Analysis of Interfacial Processes at the SOFC Electrodes by In-Situ Raman Spectroscopy

Kinetics of redox reactions and the variations of real charge-carrier concentrations across the SOFC electrode / electrolyte interfaces have critical importance for the fuel cell performance. The microscopic mechanisms of electrochemical processes in the vicinity of triple-phase boundary (TPB) can be assessed employing impedance spectroscopy, current-voltage measurements and various pulse techniques. Except for the micro-electrode approaches, however, these methods are cumulative. Moreover, unambiguous interpretation of the electrochemical measurement results requires, as a rule, to introduce complimentary experimental methods and/or to use simplified models. The present work is centered on the developments of a new combined technique for in-situ Raman spectroscopy studies of local chemical and electrochemical reactions, phase transitions, strains and morphological alterations in the SOFC electrodes under working conditions. The Raman spectroscopy was already successfully used to investigate both cathodic [1,2] and anodic [3] processes in SOFC, but the resultant information was mainly related to outer boundaries of the model electrochemical cells, primarily electrode surface, due to low penetration depth of the excitation radiation. The most important zones of the electrode systems, where the electrochemical reactions occur and ionic charge carriers are generated, cannot be achieved viewing the surface and edge areas. In the present work, this problem was solved by employing optically transparent, single-crystal membranes made of 10 mol.% Sc₂O₃ and 1% mol.% Y₂O₃ stabilized zirconia (10Sc1YSZ). In order to provide simultaneous Raman and electrochemical measurements of the cell placed under an oxygen chemical potential gradient, such as air/H₂, a special controlled-atmosphere chamber was elaborated and tested. An appropriate selection of the electrodes geometry makes it possible to directly collect Raman spectra from the TPB zone, passing the beam through single-crystal solid electrolyte onto the interface, as a function of temperature, atmosphere, current density and/or overpotential. The results of case studies focused on redox kinetics of Ni-containing cermet anodes, are presented.

This work was supported by grant 14-29-04031 of Russian Foundation for Basic Research.

 References

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