Mono-Doped and Co-Doped Nanostructured Hematite for Improved Photoelectrochemical Water Splitting

In this study, zinc-doped ( alpha-Fe2O3:Zn), silver-doped (alpha-Fe2O3:Ag) and zinc/silver codoped hematite ( alpha-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 mAcm(-2) at 1.23 V vs. reversible hydrogen electrode (RHE) was recorded for alpha-Fe2O3:Zn/Ag. The alpha-Fe2O3:Ag, alpha-Fe2O3:Zn and pristine hematite samples produced photocurrent densities of 0.270, 0.160, and 0.033 mAcm(-2), respectively. Mott-Schottky analysis showed that alpha-Fe2O3:Zn/Ag had the highest free carrier density of 8.75 x 10(20) cm(-3), while pristine alpha-Fe2O3, alpha-Fe2O3:Zn, alpha-Fe2O3:Ag had carrier densities of 1.57 x 10(19), 5.63 x 10(20), and 6.91 x 10(20) cm 3, respectively. Electrochemical impedance spectra revealed a low impedance for alpha-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.

Automated summary

Zinc-doped, silver-doped, and zinc/silver codoped hematite nanostructures were synthesized and used as photoanodes for watersplitting. The codoped sample showed the highest photocurrent density and free carrier density, as well as low impedance. The nanostructures exhibited uniformly distributed grains and absorption in the visible region.