Correlating Surface Crystal Orientation and Gas Kinetics in Perovskite Oxide Electrodes.
basic_science · Level V
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- Record sourced from PubMed, PMID 33829572.
- Also identified by DOI 10.1002/adma.202100977.
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Abstract
Solid-gas interactions at electrode surfaces determine the efficiency of solid-oxide fuel cells and electrolyzers. Here, the correlation between surface-gas kinetics and the crystal orientation of perovskite electrodes is studied in the model system La<sub>0.8</sub> Sr<sub>0.2</sub> Co<sub>0.2</sub> Fe<sub>0.8</sub> O<sub>3</sub> . The gas-exchange kinetics are characterized by synthesizing epitaxial half-cell geometries where three single-variant surfaces are produced [i.e., La<sub>0.8</sub> Sr<sub>0.2</sub> Co<sub>0.2</sub> Fe<sub>0.8</sub> O<sub>3</sub> /La<sub>0.9</sub> Sr<sub>0.1</sub> Ga<sub>0.95</sub> Mg<sub>0.05</sub> O<sub>3-δ</sub> /SrRuO<sub>3</sub> /SrTiO<sub>3</sub> (001), (110), and (111)]. Electrochemical impedance spectroscopy and electrical conductivity relaxation measurements reveal a strong surface-orientation dependency of the gas-exchange kinetics, wherein (111)-oriented surfaces exhibit an activity >3-times higher as compared to (001)-oriented surfaces. Oxygen partial pressure ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow><msub><mi>p</mi> <msub><mi>O</mi> <mn>2</mn></msub> </msub> </mrow> </math> )-dependent electrochemical impedance spectroscopy studies reveal that while the three surfaces have different gas-exchange kinetics, the reaction mechanisms and rate-limiting steps are the same (i.e., charge-transfer to the diatomic oxygen species). First-principles calculations suggest that the formation energy of vacancies and adsorption at the various surfaces is different and influenced by the surface polarity. Finally, synchrotron-based, ambient-pressure X-ray spectroscopies reveal distinct electronic changes and surface chemistry among the different surface orientations. Taken together, thin-film epitaxy provides an efficient approach to control and understand the electrode reactivity ultimately demonstrating that the (111)-surface exhibits a high density of active surface sites which leads to higher activity.