Effect of La3+ ion on the electrodeposition of manganese and cobalt oxides

Electrochemical preparations of oxide films of the perovskite (ABO3 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 La3+ ions on the electrodeposition of manganese and cobalt oxides and the chemical state of these ions in the oxides were investigated. Amorphous hydrous MnO2 and Co2O3 were deposited with an incorporation of La3+ ions in the mixed solutions Mn(NO3)3 + La(NO3)3 and Co(CH3COO)2 + La(NO3)3 respectively. The La/Mn and La/Co atomic ratios in the deposits were strongly dependent on the La(NO3)3 concentration in the solutions. The presence of La3+ ions increased the overpotential of the electrochemical oxidation of Mn2+ and Co2+ 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 La3+ ions in the Mn and Co oxides deposited from the solutions containing La(NO3)3 combined strongly with O2− ions as in La2O3.