Oxygen transport in electronically conducting perovskites



Kemal Nisancioglu, Insitut for Materialteknologi og elektrokjemi, NTNU


Electrochemical techniques based on the potential step and electrochemical impedance spectroscopy, are developed and evaluated for the simultaneous measurement of the chemical diffusion and surface exchange coefficients and thermodynamic data for mixed conducting nonstoichiometric oxides, which are relevant as cathodes for solid oxide fuel cells and as membranes for highly selective oxygen separation. Equations for data analysis are developed from fundamental phenomenological principles of mass and charge transport. A solid-state electrochemical cell is designed for minimizing the gas phase capacitance, which can be an important problem in the application of relaxation techniques. The methodology is validated by applying the techniques to determine the properties of a well-studied SrCo0.5Fe0.5O3-d material. The equivalence and complementary aspects of the two electrochemical approaches are discussed along with advantages and drawbacks.