A facile two-step synthesis of 1D nanorod, 2D nanosheet, and 3D nanocube-shaped Co3O4 was demonstrated. The formed 1D, 2D, and 3D Co3O4 were systematically probed using a structure sensitive electrochemical oxygen evolution reaction (OER), revealing that the 2D nanosheets exhibited higher catalytic activities in contrast to the 1D and 3D Co3O4, due to their high electrochemically active surface area and rich oxygen deficiencies. This study also showed that there was a tradeoff between the 2D and 3D Co3O4 in terms of OER activity and stability.