In this work, amorphous and mesoporous Co3O4 material is obtained from the calcination of loosely packed Co3O4/Co(OH)2 nanosheets which are synthesized by the formation and disassociation of cobalt–citrate complex reaction. We propose that Co nanoparticles are completely oxidized to form the stable cobalt–citrate complex in the presence of sodium citrate and oxygen, and cobalt–citrate complex disassociates to Co(OH)2 under alkaline conditions. The high surface area and mesoporous texture of granular Co3O4 materials are the consequence of the energetically favored topotactic transformation aspect in the solid-state oxidative reaction. Furthermore, mesoporous Co3O4 material exhibits excellent electrochemical capacitance prosperities, well retention to the discharging capacity in cycle lifetime, and a high specific capacitance of 427 F g−1, indicating its potential application in electrochemical capacitors and further in energy and environmental applications.