Fig. 3

Theoretical calculations of the hydrogen adsorption configured for Ir and IrNC. a, b The isosurfaces of the electron density difference for Ir and IrNC with H adsorption, respectively. c The projected density of states (DOS) distribution of adsorbed H and surficial Ir sites in IrNC, respectively. d The calculated free energy diagram of HER on the surface of Ir and IrNC at the equilibrium potential, respectively