Ultra-thin Al2O3 coatings on BiVO4 photoanodes: Impact on performance and charge carrier dynamics
Ultra-thin Al2O3 coatings on BiVO4 photoanodes: Impact on performance and charge carrier dynamics
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DOI：
10.1016/j.cattod.2017.11.014
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发表时间：
2019-02-01
期刊：
影响因子：
5.3
通讯作者：
Durrant, James R.
中科院分区：
文献类型：
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作者：
Kafizas, Andreas;Xing, Xueting;Durrant, James R.
钒酸铋(BiVO4)以其可见光活性和低成本成为最有前途的水氧化光阳极材料之一。最近的研究表明，在BiVO4光阳极上涂覆超薄的钝化层可以显著提高其性能。在这篇文章中，我们研究了使用原子层沉积(ALD)生长的超薄Al_2O_3层的使用。在最佳厚度(约0.33 nm，3个ALD循环)下，Al_2O_3膜的起始电位移动了约200 mV，增加了水氧化反应的光催化电流。当保持在1.23V-RHE时，我们观察到理论太阳光电流显著增加；从类似于0.47mAcm(-2)在未包覆的BiVO4到类似于3.0mAcm(-2)在Al2O3包覆的BiVO4。利用暂态光电流(TPC)和暂态吸收光谱(TAS)首次研究了涂覆Al_2O_3的BiVO_4光阳极中的载流子动力学。TPC显示，BiVO4层中的光生电子在大约1ms的时间内被提取。TAS分析表明，剩余的空穴氧化水的时间从100ms到1 S。超薄的Al_2O_3涂层并没有改善水氧化反应动力学，相反，它抑制了BiVO_4中亩S-毫秒标度上的双分子复合，并增加了氧化水所需的ms-S标度上长寿命空穴的产率。这归因于Al_2O_3对BiVO_4表面复合的抑制，从而抑制了在空间电荷层内形成的电荷载流子的早期时间尺度复合。
Bismuth vanadate (BiVO4) has emerged as one of the most promising photoanode materials for oxidising water due to its visible light activity and low cost. Recent studies have shown that the performance of BiVO4 photoanodes can be remarkably improved when coated with ultra-thin passivation layers. In this article we investigate the use of ultra-thin Al2O3 layers grown using atomic layer deposition (ALD). At an optimum thickness (similar to 0.33 nm, 3 ALD cycles), the Al2O3 layer favourably shifted the onset potential by similar to 200 mV and increased photocatalytic currents for the water oxidation reaction. When held at 1.23 V-RHE, we observe a remarkable increase in the theoretical solar photocurrent; from similar to 0.47 mAcm(-2) in uncoated BiVO4 to similar to 3.0 mAcm(-2) in Al2O3-coated BiVO4. Using transient photocurrent (TPC) and transient absorption spectroscopy (TAS) the charge carrier dynamics in Al2O3-coated BiVO4 photoanodes were examined for the first time. TPC showed that photogenerated electrons in the BiVO4 layer were extracted within similar to 1 ms. TAS showed that the remaining holes oxidised water from similar to 100 ms to 1 s. Ultra-thin Al2O3 coatings did not improve the reaction kinetics towards water oxidation, but rather, suppressed bi-molecular recombination on the mu s-ms timescale in BiVO4, and increased the yield of long-lived holes on the ms-s timescale required to oxidise water. This is attributed to an inhibition of surface recombination on BiVO4 by Al2O3, which inhibited the early timescale recombination of charge carriers formed within the space charge layer.