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Oriented electron tunneling transport in hierarchical Ag/SiO2/ TiO2 nanobowl arrays for plasmonic solar water splitting
Nano Research 2022, 15 (2): 1593-1602
Published: 17 August 2021
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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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