NDLI: Promoting water photooxidation on transparent WO<sub>3</sub> thin films using an alumina overlayer

Content Provider	Royal Society of Chemistry (RSC)
Author	Kim, Hyoung-il Choi, Wonyong Monllor-Satoca, Damián Tachikawa, Takashi Majima, Tetsuro Kim, Wooyul
Copyright Year	2013
Abstract	Tungsten trioxide (WO3) 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 WO3 (electrodeposited) and Al2O3/WO3 (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/AgCl), matching the thermodynamic potential for water oxidation at pH 1 (0.97 V vs. Ag/AgCl). According to the investigation of electron accumulation through optical absorption measurements, the alumina overlayer dominantly decreased the number of electron trapping sites on the WO3 surface, eventually facilitating photoelectron transfer to the external circuit in the presence of a positive bias. In addition, the laser flash photolysis measurements of WO3 and Al2O3/WO3 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.
Starting Page	3732
Ending Page	3739
Page Count	8
File Format	HTM / HTML PDF
ISSN	17545692
Volume Number	6
Issue Number	12
Journal	Energy & Environmental Science
DOI	10.1039/c3ee42151a
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	Sulfur trioxide Carrier generation and recombination Passivation (chemistry) Electroplating Atomic layer deposition Aluminium oxide Overlayer Photoelectrochemical cell Laser Flash photolysis Photocurrent List of pedophile and pederast advocacy organizations Thermodynamic potential PH Photoelectric effect Artificial photosynthesis
Content Type	Text
Resource Type	Article
Subject	Environmental Chemistry Pollution Renewable Energy, Sustainability and the Environment Nuclear Energy and Engineering

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