Metal-Insulator Transitions in β′-Cu V2O5 Mediated by Polaron Oscillation and Cation Shuttling

Parija, Abhishek; Handy, Joseph V.; Andrews, Justin L.; Wu, Jinpeng; Wangoh, Linda; Singh, Sujay; Bostwick, Aaron; Rotenberg, Eli; Yang, Wanli; Fakra, Sirine C.; Al‐Hashimi, Mohammed; Sambandamurthy, G.; Piper, Louis F. J.; Williams, R. Stanley; Banerjee, Sarbajit

doi:10.1016/j.matt.2020.01.027

Cited by 12 publications

(6 citation statements)

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“…These results would therefore justify how in a system with 3d x 2 – y 2 VBM and CBM could result in poor back-side illuminated PEC performance. Such a conceptual model could be useful to understand other polaronic systems such as p-CuFeO 2 (electron polaron in transient Fe 2+ 3d 6 CB) and n-BiVO 4 (electron polaron in transient V 4+ 3d 1 CB). , While efficacy of computational methods to evaluate polaron formation − and transport as has been demonstrated previously, the HSE evaluation of polarons in CuBi 2 O 4 would be better addressed in a follow-up article. However, our findings herein should represent an additional jumping-off point for such a focused article which would hopefully also lead to novel doping methods to extend the diffusion lengths.…”

Section: Resultsmentioning

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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Section: Resultsmentioning

confidence: 99%

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

et al. 2021

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“…For 0.33 < x < 0.66, a 5coordinate β′ position is instead favored for smaller cations, with β′-Cu 0.5 V 2 O 5 (Figure 3A) further exhibiting a split-site disorder at this position, the oscillation of which gives rise to polaron destabilization at high temperature, inducing a strong metal− insulator transition (larger cations tend to be limited to a stoichiometry of ∼0.33 for this framework). 56 When subjected to a large driving force for intercalation, an entire continuum of crystallographic sites including an unusual 2-coordinate position have been identified in ζ-V 2 O 5 to accommodate Li-ions, with the extended V 2 O 5 framework exhibiting remarkable durability across multiple transformations. 57 The removal and insertion of different guest cations while leaving the overall V 2 O 5 framework intact then allows for exploration of metastable V 2 O 5 phase space and distorted empty structures as hosts for the insertion of lone-pair cations with many interstices available for site-selective positioning.…”

Section: Lone-pair-derived Electronic States and Photocatalysismentioning

confidence: 99%

“…In stoichiometries of approximately 0 < x < 0.33, this structure hosts guest cations in the crystallographic β site, with relatively small cations (e.g., Li + in β-Li 0.33 V 2 O 5 ) assuming a 5-fold coordination geometry and larger metal ions (e.g., Pb 2+ in and β-Pb 0.3 V 2 O 5 ) assuming a highly distorted 7-fold coordination geometry (Figure A). For 0.33 < x < 0.66, a 5-coordinate β′ position is instead favored for smaller cations, with β′-Cu 0.5 V 2 O 5 (Figure A) further exhibiting a split-site disorder at this position, the oscillation of which gives rise to polaron destabilization at high temperature, inducing a strong metal–insulator transition (larger cations tend to be limited to a stoichiometry of ∼0.33 for this framework) . When subjected to a large driving force for intercalation, an entire continuum of crystallographic sites including an unusual 2-coordinate position have been identified in ζ-V 2 O 5 to accommodate Li-ions, with the extended V 2 O 5 framework exhibiting remarkable durability across multiple transformations .…”

Section: Lone-pair-derived Electronic States and Photocatalysismentioning

confidence: 99%

Lone but Not Alone: Precise Positioning of Lone Pairs for the Design of Photocatalytic Architectures

