Catalytic Activity of MS2 Monolayer for Electrochemical Hydrogen Evolution

Finding earth-abundant and inexpensive materials to catalyze the electrochemical hydrogen evolution reaction (HER) is critical for turning hydrogen into a competitive clean energy source. Breakthrough discoveries of high activity toward HER have been reported using two-dimensional transition metal dichalcogenides. Here, we performed a comprehensive investigation on the three most common MS2 single-layer materials, with M being Mo, W, V, and with ab initio calculations to lay a theoretical framework on the dynamic stability and HER activity of the common polymorphs (1H, 1T, and ZT phases) of these MS2 monolayers. First, our calculations show that the HER catalytic activity of these MS2 monolayers generally reduces with the increase of hydrogen coverage, except that, although the HER performance of 1T-VS2 is indeed best at low hydrogen coverage, the HER performance of 1H-VS2 is best when the coverage is large. In addition to the effects of hydrogen coverage, we show that the HER activity of WS2 can be improved more effectively by strain than the other two counterparts. Finally, but also most importantly, our calculations show a ranking of HER activity among these three types of MS2 monolayers being VS2 > MoS2 > WS2, at least for their basal planes under standard conditions. This theoretical analysis calls for additional experimental studies of HER activity in this subject despite the current belief of the superiority of ZT-WS2. Turning our attention to the case of VS2, we show that both the 1H and the 1T phases of VS2 monolayers are dynamically stable and HER-active. Further, by taking spin polarization into consideration, we show that VS2 monolayers, unlike their WS2 and MoS2 counterparts, possess spin-specific HER activity; as such, ignoring spin effects will not get an accurate picture of HER properties of VS2 monolayers.