Design of highly efficient noble-metal-free hydrogen evolution electrocatalysts is of great significance to the practical application of water-separation devices. Herein, we design a highly active and durable two-dimensional (2D) hierarchical Mo2C/C-N hybrid with well-dispersed small Mo2C nanocrystals decorated on nitrogen-doped carbon (C-N) frameworks via one-step ionothermal route. Encouragingly, the optimal 2D hierarchical Mo2C/C-N hybrid shows a low onset potential of 6 mV, an overpotential of 98 mV at a cathodic current density of 10 mA cm(-2), a Tafel slope of 60 mV dec(-1), and a large exchange current density of 0.311 mA cm(-2) in acidic medium. Moreover, it also displays outstanding long-term electrochemical stability, exhibiting almost 100% activity retention after 3000 cycles and 20 h of continuous testing at fixed overpotentials. The unique 2D structure of electrocatalyst possesses highly dispersed ultrasmall Mo2C nanocrystals embedded in 2D layered C-N frameworks, excellent electron transportation, abundant active sites (Mo-C), and strong interaction between Mo2C nanocrystals and C-N frameworks, leading to the remarkable catalytic activity and endurance for hydrogen evolution reaction over a wide pH range. The synthetic strategy is facile and inexpensive for large-scale production and also can be extended to fabricate various 2D hierarchical nanomaterials for electrocatalytic applications. (C) 2017 Elsevier Ltd. All rights reserved.