Chemical vapor deposition of two-dimensional transition metal sulfides on carbon paper for electrocatalytic hydrogen evolution

Hydrogen is considered one of the most likely alternative clean energy fuel to traditional fossil fuels. One of the most attractive hydrogen production strategies is water splitting, but the need for expensive Pt precious metal catalysts to catalyze the hydrogen evolution reaction (HER) is a problem. Recently, two-dimensional transition metal dichalcogenides (TMDs), especially MoS2, have attracted intense interest as a non-precious metal HER catalyst due to their low cost and relatively high catalytic activity. However, their poor electron conductivity and the limited number of active sites at their edges have greatly limited their overall catalytic performance. We report the direct growth of three representative TMDs (MoS2, NbS2 and WS2) on a conductive carbon paper substrate using chemical vapor deposition and have studied the effects of temperature and gas flow rate on their morphology and structure. All the as-grown TMDs have a 2D nanosheet morphology and were aligned perpendicular to the carbon paper. The WS2 nanosheets had the smallest sheet size with a diameter of ca. 100-200 nm and, more interestingly, were assembled into a one-dimensional nanofiber, leading to the highest HER activity. Additional electrochemical cathodic activation further improved the HER activity of the TMDs, and the structural changes after the activation were investigated by TEM combined with in-situ electrochemical Raman spectroscopy. The activated NbS2 contained large triangular or truncated triangular S vacancy areas, which is distinctly different from the individual S vacancies in MoS2.