Abstract
Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce0.85Sm0.15O1.925| La0.6Sr0.4CoO3-δ, Ce0.85Sm0.15O1.925| Pr0.6Sr0.4CoO3-δ and Ce0.85Sm0.15O1.925| Gd0.6Sr0.4CoO3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La3+ by Gd3+ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd0.6Sr0.4CoO3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O2 reduction process is limited mainly by the heterogeneous charge transfer step.
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