Predicting a new photocatalyst and its electronic properties by density functional theory

Sarker, Pranab; Prasher, Dixit; Gaillard, Nicolas; Huda, Muhammad N.

doi:10.1063/1.4821429

Cited by 25 publications

(15 citation statements)

References 66 publications

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“…We chose this value of U eff to be consistent with the previous work of a Cu-Bi-O derived compuound. 55 A 9 x 9 x 13 Monkhorst-Pack 56 -point sampling was used for ion relaxation; however, density-of-states (DOS) and optical absorption calculations were done with higher 11 x 11 x 13 -point sampling. For the defect calculations, we constructed a supercell containing 112 atoms.…”

Section: Discussionmentioning

confidence: 99%

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

et al. 2016

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a As a visible light active p-type semiconductor, CuBi2O4 is of interest as a photocatalyst for the generation of hydrogen fuel from water. Here we present the first photovoltage and photocatalytic measurements on this material and DFT results on its band structure. Single crystalline CuBi2O4 nanoparticles (25.7 ± 4.7 nm) were synthesized from bismuth and cupric nitrate in water under hydrothermal conditions. Powder X-ray diffraction (XRD) confirms the CuBi2O4 structure type and UV-Vis spectroscopy observes a 1.75 eV optical band gap. Surface photovoltage (SPV) measurements on CuBi2O4 nanoparticle films on fluorine doped tin oxide yield 0.225 V positive photovoltage at >1.75 eV photon energy confirming holes as majority carriers. The photovoltage is reversible and limited by light absorption. When dispersed in 0.075 M aqueous potassium iodide solution, the CuBi2O4 particles support photochemical hydrogen evolution of up to 16 µmol h-1 under ultraviolet but not under visible light. Based on electrochemical scans, CuBi2O4 is unstable towards reduction at -0.2 V, but pH-dependent photocurrents of 6.45 A cm -2 with an onset potential of +0.75 V vs. NHE can be obtained with 0.01 M Na2S2O8 as a sacrificial electron acceptor. The photoelectrochemical properties of CuBi2O4 can be explained on the basis of the band structure of the material. DFT calculations show the valence and conduction band edges to arise primarily from the combination of O 2p and Cu 3d orbitals, respectively, with additional contributions from Cu 3d and Bi 6s orbitals just below the Fermi level. Trapping of photoelectrons in the Cu 3d band is the cause for reductive photocorrosion of the material, while the p-type conductivity arises from copper vacancy states near the VB edge. These findings provide an improved understanding of the photophysical properties of p-CuBi2O4 and its limitations as a proton reduction photocatalyst.A) The DFT+U electronic band structures of (left) pristine CuBi2O4 and (right) VCu -CuBi2O4. The Fermi level (EF) is set at 0 eV. The presence of VCu leads to partial occupation of the bands around the VB edge. This gives rise to p-type behavior in CuBi2O4. B) The DFT+U projected density of states of VCu -CuBi2O4.

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Section: Discussionmentioning

confidence: 99%

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

et al. 2016

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“…Spin-polarized DFT calculations were performed with VASP. , Our calculations used the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional to properly describe the Cu ions with oxidation state 2+ and open-shell 3d 9 orbitals in CuBi 2 O 4 . Previous first principles calculations for CuBi 2 O 4 , Cu–Bi–O-derived materials, and other p-type semiconductors with Cu 2+ ions such as CuO and CuAl 2 O 4 have used the generalized gradient approximation plus the Hubbard U (DFT + U ) approach − with a large value of the Hubbard U parameter (∼7 eV) to correct the well-known DFT band gap underestimation. However, as shown below, we find that hybrid functionals are required to properly describe the electronic properties of CuBi 2 O 4 .…”

Section: Methodsmentioning

confidence: 99%

CuBi₂O₄: Electronic Structure, Optical Properties, and Photoelectrochemical Performance Limitations of the Photocathode

