Carbon Deposits and Pt/YSZ Overpotentials In CO/CO2 Solid Oxide Electrochemical Cells

Abstract

Through the use of in situ ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, CO2 electrolysis reactions (CO2 + 2e- → CO + O2-) and CO electro-oxidation reactions (CO + O2- → CO2 + 2e-) were studied on Pt and ceria electrodes supported on YSZ electrolytes. Electrolysis and electro-oxidation reactions were conducted in the presence of 0.5 Torr CO/CO2 gas mixtures at ~600 °C. When CO2 electrolysis reactions were promoted on ceria at +2.0 V applied bias, we observed the formation of graphitic carbon species on the ceria electrode surface. This carbon layer facilitates the electron conduction and extends the active region further away from the Au current collector. The charge transfer overpotentials at the Pt/YSZ interface were shown to be the largest resistance in the cell for both processes. By comparing with previous studies of the H2/H2O system, it is concluded that higher charge transfer resistances are associated with CO2 electro-oxidation and CO electro-oxidation at this three-phase-boundary.