The reaction rates of electrochemical reactions in solid oxide fuel cells (SOFCs) or solid oxide electrolysis cells (SOECs) can be probed by electrical measurement techniques such as impedance spectroscopy. However, interpretation of such experiments in terms of reaction mechanisms and reaction zones is far from trivial and often even impossible without additional information. Since all electrode reactions in SOFCs/SOECs based on oxide ion conductors involve either incorporation or release of oxygen atoms, a direct monitoring of the electrochemical processes by means of 18O tracer is possible. 18O tracer diffusion experiments on mixed conducting electrode materials are therefore a common means to obtain kinetic data of oxygen exchange in oxygen atmosphere (k* and D* factors) (i). In case of spatially varying reaction rates (e.g. due to active triple phase boundaries) tracer incorporation experiments have also been used for identifying electrochemically active zones and their width, particularly upon cathodic voltage in oxygen tracer atmosphere (ii).However, several additional types of tracer-based experiments are conceivable which may lead to valuable kinetic information. For example: monitoring reaction rates by 18O release, thus making reactions in H2/H2O atmosphere accessible (iii), employing H218O for probing reactions in reducing atmosphere (iv), identifying the relevance of limited ion or electron conduction in mixed conducting thin film electrodes by spatially varying tracer incorporation in oxidizing and reducing atmosphere (v).This contribution presents our most recent results of tracer experiments of all five types (i-v), i.e. with and without field and in different atmospheres. Mechanistic conclusions on resistive processes and active zones are drawn, partly in conjunction with complementary impedance studies. Examples include measurements on different thin film electrodes such as (La,Sr)CoO3-x (LSC), (La,Sr)FeO3-x (LSF), (La,Sr)MnO3 (LSM), platinum, and Sr(Ti,Fe)O3-x (STF).

Tracer ions for monitoring resistive processes and active zones of solid state electrochemical reactions in H<sub>2</sub>/H<sub>2</sub>O and oxygen atmosphere

247th National Meeting (2014)

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Tracer ions for monitoring resistive processes and active zones of solid state electrochemical reactions in H2/H2O and oxygen atmosphere

Tracer ions for monitoring resistive processes and active zones of solid state electrochemical reactions in H₂/H₂O and oxygen atmosphere