Mono-doped and co-doped nanostructured hematite for improved photoelectrochemical water splitting

Abstract

In this study, zinc-doped (a-Fe2O3:Zn), silver-doped (a-Fe2O3:Ag) and zinc/silver codoped hematite (a-Fe2O3:Zn/Ag) nanostructures were synthesized by spray pyrolysis. The synthesized nanostructures were used as photoanodes in the photoelectrochemical (PEC) cell for watersplitting. A significant improvement in photocurrent density of 0.470 mAcm2 at 1.23 V vs. reversible hydrogen electrode (RHE) was recorded for a-Fe2O3:Zn/Ag. The a-Fe2O3:Ag, a-Fe2O3:Zn and pristine hematite samples produced photocurrent densities of 0.270, 0.160, and 0.033 mAcm2, respectively. Mott–Schottky analysis showed that a-Fe2O3:Zn/Ag had the highest free carrier density of 8.75 1020 cm3, while pristine a-Fe2O3, a-Fe2O3:Zn, a-Fe2O3:Ag had carrier densities of 1.57 1019, 5.63 1020, and 6.91 1020 cm3, respectively. Electrochemical impedance spectra revealed a low impedance for a-Fe2O3:Zn/Ag. X-ray diffraction confirmed the rhombohedral corundum structure of hematite. Scanning electron microscopy micrographs, on the other hand, showed uniformly distributed grains with an average size of <30 nm. The films were absorbing in the visible region with an absorption onset ranging from 652 to 590 nm, corresponding to a bandgap range of 1.9 to 2.1 eV. Global analysis of ultrafast transient absorption spectroscopy data revealed four decay lifetimes, with a reduction in the electron-hole recombination rate of the doped samples on a timescale of tens of picoseconds.