“Bulk” 1T/2H-MoS₂ with Tunable Phases and Residual S, N Co-Doped Carbon as a Highly Active and Durable Catalyst for Hydrogen Evolution

Molybdenum sulfide (MoS2) is considered as low-cost catalyst with great potential for hydrogen evolution reaction (HER). In this contribution, a promising Mo-precursor was first designed and prepared via partial reduction of commercial (NH4)6Mo7O24·4H2O by dl-tartaric acid. A simple pyrolysis method as a new “bottom-up” approach was then developed to achieve the desired HER catalysts by using the Mo-precursor. The resulting catalysts consist of multiphasic 1T/2H-MoS2 and residual S, N co-doped carbon (SNC) with oxygen functional groups. In comparison with (NH4)6Mo7O24·4H2O, Mo-precursor with high content of Mo5+ promotes the full formation of MoS2, while its high content of carbon is more favorable to gain the residual SNC in the resulting catalysts. The further results demonstrate that the percentages of 1T-MoS2 and the content of the residual SNC can be facilely tuned by the pyrolysis temperatures or the Mo/S feeding molar ratios. Notably, although the resulting catalysts exhibit the “bulk” and irregular morphology with low specific surface areas, the high percentages of 1T-MoS2 as the primary advantage, the highly exposed active sites mainly stemming from disordered stacking of S–Mo–S layers, and the high content of the SNC residues are synergistically responsible for their high electrocatalytic HER activity. The high thermal stability of 1T-MoS2 and the excellent durability and stability during HER processes are attributed to the stabilizing effects of the residual SNC. Under the optimized synthetic conditions, the achieved Mo/S(0.2)-450 has a low overpotential of ∼130 mV at 10 mA cm–2, a low Tafel slope of 77 mV dec–1, a high specific activity of 17.53 μA cmCat.–2, and the excellent durability and stability in 0.5 M H2SO4. This work can provide a promising Mo-precursor and a facile route to developing the highly efficient HER catalysts.