A review on cathode processes and materials for electro-reduction of carbon dioxide in solid oxide electrolysis cells

Excessive emission of CO2 may jeopardize the environment and livelihood of mankind. To achieve a sustainable future, solid oxide electrolysis cells (SOECs) are increasingly attractive as an efficient technology combining both CO2 reduction and renewable energy storage. The SOEC cathode is a critical component where CO2 reduction reaction (CO2RR) occurs. Consequently, extensive efforts are devoted to searching for the SOEC cathode materials with enhanced catalytic activity and durability. To better design such SOEC cathode materials, this review discusses the fundamentals of CO2 electro-reduction including thermal dynamics and kinetics, and then summarizes the recent advances in understanding reaction mechanisms and exploring cathode materials. For CO2 electrolysis, proper CO2 adsorption and fast charge transfer from electro-catalyst to the adsorbed CO2 species can directly promote the cathodic kinetics. Nickel in the conventional cermet cathode is catalytically active, but easily oxidize in CO2 without CO or H-2. As potential substitution, certain types of redox stable oxides possessing both ionic and electronic conductivity are investigated, enabling direct CO2 electrolysis without safe gas.