We report the first-principles electronic structure of BiVO 4, a promising photocatalyst for hydrogen generation. BiVO 4 is found to be a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center. Coupling between Bi 6s and O 2p forces an upward dispersion of the valence band at the zone boundary; however, a direct gap is maintained via coupling between V 3d, O 2p, and Bi 6p, which lowers the conduction band minimum. These interactions result in symmetric hole and electron masses. Implications for the design of ambipolar metal oxides are discussed. © 2009 American Chemical Society

Substitutional doping can improve the electronic properties of R-Fe 2 O 3 for the solar photoelectrochemical (PEC) applications. Generally speaking, nonisovalent substitutional doping helps to enhance the electronic conductivity of R-Fe 2 O 3 . However, we found that the introduction of strain in the lattice, which is achieved by isovalent substitutional doping of an Al, can also improve the electronic properties. R-Fe 2 O 3 films with the Al dopant atomic concentration varying from 0 to 10% were prepared by electrodeposition, and their performance for photoelectrochemical hydrogen production was characterized. Results indicate that the incident photon conversion efficiency (IPCE) for ∼0.45 at-% Al substitution increases by 2-to 3-fold over undoped samples. Density-functional theory (DFT) was utilized to interpret the experimental findings. It was shown that although no substantial change to the electronic structure, a contraction of the crystal lattice due to the isovalent replacement of Fe 3þ by an Al 3þ benefits the small polaron migration, resulting in an improvement in conductivity compared to the undoped samples.

Aliovalently Al3+ doped strontium titanate enables overall water splitting in type 1 baggie particle suspension reactors in direct sunlight.

No abstract

We present a density-functional theory study on the electronic structure of pure and 3d transition metal ͑TM͒ ͑Sc, Ti, Cr, Mn, and Ni͒ incorporated ␣-Fe 2 O 3. We find that the incorporation of 3d TMs in ␣-Fe 2 O 3 has two main effects such as: ͑1͒ the valence and conduction band edges are modified. In particular, the incorporation of Ti provides electron carriers and reduces the electron effective mass, which will improve the electrical conductivity of ␣-Fe 2 O 3. ͑2͒ The unit cell volume changes systematically such as: the incorporation of Sc increases the volume, whereas the incorporation of Ti, Cr, Mn, and Ni reduces the volume monotonically, which can affect the hopping probability of localized charge carriers ͑polarons͒. We discuss the importance of these results in terms of the utilization of hematite as a visible-light photocatalyst.

No abstract

A density functional theory (DFT) study on stoichiometric bismuth titanate pyrochlore (Bi 2 Ti 2 O 7 -BTO) is presented. Pseudopotential plane wave calculations were carried out to determine band gaps, density of states (DOS), and partial density of states (PDOS) of BTO. The theoretically determined optical property of BTO with a direct band gap of 2.6 eV corresponds to a red shift of 70 nm in absorption activity compared to titanium dioxide (TiO 2 ). A rationale has been developed to determine various possibilities of adding impurity elements within the BTO structure to enhance the visible light absorption. Mainly the effects of 3d element (Fe, Ni, Cr, Mn, and V) substitution in the crystal structure of BTO at the titanium position have been the focus of this study. The substitution of these elements shows the formation of different midgap states which indicates the flexibility of the BTO structure to tunability. Among the elements studied, Fe substitution showed a shift in the valence band toward the conduction band. This band gap reduction may facilitate a better electron transfer process. These theoretical results suggest that BTO can be a promising candidate for photocatalytic applications, such as solar-assisted water splitting reactions.

Solution combustion synthesis (SCS) is shown to be versatile for the rapid-one-pot synthesis of three compounds and four polymorphs in the Cu−V−O ternary family: α-CuV 2 O 6 , αand β-Cu 2 V 2 O 7 , and γ-Cu 3 V 2 O 8. These compounds feature copper/vanadium stoichiometric ratios ranging from 1:1 to 3:1; their structural, electronic, optoelectronic, and photoelectrochemical attributes were comprehensively characterized by a combination of theoretical and experimental techniques. The main contribution of the present study is the demonstration that a range of stoichiometries in this compound family can be derived simply by tuning the precursor mole ratio in the SCS procedure. The Cu−V−O family of samples, derived by SCS, is shown to exemplify the strong effect of compound stoichiometry on the optoelectronic and photoelectrochemical properties. Overall, α-CuV 2 O 6 showed the best performance, rooted in the direct nature of the optical transition in this material. Finally, SCS is very timeefficient and the various compositions can be obtained in a matter of minutes, as opposed to hours or even days in classical solution-based or ceramic synthesis routes.