Theoretical Study On The Electronic Properties Modulation And Catalytic Performance Of 2D Group ? Monochalcogenides

The rapid growth in world population in recent years and consequent rapid increase in energy demand,the development and utilization of new renewable clean energy sources is imminent.Compared with fossil fuels,which are cheap and pollute the environment,hydrogen is an ideal renewable clean energy source.It is environmentally friendly and has a high calorific value.At present,the splitting of water by sunlight is an effective method to obtain high-purity hydrogen,and the difficulty of this method is how to find efficient and stable photocatalysts from a variety of materials.Traditional photocatalytic materials often face some problems,such as unsuitable band edge locations and low sunlight utilization,leading to low photocatalytic water splitting efficient.Due to its unique structure and excellent properties,two-dimensional nanomaterials are expected to become the main candidates for the next-generation semiconductor photocatalysts.Recently,the monolayer metal chalcogenide group-III?MXs,M=Ga,In;X=S,Se,Te?has become one of the hot topics in the research of new two-dimensional semiconductor materials.Compared with graphene,black phosphorus,and transition metal sulfides,which have been widely studied,two-dimensional MXs have a wider and easier to regulate band gap.Based on first-principles calculations,this paper mainly studies the geometric structure and electronic properties of two-dimensional MXs and derived Janus materials.Furthermore,guided by the results of property calculations,its performance in photocatalytic water splitting was explored.The specific research content is as follows:?1?We first built a series of two-dimensional?2D?monos-layer and few-layers MXs?M=Ga,In;X=S,Se?.The results show that the few-layers of MXs are layer-dependent:The band gap value decreases as the number of layers increases,and the binding energy increases as the number of layers increases.At the same time,GaSe tends to change from an indirect band gap semiconductor to a direct band gap semiconductor as the number of layers increases.In particular,few-layers GaSe has high stability,suitable band edge positions,optimal band gap values,high carrier mobility(880-7000 cm²V^-1s^-1),effective separation of photogenerated electron-hole pairs in space and excellent light absorption ability,and are expected to be used as the next generation of two-dimensional fully hydrolyzed photocatalysts in the visible light range.?2?Secondly,based on a monolayer GaX,we construct derived Janus Ga₂XY?X/Y=O,S,Se,and Te?structures.Theoretical calculations show that except for Ga₂OTe,these monolayers are stable semiconductor materials with band gaps in the range of 1.00-3.24 eV.Due to the introduction of dipoles,the in-plane piezoelectric coefficient of Janus monolayer(d₁₁=3.09-5.67 pm V^-1)is significantly enhanced compared to GaX(d₁₁=0.41-3.04 pm V^-1),the resulting out-of-plane piezoelectric coefficient in 0.11-0.34 pm V^-1.Interestingly,unlike the Janus structures without oxygen,the dipole direction of the oxygen-containing Janus monolayers is reversed due to the different charge distribution on both sides.?3?Finally,we carried out research on the catalytic activity of hydrogen evolution reaction of monolayer GaX and derived Janus Ga₂XY.Among them,the hydrogen adsorption Gibbs free energy?G_H*?0.36 eV?of Ga₂OSe is the smallest among all the studied monolayers.At different adsorption sites on the same Janus side,hydrogen atoms adsorbed on top of chalcogen atoms with large electronegativity have lower?G_H*values;at the same chalcogen adsorption site of different Janus,the hydrogen adsorption?G_H*value is smaller in the structure with larger stretch.When 0.3%strain is applied to Ga₂OSe,the?G_H*value?0.01eV?is lower than that of some platinum-based materials.The ultra-low overpotential brings better catalytic hydrogen evolution performance.In addition,Ga₂OSe has a higher light absorption coefficient(10⁵ cm^-1)and lower exciton binding energy?0.71eV?,indicating that it is a potential hydrogen evolution photocatalyst.