Covalently Linked Heterostructures of Phosphorene with MoS₂/MoSe₂ and Their Remarkable Hydrogen Evolution Reaction Activity

Hydrogen production by photochemical and electrochemical means is an important area of research related to renewable energy. 2D nanomaterials such as C3N4 and MoS2 have proven to be active for the hydrogen evolution reaction (HER). Phosphorene, a mono-elemental 2D layer of phosphorus, is known to catalyze the HER, but the activity is marginal. The use of phosphorene is also limited by its ambient instability. We have been able to prepare covalently cross-linked nanocomposites of phosphorene with MoS2 as well as MoSe2. The phosphorene-MoS2 nanocomposite shows excellent photochemical HER activity yielding 26.8 mmol h-1 g-1 of H2, while only a negligible amount is produced by the physical mixture of phosphorene and MoS2. The phosphorene-MoS2 composite also displays high electrochemical HER activity with an onset overpotential of 110 mV, close to that of Pt. The enhanced HER activity of the phosphorene-MoS2 nanocomposite can be attributed to the ordered cross-linking of the 2D sheets, increasing the interfacial area as well as the charge-transfer interaction between phosphorene and MoS2 layers. The phosphorene-MoSe2 nanocomposite also exhibits good photochemical HER activity.