Carbon-based materials have been attracting intense interest for electrocatalysis due to their various merits, such as abundance, low cost, high conductivity and tunable molecular structures. However, to date, the electrochemical activities of these electrocatalysts are mainly attributed to different active dopants (e.g. N, B, P or S), leading to a common concept that heteroatom doping is essential for carbon-based electrocatalysts. Recently, we presented a new concept where the specific topological defects could activate the oxygen reduction reaction (ORR) and developed a facile method to create such unique defects. Subsequent research has extended this new mechanism to other reactions, such as the hydrogen and oxygen evolution reactions (HER and OER) and confirmed that heteroatom doping is not essential but that these defects can serve as actives sites for electrochemical reactions. This new theory then creates a new research direction in electrocatalysis. In this short review, we summarise the origin and presentation of the defect mechanism concept, the possible topological defect structures that are effective for electrochemical reactions, the formation of desirable defects, the challenges in the synthesis and characterization of typical defects and future research directions on the electrochemical defect mechanism.