Impedance studies of cathode/electrolyte behaviour in SOFC

• Published in: Electrochimica acta Vol. 53; no. 25; pp. 7491 - 7499
• Main Authors: Vladikova, D.E., Stoynov, Z.B., Barbucci, A., Viviani, M., Carpanese, P., Kilner, J.A., Skinner, S.J., Rudkin, R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 30.10.2008; Elsevier
• Subjects: Applied sciences; Cathode reaction; Composite cathode materials; Differential impedance analysis; Electrochemical impedance spectroscopy; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Solid oxide fuel cells; Solid oxide fuel cells; Cathode reaction; Differential impedance analysis; Electrochemical impedance spectroscopy; Composite cathode materials; Gold; Perovskite type compound; Cathode; Solid electrolyte; Transition metal; Electrode material; Solid oxide fuel cell; Zirconia; Silver; Yttrium Oxides; Platinum; Composite electrode; Zirconium Oxides; Electrical impedance; Lanthanum Manganese Strontium Oxides; Modified material
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2007.11.037

This paper reports impedance studies of the cathode/electrolyte behaviour in solid oxide fuel cells (SOFC), based on comparative investigation of half-cells with yttria stabilized zirconia (YSZ) electrolyte and different cathode materials: lanthanum strontium manganite (LSM), and composite LSM/YSZ with low ionic conductivity as well as the electron conducting Ag, Pt and Au. For improved impedance data analysis the technique of the differential impedance analysis is applied. It ensures structural and parametric identification without preliminary assumptions about the working model. It is found that despite the low ionic conductivity of LSM, the cathode reaction of the oxide cathode materials is a two-step process including: (i) charge transfer with activation energy of the resistivity E a increasing with the temperature and (ii) transport of oxygen ions through the bulk of the electrode (rate-limiting stage) with E a independent on the temperature. For the metal (electron conducting) electrodes, the reaction behaviour is described with one step process with higher E a at higher temperatures. The activation energy of the electrolyte conductivity decreases with the increase of the temperature. The observed changes in E a for the electrolyte and the cathode reaction (the charge transfer step for the LSM-based electrodes) appear in the same temperature interval. This interesting coincidence suggests for correlation between the bulk (electrolyte) and surface conduction properties. Approaches for improvement of both the ionic conductivity and the supply with electrons in LSM should be also searched.