Water-Induced Decoupling of Tracer and Electrochemical Oxygen Exchange Kinetics on Mixed Conducting Electrodes

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• 作者：Andreas Nenning ; Edvinas Navickas ; Herbert Hutter ; Jürgen Fleig
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：July 21, 2016
• 年：2016
• 卷：7
• 期：14
• 页码：2826-2831
• 全文大小：459K
• 年卷期：0
• ISSN：1948-7185

文摘

Isotope exchange depth profiling and electrochemical impedance spectroscopy are usually regarded as complementary tools for measuring the surface oxygen exchange activity of mixed conducting oxides, for example used in solid oxide fuel cell (SOFC) electrodes. Only very few studies compared electrical (k^q) and tracer (k*) exchange coefficients of solid–gas interfaces measured under identical conditions. The 1:1 correlation between k^q and k* often made is thus more an assumption than experimentally verified. In this study it is shown that the measured rates of electrical and tracer exchange of oxygen may strongly differ. Simultaneous acquisition of k^q and k* on La_0.6Sr_0.4FeO_3-δ and SrTi_0.3Fe_0.7O_3-δ thin film electrodes revealed that k* > 100 k^q in humid oxidizing (¹⁶O₂ + H₂¹⁸O) and humid reducing (H₂ + H₂¹⁸O) atmospheres. These results are explained by fast water adsorption and dissociation on surface oxygen vacancies, forming two surface hydroxyl groups. Hence, interpreting experimentally determined k* values in terms of electrochemically relevant oxygen exchange is not straightforward.