Soft X-ray spectroscopic studies of the electronic structure of M:BiVO<sub>4</sub>(M = Mo, W) single crystals

Jovic, Vedran; Laverock, J.; Rettie, Alexander J. E.; Zhou, Jianshi; Mullins, C. Buddie; Singh, V. R.; Lamoureux, Bethany; Wilson, David J.; Su, Tzu‐Sen; Jović, Branislav; Bluhm, Hendrik; Söhnel, Tilo; Smith, Kevin

doi:10.1039/c5ta07898a

Cited by 38 publications

(75 citation statements)

References 40 publications

(116 reference statements)

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“…2 (b) and indicate the presence of V 5+ in monoclinic scheelite structure of BiVO4. 11,30 It is immediately clear that the L3 edge, shows increased spectral weight at higher energies (just above the t2 peak) for E||ab relative to E||c. This observation is also evident at the L2 edge.…”

Section: Resultsmentioning

confidence: 99%

“…11 Note that survey and O 1s spectra collected after 300 o C heat treatment in a 1×10 -6 Torr oxygen atmosphere are shown in Supplementary Fig. 1 (a)-(b).…”

Section: Resultsmentioning

confidence: 99%

“…Based on formerly determined band gap energies of 2.5-2.7 eV, the EF in Fig. 1(a) is closer to the conduction band (CB) onset (indicating that the sample is n-type). 6,11 Briefly, the BiVO4 VB density of states contains strong contributions from O 2p states extending to ~6 eV below the EF, along with Bi 6p and V 3d states at ~8-4 eV (green in Fig. 1 (a)).…”

Section: Resultsmentioning

confidence: 99%

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A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

Jovic

Rettie

Singh

et al. 2016

Phys. Chem. Chem. Phys.

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(2016). A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals. Physical Chemistry Chemical Physics, 18(46) Abstract: Doped BiVO4 is a promising photoelectrochemical water splitting anode, whose activity is hampered by poor charge transport. Here we use a set of x-ray spectroscopic methods to probe the nature of localized electron states in W:BiVO4 and variations in the electronic structure along the crystal axes related to the materials conductivity anisotropy. We verify that tungsten substitutes as W 6+ for V 5+ in BiVO4. This results in the presence of inter-band gap states related to electrons at V 4+ sites of e symmetry. The energetic position of the states in the 2 band gap suggest that they are highly localized and may act as recombination centres.Polarization dependent x-ray absorption spectra reveal anisotropy in the electronic structure between the ab-plane and c-axis. Results show the superior hybridization between V 3d and O 2p states, higher V wavefunction overlap and broader conduction bands in the ab-plane than in the c-axis. These insights into the electronic structure are discussed in the context of existing experimental and theoretical reports regarding charge transport in BiVO4.

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Section: Resultsmentioning

confidence: 99%

“…11 Note that survey and O 1s spectra collected after 300 o C heat treatment in a 1×10 -6 Torr oxygen atmosphere are shown in Supplementary Fig. 1 (a)-(b).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

Jovic

Rettie

Singh

et al. 2016

Phys. Chem. Chem. Phys.

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“…[13][14][15][16][17][18][19] The underlying origin of the observed performance improvement remains an active area of investigation, with spectroscopic studies indicating a decrease in electron trap state concentration producing an increase in electron and hole mobilities 10 and/or increased charge carrier concentration induced by electron donating elements, in particular W and Mo. 20 Changes in the band gap and movement of band edges have also been reported. 21 Several combinatorial studies have contributed to this broad mBiVO4 alloying effort through systematic variation of alloy concentration using wet chemical synthesis or physical vapor deposition techniques.…”

Section: Introductionmentioning

confidence: 99%

Combinatorial alloying improves bismuth vanadate photoanodes via reduced monoclinic distortion

Newhouse

Guevarra

Umehara

et al. 2018

Energy Environ. Sci.

