Facile synthesis of MoS 3 /carbon nanotube nanocomposite with high catalytic activity toward hydrogen evolution reaction

Hydrogen has been proposed as a future energy carrier in the transition from the current hydrocarbon economy. Exploring advanced materials for electrocatalytic and photoelectrochemical water splitting has become one of the most important issues for bulk and inexpensive hydrogen production. In this study, the nanocomposite of MoS3 and multi-walled carbon nanotubes (MWCNTs) with the high catalytic activity toward hydrogen evolution reaction (HER) was easily synthesized using wet chemistry process. With the aid of functional groups present in MWCNTs, amorphous MoS3 nanoparticles were highly dispersed over MWCNT surface. It was found that MoS3 on the MWCNTs was electrochemically reduced to MoS2 before HER and thus the amorphous MoS2 was identified as the actual catalyst for HER. Furthermore, MoS2 with amorphous structure exhibited the higher HER activity than crystalline MoS2 due to the fact that the former had a higher number of exposed edges. In addition, the catalytic activity of nanocomposite of MoS3 and MWCNTs was increased with decreasing the loading amount of MoS3 on MWCNTs and the optimal MoS3 loading on MWCNTs was 33wt%. Based on the extensive transmission electron microscopy analysis and capacitance measurements, the catalytic activity of the nanocomposite was highly correlated to its active surface area which was controlled by MoS3 morphology on MWCNT surface. The nanocomposite of MoS3 and MWCNTs exhibited excellent HER activity with a small overpotential of ∼0.13V, large cathodic currents and a Tafel slope as small as 40mV/decade. The impedance measurements suggested that the high catalytic activity of nanocomposite of MoS3 and MWCNTs was stemmed from the synergistic effect from the highly exposed edges of amorphous MoS3 nanoparticles and the excellent electrical coupling to the conductive MWCNT network. Furthermore, it was found that the current density of this hybrid catalyst was decreased to 88% of the initial value after the continuous 500 cycling, which showed the reasonable stability in the long-term operation. The present work suggested that the highly active and stable nanocomposite of MoS3 and MWCNTs showed a great potential as a low cost alternative to Pt in water splitting.