The electrochemical determination of oxygen ion diffusion coefficients in La0.50Sr0.50CoO3−y Experimental results and related properties

Results of an electrochemical method for the determination of oxygen ion diffusion coefficients DO2− in porous pellets of La0.50Sr0.50CoO3−y are presented. Log DO2− can be expressed as log DO2−=−(2.3±0.2) 103/T−(6.6±0.6) cm2 s−1. The activation energy Ea for the diffusion process equals 44 kJ mol−1. Further the related electrochemical measurement and the adjustment of the oxygen deficiency y are described. At 75°C the following empirical Nernst relation between the electrode potential E (vs. a Pt/H2 (1 atm) electrode in the same solution) and Δy is found: E=627–108 ln (Δy + 0.0054) mV. (Δy=y−y0; y0=mole fraction of vacancies at the reversible O2 potential of 1190 mV). The use of La0.50Sr0.50CoO3−y as a solid solution electrode in practical storage cells seems to be excluded for thermodynamic and kinetic reasons.