The reactions of carbon dioxide electrolysis (CO2 + 2e- ? CO + O2-) and carbon monoxide electro-oxidation (CO + O2- ? CO2 + 2e-) over specially designed ceria-based solid oxide electrochemical cells (SOC) have been studied by in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) in the presence of 0.5 Torr CO/CO2 gas mixtures at ~600 �C. The presence of carbonate species on the ceria surface as reaction intermediates is revealed. When a +2.0 V applied bias promotes CO2 electrolysis on ceria electrodes, we observe a build-up 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 formation of carbonate (CO2 + O2-(ceria) ? CO32-) by pre-coordination of CO2 to the ceria surface precedes a rate limiting electron transfer process which involves the reduction of carbonate (CO32- + 2e- ? CO + 2O2-). During CO electro-oxidation on ceria at -1.5 V applied bias, 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. These results provide mechanistic details of the electrochemically driven surface charge transfer processes under operating conditions.

Carbon dioxide electrolysis and carbonate intermediates on ceria: An in situ ambient-pressure X-ray photoelectron spectroscopy study on solid oxide electrochemical cells

247th National Meeting (2014)

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