Enhancement of hydrogen storage capacity is a great challenge that the research community is facing. The challenge lies on the fact of interdependence of hydrogen storage and release processes. It presents that the hydrogen release would be difficult if the hydrogen can be stored easily or vice versa. This work strategically tackles this critical issue through density functional theory (DFT) calculations by applying defect engineering on graphene, and also changing the hydrogenation/dehydrogenation and hydrogen diffusion chemical potentials via applying electric field. It is found that hydrogen molecules are dissociatively adsorbed on N-doped graphene spontaneously in the presence of a perpendicular electric field F. After adsorption, H atoms diffuse on N-doped graphene surface with low energy barrier and the graphene can be fully hydrogenated. By removing the electric filed, the stored hydrogen can be released efficiently under ambient conditions. It demonstrates that the N-doped graphene is a promising hydrogen storage material with the storage capacity up to 6.73 wt%. The electric field can act as a switch for hydrogen uptake/release processes.