调控Cs_(3)Bi_(2)Br_(9)@V_(O)-In_(2)O_(3)S型异质结的费米能级和内建电场促进光生电荷分离和二氧化碳还原

Modulation of Fermi level gap and internal electric field over Cs_3Bi_2Br_9@V_O-In_2O_(3)S-scheme heterojunction for boosted charge separation and CO_(2)photoconversion

近年来,卤化物钙钛矿材料由于具有合适的能带结构和良好的可见光捕获能力,被广泛应用于光催化还原CO_(2).然而,单一的卤化物钙钛矿的载流子辐射复合严重,导致其电荷分离效率较低,并且对CO_(2)的捕获能力较差,进而限制了其在光催化领域的实际应用.构建异质结被认为是解决单一半导体光催化剂光生载流子分离效率低等问题的有效策略.研究表明,S型异质结不仅可以实现光生载流子的有效分离,而且其独特的光生电荷传输路径还可以使异质结体系保留较强的氧化还原能力,利于光催化反应进行.本文以提高Cs_(3)Bi_(2)Br_(9)钙钛矿量子点的载流子分离效率和CO_(2)吸附能力为目标,构建了Cs_(3)Bi_(2)Br_(9)@V_(O)-In_(2)O_(3)(CBB@V_(O)-In_(2)O_(3))S型异质结,并探究了氧空位在该异质结光催化还原CO_(2)中的作用.首先,将Cs_(3)Bi_(2)Br_(9)钙钛矿量子点(PQD)嵌入到介孔In_(2)O_(3)基体中,构建了CBB@In_(2)O_(3)S型异质结.然后,将氧空位(V_(O))引入到异质结的还原型半导体(介孔In_(2)O_(3))中,增大了CBB和V_(O)-In_(2)O_(3)之间的费米能级(EF)差异,进而增强了CBB@V_(O)-In_(2)O_(3)S型异质结的内建电场.电子自旋共振谱、X射线光电子能谱(XPS)、紫外-可见漫反射光谱(UV-visDRS)等结果表明,In_(2)O_(3)中成功引入了氧空位.表面电荷密度和表面光电压测试结果表明,CBB@In_(2)O_(3)异质结的内建电场强度为单一CBB的4.07倍,而CBB@V_(O)-In_(2)O_(3)异质结的内建电场强度比单一的CBB提升了11.69倍,进一步证明在In_(2)O_(3)中引入氧空位可以增大两种材料的费米能级差异及内建电场强度.密度泛函理论(DFT)理论计算结果表明,氧空位的引入能够使In2O3的费米能级向上移动,使In_(2)O_(3)和CBB之间的费米能级差异增大,与实验结果相一致.这种增强的内建电场为光生载流子的定向迁移提供了更强的驱动力,从而有效提高了该S型异质结的电荷分离效率.采用UV-visDRS,Tauc曲线和莫特-肖特基图谱等分析了In_(2)O_(3)和CBB的能级结构,发现两种材料的能级位置交错排列,有利于形成S型异质结.瞬态吸收光谱、光辅助开尔文力显微镜和原位XPS等结果表明,该异质结的电荷转移模式为S型.该S型异质结的内建电场促进了电荷的高效分离,使得CBB@V_(O)-In_(2)O_(3)异质结表现出较好的光催化CO_(2)还原为CO的性能,其生成CO的产率为130.96μmolg-1h-1.此外,该CBB@V_(O)-In_(2)O_(3)S型异质结表现出良好的光催化稳定性,经过10次循环实验后,其催化CO_(2)还原的性能未发生明显的下降.通过原位漫反射红外傅立叶变换光谱研究了反应中间体和CO_(2)光转化途径.结合DFT计算发现,V_(O)-In_(2)O_(3)中的氧空位作为活性位点,能够优化反应中间体的配位模式,从而降低了光催化还原CO_(2)的活化能.综上所述,调控S型异质结的内建电场是提高异质结电荷分离效率、提升材料光催化性能的有效策略.本文构建了Cs_(3)Bi_(2)Br_(9)@V_(O)-In_(2)O_(3)(CBB@V_(O)-In_(2)O_(3))S型异质结,并探究了氧空位在该异质结光催化还原CO_(2)中的作用,为高效S型异质结光催化材料的设计提供了一种新思路,也为探索氧空位在S型异质结中的作用及人工光合成催化剂的制备提供一定参考.

Modulating the internal electric field(IEF)represents a potential strategy to stimulate the photocatalytic activity of heterojunctions,especially S-scheme photocatalysts.Herein,a Cs_(3)Bi_(2)Br_(9)@V_(O)-In_(2)O_(3)(CBB@V_(O)-In_(2)O_(3))S-scheme heterojunction,of which Cs_(3)Bi_(2)Br_(9) perovskite quantum dots(PQDs)are embedded into mesoporous V_(O)-In_(2)O_(3)hosts,is rationally designed as a cornerstone for further IEF manipulation.Briefly,by introducing oxygen vacancies(VO)into the composed reduction semiconductor(mesoporous In_(2)O_(3)),an enlarged Fermi level(EF)gap between CBB and V_(O)-In_(2)O_(3) is achieved,yielding an intensified IEF over the CBB@V_(O)-In_(2)O_(3)heterojunction.Such an enhanced IEF affords a much more robust driving force for directional carrier delivery,leading to accelerated carrier transfer of CBB@V_(O)-In_(2)O_(3)heterojunction.Consequently,the optimized CBB@V_(O)-In_(2)O_(3) heterojunction features desirable CO_(2)-to-CO conversion efficiency,and its CO production rate reaches 130.96μmol g^(-1)h^(-1).The reaction intermediates and CO_(2)photoconversion pathway were unraveled by in-situ diffuse reflectance infrared Fourier transform spectroscopy.Combining with the DFT calculation,it was revealed that oxygen vacancies in V_(O)-In_(2)O_(3) act as reactive centers,which optimize the coordination modes of the intermediates,thus reducing the activation energy for photocatalytic CO_(2)reduction.Our work demonstrates that the IEF modulation of S-scheme-based heterojunction could significantly boost the charge separation and then to drive efficient catalytic reaction,achieving high-efficiency solar fuel production.