et al. 2021

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As CuBi 2 O 4 is an emerging p-type semiconductor for applications as a photocathode in photoelectrochemical (PEC) solar fuel production, there is much to be understood about the uniqueness and commonalities the material exhibits in comparison to other, more well-known metal oxide semiconductor systems. We examine p-CuBi 2 O 4 thin films grown by reactive co-sputtering with a comprehensive spectroscopic and first principles characterization methodology to describe its fundamental electronic structure and optical properties while addressing intrinsic limitations in the observed PEC performance. The optical properties are evaluated from 180 to 2500 nm with a multi-modal approach using spectroscopic ellipsometry, UV−vis, and photothermal deflection spectroscopy to obtain the complex dielectric function and 5 orders of magnitude of the absorption coefficient. The films are evaluated under PEC conditions appropriate for CO 2 reduction conditions (0.1 M HCO 3 2− ) with the inclusion of electron scavenger (S 2 O 8 2− ) to minimize catalytic limitations. While the theoretical maximum photocurrent density was 4.68 mA cm −2 , the realized photocurrent was 1.18 mA cm −2 with front-side illumination and an onset potential of about 1.1 V RHE . The thickness dependence of the photocurrent under back-side illumination exposed a limited electron diffusion length of 45 nm attributed to electron small polaron transport. Connections are established between electronic structure, optical properties, and PEC performance through a combination of X-ray spectroscopies (X-ray absorption spectroscopy, X-ray emission spectroscopy, resonant inelastic X-ray scattering, and X-ray photoelectron spectroscopy) and ab initio modeling. These results not only provide the basis for understanding the observed polaron limitations but also form the basis of a broader connection to other material systems which are governed by polaronic limitations. This study provides a conceptual framework to interconnect observations made through the multiple types of advanced characterization methodologies presented. Ultimately, this work aims to assist the development of CuBi 2 O 4 beyond its intrinsic limitations for its application in solar fuel production.

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“…Currently, the scientific studies on the electronic properties of pure and doped CuWO 4 have been mainly focused on the photocatalytic (PC) degradation of organic dyes (Rhodamine B, eosin yellow dye and methylene blue) under ultraviolet and visible light [53][54][55], magnetic [56][57][58][59], photoelectrochemical water splitting [60][61][62][63][64], visible and solar-assisted water splitting [65,66], photoanode for solar water oxidation [67,68], electrical transport [69], and photoluminescence (PL) [24,53,70]. An important point to be considered is that the theoretical studies [16,[71][72][73][74][75], performed by means of ab initio calculations based on the density-functional theory (DFT) for the electronic structure of CuWO 4 crystals, have shown that the conduction band (CB) of this oxide is composed of 3d orbitals (Cu atoms) and 5d orbitals (W atoms), while the valence band (VB) is formed of 2p orbitals (O atoms).…”

Section: Introductionmentioning

confidence: 99%

Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals

Souza

Sczancoski

Nogueira

et al. 2017

Ultrasonics Sonochemistry

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Copper tungstate (CuWO) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1h. The structural evolution, growth mechanism and photoluminescence (PL) properties of these crystals were thoroughly investigated. X-ray diffraction patterns, micro-Raman spectra and Fourier transformed infrared spectra indicated that crystals heat treated and 100°C and 200°C have water molecules in their lattice (copper tungstate dihydrate (CuWO·2HO) with monoclinic structure), when the crystals are calcinated at 300°C have the presence of two phase (CuWO·2HO and CuWO), while the others heat treated at 400°C and 500°C have a single CuWO triclinic structure. Field emission scanning electron microscopy revealed a change in the morphological features of these crystals with the increase of the heat treatment temperature. Transmission electron microscopy (TEM), high resolution-TEM images and selected area electron diffraction were employed to examine the shape, size and structure of these crystals. Ultraviolet-Visible spectra evidenced a decrease of band gap values with the increase of the temperature, which were correlated with the reduction of intermediary energy levels within the band gap. The intense photoluminescence (PL) emission was detected for the sample heat treat at 300°C for 1h, which have a mixture of CuWO·2HO and CuWO phases. Therefore, there is a synergic effect between the intermediary energy levels arising from these two phases during the electronic transitions responsible for PL emissions.

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Predicting a new photocatalyst and its electronic properties by density functional theory

Cited by 25 publications

References 66 publications

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

CuBi₂O₄: Electronic Structure, Optical Properties, and Photoelectrochemical Performance Limitations of the Photocathode

Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals

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Predicting a new photocatalyst and its electronic properties by density functional theory

Cited by 25 publications

References 66 publications

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi2O4 nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi2O4 nanocrystals

CuBi2O4: Electronic Structure, Optical Properties, and Photoelectrochemical Performance Limitations of the Photocathode

Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals

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Product

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Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

CuBi₂O₄: Electronic Structure, Optical Properties, and Photoelectrochemical Performance Limitations of the Photocathode