Ⅱ型C_(2)N/ZnO异质结水分解光催化剂的第一性原理研究

First-principles Calculation of Type-ⅡC_(2)N/ZnO Heterojunction as a WaterSplitting Photocatalyst

基于单层C_(2)N和ZnO,构建了一种新型2D范德华(vdW)异质结。在第一性原理下进行密度泛函理论计算,系统地研究了C_(2)N/ZnO异质结的光催化应用。结果表明,C_(2)N/ZnO异质结具有1.68 eV的直接带隙,其Ⅱ型带对准可以促使光生电子和空穴分离在不同层上。由Mulliken电荷布局分析可知,C_(2)N层有0.53个电子转移到ZnO层,在异质结界面处形成了一个较强的内建电场E int,抑制了光生电子空穴对的复合。此外,C_(2)N/ZnO异质结的带边位置跨过了pH=2~7时的水氧化还原电位,同时拉伸应变可以增大其光催化水分解pH范围。特别地,C_(2)N/ZnO异质结保留了高载流子迁移率和优异的光吸收性能,太阳能-氢能(STH)转换效率可达到24.6%。因此,C_(2)N/ZnO异质结是一种具有应用前景的水分解光催化剂。

The novel 2D van der Waals(vdW)heterojunction is constructed based on C_(2)N and ZnO monolayers.In this work,we investigate the photocatalytic application of C_(2)N/ZnO heterojunction systematically by conducting density functional theory calculations with first-principles.The results clear that the C_(2)N/ZnO heterojunction is a direct band gap semiconductor with 1.68 eV band gap,and its type-II band alignment can facilitate the separation of photoexcited electrons and holes on different layers.From the Mulliken population analysis,0.53 electrons from the C_(2)N layer are transferred to the ZnO layer,forming a formidable built-in electric field E int that curbs the recombination of photoexcited electron-hole pairs at the interface.Additionally,the band edge positions of the C_(2)N/ZnO heterojunction straddle the water redox potential at pH=2 to 7,and the pH range of photocatalytic water decomposition increases under the tensile strain.Especially,the high carrier mobility and outstanding light absorption characteristic are retained in the C_(2)N/ZnO heterojunction,and the solar-to-hydrogen(STH)conversion efficiency is as high as 24.6%.So the C_(2)N/ZnO heterojunction is a prospective water splitting photocatalyst.