Beyond band bending in the WO 3 /BiVO 4 heterojunction: insight from DFT and experiment
Beyond band bending in the WO 3 /BiVO 4 heterojunction: insight from DFT and experiment
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超越 WO 3 /BiVO 4 异质结的能带弯曲：DFT 和实验的见解
DOI：
10.1039/c8se00420j
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发表时间：
2019
影响因子：
5.6
通讯作者：
Ràfols I Bellés C
中科院分区：
文献类型：
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作者：
Ràfols I Bellés C
异质结光催化剂可以显著提高光催化分解水的效率。众所周知，这种改善的关键在于发生电荷分离的界面区域。了解这种界面增强的原因可以设计出性能更好的分水装置。因此，在这项工作中，我们发展了一种新的理论-实验相结合的方法来研究光催化异质结--WO_3/BiVO_4模型体系，在该模型体系中，水的分裂的量子效率在某些波长可以接近于1。我们对这种异质结的光电化学测量表明，当通过BiVO4侧而不是WO3侧照射时，其性能比其单独的组分显著增强。这表明跨结的电子转移(即从BiVO4到WO_3)比空穴转移(即从WO_3到BiVO_4)更有效。我们的经典能带弯曲模型预测了明显的界面势垒，但不能解释在背光照射下性能下降的原因。用原子论模型研究了界面重构和化学相互作用对体系电子结构的影响。该模型揭示了非交错的价带，而不是交错的导带，这是由于两种材料中价带轨道在界面上的强烈杂化。这种非交错的价带不为空穴转移(即在背光下从WO_3到BiVO_4)的电荷分离提供能量驱动力。因此，只有在前照明下才能观察到性能的显著改善。这种结合了实验和理论的方法，使人们对异质结光催化剂体系有了更全面的了解，并对两种半导体材料结合在一起时产生的界面效应提供了独特的见解，超越了传统的能带弯曲模型。
Heterojunction photocatalysts can significantly enhance the efficiency of photocatalytic water splitting. It is well known that the key to such improvements lies at the interfacial region where charge separation occurs. Understanding the origins of this interfacial enhancement can enable the design of better performing water splitting devices. Therefore, in this work, a novel theoretical–experimental approach is developed for the study of photocatalytic heterojunctions using the model system – WO3/BiVO4, where it has been shown that the quantum efficiency of water splitting can approach unity at certain wavelengths. Our photoelectrochemical measurements of this heterojunction show a significantly enhanced performance over its separate components when illuminated through the BiVO4 side but not the WO3 side. This is indicative of more efficient electron transfer (i.e. from BiVO4 to WO3) than hole transfer (i.e. from WO3 to BiVO4) across the junction. Our classical band bending model of this junction predicts noticeable interfacial barriers, but could not explain the reduced performance under back illumination. Our atomistic model was used to investigate the effect of interfacial reconstructions and chemical interactions on the electronic structure of the system. The model reveals a non-staggered valence band, in contrast to the staggered conduction band, due to strong hybridization of valence band orbitals in both materials across the interface. This non-staggered valence band does not provide an energetic driving force for charge separation for hole transfer (i.e. from WO3 to BiVO4 under back illumination). Hence, a significant improvement in performance is only observed under front illumination. This combined approach, using both experiment and theory, results in a more complete understanding of a heterojunction photocatalyst system and provides unique insight into the interfacial effects that arise when two semiconductor materials are brought together, going beyond traditional band bending models.