MoS2 Stacking Matters: 3R Polytype Significantly Outperforms 2H MoS2 for the Hydrogen Evolution Reaction.

Transition metal dichalcogenides (TMDs) are an intriguing family of materials with large application potential in a variety of scientific fields ranging from electronics to electrocatalysis. Within this group of materials, MoS2 has been attracting a lot of scientific attention due to its chemical and physical properties. In this report, we studied the exfoliation of the largely unexplored 3R MoS2 polytype prepared by high-temperature, high-pressure synthesis. Bulk as well as sodium naphthalenide exfoliated materials were studied in terms of their quality and performance for the hydrogen evolution reaction (HER). The HER performance was benchmarked versus the commonly available 2H polytype. The reported results show that the 3R polytype is more suitable for the conversion of MoS2 into the metallic 1T phase, which was attributed to surface oxidation occurring in the 2H polytype. Higher content of the 1T phase then resulted in an overall lower overpotential of -0.25 V vs. RHE for the 3R polytype compared with the overpotential of -0.30 V for the 2H polytype. These results show that the 3R polytype might serve as a better starting point for the synthesis of highly active chemically exfoliated MoS2 catalysts for hydrogen evolution.