【作者】 王静；

【导师】 段理；

【作者基本信息】 长安大学 ， 材料与化工（专业学位）， 2023， 硕士

【摘要】 探索性能优异的析氢/氧光催化剂是太阳能应用的有效途径之一。二维半导体光催化剂拥有较大的比表面积和独特的物理特性,但材料内光生电子和空穴的快速复合限制了其光催化效率。当两种半导体材料垂直堆叠形成Ⅱ型异质结后,可实现光生载流子在空间上的有效分离,从而延长其生存寿命,明显提高了光解水性能。因此,本文构建了HfS₂/GaS和PtSe₂/SnS₂异质结,并深入研究了其光电性质和光催化性能。首先设计了HfS₂/GaS范德华异质结,以实现高效和自发的水分解。第一性原理计算结果表明水还原电位和氧化电位都位于HfS₂/GaS异质结的带隙（2.04 e V）内,保证了可以发生水分裂。Ⅱ型能带排列和较大的内建电场确保了光生电子-空穴的空间有效分离,高的电子和空穴迁移率也可以使光生载流子快速到达表面。通过计算异质结的GaS表面析氧反应和HfS₂表面析氢反应的自由能,发现其在光照下可以自发催化水分解反应。值得注意的是,构建成异质结后析氢效率显著提升,达到14.91%,高于商业使用水分解光催化剂的标准。此外,平面内施加1-6%的双轴拉伸应变后,光催化分解水的氧化还原反应仍可以在异质结上进行,且应变的施加可有效调节HfS₂/GaS异质结的电子和光学性质。因此,HfS₂/GaS异质结是一种很有前景的光催化分解水材料。另外,直接Z型光催化剂由于其较强的光催化和可见光吸收能力而受到广泛关注。利用密度泛函理论,研究了PtSe₂/SnS₂异质结的电子和光学性质以及光催化机理。与PtSe₂、SnS₂单层和传统Ⅱ型光催化剂HfS₂/GaS相比,PtSe₂/SnS₂异质结具有更小的带隙、更显著的光吸收能力和更优异的析氢效率。能带和态密度的计算结果说明异质结为Ⅱ型能带排列。进一步的功函数计算表明,内置电场的方向为PtSe₂到SnS₂侧,证实了电荷转移机制为直接Z型。在水分解反应中,自由能计算结果显示PtSe₂侧的析氢反应和SnS₂侧的析氧反应在光照下可自发进行。此外,PtSe₂/SnS₂异质结在紫外和可见光范围内有明显的光吸收,表明对太阳光有良好的响应。有趣的是,在施加双轴应变后,带边位置仍然满足水分解的要求,并保持相当大的可见光吸收能力。因此,PtSe₂/SnS₂异质结可以作为一种用于制氢和制氧的潜在的直接Z型光催化剂。更多还原

【Abstract】 Exploring excellent performance of photocatalysts for hydrogen/oxygen evolution reactions is an effective way for solar energy applications.Two-dimensional semiconductor photocatalysts have large specific surface area and unique physical characteristics,but the rapid recombination of photogenerated electrons and holes in the material limits the photocatalytic efficiency.When the two semiconductor materials are vertically stacked to form type-Ⅱheterostructure,the photogenerated carriers can be separated effectively,so as to prolong the life of photogenerated charge and improve the photocatalytic performance obviously.Therefore,HfS₂/GaS and PtSe₂/SnS₂ heterostructures have been constructed in this paper.And their photoelectric properties and photocatalytic performance have been studied in depth.Firstly,a HfS₂/GaS van der Waals heterostructure has been designed to achieve efficient and spontaneous water decomposition.Through first-principles calculation,HfS₂/GaS heterostructure has been proved to be a stable and promising photocatalyst with the following obvious advantages:both water reduction and oxidation potentials are located in the band gap（2.04 e V）of HfS₂/GaS heterostructure,ensuring the water splitting can occur.The type-Ⅱband structure and built-in electric field ensure the effective separation of photoelectron-hole,and the high mobility of electrons and holes can also predict high photocatalytic activity.By calculating the free energy of the oxygen evolution reaction on the surface of GaS and the hydrogen evolution reaction on the surface of HfS₂ of the heterostructure,it’s found that the water decomposition reaction can occur spontaneously under light.It is worth noting that the hydrogen evolution efficiency after the construction of heterostructure is significantly improved,reaching 14.91%,which is higher than the standard for commercial use of water decomposition photocatalysts.Furthermore,after 1-6%in-plane biaxial tensile strain are applied,the redox reaction of photocatalytic decomposition water can still occur on the HfS₂/GaS heterostructure.And the application of strain can effectively regulate the optical and electronic properties.Therefore,HfS₂/GaS heterostructure could be a promising candidate material for the photocatalytic decomposition of water.In addition,the direct Z-scheme heterostructure has attracted much attention due to its strong photocatalytic and visible light absorption capacity.Using first principles calculations,we explore the electronic and optical properties and photocatalytic mechanism of PtSe₂/SnS₂heterostructure.Compared with PtSe₂,SnS₂ monolayer and traditional type-Ⅱphotocatalyst（HfS₂/GaS heterostructure）,PtSe₂/SnS₂ heterostructure has smaller band gap,more significant light absorption capacity and better hydrogen evolution efficiency.The results of band and state density show that the heterostructure form the type-Ⅱband arrangement.Further work function calculations indicate that the direction of the built-in electric field is PtSe₂ to SnS₂,confirming the charge transfer mechanism is Z-scheme.In the water decomposition reaction,the free energy calculation results show that hydrogen evolution reaction on PtSe₂ side and oxygen evolution reaction on SnS₂ side can occur spontaneously under light.Besides,PtSe₂/SnS₂heterostructure has obvious light absorption in the range of ultraviolet and visible light,indicating it’s sensitive to sunlight.Interestingly,the band edge position still meets the requirement of water decomposition and retains considerable visible light absorption capacity after biaxial strain is applied.Therefore,PtSe₂/SnS₂ heterostructure can be used as a potential direct Z-scheme photocatalyst for hydrogen and oxygen production.更多还原