A photochemical synthesis route to typical transition metal sulfides as highly efficient cocatalyst for hydrogen evolution: from the case of NiS/g-C3N4

Precise deposition of cocatalysts on the outlet points of photo-generated electrons is helpful for highly efficient photocatalytic hydrogen evolution. Up to now, photochemical preparation of hydrogen production cocatalysts composed of earth-abundant elements is still great challenging and rarely reported. Herein, from the case of NiS/g-C3N4, a general photochemical synthesis route to typical transition metal sulfides as cocatalyst for hydrogen evolution was proposed. NiS were prepared by a facile and rapid photochemical method. The content of deposited NiS can be simply adjusted by the change of irradiation time. The optimized photocatalytic hydrogen evolution rate mounted up to 16 400 μmol g−1 h−1 with 0.76 wt% NiS loading, which is about 2500 times higher than that of pure g-C3N4. The photocatalytic H2 evolution rate was stable after 40 h. The turnover number (TON) reached 1230 000 in 52 h with a turnover frequency (TOF) of 23 600 for NiS. Furthermore, the hydrogen evolution of the NiS/g-C3N4 composite photocatalyst reached 28.3 mmol g−1 during 7 h under natural sunlight. The presence of NiS cocatalyst can efficiently promote the separation of photogenerated electron-hole pairs of g-C3N4, which was supported by the steady-state photoluminescence spectroscopy and photoelectro- chemical analyses.