Polypyrrole and La 1− xSr xMnO 3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium

Abstract

Composite G/PPy/PPy(La 1− x Sr x MnO 3)/PPy electrodes made of the perovskite La 1− x Sr x MnO 3 embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La 1− x Sr x MnO 3) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm −3 pyrrole (Py) plus 0.05 mol dm −3 K 2SO 4 with and without containing a suspension of 8.33 g L −1 oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm −3 K 2SO 4 plus 5 mmol dm −3 KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.