Excited electron dynamics in the 2H-1T heterophase of monolayer MoS2: time dependent density functional theory study for photo-catalytic mechanism process

Abstract

Monolayer MoS2, a two-dimensional transition metal dichalcogenide (TMD) structure material, has been intensively investigated, because of its photovoltaic and photo-catalytic features. It is well-known that monolayer MoS2 has two different phases, 2H and 1T. The 2H phase of MoS2 is a semiconductor with direct band gap about 2.4 eV, and 1T phase of MoS2 has meta-stable metallic phase. Recently, it was shown that heterostructure containing both 2H and 1T phases can be formed and its microscopic structure is controllable via phase transition. Such a heterostructure of MoS2 is expected to be utilized in various applications. We investigated electron dynamics of heterostructure of MoS2, especially focused on the excited electrons from the 2H phase region. The excited electrons transfer to the 1H phase region, and were accumulated in there. This phenomena can be utilized for the oxygen reduction reaction (ORR) catalyst material. For the ORR mechanism, the oxygen molecule should be adsorbed on the catalytic active site easily and the 2 or 4 electrons can be transferred from the active site to the oxygen molecule. In this study, we have investigated the electron dynamics of the excited-electrons from the 2H phase region and the free energy profile and oxygen adsorption barrier for the ORR catalyst. The electron dynamics was calculated by real-time time dependence density functional theory (rt-TDDFT) developed in our group, and we suggest the new low-dimensional ORR photo-catalyst using the excited-electron in 2H phase MoS2.