A novel route to visualize the hot electron transfer process in Ag@SiO2-TiO2 for solar-hydrogen conversion

Abstract

The wrapping of plasmonic metal particles with silica shell is considered to be one of the effective means to make full use of hot electrons for solar-hydrogen conversion. Ag@SiO2-TiO2 structures with different shell thicknesses (2, 3, 5, 7 and 11 nm) as hot-electron devices were fabricated, and their local electric field was simulated by the COMSOL software. A novel method was proposed to visually characterize the migration of hot electrons, which was represented by multiphysics coupling. The simulated current flow indicates the transfer direction of hot electrons, and the variation of electron-hole concentration implies the gain and loss of electrons. The results demonstrate that the applied thinner silica shell not only decreases the barrier to the hot electron transport out of shell, but also intensify local electric field. When the silica shell thickness is 2 nm, the amount of hot electrons migrated out of shell is high, such that the photogenerated electrons in TiO2 have more chances for jumping to higher energy states, which results in the enhanced separation of electrons and holes. The photocurrent and photovoltage of Ag@SiO2 (2 nm)-TiO2 were respectively 1.68 and 1.54 times higher than those of Ag-TiO2 denoting the highest carriers’ migration and utilization efficiency.