Self-improvement of solar water oxidation for the continuously-irradiated hematite photoanode.

ABSTRACT

Improving bulk- or surface-properties has been found as an effective route to regulate and enhance the photoelectrochemical (PEC) performances of some metal-oxide photoelectrodes. However, both bulk and surface self-improvement resulting from the photocharging (PC) effect is rarely reported and as a result the underlying mechanism of the PC effect is not fully understood. Here, we demonstrate that the hematite photoanode integrated with Sn doping and a TiO2 underlayer shows a substantial increase in the photocurrent density (i.e., from 0.69 to 1.12 mA cm-2 at 1.23 V relative to the standard hydrogen electrode) and a cathodic shift of the onset potential after being irradiated by a one-sun simulator for 12 h. The primary reasons for these can be categorized into two fundamental factors (1) the enhanced bulk conductivity and the resulting decrease in carrier bulk recombination from the gradually increasing ratio of Fe2+ and Fe3+; (2) the reduced carrier surface recombination from the photogenerated passivation layer. Ultimately, both the bulk and surface electrical properties of the hematite photoanode are substantially self-improved under continuous irradiation. This work deepens the understanding of the PC effect and proves that it is a promising technique for the PEC-performance enhancement of the hematite photoanode.