatalyst materials such as acceptor-doped ceria inhibit carbon deposition. However, the mechanisms by which electrochemical driven carbon deposition occurs or is inhibited are not understood. In this study we used operando X-ray photoelectron spectroscopy to probe the fundamental mechanisms of carbon deposition during electrochemical reduction of CO2 at 550 C and 500 mTorr pressure using model electrodes. The onset overpotential, role of surface adsorbates and intermediates, and reversibility of carbon deposition, were studied in detail on different electrode materials with electrical and spectroscopic measurements.