In Situ Characterization of Ceria Oxidation States in High-Temperature Electrochemical Cells with Ambient Pressure XPS

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• 作者：Steven C. DeCaluwe ; Michael E. Grass ; Chunjuan Zhang ; Farid El Gabaly ; Hendrik Bluhm ; Zhi Liu ; Gregory S. Jackson ; Anthony H. McDaniel ; Kevin F. McCarty ; Roger L. Farrow ; Mark A. Linne ; Zahid Hussain
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：November 25, 2010
• 年：2010
• 卷：114
• 期：46
• 页码：19853-19861
• 全文大小：380K
• 年卷期：v.114,no.46(November 25, 2010)
• ISSN：1932-7455

文摘

Ambient pressure X-ray photoelectron spectroscopy (XPS) is used to measure near-surface oxidation states and local electric potentials of thin-film ceria electrodes operating in solid oxide electrochemical cells for H<sub>2sub>O electrolysis and H<sub>2sub> oxidation. Ceria electrodes which are 300 nm thick are deposited on YSZ electrolyte supports with porous Pt counter electrodes for single-chamber tests in H<sub>2sub>/H<sub>2sub>O mixtures. Between 635 and 740 °C, equilibrium (zero-bias) near-surface oxidation states between 70 and 85% Ce<sup>3+sup> confirm increased surface reducibility relative to bulk ceria. Positive cell biases drive H<sub>2sub>O electrolysis on ceria and further increase the percentage of Ce<sup>3+sup> on the surface over 100 μm from an Au current collector, signifying broad regions of electrochemical activity due to mixed ionic-electronic conductivity of ceria. Negative biases to drive H<sub>2sub> oxidation decrease the percentage of Ce<sup>3+sup> from equilibrium values but with higher electrode impedances relative to H<sub>2sub>O electrolysis. Additional tests indicate that increasing H<sub>2sub>-to-H<sub>2sub>O ratios enhances ceria activity for electrolysis.