ACo₂O₄ samples were synthesized as water oxidation catalysts. The samples were characterized by multiple experiments to confirm their uniform morphology, which belongs to the spinel structure (Fd3m space group). The catalytic activity of ACo₂O₄ samples was investigated under photochemical, chemical, and electrochemical conditions; it follows the catalytic activity order NiCo₂O₄ > CuCo₂O₄ > ZnCo₂O₄. This activity sequence results from different doping metal ions in {Co₄O₄} motifs, which act as the active sites of water oxidation. Electrochemical impedance spectroscopy and other experimental data demonstrate that ACo₂O₄ samples doped with different metal ions may influence the rate of charge and electron transport. Therefore, the catalytic activity of water oxidation followed the above order.