Site-specific catalytic activity in exfoliated MoS₂single-layer polytypes for hydrogen evolution: basal plane and edges

Abstract

We performed ab initio calculations on the basic set of MoS 2 single-layer materials, namely the 1H, 1T and 1T 0 polytypes, to lay a theoretical framework on the emerging breakthrough-discoveries of high activity towards the hydrogen evolution reaction (HER) in exfoliated MoS 2 and related materials. Our calculations show that for exfoliated MoS 2 , 1T 0 is the most HER active polytype, with active sites both on the basal plane and at the edges of the layered grains. In comparison, the basal planes of the 1H and 1T polytypes are HER inactive and their edge-sites are not as active as those of the 1T 0 polytype. We also found that 1T-MoS 2 is unstable and easily transforms into 1T 0 -MoS 2 , and the 1T 0 phase is metastable with a considerable barrier >0.7 eV to bar its transformation into the most stable 1H phase. Further, unlike the case of exfoliated WS 2 , the HER activity of exfoliated MoS 2 is not so critically affected by the lattice strain. In addition, in contrast to the 1T 0 -WS 2 , the 1T 0 -MoS 2 is not metallic but has a very small bandgap of 0.1-0.2 eV. Hence, 1T 0 -MoS 2 should have a high enough conductivity and other suitable properties for it to function as an electrochemical HER catalyst.

Strain engineering the magnetic states of vacancy-doped monolayer MoSe 2

“…1(b) and (c), which indicate that MoSe 2 monolayer is semiconductor with a direct band gap of 1.45 eV. Additional, the spinpolarization calculation shows 1H-MoSe 2 is nonmagnetic, which is similar with monolayer MoS 2 [33]. Further calculation was performed by adopting the hybrid functional (HSE06) [34,35] to predict accurate band gap.…”

Mechanism of Hydrogen Evolution Reaction on 1T-MoS2 from First Principles

“…47,48,50 The adsorbed H prefers to bind to the surface S atoms, regardless of the coverage. Our previous work showed that the metastable 1T MoS 2 can be stabilized by hydrogenation and after a crossover coverage of 25%, the 1T phase becomes more stable than the 2H phase.…”

Oxidation suppression during hydrothermal phase reversion allows synthesis of monolayer semiconducting MoS2 in stable aqueous suspension

“…In this mechanism, the MoS 2 surface serves as both an anode and a cathode; electrons are generated at one site through an anodic reaction and conduct to the second site where a cathodic reaction occurs with the surrounding medium (see eqn (1) and (2)). The rapid oxidation of the 1T/1T′ phase is hypothesized to be the direct result of its electrical conductivity, 33–35 which allows the required internal electron transfer, while the insulating 1H phase does not. The driving force for the corrosion-type mechanisms can be calculated using the computational hydrogen electrode (CHE) technique 36,37 applied to these two initiation reactions: $$\text{Anodic}:\ast +{\mathrm{H}}_2\mathrm{normalO}\to \ast \text{OH}+false({\mathrm{H}}^{+}+{\mathrm{e}}^{-}false)$$ $$\text{Cathodic}:\ast +{\mathrm{O}}_2+false({\mathrm{H}}^{+}+{\mathrm{e}}^{-}false)\to \ast \text{OOH}$$ where “*” denotes a site on the MoS 2 nanosheet.…”