Transition metal phosphides are considered as the most prospective replacements for noble metal cocatalysts used for H-2 evolution during photocatalytic water splitting. In this work, Ni2P/g-C3N4 composite photocatalyst was synthesized using a simple in -situ hydrothermal method by one step. Benefiting from the excellent light trapping, efficient transfer of charge carriers and strong stability of Ni2P nanoparticles, as well as the stable interface contact between Ni2P and g-C3N4, the Ni2P/g-C3N4 exhibit greatly enhanced H-2 evolution performance during photocatalytic water splitting. The optimized H-2 evolution rate can reach 3344 mu mol h(-1) g(-1) over 17.5 wt% Ni2P/g-C3N4, which is 68.2 times greater than that of pure g-C3N4 and even much greater than that of 15 wt% Pt/g-C3N4. The apparent quantum efficiency (QE) is about 9.1% under 420 nm monochromatic. The enhancement mechanism was demonstrated in detail by transient photocurrent responses, photoluminescence spectra and electrochemical impedance spectroscopy. This work develops a facile strategy to fabricate transition metal phosphide/semiconductor heterojunction systems with potential application for photocatalytic H-2 evolution. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.