Electrochemical water splitting by electricity from the renewable power sources is one of the most promising pathways for green and sustainable hydrogen production. The key is to synthesize earth-abundant and noble-metal-free electrocatalysts with outstanding hydrogen evolution reaction (HER) activity and durability in wide-pH electrolytes by simple and cost-effective methods. Herein, we reported a one-step synthesis of uniform, ultrafine molybdenum carbide (Mo2C) and molybdenum nitride (Mo2N) hybrid [together as Mo-2(CN)] inserted carbon nanosheets as efficient electrocatalyst for HER. The assynthesized catalyst showed an excellent HER activity in acid medium, and even superior performance was obtained in the alkaline medium. The optimal Mo-2(CN) annealed at 750 degrees C showed an overpotential of -80 mV at 10 mAcm(-2) and a Tafel slope of 40 mV dec(-1); the former strikingly outperforms commercial 20% Pt/C materials (-112 mV). Moreover, Mo-2(CN) gave an onset voltage of -33mV and overpotential of -202 mV at 100 mA cm(-2) with merely a mass loading of 0.2 mg cm(-2), which are, to date, among the best records for Mo-based catalysts in both media. The nanosheet structure providing large active area and quick charge transfer, and the synergistic effects between Mo2C and Mo2N toward HER are ascribed to the outstanding electrocatalytic activity according to the capacitive current and turnover frequency analysis. The remarkable catalytic activity and operational durability in wide pH ranges guarantee their potential for highly efficient hydrogen production. (C) 2018 Elsevier Ltd. All rights reserved.