Effect of La 3+ ion on the electrodeposition of manganese and cobalt oxides

Abstract

Electrochemical preparations of oxide films of the perovskite (ABO 3 where A = La, B = Mn, Co) type are based on the electrodeposition of B oxides from solutions containing cations of both A and B. The effect of La 3+ ions on the electrodeposition of manganese and cobalt oxides and the chemical state of these ions in the oxides were investigated. Amorphous hydrous MnO 2 and Co 2O 3 were deposited with an incorporation of La 3+ ions in the mixed solutions Mn(NO 3) 3 + La(NO 3) 3 and Co(CH 3COO) 2 + La(NO 3) 3 respectively. The La/Mn and La/Co atomic ratios in the deposits were strongly dependent on the La(NO 3) 3 concentration in the solutions. The presence of La 3+ ions increased the overpotential of the electrochemical oxidation of Mn 2+ and Co 2+ ions in the solutions, resulting in suppression of the electrodeposition of the oxides. It was presumed from inductively coupled plasma atomic emission spectroscopy, Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy measurements that La 3+ ions in the Mn and Co oxides deposited from the solutions containing La(NO 3) 3 combined strongly with O 2− ions as in La 2O 3.