Phase-controlled and shape-controlled nickel phosphides were synthesized using nickel chloride, nontoxic red phosphorus and polyvinyl pyrrolidone (PVP). The hexagonal Ni2P and tetragonal Ni12P5 could be transformed via adjusting the amount of polyvinyl pyrrolidone. Besides, the addition of PVP could regulate the particle size of nickel phosphides, so that the large irregular shaped nickel phosphides turned into homogeneous nanoparticles, which further formed three-dimensional porous structure. And its formation mechanism has also been discussed in this paper. The hydrodechlorination catalytic activities of nickel phosphides were promoted markedly with moderate quantity of PVP. While, excessive PVP would cover the active sites of catalysts and lead the catalytic activity decreased. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.