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Developing highly active bifunctional electrocatalysts for oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)is of great significance in energy conversion and storage technologies.In this study,we systematically investigated the OER/ORR electrocatalytic activity of TMN4@G system by using density functional theory(DFT)calculations.Globally,IrN4@G is a very promising bifunctional catalyst for both OER and ORR with the extremely low overpotentials of 0.30 and 0.26 V,respectively.Such outstand-ing electrocatalytic performance is mainly attributed to the synergistic effect of Ir and N.More impor-tantly,by constructing 2D activity volcano plots,we obtained the limiting overpotentials of TMN4@G system with the values of 0.26 V for OER and 0.24 V for ORR.These findings open up new opportunities for further exploring graphene-based materials for highly efficient OER/ORR electrocatalysts.