Electrochemical water splitting into H 2 and O 2 provides a promising and sustainable strategy for the future production of clean energy. Herein, we report an ammonium nitrate (AN)assisted synthetic strategy to prepare Co, Co 2 P@CoP nanoparticles embedded in biomass-derived porous carbons as bifunctional electrodes for water splitting. The use of AN is not only activating biomass to porous carbons, but also reducing the synthetic temperature significantly. The synergistic effects of the Co 2 P@CoP heterostructure could lead to a low adsorption energy of hydrogen (ΔG H*) and conduction band bending, together with the N/S-codoped porous carbons could provide large specific surface area and desirable electrondonating feature, contribute to the remarkable performance with overpotentials of 0.129 and 0.212 V for hydrogen evolution reaction (HER) in 0.5 mol L À 1 H 2 SO 4 and 1 mol L À 1 KOH, and 0.328 V for oxygen evolution reaction (OER) in 1 mol L À 1 KOH, at a current density of 10 mA cm À 2. Moreover, the Co 2 P@CoP/PC catalysts enable overall water splitting with a small cell voltage of 1.63 V to achieve 10 mA cm À 2 and exhibit long-term durability over 1000 min.