Developing low-cost and highly efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is attractive for overall water splitting. Herein, we firstly use the globally generated green cornstalks as the carbon source to prepare highly efficient bifunctional pure beta-phase molybdenum carbide (beta-Mo2C) electrocatalysts. Due to the highly intrinsic activity of beta-Mo2C, high porosity of the resultant and synergistic effect between the Mo2C and carbon matrix, the as-prepared catalyst exhibits excellent electrocatalytic activities with low overpotentials of 130 mV and 274 mV to achieve a current density of 10 mA cm(-2) for the HER and OER, respectively. As a bifunctional electrocatalyst for overall water splitting, the electrolyzer only needs a cell voltage of 1.65 V at 10 mA cm(-2) in alkaline water, as well as long-term stability of 30 h. This intriguing preparation strategy will open up an exciting new avenue for the synthesis of other carbides. (C) 2018 Elsevier Ltd. All rights reserved.