Electrochemical reduction of carbon dioxide using solid oxide electrolysis cells

Selective electrochemical conversion of CO₂ to platform fuels and chemicals using renewable energy sources has become a contemporary research area of interest because of the need to recycle and minimize adverse environmental impacts of CO₂. Solid oxide electrolysis cells (SOECs) are solid-state electrochemical devices with significant potential in this area because of their ability to efficiently and selectively convert CO₂ to CO or, when coupled with water electrolysis, to produce syngas (CO and H₂). Both CO and syngas are precursors for the synthesis of fuels and chemicals using existing technologies, i.e., Fischer-Tropsch process. Although promising, these systems are limited by the high activation overpotential losses induced by the kinetics of CO₂ reduction at the cathode and the stability of metal-based electrocatalysts for this chemistry. Furthermore, the complexity and high operating temperatures of these systems bring challenges to the understanding of the mechanism that governs electrochemical reduction of CO₂, making the optimization of the activity and stability of SOEC cathode electrocatalysts very challenging.

Our group has focused on combining experimental and theoretical techniques to understand the chemical/electrochemical steps that govern high temperature electrochemical reduction of CO₂ to CO on a series of metal and mixed metal oxide electrocatalysts. We have shown that the binding strength of oxygen on the surface of metal electrocatalysts can be used as a descriptor of the activity and stability of these electrocatalysts for CO₂ reduction in SOECs, with Fe resulting in the highest activity but lowest overall stability. We have found that incorporation of Fe cations in mixed ionic and electronic metal oxide structures can alleviate the stability issues, however electrochemical rates are lower than in the case of metal-based electrocatalysts. Based on these insights we have devised ways to design optimal SOEC cathode electrocatalysts for CO₂ reduction in SOECs.