Electrocatalytic properties of spinel-type MxCo3-xO4 oxides prepared by a new sol-gel route for O-2 evolution in alkaline solutions

Electrocatalytic properties of the spinel-type MxCo3-xO4 (M = Cu, Ni or Mn) oxides, prepared by a new sol-gel route, for O-2 evolution in alkaline sol utions have been studied using AC impedance, cyclic voltammetry and Tafel p olarization techniques. The oxides have been produced in the film form on p retreated Ni-supports by an oxide-slurry painting method. Results show that 0.25 and 0.5 mol Ni/or Cu substitutions in the base oxide enhance the oxid e roughness greatly; but their higher substitutions (> 0.5 mel) do not impr ove the roughness further. Mn-substitutions seem to have little influence o n the oxide roughness. Cu and Ni substitutions enhance the apparent electro catalytic activity of the oxide also; the electrocatalytic influence, howev er, is highest with 0.5 mol in the case of Cu and 0.75 mol in the case of N i-substitution. The apparent electrocatalytic activity is improved with 0.2 5 mol Mn also. In contrast, the real electrocatalytic activity of the oxide is considerably reduced in the presence of Ni, Cu and 0.5-1.0 mol Mn. Tafe l slope and the reaction order for the O-2 evolution reaction on each oxide are similar to2.3 RT/F and similar to1, respectively.