rGO/CNTs Supported Pyrolysis Derivatives of [Mo₃S₁₃]^2– Clusters as Promising Electrocatalysts for Enhancing Hydrogen Evolution Performances

Reduced graphene oxide/carbon nanotube (rGO/CNTs) supported [Mo₃S₁₃]^2– clusters and [Mo₃S₁₃]^2– pyrolysis derivatives were synthesized as electrocatalysts for hydrogen production. We investigated the physio-chemical characteristics and electrocatalytic abilities of the [Mo₃S₁₃]^2– clusters and their pyrolysis derivatives. TEM images of pyrolysis derivatives of [Mo₃S₁₃]^2– clusters indicated that some crystalline derivatives were surrounded by the amorphous derivatives at an annealing temperature of 200–270 °C, and some well-crystallized MoS₂ with diameters of 50–100 nm were observed in the pyrolysis derivatives at 500 °C. Both the structure transition and the HER performance of [Mo₃S₁₃]^2– pyrolysis derivatives were mapped in terms of temperature. The atomic ratio of S:Mo significantly decreased from 3.48 to 1.89 as the annealing temperature increased, which indicated the multiple transition forms in pyrolysis derivatives. XPS, XRD, and Raman spectra also indicated the decreased density of edge sites and a poor extent of ordering in the layers of pyrolysis derivatives as the annealing temperature increased. These results corresponded well to the HER activities of the rGO/CNTs macrostructures anchored with different pyrolysis derivatives. The rGO/CNTs anchored with pyrolysis derivatives (annealed at 270 °C) of [Mo₃S₁₃]^2– exhibited an overpotential of ∼178 mV (10 mA cm^–2) with Tafel slope value located at 64.2 mV/dec, which showed relatively higher HER performances than most analogous single-metal molybdenum sulfide nanocomposites. They also exhibited a performance close to those of multimetal nanocomposites