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Hierarchical Ag/SiO2/TiO2 nanobowl (NB) arrays were fabricated for use as plasmonic photoanodes for solar-hydrogen conversion. The nanobowls had large pore size and were composed of an upper TiO2 nanoring and a lower TiO2 nanohole. A thin SiO2 inter-layer was introduced as an electron transmission channel to change the mechanism of hot electron transport. Simulations were performed to characterize the variation of electron concentration in Ag/SiO2/TiO2 NB arrays, taking into account both the optical transition of photogenerated electrons, and electron tunneling. The multiphysics coupling function of COMSOL software provided the light source for optical transition of photogenerated electrons, and a Wentzel-Kramers-Brillouin model was employed to represent the tunneling. The results demonstrate that the TiO2 nanoring was a transporter, which transmitted electrons downward to the nanohole. The SiO2 layer replaces the Schottky barrier to become a bridge for tunneling of hot electrons in high- and low-energy states into TiO2. Moreover, the coverage of the SiO2 layer helped increase the light absorption of TiO2, it also reduced the near electric field coupling between Ag and TiO2. Accordingly, under AM 1.5 light irradiation, the photocurrent density and average hydrogen evolution rate of Ag/SiO2/TiO2 were 1.8 and 2.2 times higher, respectively, than those of pure TiO2, implying far more efficient migration of carriers.


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Oriented electron tunneling transport in hierarchical Ag/SiO2/ TiO2 nanobowl arrays for plasmonic solar water splitting

Show Author's information Zexin YuLixia Sang( )Angran CaoYunlong Gao
MOE Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Beijing Key Laboratory of Heat Transfer and Energy Conversion, Beijing Municipality Beijing University of TechnologyBeijing 100124 China

Abstract

Hierarchical Ag/SiO2/TiO2 nanobowl (NB) arrays were fabricated for use as plasmonic photoanodes for solar-hydrogen conversion. The nanobowls had large pore size and were composed of an upper TiO2 nanoring and a lower TiO2 nanohole. A thin SiO2 inter-layer was introduced as an electron transmission channel to change the mechanism of hot electron transport. Simulations were performed to characterize the variation of electron concentration in Ag/SiO2/TiO2 NB arrays, taking into account both the optical transition of photogenerated electrons, and electron tunneling. The multiphysics coupling function of COMSOL software provided the light source for optical transition of photogenerated electrons, and a Wentzel-Kramers-Brillouin model was employed to represent the tunneling. The results demonstrate that the TiO2 nanoring was a transporter, which transmitted electrons downward to the nanohole. The SiO2 layer replaces the Schottky barrier to become a bridge for tunneling of hot electrons in high- and low-energy states into TiO2. Moreover, the coverage of the SiO2 layer helped increase the light absorption of TiO2, it also reduced the near electric field coupling between Ag and TiO2. Accordingly, under AM 1.5 light irradiation, the photocurrent density and average hydrogen evolution rate of Ag/SiO2/TiO2 were 1.8 and 2.2 times higher, respectively, than those of pure TiO2, implying far more efficient migration of carriers.

Keywords: tunneling, nanobowl, hot electron, Wentzel-Kramers-Brillouin (WKB) approximation, SiO2 layer

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Acknowledgements

Publication history

Received: 20 February 2021
Revised: 20 June 2021
Accepted: 22 June 2021
Published: 17 August 2021
Issue date: February 2022

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© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021

Acknowledgements

Acknowledgements

The authors are grateful to the National Natural Science Foundation of China (No. 51776009) for their financial support.

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