Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTa<sup>IV</sup>O<sub>2</sub>N

Bubeck, Cora; Widenmeyer, Marc; Denko, Alexandra T. De; Richter, Gunther; Coduri, Mauro; Salas‐Colera, Eduardo; Goering, E.; Zhang, Hongbin; Yoon, Songhak; Osterloh, Frank E.; Weidenkaff, Anke

doi:10.1039/d0ta02136a

Cited by 12 publications

(11 citation statements)

References 79 publications

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“…The corresponding photovoltage (ΔCPD) is caused by the transfer of photogenerated charge carriers toward or away from the Kelvin probe . This provides information about the majority carrier type, the effective band gap, defects, and the photochemistry of the sample, as detailed in previous studies. ,− …”

Section: Results and Discussionmentioning

confidence: 94%

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

et al. 2021

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Metavanadates MV 2 O 6−δ (M = Zn and Cu) are synthesized by using a deep eutectic solvent (DES), a mixture of hydrogen bond donor and acceptor, as a reaction medium. Dissolution of stable binary metal oxides in a DES followed by a heat treatment yields phase-pure vanadates. According to in situ powder X-ray diffraction, ternary phases (α-Zn 2 V 2 O 7 and β-Cu 2−x V 2 O 7 , x ∼ 0.27) are intermediates in the reaction pathway taken. Identifying a polymorphic phase transformation temperature for CuV 2 O 6 as well as the narrow temperature range between formation and decomposition for both metavanadates allows for tackling the challenge of the synthesis of these materials. The oxygen vacancy introduced by the DES route is accompanied by the formation of reduced V 4+ and Cu + in the oxide matrix, based on X-ray photoelectron spectroscopy. These oxygen vacancies modify the vibrational modes in the corresponding Raman spectra and are also responsible for broad optical absorptions in the 1.8−1.1 eV range. The optical band gaps of the materials are found at 1.8 eV (CuV 2 O 6 ) and 2.2 eV (ZnV 2 O 6 ), approximately 0.1−0.3 eV below the values reported in the literature. The reduced band gaps and sub-band gap photon absorption are key features of the oxygendeficient metavanadates. Surface photovoltage spectroscopy reveals that all the synthesized vanadates are n-type materials with electrons as the majority charge carriers, and photoelectrochemical measurements confirm photoanodic currents for methanol oxidation. These results provide insight into the synthesis and structure−property relationship of the metavanadates for their potential use as photoanodes.

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Section: Results and Discussionmentioning

confidence: 94%

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

et al. 2021

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“…31 Regarding the electronic properties, tuning of the band gap has been achieved in Y-substituted LaTaO 2 N from an orthorhombic strain. 32 From the perspective of photocatalysis, controlling the morphological and structural variations of LaTiO 2 N and CoO x nanoparticles could influence the strain in the structure and hence promote the photocatalytic O 2 evolution. 33 It has also been reported that Au−SrTiO 3 with tensile strain, where the strain is induced by the difference of the thermal expansion coefficient between Au and SrTiO 3 , shows 10.5 times higher photocatalytic activity for water splitting than the unstrained Au−SrTiO 3 .…”

Section: ■ Introductionmentioning

confidence: 99%

“…Furthermore, a ferroelectric response in tensile-strained SrTaO 2 N films is observed due to a change of the anion ordering as a function of the applied strain . Regarding the electronic properties, tuning of the band gap has been achieved in Y-substituted LaTaO 2 N from an orthorhombic strain . From the perspective of photocatalysis, controlling the morphological and structural variations of LaTiO 2 N and CoO x nanoparticles could influence the strain in the structure and hence promote the photocatalytic O 2 evolution .…”

Section: Introductionmentioning

confidence: 99%

Theoretical Insight on Anion Ordering, Strain, and Doping Engineering of the Oxygen Evolution Reaction in BaTaO₂N

2021

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Oxynitride perovskites such as BaTaO 2 N are among the most promising materials to achieve efficient direct solar-to-chemical conversion. Albeit photoelectrochemical water splitting has been demonstrated, the required overpotentials remain prohibitively large compared with the theoretically accessible values, particularly for the oxygen evolution reaction (OER). Here, we apply density functional theory (DFT) calculations to investigate the use of strain and cationic doping with Ca and Sr to optimize the OER theoretical overpotential. For the TaON-terminated BaTaO 2 N (001) surface, 4% compressive uniaxial strain can lower the theoretical overpotential to η = 0.59 V, under operational conditions. For the most stable TaO 2 N-(100) termination, 1% tensile uniaxial strain, which is perfectly accessible by experiments, is enough to reduce the theoretical overpotential from η = 0.43 V to η = 0.37 V under (photo)electrochemical conditions. This value is close to the minimum predicted theoretical overpotential and points out how strain engineering could be efficiently used to improve the electrocatalytic reactions.

