How the surface state of nickel/gadolinium-doped ceria cathodes influences the electrochemical performance in direct CO2 electrolysis

The effect of the surface state on electrochemical performance nickel gadolinium-doped ceria (NiGDC) cermet electrodes in direct CO2 electrolysis was studied by operando near ambient pressure X-ray photoelectron spectroscopy combined with on-line gas phase and electrical measurements. limited at overpotentials below carbon deposition threshold to avoid irreversible cathode deactivation. results revealed dynamic evolution NiGDC electrode disclose side reactions associated activation electrolysis. Comparison reduced oxidized shows that metallic Ni is a prerequisite for electrolysis, least low potentials, suggesting electoreduction occurs primarily three boundaries between gas, partially ceria. We also provide evidences situ reduction NiO upon polarization CO2, implying addition reductive gases not indispensable maintain state. Inspired this observation, we use conventional button cell setup demonstrate improved i-V characteristics as compared CO2/H2 fuel conditions rationalize behavior based NAP-XPS results.