Translucent Thin Film Fe_2O_3 Photoanodes for Efficient Water Splitting by Sunlight:Nanostructure-Directing Effect of Si-Doping

摘要

Following Fujishima and Honda's light-induced water-splitting experiment with a TiO_2 semiconductor photoanode in 1972,worldwide research has been focused on the conversion of sunlight into hydrogen as a clean and renewable source of energy.Shifting the activity of the photoanode into the visible has been a major challenge so far.Iron oxide (alpha-Fe_2O_3,or hematite) has unique properties for application in photoelectrolysis reactors.Apart from its ability to absorb a large part of the solar spectrum,its chemical stability,nontoxicity,abundance,and low cost can make it a tempting research target.However,challenges are set by its notoriously short hole diffusion length and the low absorption coefficient due to its indirect band gap (ca.2.1 eV).In addition,the conduction band of hematite is positioned too positively to reduce water to hydrogen directly.This is overcome by applying an external bias voltage supplied by a dye-sensitized solar cell (dsc) in a tandem-cell configuration.The dye cell provides the required potential for hydrogen evolution by absorbing the red part of the solar spectrum which is transmitted by the hematite electrode.