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

Abstract

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.

Interfacial insight in multi-junction metal oxide photoanodes for water-splitting applications

“…Moreover, it has been shown theoretically that Sn doping can lead to decreased effective masses of the charge carriers and hence to higher charge carrier mobilities. [33] Since the unfavorable charge transport properties of hematite are considered to be a main reason for high electron-hole recombination rates, an enhancement of the conductivity via doping is a crucial requirement to obtain high photocurrents with hematite photoelectrodes. [34] In the next step we investigated the possible effects of Sn doping on the electrostatic potential within hematite, in order to clarify whether Sn doping might lead to a favorable downward band bending that drives electrons from the hematite bulk to the FTO substrate and holes in the opposite direction.…”

Review of Sn‐Doped Hematite Nanostructures for Photoelectrochemical Water Splitting

“…In these previous reports, the role of Sn doping on the electronic and optical properties of hematite nanostructure has been extensively studied. Based on the first‐principles calculations within the GGA+ U approximation, Sn doping can narrow the bandgap of hematite . The incorporated Sn dopants also lead to a lattice distortion of hematite, which enhancing its optical absorption coefficient .…”

“…Additionally, a more electrically conductive semiconductor electrode can reduce the energy loss due to the internal resistance of electrode and the contact resistance at the semiconductor/back contact interface . The electronic structure calculation based on the first‐principles calculations within the GGA+ U approximation showed that Sn‐doped hematite exhibits an improved electrical conductivity due to the reduction of electron effective mass at the conduction band minimum . Heavily Sn‐doped hematite also appears to have a reduced bandgap, which leads to enhanced utilization ratio of solar energy and the expansion of optical absorption scope …”

“…The electronic structure calculation based on the first‐principles calculations within the GGA+ U approximation showed that Sn‐doped hematite exhibits an improved electrical conductivity due to the reduction of electron effective mass at the conduction band minimum . Heavily Sn‐doped hematite also appears to have a reduced bandgap, which leads to enhanced utilization ratio of solar energy and the expansion of optical absorption scope …”

Atomically Altered Hematite for Highly Efficient Perovskite Tandem Water‐Splitting Devices

“…X-ray diffraction clearly indicates that Sn is present within the crystallized Fe 2 O 3, whereas HRTEM, EDS, and XPS indicatet he formationo faSnO 2 overlayer.E lectronic structure calculations have attributed the effect of Sn doping to be predominantly an increasei nc arrier concentration [30] or even ar eduction in the electron effective masses. [31] Although we have no evidence of mobility improvement,e stimation using Mott-Schottky analysisi ndicates ah igher carrier density for the ALD-treated samples highlighting the doping effect of Sn (relative to untreated Fe 2 O 3 ). However,s uch an increasei nd oping density should reduce the space-charge width, which determines the collection length of the minority carriers being driven towardst he electrolyte interface.…”