Through the use of in situ ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, carbon dioxide electrolysis reactions (CO2 + 2e- ? CO + O2-) and carbon monoxide electro-oxidation reactions (CO + O2- ? CO2 + 2e-) over cerium oxide electrodes have been investigated in the presence of 0.5 Torr CO/CO2 gas mixtures at ~600 �C. Carbonate species are identified on the ceria surface as reaction intermediates. When CO2 electrolysis is promoted on ceria electrodes at +2.0 V applied bias, we observe an increase in the concentration of carbonate over a 400-�m-wide active region on the ceria surface, accompanied by Ce3+/Ce4+ redox changes. The increase in the CO32- steady-state concentration suggests that the process of pre-coordination of CO2 to the ceria surface to form a carbonate intermediate (CO2 + O2-(ceria) ? CO32-) precedes a rate-limiting electron transfer process involving carbonate reduction to give CO and oxide ions (CO32- + 2e- ? CO + 2O2-). When the applied bias is switched to -1.5 V to promote CO electro-oxidation on ceria, the surface carbonate concentration slightly decreases from the equilibrium value, indicating that the electron transfer process is also a rate-limiting process in the reverse direction.

Mechanistic studies of high temperature water and CO<sub>2</sub> electrolysis through the use of <i>in situ</i> ambient pressure XPS studies

247th National Meeting (2014)

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Mechanistic studies of high temperature water and CO2 electrolysis through the use of in situ ambient pressure XPS studies

Mechanistic studies of high temperature water and CO₂ electrolysis through the use of in situ ambient pressure XPS studies