PbO2 + Co3O4, Tl2O3 + Co3O4 and Ni + Co3O4 composite layers have been obtained by either anodic (oxide matrices) or cathodic (Ni-matrix) electrodeposition. Their electrocatalytic activity in the oxygen evolution reaction has been investigated with the aim of assessing the effect of concentration of Co3O4 and surface roughness. Different composites showed a different dependence of oxygen evolution current density on Co3O4 content. Only in the case of PbO2 + Co3O4, the electrode effective area appeared to increase with the dispersed phase concentration, resulting in a non-linear relationship between oxygen evolution rate and Co3O4 content.