Ultrathin layered Zn-doped MoS₂ nanosheets deposited onto CdS nanorods for spectacular photocatalytic hydrogen evolution

The utilization of non-precious and noble-metal free catalysts for the photo conversion of water into hydrogen is of significant interest. In particular, the typical layered MoS₂ has attracted interest as a low-cost alternative to platinum in the photocatalytic hydrogen evolution system. However, theoretical studies have suggested that the activity of the MoS₂ co-catalyst arises only at the S sites on the edges of grains, and not on the basal planes. In this respect, the doping of a foreign metal into the MoS₂ system is an interesting method for boosting the hydrogen production rate by increasing the conductivity and number of active sites. Herein, simple methods are used to decorate CdS nanorods with earth-abundant, few-layered zinc-doped MoS₂ nanosheets (Zn-MoS₂/CdS), and the so-obtained Zn-MoS₂/CdS composite is used for the photocatalytic hydrogen evolution reaction under solar irradiation in the presence of lactic acid as a hole scavenger. Thus, the catalyst is shown to provide significant hydrogen generation activity, along with excellent and continuous photo stability for more than 60 h under optimal conditions. Moreover, the hydrogen evolution rate of the Zn-MoS₂/CdS composite is up to ~75-fold greater than that of the pure CdS. The loading of Zn-MoS₂ is shown to increase the synergistic effects of the photocatalyst due to the effective separation of charge carriers, extensive exposure of catalytic sites, and high dispersion of the few-layered Zn-MoS₂. In addition, the stability of the optimized material is enhanced by the doping of Zn metal into the MoS₂. To the best of our knowledge, the hydrogen evolution activity of the as-prepared composite is the highest ever reported for the CdS and single metal-doped MoS₂-based catalysts. Hence, this type of Zn-MoS_2/CdS composite is strongly believed to have great potential as a low-cost, highly-efficient, noble-metal free catalyst for the photocatalytic reduction of water.