Electrocatalytic properties of Sr-doped LaMnO₃ obtained by a new sol-gel route in relation to O₂ evolution in alkaline solution

Abstract

Lanthanum manganites with molecular formula La_1-xSr_xMnO₃ (0 x 0.5) have been synthesized in a powder form at 700°C using citric acid and ethylenediamine as gelling agents. These powders have been reproduced in the film forms on pretreated Ni-supports by an oxide-slurry painting technique. The study has indicated that Sr-substitution increased both the apparent as well as the true catalytic activity of the oxide and that it has no regular effect on the oxide roughness. The Tafel slope and the reaction order with respect to OH^- concentrations at low overpotential have been observed to be approximately

2.3 × 2<i>RT1F </i>and unity, respectively. Sr-substitution seems to slightly decrease the apparent electrochemical activation energy (Δ<i>H</i>_cl^#0), while it has no effect on the true electrochemical activation energy (Δ<i>H</i>_c^#0) and on the entropy of activation (Δ<i>S</i>^#0) of the reaction.