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

Abstract

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 H₂ 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 Cd_0.5Zn_0.5S (CZS). The surface reaction of the CZS/Ni₂P@CN composite in photocatalytic H₂ 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 Cd_0.5Zn_0.5S to Ni₂P. As a result of the unique interfaces and structure among Ni₂P, CN and Cd_0.5Zn_0.5S, the CZS/Ni₂P@CN-5% possesses an excellent photocatalytic H₂ evolution rate (∼28.53 mmol h⁻¹ g⁻¹), which is up to 2.31 times as high as that of pristine Cd_0.5Zn_0.5S. This work brings a novel route to design marvellous co-catalysts in composite photocatalyst systems for boosting photocatalytic H₂ production.