Amorphous Molybdenum Sulfide on Graphene–Carbon Nanotube Hybrids as Highly Active Hydrogen Evolution Reaction Catalysts

In this study, we report on the deposition of amorphous molybdenum sulfide (MoS_x, with x ≈ 3) on a high specific surface area conductive support of Graphene–Carbon Nanotube hybrids (GCNT) as the Hydrogen Evolution Reaction (HER) catalysts. We found that the high surface area GCNT electrode could support the deposition of MoS_x at much higher loadings compared with simple porous carbon paper or flat graphite paper. The morphological study showed that MoS_x was successfully deposited on and was in good contact with the GCNT support. Other physical characterization techniques suggested the amorphous nature of the deposited MoS_x. With a typical catalyst loading of 3 mg cm^–2, an overpotential of 141 mV was required to obtain a current density of 10 mA cm^–2. A Tafel slope of 41 mV decade^–1 was demonstrated. Both measures placed the MoS_x-deposited GCNT electrode among the best performing molybdenum sulfide-based HER catalysts reported to date. The electrode showed a good stability with only a 25 mV increase in overpotential required for a current density of 10 mA cm^–2, after undergoing 500 potential sweeps with vigorous bubbling present. The current density obtained at −0.5 V vs SHE (Standard Hydrogen Electrode potential) decreased less than 10% after the stability test. The deposition of MoS_x on high specific surface area conductive electrodes demonstrated to be an efficient method to maximize the catalytic performance toward HER.