Vanadium Oxide Layers Research Articles

Memristive response of a new class of hydrated vanadium oxide intercalation compounds

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Nanostructured layered vanadium oxide as cathode for high-performance sodium-ion batteries: a perspective

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Promising zinc-ion battery cathode created

The projected low cost and inherent safety of rechargeable aqueous zinc-ion batteries make energy storage devices based on the technology seem like a real winner. Large stationary versions of such batteries could be particularly useful for grid storage applications involving intermittent power sources such as wind turbines and solar panels. But the batteries haven’t gotten off the ground yet, mainly because of unsatisfactory cathodes, which cause the devices to act sluggishly and die quickly. University of Waterloo researchers led by Linda F. Nazar have now come up with a layered vanadium oxide featuring interlayer zinc ions and water molecules that seems to bypass those problems (Nat. Energy 2016, DOI: 10.1038/nenergy.2016.119). The team used a microwave-driven hydrothermal method to synthesize ribbonlike single crystals of Zn0.25V2O5•nH2O (n = 0.85–1.0) and fashioned cathodes from thin films of the material. They paired the cathodes with metallic zinc anodes to make test cells. Analyses based

Vanadium-Based Nanomaterials As Cathodes for Mg-Ion Batteries

Exchanging the active specie, Li+ in Li-ion batteries by multivalent, abundant and cheap cations, such as Mg2+, are projected to boost the energy density and lower the cost per kilo-watt-hour significantly, making the Mg-ion battery technology a promising candidate for one of the battery technologies of the future.1,2 The increase in energy density is i.a. a result of the divalent Mg2+ carrying twice as much charge as the monovalent Li+.1,2 However, the higher charge also poses a problem as it significantly increases the charge density of the ion, which results in stronger interactions with the host lattice of the electrodes and hampers facile ion transport. Therefore, development of novel electrode materials for effective Mg-ion storage is a vital step for the realization of this battery technology.3 In this study, we have synthesized series of vanadium oxides with varying chemical composition and varying nanotopologies, e.g. nanosheets, xerogels and nanotubes. The mechanism for Mg-intercalation and deintercalation is studied by electroanalysis, impedance spectroscopy and through operando synchrotron powder X-ray diffraction measured during battery operation. These results show e.g. that Mg-intercalation in multivalled V7O16-nanotubes occurs within the space between the individual vanadium oxide layers building the walls of the nanotubes while the underlying V7O16 frameworks constructing the walls are affected only to a minor degree by the intercalation. Our investigation provides new insights into the size requirements of the channels/layers in the host frameworks that will allow for efficient Mg-ion storage. Reference: R. van Noorden, Nature 2014, 507, 26Pellion Technologies, “Moving Beyond Lithium with Low-Cost, High-Energy, Rechargeable Magnesium Batteries”, Pellion White Paper, September 2011P. Saha, M. K. Datta, O. I. Velikokhatnyi, A. Manivannan, D. Alman, P. N. Kumta, Progress in Materials Science 2014, 66, 1.

Thin films of pure vanadium nitride: Evidence for anomalous non-faradaic capacitance

An impressive gravimetric capacitance of 1300 F g−1 (surface capacitance ∼3.3 mF cm−2) reported by Choi et al., 2006 for nanosized vanadium nitride has stimulated considerable interest in vanadium nitride as a potential electrode material for energy storing systems – supercapacitors. The postulated mechanism of charge storage in vanadium nitride materials involves redox reactions in the thin surface layer of vanadium oxide while the core vanadium nitride serves exclusively as a conducting platform. In this study we have synthesized pure oxygen-free vanadium nitride films and have found that they are capable of delivering a surface capacitance of up to ∼3 mF cm−2 at a potential scan rate of 3 mV s−1 and ∼2 mF cm−2 at a potential scan rate of 1 V s−1 in aqueous electrolytes. Combining electrochemical testing with X-ray photoelectron spectroscopy characterization has revealed that redox reactions play no or little role in the electrochemical response of pure VN, in contrast to the common wisdom stemming from the electrochemical response of oxygen-containing films. An alternative charge storage mechanism – space charge accumulation in a subsurface layer of ∼100 nm – was put forward to explain the experimentally observed capacitance of VN films in aqueous electrolytes.

Efficient Charge Injection in Organic Field‐Effect Transistors Enabled by Low‐Temperature Atomic Layer Deposition of Ultrathin VOx Interlayer

Charge injection at metal/organic interface is a critical issue for organic electronic devices in general as poor charge injection would cause high contact resistance and severely limit the performance of organic devices. In this work, a new approach is presented to enhance the charge injection by using atomic layer deposition (ALD) to prepare an ultrathin vanadium oxide (VOx) layer as an efficient hole injection interlayer for organic field‐effect transistors (OFETs). Since organic materials are generally delicate, a gentle low‐temperature ALD process is necessary for compatibility. Therefore, a new low‐temperature ALD process is developed for VOx at 50 °C using a highly volatile vanadium precursor of tetrakis(dimethylamino)vanadium and non‐oxidizing water as the oxygen source. The process is able to prepare highly smooth, uniform, and conformal VOx thin films with precise control of film thickness. With this ALD process, it is further demonstrated that the ALD VOx interlayer is able to remarkably reduce the interface contact resistance, and, therefore, significantly enhance the device performance of OFETs. Multiple combinations of the metal/VOx/organic interface (i.e., Cu/VOx/pentacene, Au/VOx/pentacene, and Au/VOx/BOPAnt) are examined, and the results uniformly show the effectiveness of reducing the contact resistance in all cases, which, therefore, highlights the broad promise of this ALD approach for organic devices applications in general.

