Nickel phosphonate-derived Ni2P@N-doped carbon co-catalyst with built-in electron-bridge for boosting photocatalytic hydrogen evolution

To construct photocatalytic systems that can efficiently convert solar energy to hydrogen energy, numerous studies have been focused on transition metal phosphide (TMP) co-catalysts, which display low overpotential and cost less than noble metals. However, as co-catalysts, the performance of pure TMPs is not satisfactory in photocatalytic H-2 evolution, especially with regard to the acceleration of surface reaction kinetics and charge transfer through interfaces in the photocatalyst system. Herein, a nitrogen-doped carbon shell-coated nickel phosphide (Ni2P@CN) co-catalyst, which was fabricated via a one-step pyrolysis strategy with nickel phosphonate as the precursor and no extra P sources added, was composited with Cd0.5Zn0.5S (CZS). The surface reaction of the CZS/Ni2P@CN composite in photocatalytic H-2 production was effectively accelerated owing to the abundant surface active sites afforded by the Ni2P@CN co-catalyst. Moreover, a series of experiments have demonstrated that the nitrogen-doped carbon shell (CN) encapsulates Ni2P and acts as a "built-in electron bridge" that provides a fast charge transfer channel from Cd0.5Zn0.5S to Ni2P. As a result of the unique interfaces and structure among Ni2P, CN and Cd0.5Zn0.5S, the CZS/Ni2P@CN-5% possesses an excellent photocatalytic H-2 evolution rate (similar to 28.53 mmol h(-1) g(-1)), which is up to 2.31 times as high as that of pristine Cd0.5Zn0.5S. This work brings a novel route to design marvellous co-catalysts in composite photocatalyst systems for boosting photocatalytic H-2 production.