Hydrogen Evolution Reaction Activity of Graphene–MoS₂ van der Waals Heterostructures

Determining a suitable noble-metal-free catalyst for hydrogen evolution reaction (HER) by photoelectrocatalytic (PEC) water splitting is an enduring challenge. Here, the molecular origin of number of layers and stacking sequence-dependent PEC HER performance of MoS 2 /graphene (MoS 2 /GR) van der Waals (vdW) vertical heterostructures is studied. Density functional theory (DFT) based calculations show that the presence of MoS 2 induces p-type doping in GR, which facilitates hydrogen adsorption in the GR side compared to the MoS 2 side with Δ G H closer to 0 eV in the MoS 2 /GR bilayer vertical stacks. The activity maximizes in graphene with monolayer MoS 2 and reduces further for bilayer and multilayers of MoS 2 . The PEC HER performance is studied in various electrodes, namely, single-layer graphene, single- and few-layered MoS 2, and their two different types of vertical heterojunctions having different stacking sequences. The graphene on top of MoS 2 sequence showed the highest photoresponse with large reaction current density and lowest charge-transfer resistance toward HER, in aggrement with the DFT calculations. These findings establish the role of stacking sequence in the electrochemistry of atomic layers, leading to the design of new electrocatalysts by combinatorial stacking of a minimal number of layers.