A simply as-prepared nickel phosphotungstate complex was used as a carbon-free homogeneous catalyst for the H-2 evolution from water splitting under visible light irradiation (lambda >= 400 nm). Its catalytic activity, the rate of the H-2 evolution about 237 mu mol h(-1), was much higher than those of the Ni2+ ions and cobalt phosphotungstate complex. Spectroscopic studies suggested that the Ni2+ ions could react with Na8HPW9O34 to form a complex with a unique double-sandwich structure in the as-prepared sample. And the electrochemical experimental results revealed that it possessed two satisfactory redox potentials, which were in favor of the electrons transfer in our photoinduced hydrogen production system. Furthermore, the electron-transfer steps for the H-2 evolution from water splitting in the present system were investigated in detail. On the basis of the luminescence analysis results, it was found that the reductive quenching pathway was dominant for the photosensitizer in the present system. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.