Abstract: Insights into the relationship between the crystal planes of metal oxides and the catalytic activity of the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) are essential for developing efficient renewable energy technologies. Herein, spinel Co3O4 nanomaterials were synthesized controllably with the specified morphologies of nanocubes, nanosheets, and nanoplates with different exposed planes of {100}, {110}, and {111}, respectively. The effects of the crystal planes of Co3O4 on the activity for the OER, ORR, and HER were subsequently investigated in alkaline media. Different electrocatalytic performances are possibly attributed to the abundance ratios of Co3+/Co2+ over the different exposed planes. The surface Co3+ ions exhibit higher activity for the OER and HER, whereas the surface Co2+ ions exhibit better performance for the ORR; moreover, higher electroconductivity enhances the polarization current for ORR and HER except OER.