Metal-embedded nitrogen-doped carbon materials have been proposed as novel hydrogen evolution reaction (HER) catalysts to replace platinum-based materials, while these alternatives usually exhibit low activity and gradual deactivation during their use. Here, leaf-like cobalt-embedded nitrogen-doped porous carbon sheet (Co-NC) for the HER is obtained by simple pyrolysis of a two-dimensional metal organic framework. The Co-NC annealed at 800 degrees C exhibits large surface area and the active metallic cobalt species embedded in the N-doped carbon layers, which leads to the lower overpotential, higher current density, and superior durability in alkaline media. However, the Co-NC annealed at 600 degrees C shows abundant nitrogen-coordinated cobalt species, which favors the high HER activity under acidic condition. These structural properties of the Co-NC enable the efficient HER activity by increasing the active sites and enhancing mass transfer of water molecules or protons at the interface where the reaction takes place. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.