Three different metal oxides based on Mn2O3 with TiO2 or NiO were synthesised. Pt or PtNi nanoparticles were anchored on each support, creating a set of nine samples that were tested for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). PtNi/Mn2O3-NiO showed the most promising results for ORR as evidenced by the lowest Tafel slope, the highest diffusion-limited current density and number of electrons exchanged, along with the highest stability. The best performance of PtNi/Mn2O3-NiO reflects its highest electrochemical surface area and the lowest charge-transfer resistance. Furthermore, this catalyst showed high activity for the OER as evidenced by the low Tafel slope and high current density at an overpotential of 400 mV. The present study indicated different active sites for the two reactions, i.e., PtNi NPs for the ORR and NiO for the OER.