Oriented electron tunneling transport in hierarchical Ag/SiO2/TiO2 nanobowl arrays for plasmonic solar water splitting
Zexin Yu, Lixia Sang, Angran Cao, Yunlong Gao
Abstract
Hierarchical Ag/SiO 2 /TiO 2 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 TiO 2 nanoring and a lower TiO 2 nanohole. A thin SiO 2 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/SiO 2 /TiO 2 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 TiO 2 nanoring was a transporter, which transmitted electrons downward to the nanohole. The SiO 2 layer replaces the Schottky barrier to become a bridge for tunneling of hot electrons in high- and low-energy states into TiO 2 . Moreover, the coverage of the SiO 2 layer helped increase the light absorption of TiO 2 , it also reduced the near electric field coupling between Ag and TiO 2 . Accordingly, under AM 1.5 light irradiation, the photocurrent density and average hydrogen evolution rate of Ag/SiO 2 /TiO 2 were 1.8 and 2.2 times higher, respectively, than those of pure TiO 2 , implying far more efficient migration of carriers.