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“…Magnetism measurements suggest that reduced Ta species such as Ta 4+ are also present in the bulk (Figure S15). These defects appear to be intrinsic and are widely seen in many Ta-based metal oxynitrides subject to high temperature ammonolysis. ,− These defects often act as deep trapping sites or recombination centers which are detrimental to photocatalytic activity. , A very short diffusion length of photocarriers is expected for LaTaON 2 as these defects are electronically active in capturing photocarriers. , In this regard, PSCs with thin skeletons would be extremely useful in maximizing photocarriers’ migration from bulk to the surface. This is clearly reflected from a large activity difference between LaTaON 2 -P and LaTaON 2 -S for photocatalytic water oxidation into O 2 .…”

Section: Resultsmentioning

confidence: 99%

LaTaON₂ Mesoporous Single Crystals for Efficient Photocatalytic Water Oxidation and Z-Scheme Overall Water Splitting

Chang

Wang

et al. 2021

ACS Nano

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LaTaON2 porous single crystals (PSCs), integrating structural coherence and porous microstructures, will warrant promising photocatalytic performance. The absence of grain boundaries in PSCs ensures rapid photocarrier transportation from bulk to the surface, thereby mitigating photocarriers’ recombination. Porous microstructures not only provide ample reachable surface to host photochemical reactions but also reinforce photon-matter interactions by additional photon reflection/scattering. Here, we have synthesized LaTaON2 PSCs via a topotactic route and show significantly improved photocatalytic performance. Efficient water oxidation into O2 has been realized by LaTaON2 PSCs with an apparent quantum efficiency as high as 5.7% at 420 ± 20 nm. Stable overall water splitting into stoichiometric H2 and O2 has also been achieved in a Z-scheme setup using LaTaON2 PSCs as the O2 evolution photocatalyst. These results not only prove that PSCs facilitate photocarrier migrations, which in turn deliver exceptional photocatalytic performance, but also imply that PSCs are useful to reinvigorate conventional semiconductor photocatalysts toward efficient solar energy conversions.

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Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTa^IVO₂N

Abstract:
Microstructure controlled ammonolysis allowed the synthesis of oxynitrides La_1−xY_xTa^IVO₂N (x ≤ 0.3) and YTa(O,N)₃ of which the first ones showed a remarkable up-built of photovoltage even in the presence of reduced tantalum (e.g. Ta⁴⁺).

Cited by 12 publications

References 79 publications

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Theoretical Insight on Anion Ordering, Strain, and Doping Engineering of the Oxygen Evolution Reaction in BaTaO₂N

LaTaON₂ Mesoporous Single Crystals for Efficient Photocatalytic Water Oxidation and Z-Scheme Overall Water Splitting

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Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTaIVO2N

Abstract: Microstructure controlled ammonolysis allowed the synthesis of oxynitrides La1−xYxTaIVO2N (x ≤ 0.3) and YTa(O,N)3 of which the first ones showed a remarkable up-built of photovoltage even in the presence of reduced tantalum (e.g. Ta4+).

Cited by 12 publications

References 79 publications

Local Structural Disorder in Metavanadates MV2O6 (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Local Structural Disorder in Metavanadates MV2O6 (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Theoretical Insight on Anion Ordering, Strain, and Doping Engineering of the Oxygen Evolution Reaction in BaTaO2N

LaTaON2 Mesoporous Single Crystals for Efficient Photocatalytic Water Oxidation and Z-Scheme Overall Water Splitting

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Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTa^IVO₂N

Abstract:
Microstructure controlled ammonolysis allowed the synthesis of oxynitrides La_1−xY_xTa^IVO₂N (x ≤ 0.3) and YTa(O,N)₃ of which the first ones showed a remarkable up-built of photovoltage even in the presence of reduced tantalum (e.g. Ta⁴⁺).

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Local Structural Disorder in Metavanadates MV₂O₆ (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Theoretical Insight on Anion Ordering, Strain, and Doping Engineering of the Oxygen Evolution Reaction in BaTaO₂N

LaTaON₂ Mesoporous Single Crystals for Efficient Photocatalytic Water Oxidation and Z-Scheme Overall Water Splitting