N-doped carbon materials have been regarded as potential replacements for Pt-based electrocatalysts for oxygen reduction reaction (ORR). However, the exact catalytic mechanisms are still not completely understood and there is a controversy about which type of N determines the selectivity of the reaction. This study reports a simple pyrolysis method to prepare hierarchical porous-structured N-doped graphene using 4-nitroimidazole as both C and N sources without the presence of two-dimensional template. The as-prepared Ndoped graphene exhibits efficient four-electron transfer pathway for ORR with an onset potential of 0.943 V, a half-wave potential of 0.823 V, and a limiting current density of 5.58 mA cm À 2 in 0.1 M KOH solution. In contrast, N-doped platelet-like carbon consisted mainly of micropores prefers the two-electron pathway with a high selectivity toward peroxide generation over 90 % at potential range of 0.20-0.62 V. We demonstrate that the ORR selectivity is dependent on the H 2 O transfer dynamics which are controlled by the porous structure. Sluggish H 2 O transfer rate induces HO 2 À formation, whereas fast H 2 O transfer rate ensures the desired four-electron pathway. This study gives further insight into the ORR selectivity and provides feasible strategies for fabricating N-doped carbon materials as promising catalysts for either four-electron oxygen reduction or H 2 O 2 production in alkaline solution.