Defect engineering is an efficient strategy to modulate the physical and chemical properties of electrocatalysts with the aim to achieving high-performance catalysis. In this work, defect-rich and carbondoping Co3O4 nanosheets are successfully prepared through one-step room temperature CH4 plasma. The CH4 plasma can not only etch the surface of Co3O4 to bring intrinsic defects, but also atomically dope carbon into the Co3O4. Benefiting from this defect engineering strategy, the electronic and composition of Co3O4 is modulated with optimized intermediate binding. The formation of oxygen vacancy in Co3O4 can significantly enhance the OER activity and the formation of CoeC bond in Co3O4 can deliver an ideal HER activity. Even more, the synergistic effect of dual-type point defects may further enhance the electrocatalytic activity for both HER and OER. As a result, the as-prepared carbon-doping Co3O4 exhibits low overpotential along with good stability in alkaline media for both HER and OER. This finding will open up a new way to engineer the electronic structure of the metal oxides to design highly efficient bi-functional electrocatalysts. (c) 2019 Elsevier Ltd. All rights reserved.