Theoretical Investigations On The Structures And Electrocatalytic Hydrogen Evolution Of Boundaries In Two-Dimensional Transition Metal Dichalcogenides

With the increasing depletion of conventional energy,the increasingly serious problems of ecological degradation and energy shortages have been widely concerned by the international community and governments.At this point,the development of hydrogen evolution reaction(HER)process from electrolytic water splitting is in line with the urgent requirement of China's energy structure decarbonization transition.As ideal hydrogen evolution electrodes,noble metals are difficult to be widely used in large-scale industrial production due to their high price and shortage of reserves.Therefore,seeking for efficient and inexpensive alternative catalyst materials is one of research hotspots in energy field.In this regard,two-dimensional transition metal dichalcogenides(TMDCs),represented by molybdenum disulfide,have attracted broad scientific concern due to their unique crystal structures and physicochemical properties,but their hydrogen generation performance is often restricted by the limited number of highly active edge sites.Thus,boosting up the reactive sites in the basal plane of TMDCs is urgently demanded.Some experimental studies have confirmed that defect modulation and phase transition can improve the catalytic activity of TMDCs effectively,but how the formation of boundaries in multiphase and pure phase in these processes influences hydrogen evolution performance is not clear.Here,first-principles calculations have been performed to explore the effects of boundary formation in multiphase and pure phase of TMDCs(MoS2 and MoSe2)on the electrocatalytic HER performance,and the microscopic mechanism for HER catalysis on the surface of the materials is demonstrated at the atomic level.The main contents and results are as follows:1.In this paper,we systematically studied the boundary structures in 2H and 1T'multiphase coexistence of MoS2 and their important influences on the electrocatalytic HER by first-principles calculations.The calculation results indicated that the zigzag 2H/1T' phase boundaries exhibit an optimal performance for the Volmer reaction and the electrical conductivities of interfaces are significantly enhanced compared to that of the pristine 2H phase.In addition,the Volmer-Heyrovsky reaction mechanism is the dominant reaction path for hydrogen evolution on 2H/1 T' MoS2 interfaces due to its lower kinetic activation barrier.2.The structural stabilities of MoS2 grain boundaries in pure phase were explored by first-principles calculations,and the Gibbs free energy for H adsorption was calculated as a rational descriptor to evaluate the HER activity.The results showed that the introduction of grain boundaries helps to promote the electrocatalytic HER activity of monolayer MoS2,where the contribution of Mo atoms at grain boundaries can be explained by the d-band theory after narrowing the integration region.Moreover,this work demonstrated that the Volmer-Heyrovsky reaction mechanism is the main path in the hydrogen evolution process on MoS2 grain boundaries from atomic scale.3.In addition to MoS2,we further systematically evaluated the effects of boundaries and defects in MoSe2 on the HER performance of materials.The results revealed that both surface boundaries and defects can enhance the electrocatalytic HER activity of MoSe2 to different degrees,which is similar to the performance in layered MoS2.The strategies we used to consider the structures and electrocatalytic HER effects of boundaries in 2H phase and 2H/1T' multiphase of MoS2 and MoSe2 are also applicable to other TMDCs materials.