Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 114, Issue 46, Pages 19853-19861Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp107694z
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Funding
- Office of Naval Research [N000140510711]
- Office of Energy Research, Office of Basic Energy Sciences, and Chemical Sciences Division of the U.S. Department of Energy [DEAC02-05CH11231]
- United States Department of Energy [DE-AC04-94AL85000]
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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 H2O electrolysis and H-2 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-2/H2O mixtures. Between 635 and 740 degrees C, equilibrium (zero-bias) near-surface oxidation states between 70 and 85% Ce3+ confirm increased surface reducibility relative to bulk ceria. Positive cell biases drive H2O electrolysis on ceria and further increase the percentage of Ce3+ on the surface over 100 mu m from an Au current collector, signifying broad regions of electrochemical activity due to mixed ionic-electronic conductivity of ceria. Negative biases to drive H-2 oxidation decrease the percentage of Ce3+ from equilibrium values but with higher electrode impedances relative to H2O electrolysis. Additional tests indicate that increasing H-2-to-H2O ratios enhances ceria activity for electrolysis.
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