Layer by Layer Deposition of 1T′-MoS2 for the Hydrogen Evolution Reaction

The layer by layer (LbL) method has been used to assemble catalytic materials for the electrochemical hydrogen evolution reaction (HER). The electrocatalytic activity of LbL deposited 1T-MoS2 (metallic phase) on a fluorine-doped tin oxide substrate was investigated for the HER as a function of the number of deposition layers (mass loading). The morphology, thickness, and roughness of the deposited MoS2, layers as a function of the number of deposition layers were investigated using atomic force microscopy and scanning electron microscopy. The average roughness of the surface increased with the number of deposition layers, indicating that the thickness of the deposited layered material became heterogeneous with increasing layer number. The primary conversion of the deposited 1T-MoS2 to the semiconducting 2H-MoS2 phase via exposure to 532 nm wavelength light, confirmed by Raman spectroscopy and scanning tunneling spectroscopy, allowed a comparison of the HER activity of the two phases at a constant mass loading and surface area on the same substrate. For a given number of deposition layers (i.e., similar mass loading), 1T-MoS2 exhibited a lower overpotential for the HER than the 2H-MoS, (with a minority 1T' component) phase. For example, at a sample thickness of 19.7_2.8 nm (20 LbL layers) the overpotentials for the HER for submonolayer amounts of 1T-MoS2 and after exposure to 532 nm light were 0.54 and 0.61 V, respectively (at a current density of -2 mA/cm(2)). Overall, the overpotential for HER associated with both MoS2 phases decreased as the mass loading increased.

Automated summary

The layer by layer (LbL) method was used to assemble catalytic materials for the electrochemical hydrogen evolution reaction (HER). The catalytic activity of the assembled material was investigated as a function of the number of deposition layers. The results showed that the thickness and roughness of the deposited material increased with the number of layers. Upon conversion of the deposited material to a semiconducting phase, the HER activity of the two phases was compared. It was found that the 1T-MoS2 phase exhibited lower overpotential for the HER compared to the 2H-MoS2 phase. The overpotential decreased as the mass loading increased.