CdS p–n heterojunction co-boosting with Co3O4 and Ni-MOF-74 for photocatalytic hydrogen evolution

A high-efficiency Ni-MOF-74/CdS/Co3O4 composite catalyst, the CdS co-boosting with Ni-MOF-74 and Co3O4, is successfully prepared. The maximum amount of hydrogen evolution reaches about 581 μmol for 5 h over the Ni-MOF-74/CdS/Co3O4 (10 wt% Co) photocatalyst under visible light irradiation, which is 16.2 times higher than that over pure CdS. The detailed physical and chemical inner mechanism of the Ni-MOF-74/CdS/Co3O4 composite catalyst is investigated by means of XRD, SEM, TEM, XPS, BET, UV-visible DRS etc. In the most valuable aspect, we investigate the photoelectron and hole transfer mechanism by photoluminescence spectroscopy, excited state electron decay, and photoelectrochemical experiments. The results show that the lower electron and hole pair recombination, larger electron transfer rate constant (KET = 0.2 × 109 s-1), larger electron injection efficiency (ηinj = 44.7%), smaller carrier charge resistance in the semiconductor film (Rfilm = 3523 Ω cm2), and smaller charge transfer and reaction resistance at the interface between the semiconductor and the electrolyte (Rct = 1.96 Ω cm2) together accelerate the charge separation and transfer, thereby enhancing photocatalytic performance.