Electrochemical characteristics of La_(0.6)Sr_(0.4)CoO_(3-delta),Pr_(0.6)Sr_(0.4)CoO_(3-delta) and Gd_(0.6)Sr_(0.4)CoO_(3-delta) on Ce_(0.85)Sm_(0.15)O_(1.925) electrolyte

摘要

Cyclic voltammetry,chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_(0.85)Sm_(0.15)O_(1.925)|La_(0.6)Sr_(0.4)CoO_(3-delta),Ce_(0.85)Sm_(0.15)O_(1.925)| Pr_(0.6)Sr_(0.4)CoO_(3-delta) and Ce_(0.85)Sm_(0.15)O_(1.925)|Gd_(0.6)Sr_(0.4)CoO_(3-delta) .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 La~(3+) by Gd~(3+) 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 Gd_(0.6)Sr_(0.4)CoO_(3-delta) and the kinetically mixed process (diffusion + charge transfer) for Pr_(0.6)Sr_(0.4)CoO_(3-delta) and La_(0.6)Sr_(0.4)CoO_(3-delta) have been established.At higher temperature (T >= 993 K) and more negative potentials,the O_2 reduction process is limited mainly by the heterogeneous charge transfer step.