Sn-doped Hematite Research Articles

Array fabrication and photoelectrochemical properties of Sn-doped vertically oriented hematite nanorods for solar cells

We report on the synthesis and characterization of Sn-doped hematite nanorods as well as their implementation as the photoanode for solar cells. Hematite nanorods are prepared on fluorine-doped tin oxide (FTO) substrates by a hydrothermal method, followed by a two-step sintering in air, and Sn-doping is achieved by adding SnCl4 into the mixture solution during the hydrothermal process. In comparison to un-doped hematite, Sn-doped hematite nanorods exhibit a higher array growth density along the direction [110], which indicates that the Sn-doping can facilitate the vertically oriented growth of the hematite nanorod arrays; moreover, the Sn-doping can result in enhanced photocurrent density and photoelectrical efficiency due to the improved carrier density. These new findings will provide new information to enhance the photoelectrochemical characteristics of hematite, one of the best potential photoanode materials.

Theoretical Understanding of Enhanced Photoelectrochemical Catalytic Activity of Sn-Doped Hematite: Anisotropic Catalysis and Effects of Morin Transition and Sn Doping

To investigate the influence of the Morin transition on the photoelectrochemical (PEC) activity of hematite, electronic properties in different magnetic phases were studied on the basis of the first-principles calculations within the GGA+U approximation. The results show that the effective electron mass in the (0001) plane changes remarkably due to the spin–flop transition, while the effective electron masses in other Miller planes are not sensitive to the spin orientation around irons. The electronic structure calculations of Sn-doped hematite predict that the improved PEC activities of Sn-doped hematite are proved to arise from a shrinking of the band gap, decreasing of the effective electron mass, and thus enhanced electronic conductivity. More interestingly, the heavier doping of Sn (≥16.7 atom %) in hematite would induce a new level between the valence band maximum (VBM) and Fermi level E_F, which facilitates its PEC activity of visible light water splitting.

Sn-Doped Hematite Nanostructures for Photoelectrochemical Water Splitting

We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn(4+) substitution at Fe(3+) sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm(2) at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm(2) at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron-hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.

Structural and magnetic analysis of the transformation of Sn-doped magnetite to Sn-doped hematite by mechanical milling

Spinel-related Sn-doped Fe3O4 has been ball milled for different times up to 35h. Milling was found to transform the material to corundum-related Sn-doped α-Fe2O3. The influence of the milling time, the crystallite size, and the cationic distribution on transformation process is being analyzed with x-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The relatively fast spinel-to-corundum structural transformation observed is associated with more Fe3+ ions being reduced to Fe2+ due to doping with Sn4+ ions.