High Yield Exfoliation of WS₂ Crystals into 1-2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS₂/CdS Nanorod Composites

Monolayer WS₂ has interesting properties as a direct bandgap semiconductor, photocatalyst, and electrocatalyst, but it is still a significant challenge to prepare this material in colloidal form by liquid-phase exfoliation (LPE). Here, we report the preparation of 1-2 layer semiconducting WS₂ nanosheets in a yield of 18-22 wt % by a modified LPE method that involves preintercalation with substoichometric quantities of n-butyllithium. The exfoliated WS₂ nanosheeets are n-type, have a bandgap of ∼1.78 eV, and act as a cocatalyst with CdS nanorods in photocatalytic hydrogen evolution using lactate as a sacrificial electron donor. Up to a 26-fold increase in H₂ evolution rate was observed with WS₂/CdS hybrids compared with their pure CdS counterpart, and an absorbed photon quantum yield (AQE) of >60% was measured with the optimized photocatalyst.