et al. 2022

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With current economic growth and consumption trends projected to bring about a precipitous and rapid rise of the global temperature, the world stands at a crossroads with regards to climate change. The rate at which greenhouse gas emissions from fossil fuels, industry, and land-use is curtailed over the next decade will determine the trajectory of global warming for the rest of the century. It is increasingly apparent that far-reaching decarbonization of the transportation infrastructure will need to be supplemented by extensive carbon capture, storage, and utilization. Taking a leaf from Nature's playbook, photocatalytic architectures that can utilize water or CO 2 in conjunction with energy harvested from sunlight and store it in the form of energy-dense chemical bonds represent an attractive proposition. Harnessing solar irradiance, through solar energy conversion involving photovoltaics, as well as the photocatalytic generation of solar fuels, and the photocatalytic reduction of CO 2 have emerged as urgent imperatives for the energy transition. Functional photocatalysts must be capable of efficiently absorbing sunlight, effectively separating electronhole pairs, and ensuring they are delivered at appropriate potentials to catalytic sites to mediate redox reactions. Such photocatalytic architectures must further direct redox events down specific pathways to yield desired products, and ensure the transport of reactants between catalytic sites; all with high efficiency and minimal degradation. In this Perspective, we describe a palette of heterostructures designed to promote robust and efficient direct solar-driven water splitting and CO 2 reduction. The heterostructures comprise M x V 2 O 5 or M x M y ′V 2 O 5 , where M is a p-block cation, M′ is an s-, p-, or d-block cation, and V 2 O 5 represents one of multiple polymorphs of this composition interfaced with semiconductor quantum dots (QDs, binary or ternary II−VI or III−V QDs). The stereochemically active 5/6s 2 electron lone pairs of p-block cations in M x V 2 O 5 give rise to filled midgap electronic states that reside above the O 2p-derived valence band. Within heterostructures, the photoexcitation of QDs results in the transfer of holes to the midgap states of M x V 2 O 5 or M x M y ′V 2 O 5 on subpicosecond time scales. Ultrafast charge separation minimizes the photoanodic corrosion of QDs, which has historically been a major impediment to their use in photocatalysis, and enables charge transport and the subsequent redox reactions underpinning photocatalysis to compete with electron−hole recombination. The energy positioning and dispersion of lone pair states is tunable through multiple chemical and compositional levers accessible across the palette of M x V 2 O 5 or M x M y ′V 2 O 5 compounds: choice of lone-pair cation M and its stoichiometry x, atomic connectivity of V 2 O 5 polymorphs, cointercalation of M′ cations in "quaternary" vanadium oxide bronzes, anionic substitution, and alternative lone pair vanadate frameworks with altogether different c...

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“…Millimeter-sized single-crystals of b'-Cu 0.64 V 2 O 5 with a black lustrous appearance have been obtained from melt growth as described in the Experimental Section. [20] Cu-ions are leached by treatment with a 0.21m aqueous solution of Na 2 S 2 O 8 . Leaching of Cu ions is initiated at the crystal edges and can be visualized by optical microscopy.…”

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An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

et al. 2020

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The diffusion pathways of Li‐ions as they traverse cathode structures in the course of insertion reactions underpin many questions fundamental to the functionality of Li‐ion batteries. Much current knowledge derives from computational models or the imaging of lithiation behavior at larger length scales; however, it remains difficult to experimentally image Li‐ion diffusion at the atomistic level. Here, by using topochemical Li‐ion insertion and extraction to induce single‐crystal‐to‐single‐crystal transformations in a tunnel‐structured V2O5 polymorph, coupled with operando powder X‐ray diffraction, we leverage single‐crystal X‐ray diffraction to identify the sequence of lattice interstitial sites preferred by Li‐ions to high depths of discharge, and use electron density maps to create a snapshot of ion diffusion in a metastable phase. Our methods enable the atomistic imaging of Li‐ions in this cathode material in kinetic states and provide an experimentally validated angstrom‐level 3D picture of atomic pathways thus far only conjectured through DFT calculations.

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Metal-Insulator Transitions in β′-Cu V2O5 Mediated by Polaron Oscillation and Cation Shuttling

Cited by 12 publications

References 74 publications

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

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

Lone but Not Alone: Precise Positioning of Lone Pairs for the Design of Photocatalytic Architectures

An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

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Metal-Insulator Transitions in β′-Cu V2O5 Mediated by Polaron Oscillation and Cation Shuttling

Cited by 12 publications

References 74 publications

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

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

Lone but Not Alone: Precise Positioning of Lone Pairs for the Design of Photocatalytic Architectures

An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

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

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