Electrons and Hydroxyl Radicals Synergistically Boost the Catalytic Hydrogen Evolution from Ammonia Borane over Single Nickel Phosphides under Visible Light Irradiation

Graphical Light on HER ! Through regulating the structures of semiconducting nickel phosphides, their efficiency of room-temperature catalytic hydrogen evolution was remarkably enhanced, which was ascribed to the visible-light-driven synergistic effect of photogenerated electrons and hydroxyl radicals. From the perspective of tailoring the reaction pathways of photogenerated charge carriers and intermediates to remarkably enhance the solar-to-hydrogen energy conversion efficiency, we synthesized the three low-cost semiconducting nickel phosphides Ni 2 P, Ni 12 P 5 and Ni 3 P, which singly catalyzed the hydrogen evolution from ammonia borane (NH 3 BH 3 ) in the alkaline aqueous solution under visible light irradiation at 298 K. The systematic investigations showed that all the catalysts had higher activities under visible light irradiation than in the dark and Ni 2 P had the highest photocatalytic activity with the initial turnover frequency (TOF) value of 82.7 min −1 , which exceeded the values of reported metal phosphides at 298 K. The enhanced activities of nickel phosphides were attributed to the visible-light-driven synergistic effect of photogenerated electrons (e − ) and hydroxyl radicals ( . OH), which came from the oxidation of hydroxide anions by photogenerated holes. This was verified by the fluorescent spectra and the capture experiments of photogenerated electrons and holes as well as hydroxyl radicals in the catalytic hydrogen evolution process.