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Promoting water photooxidation on transparent WO_3 thin films using an alumina overlayer

机译：使用氧化铝覆盖层促进透明WO_3薄膜上的水光氧化

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摘要

Tungsten trioxide (WO_3) is being investigated as one of the most promising materials for water oxidation using solar light. Its inherent surface-related drawbacks (e.g., fast charge recombination caused by surface defect sites, the formation of surface peroxo-species, etc.) are nowadays being progressively overcome by different methods, such as surface passivation and the deposition of co-catalysts. Among them, the role of surface passivation is still poorly understood. Herein, transparent WO_3 (electrodeposited) and AI_2O_3/WO_3 (prepared by atomic layer deposition, ALD) thin film electrodes were employed to investigate the role of an alumina overlayer by using both photoelectrochemical and laser flash photolysis measurements. Films with a 5 nm-alumina overlayer (30 ALD cycles) showed an optimum photoelectrochemical performance, portraying a 3-fold photocurrent and Faradaic efficiency enhancement under voltage biases. Moreover, IPCE measurements revealed that alumina effect was only significant with an applied potential ca. 1 V (vs. Ag/AgCI), matching the thermodynamic potential for water oxidation at pH 1 (0.97 V vs. Ag/AgCI). According to the investigation of electron accumulation through optical absorption measurements, the alumina overlayer dominantly decreased the number of electron trapping sites on the WO_3 surface, eventually facilitating photoelectron transfer to the external circuit in the presence of a positive bias. In addition, the laser flash photolysis measurements of WO_3 and AI_2O_3/WO_3 thin films clearly showed that the electron trapping decreased in the presence of the alumina overlayer whereas the hole trapping relatively increased with alumina, facilitating water photooxidation and rendering a more sluggish recombination process. These results provide a physical insight into the passivation process that could be used as a guideline for further development of efficient photoanodes in artificial photosynthesis.
机译：三氧化钨（WO_3）被研究为使用太阳光进行水氧化的最有前景的材料之一。如今，其固有的与表面有关的缺点（例如，由表面缺陷位点引起的快速电荷复合，表面过氧物种的形成等）逐渐通过不同的方法克服，例如表面钝化和助催化剂的沉积。其中，对表面钝化的作用仍知之甚少。在此，采用透明的WO_3（电沉积）和Al_2O_3 / WO_3（通过原子层沉积，ALD）薄膜电极通过光电化学和激光闪光光解测量来研究氧化铝覆层的作用。具有5 nm氧化铝覆盖层的薄膜（30个ALD循环）显示出最佳的光电化学性能，描绘了在电压偏置下3倍的光电流和法拉第效率的提高。此外，IPCE测量表明，仅在施加电势的情况下，氧化铝的作用才很明显。 1 V（vs。Ag / AgCI），与pH 1时水氧化的热力学势相匹配（0.97 V vs. Ag / AgCI）。根据通过光吸收测量对电子积累的研究，氧化铝覆盖层显着减少了WO_3表面上的电子捕获位点的数量，最终在存在正偏压的情况下促进了光电子向外部电路的转移。此外，WO_3和AI_2O_3 / WO_3薄膜的激光闪光光解测量清楚地表明，在存在氧化铝覆盖层的情况下电子俘获减少，而空穴俘获随氧化铝而相对增加，从而促进了水的光氧化作用，并使复合过程更加缓慢。这些结果提供了对钝化过程的物理见解，可以用作进一步开发人造光合作用中有效光阳极的指南。

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  • 来源
    《Energy & environmental science》 |2013年第12期|3732-3739|共8页
  • 作者

    Wooyul Kim; Takashi Tachikawa; Damian Monllor-Satoca; Hyoung-il Kim; Tetsuro Majima; Wonyong Choi;

  • 作者单位

    School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea;

    The Institute of Scientific and Industrial Research (SANKEN), Osaka University,Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan;

    School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea;

    School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea;

    The Institute of Scientific and Industrial Research (SANKEN), Osaka University,Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan;

    School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea;

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