Charge Mediated Semiconducting-to-Metallic Phase Transition in Molybdenum Disulfide Monolayer and Hydrogen Evolution Reaction in New 1T′ Phase

Abstract

The phase transition of single layer molybdenum disulphide (MoS 2 ) from semi-conducting 2H to metallic 1T and then to 1T' phases, and the effect of the phase transition on hydrogen evolution reaction (HER) are investigated within this work by density functional theory. Experimentally, 2H-MoS 2 has been widely used as an excellent electrode for HER and can get charged easily. Here we find that the negative charge has a significant impact on the structural phase transition in a MoS 2 monolayer. The thermodynamic stability of 1T-MoS 2 increases with the negative charge state, comparing with the 2H-MoS 2 structure before phase transition and the kinetic energy barrier for a phase transition from 2H to 1T decreases from 1.59 eV to 0.27 eV when 4 e -are injected per MoS 2 unit. Additionally, 1T phase is found to transform into the distorted structure (1T' phase) spontaneously. On their activity toward hydrogen evolution reaction, 1T'-MoS 2 structure hydrogen coverage shows comparable hydrogen evolution reaction activity to the 2H-MoS 2 structure. If the charge transfer kinetics is taken into account, the catalytic activity of 1T'-MoS 2 is superior to that of 2H-MoS 2 . Our finding provides a possible novel method for phase transition of MoS 2 , and enriches understanding of the catalytic properties of MoS 2 for HER.

Electron beam-formed ferromagnetic defects on MoS2 surface along 1 T phase transition

“…It is notable that the total energy of 1T-MoS 2 is much higher than that of 1H-MoS 2 by 0.8 eV41. However, the 1 H to 1 T phase transition can be driven by lowering the energy barrier via the charge injection of electron irradiation42.…”

Metallic MoS2 for High Performance Energy Storage and Energy Conversion

“…In 2H MoS 2 (semiconducting phase), the Mo atom layer in hexagonal MoS 2 is sandwiched between S layers with a trigonal prismatic coordination of Mo atom . By contrast, the tetragonal MoS 2 , marked as ordered 1T MoS 2 or distorted 1T′ MoS 2 (metallic phase), has an octahedral coordination of Mo atoms . Based on this structural difference, the semiconducting and metallic MoS 2 exhibit different properties, which has been discussed elaborately in the following paragraphs.…”

Nanostructured catalysts for electrochemical water splitting: current state and prospects

“…However, it should be noted that the perfect 1T phase is metastable and sometimes such a structure is dynamically unstable 97 . Recently, Du et al 99 reported a phase transition method, in which through a negative charge injection method, semiconducting 2H-MoS2 was transformed to metallic 1T MoS2 and further distorted into the 1T′-MoS2 phase. Revealed by the work of Kuo et al 98 , the basal plane of 1T′-MX2 (M = Mo, W; X = S, Se, Te) 2D materials had lower energy and were more stable than the corresponding 1T counterparts.…”