Promoting water photooxidation on transparent WO3 thin films using an alumina overlayer

Wooyul Kim, Takashi Tachikawa, Damián Monllor-Satoca, Hyoung Il Kim, Tetsuro Majima, Wonyong Choi

Research output: Contribution to journalArticle

81 Citations (Scopus)

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 Al2O 3/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.

Original languageEnglish
Pages (from-to)3732-3739
Number of pages8
JournalEnergy and Environmental Science
Volume6
Issue number12
DOIs
Publication statusPublished - 2013 Dec 1

Fingerprint

Photooxidation
Aluminum Oxide
photooxidation
aluminum oxide
Alumina
Thin films
Water
Passivation
trapping
Atomic layer deposition
Photolysis
photolysis
electron
water
recombination
Electrons
laser
oxidation
Oxidation
Photosynthesis

All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Pollution

Cite this

Kim, Wooyul ; Tachikawa, Takashi ; Monllor-Satoca, Damián ; Kim, Hyoung Il ; Majima, Tetsuro ; Choi, Wonyong. / Promoting water photooxidation on transparent WO3 thin films using an alumina overlayer. In: Energy and Environmental Science. 2013 ; Vol. 6, No. 12. pp. 3732-3739.
@article{79dae90a930140328ff8ec82dc3e65bd,
title = "Promoting water photooxidation on transparent WO3 thin films using an alumina overlayer",
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 Al2O 3/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.",
author = "Wooyul Kim and Takashi Tachikawa and Dami{\'a}n Monllor-Satoca and Kim, {Hyoung Il} and Tetsuro Majima and Wonyong Choi",
year = "2013",
month = "12",
day = "1",
doi = "10.1039/c3ee42151a",
language = "English",
volume = "6",
pages = "3732--3739",
journal = "Energy and Environmental Science",
issn = "1754-5692",
publisher = "Royal Society of Chemistry",
number = "12",

}

Promoting water photooxidation on transparent WO3 thin films using an alumina overlayer. / Kim, Wooyul; Tachikawa, Takashi; Monllor-Satoca, Damián; Kim, Hyoung Il; Majima, Tetsuro; Choi, Wonyong.

In: Energy and Environmental Science, Vol. 6, No. 12, 01.12.2013, p. 3732-3739.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Promoting water photooxidation on transparent WO3 thin films using an alumina overlayer

AU - Kim, Wooyul

AU - Tachikawa, Takashi

AU - Monllor-Satoca, Damián

AU - Kim, Hyoung Il

AU - Majima, Tetsuro

AU - Choi, Wonyong

PY - 2013/12/1

Y1 - 2013/12/1

N2 - 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 Al2O 3/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.

AB - 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 Al2O 3/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.

UR - http://www.scopus.com/inward/record.url?scp=84887920068&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84887920068&partnerID=8YFLogxK

U2 - 10.1039/c3ee42151a

DO - 10.1039/c3ee42151a

M3 - Article

AN - SCOPUS:84887920068

VL - 6

SP - 3732

EP - 3739

JO - Energy and Environmental Science

JF - Energy and Environmental Science

SN - 1754-5692

IS - 12

ER -