Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells

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• 作者：Chunjuan Zhang ; Yi Yu ; Michael E. Grass ; Catherine Dejoie ; Wuchen Ding ; Karen Gaskell ; Naila Jabeen ; Young Pyo Hong ; Andrey Shavorskiy ; Hendrik Bluhm ; Wei-Xue Li ; Gregory S. Jackson ; Zahid Hussain ; Zhi Liu ; Bryan W. Eichhorn
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：August 7, 2013
• 年：2013
• 卷：135
• 期：31
• 页码：11572-11579
• 全文大小：462K
• 年卷期：v.135,no.31(August 7, 2013)
• ISSN：1520-5126

文摘

Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H₂O + 2e^{鈥?/sup> 鈫?H₂ + O2鈥?/sup>) and electro-oxidation of hydrogen (H₂ + O2鈥?/sup> 鈫?H₂O + 2e鈥?/sup>) at 700 掳C in 0.5 Torr of H₂/H₂O on ceria (CeO_2鈥?i>x) electrodes. The experiments reveal a transient build-up of surface intermediates (OH鈥?/sup> and Ce3+) and show the separation of charge at the gas鈥搒olid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH鈥?/sup> and incorporated O2鈥?/sup> differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH鈥?/sup> and O2鈥?/sup> shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H₂O + Ce3+ Ce4+ + OH鈥?/sup> + H鈥?/sup>) is rate limiting in both the forward (water electrolysis) and reverse (H₂ electro-oxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas鈥搒olid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH鈥?/sup>/O2鈥?/sup> potential separation resides in the reduced polarization of the Ce鈥揙H bond due to the increase of Ce3+ on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions.}