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Improving the efficiency of solar-power oxygen evolution is both critical for development of solar fuels technologies and challenging due to the broad set of properties required of a solar fuels photoanode. Bismuth vanadate, in particular the monoclinic clinobisvanite phase, has received substantial attention and has exhibited the highest radiative efficiency among metal oxides with a band gap in the visible range. Efforts to further improve its photoelectrochemical performance have included alloying one or more metals onto the Bi and/or V sites, with progress on this frontier stymied by the difficulty in computational modelling of substitutional alloys and the high dimensionality of co-alloying composition spaces. Since substituional alloying simultaneously changes multiple materials properties, understanding the underlying cause for performance improvements is also challenging, motivating our application of combinatorial materials science techniques to map photoelectrochemical performance of 948 unique bismuth vanadate alloy compositions comprising 0 to 8% alloys of P, Ca, Mo, Eu, Gd, and W along with a variety of compositions from each pairwise combination of these elements. Upon identification of substantial improvements in the (Mo,Gd) co-alloying space, structural mapping was performed to reveal a remarkable correlation between performance and a lowered monoclinic distortion. First-principles density functional theory calculations indicate that the improvements are due to a lowered hole effective mass and hole polaron formation energy, and collectively, our results identify the monoclinic distortion as a critical parameter in the optimization and understanding of bismuth vanadate-based photoanodes. IntroductionThe production of fuels via photoelectrochemistry (PEC) has been recognized as a promising method for capturing and storing intermittent solar energy, in particular as renewable transportation fuels. 1 Regardless of the fuel to be generated, the oxygen evolution reaction at the photoanode is critical; hence development of stable, efficient, n-type semiconductors composed of earth abundant elements and producible by scalable, cost-effective methods has received increasing research attention. [2][3][4] Bismuth vanadate, BiVO4, in particular has become the oxide semiconductor serving as the platform to develop and demonstrate a toolkit of techniques for improving and understanding the fundamental properties and photoelectrochemical performance of novel oxide-based semiconductors, despite its non-optimal bandgap. 2,5 As recently reviewed, the methods of improving the properties include heterojunction formation, alloying or doping, hydrogen or nitrogen annealing, nanostructuring to enhance charge collection, microstructuring for photon management, and surface coating to passivate surface defects and enhance catalysis. 3,4,[6][7][8][9] The highest performing BVO-based photoanodes reported to date have all incorporated several of these strategies in order to produce photocurrent densities in the range of app...

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“…Through the RIXS investigations, the aforementioned blue-shift of the X-ray emission, which corresponds to the occurrence of the indirect bandgap, has been seen in diamond, Be chalcogenides, metal doped and pristine BiVO 4 , and Fe 2 O 3 . [37][38][39][40][41] To further demonstrate the correlation between size and band gap we refer to previous studies on the electronic properties of Fe 2 O 3 by Vayssieres et al 40,42 Previously, observed at the high emission energy region. The blue-shift of the emission spectra is a strong indication that Fe 2 O 3 is an indirect bandgap semiconductor.…”

Section: Studies Of Pristine 3d Tmos: Size Effects On the Tio 2 Fe mentioning

confidence: 99%

X-ray spectroscopies studies of the 3d transition metal oxides and applications of photocatalysis

Kapilashrami

Chuang

et al. 2017

MRS Communications

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Abstract:Recent advances in synchrotron based X-ray spectroscopy enable materials scientists to emanate finger prints on important materials properties e.g. electronic, optical, structural and magnetic properties, in real time and under nearly real-world conditions. This characterization in combination with optimized materials synthesis routes and tailored morphological properties could contribute greatly to the advances in solid-state electronics and renewable energy technologies. In connection to this, such perspective reflects the current materials research in the space of emerging energy technologies, namely photocatalysis, with a focus on transition metal oxides (TMOs), mainly on the Fe 2 O 3 and TiO 2 based materials.

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Soft X-ray spectroscopic studies of the electronic structure of M:BiVO₄(M = Mo, W) single crystals

Abstract: X-ray spectroscopy reveals the presence of inter-band gap electronic states of egsymmetry in M:BiVO4(M = Mo, W) PEC anodes.

Cited by 38 publications

References 40 publications

A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

Combinatorial alloying improves bismuth vanadate photoanodes via reduced monoclinic distortion

X-ray spectroscopies studies of the 3d transition metal oxides and applications of photocatalysis

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Soft X-ray spectroscopic studies of the electronic structure of M:BiVO4(M = Mo, W) single crystals

Abstract: X-ray spectroscopy reveals the presence of inter-band gap electronic states of egsymmetry in M:BiVO4(M = Mo, W) PEC anodes.

Cited by 38 publications

References 40 publications

A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

Combinatorial alloying improves bismuth vanadate photoanodes via reduced monoclinic distortion

X-ray spectroscopies studies of the 3d transition metal oxides and applications of photocatalysis

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Soft X-ray spectroscopic studies of the electronic structure of M:BiVO₄(M = Mo, W) single crystals