Solid Electrolyte Coulometric Studies of Oxide State and Kinetics

The oxide stoichiometry of La 1–XSr xCo 1–YFe yO 3–δ d perovskite powders was investigated by means of solid electrolyte coulometry. Experiments were performed at reduced oxygen partial pressures between 1.3 × 10 −3 atm and 6 × 10 −5 atm, applicable to cathodic bias under solid oxide fuel cell operating conditions. It was found that the degree of oxygen non-stoichiometry (δ) increased with increasing temperature, decreasing oxygen partial pressure and increasing Sr or Co content. Transient re-equilibrium experiments, following a small perturbation in the temperature or oxygen pressure, were carried out to investigate the oxygen transport and surface absorption kinetics. Using a suitable diffusion model and non-linear parameter optimization, the surface exchange coefficient ( k) and chemical diffusion coefficient ( D) of oxygen were obtained from the transients. The results were found to be consistent with those of other relaxation techniques.