Conformal BiVO_(4)/WO_(3) nanobowl array photoanode for efficient photoelectrochemical water splitting

高匹配的BiVO_(4)/WO_(3)纳米碗异质结光阳极用于高效光电化学分解水

As one of the most promising photoanode candidates for photoelectrochemical(PEC)water splitting,the photocurrent density of BiVO_(4) still needs to be further improved in order to meet the practical application.In this work,a highly‐matched BiVO_(4)/WO_(3) nanobowl(NB)photoanode was constructed to enhance charge separation at the interface of the junction.Upon further modification of the BiVO_(4)/WO_(3)NB surface by NiOOH/FeOOH as an oxygen evolution cocatalyst(OEC)layer,a high photocurrent density of 3.05 mA cm^(−2) at 1.23 V vs.RHE has been achieved,which is about 5‐fold higher than pristine BiVO_(4) in neutral medium under AM 1.5 G illumination.5 times higher IPCE at 450 nm is also achieved compared with the BiVO_(4) photoanode,leading to about 95%faradaic efficiency for both H_(2) and O_(2) gas production.Systematic studies attribute the significantly enhanced PEC performance to the smaller BiVO_(4) particle size(<90 nm)than its hole diffusion length(~100 nm),the improved charge separation of BiVO_(4) by the single layer WO_(3) nanobowl array and the function of OEC layers.Such WO_(3)NB possesses much smaller interface resistance with the substrate FTO glass and larger contact area with BiVO_(4) nanoparticles.This approach provides new insights to design and fabricate BiVO_(4)‐based heterojunction photoanode for higher PEC water splitting performance.

光电化学(PEC)分解水制氢,已成为将太阳能转化为绿色可持续氢能极具潜力的途径之一.目前,单斜相钒酸铋(BiVO_(4))因其合适的带隙及能带位置、无毒且含量丰富等优点,被认为是理想的光阳极材料.然而,BiVO_(4)较低的载流子迁移率(4×10^(−2) cm^(2) V^(−1) s^(−1))和较短的空穴扩散长度(<100 nm),导致BiVO_(4)光阳极电子-空穴复合较严重,极大地限制了其性能.为克服上述缺陷,除减小BiVO_(4)纳米颗粒的粒径以匹配其较短的空穴扩散长度,使空穴能有效转移到其表面参与水氧化反应;或在其表面沉积一层薄的氧气释放反应助催化剂(OEC)层以增强水氧化反应动力学以外,还应关注如何进一步有效提升BiVO_(4)电荷分离效率.因此,在BiVO_(4)和氟掺杂的氧化锡(FTO)电极界面之间插入另一种半导体材料构筑异质结以促进BiVO_(4)电荷分离,进一步提升BiVO_(4)电荷分离效率.本文采用成本低廉、可控性高的单层胶体晶体(MCC)方法首先合成了单层WO_(3)纳米碗(WO_(3)NB)阵列,再通过分步沉积法在单层WO_(3)NB表面原位生长BiOI,确保BiOI在WO_(3)NB表面的完全覆盖,最后通过热处理将BiOI转化为BiVO_(4)纳米颗粒成功构建高匹配的BiVO_(4)/WO_(3)NB异质结.在这种新颖的结构设计中,小尺寸的BiVO_(4)纳米颗粒(~90 nm)均匀地沉积在WO_(3)纳米碗(内径约为920 nm)表面.高度有序的WO_(3)NB阵列担载了BiVO_(4)的小尺寸和纳米结构,最小化了WO_(3)颗粒间的晶界缺陷,并增加了与BiVO_(4)纳米粒子的接触面积.结合X射线粉末衍射、X射线光电子能谱、高分辨透射电子显微镜和能带分析发现,BiVO_(4)与WO_(3)NB匹配的能带位置和高度匹配的BiVO_(4)/WO_(3)NB界面可显著增强BiVO_(4)与WO_(3)NB之间的电荷传输;此外,光致发光光谱和电化学阻抗测试结果表明,由于制备的BiVO_(4)纳米颗粒尺寸小于其空穴扩散长度(~100 nm),可确保空穴更有效的传递到NiOOH/FeOOH层中并参与表面水氧化反应;在OEC/BiVO_(4)和BiVO_(4)/WO_(3)NB两种结的协同作用下制备的NiOOH/FeOOH/BiVO_(4)/WO_(3)NB光阳极在中性电解质溶液Na_(2)SO_(4)溶液中,1.23 V vs.RHE偏压下的光电流密度为3.02 mA cm^(−2),法拉第效率达95%.本文研究结果为设计与构筑高匹配多重“结”BiVO_(4)光阳极提供了有效策略.