Mechanical strengthening in self-lubricating CrAlN/VN multilayer coatings for improved high-temperature tribological characteristics

Abstract CrAlN/VN multilayer coatings are periodically fabricated with various bilayer periods by RF magnetron sputtering. Crystalline phases and preferred orientations of thin films are characterized by the X-ray diffractometer. Through SEM and dark-field TEM inspections, a dense and coherent columnar structure is revealed in CrAlN/VN coatings. In the ball-on-disc test at 700 °C, all the multilayer coatings exhibit preferable anti-wear performance, which is attributed to interfacial strengthening and the formation of lubricated vanadium oxide layers on the worn surface. Especially, the lowest friction coefficient of 0.33 and wear rate of 1.6 × 10− 5 mm3 N− 1 m− 1 are revealed in multilayer coating with bilayer period of 16 nm. As compared with CrAlN monolayer, the worn surface in multilayer coating is relatively intact under high-temperature wear torture. A hybrid mechanism including structural strengthening and elemental contribution is proposed to highlight the favorable anti-wear property in CrAlN/VN multilayer coatings at elevated temperature.

New Lanthanide Mixed-Valent Vanadium(III/IV) Oxosilicates, Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd), Crystallizing in a Quasi Two-Dimensional Rutile-Based Structure.

A family of lanthanide mixed-valent vanadium(III/IV) oxosilicates Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd) was synthesized as high-quality single crystals via a high-temperature molten salt method. An in situ reduction of V(V) to V(III/IV) as well as of Ce(IV) to Ce(III) was achieved utilizing Zn metal as the reducing agent, some of which is incorporated into the crystal structure. Ce4V(4.77)Zn(0.23)Si4O22, to the best of our knowledge, is the first example of a cerium-containing mixed-valent vanadium silicate. The crystal structures were determined by single-crystal X-ray diffraction, and the four isostructural oxosilicates were determined to crystallize in the chevkinite-structure type in the monoclinic space group I2/a. The unit cells of the Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd) series are related to the reported C2/m phases Ln4V5Si4O22 (Ln = La, Pr, and Nd) by a doubling of the c-axis and a loss of a mirror plane. The three-dimensional crystal structure consist of two-dimensional rutile-based vanadium oxide and lanthanide oxide layers linked via Si2O7 groups. The temperature dependence of the magnetic susceptibility of these compounds was measured, and only the Nd analogue exhibited a magnetic transition at 5 K; all samples displayed a discontinuity or deviation from linearity at ca. 130-150 K.

Dissimilar Crystal Dependence of Vanadium Oxide Cathodes in Organic Carbonate and Safe Ionic Liquid Electrolytes.

Advances in Li metal anode stabilization, solid-state electrolytes, and capabilities to insert a variety of active ions (Li(+), Na(+), Mg(2+), and Al(3+)) have renewed the interest in layered vanadium oxides. Here we show that crystal characteristics such as size and crystallinity are fundamental variables that control the dissimilar electrochemical capabilities of 1D vanadium oxides immersed in different electrolytes (organic carbonates and safe electrolytes containing 80% of ionic liquid). We show that this opposite behavior can be understood in terms of a subtle interplay between crystal characteristics (size and crystallinity), electrolyte degradability, and the ionic conductivity of the electrolyte. Thus, through this control we are able to obtain pure 1D vanadium oxides that show reversibility in carbonate electrolytes at a cutoff voltage of 1.5 V (voltage region where insertion of more than two lithium ions is possible). Furthermore, these materials are able to uptake ca. 1.0 mol of Li at a rate of 20C (1C = 295 mAh/g) and retain excellent capabilities (Coulombic efficiency of 98% after 200 cycles at a rate of 5C). Finally, what, to our knowledge, is really remarkable is that this optimization allows building vanadium oxide electrodes with an excellent electrochemical response in a safe electrolyte composition (80% of ionic liquid). Specifically, we reach uptakes also at a cutoff voltage of 1.5 V of ca. 1.0 mol of Li after 200 cycles at 5C (charge/discharge) with Coulombic efficiencies higher than 99.5%.

Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO.

Catalytic oxidation of ammonia and CO has been studied in the 10(-4) mbar range using a catalyst prepared by depositing ultra-thin vanadium oxide layers on Rh(111) (θV ≈ 0.2 MLE). Using photoemission electron microscopy (PEEM) as a spatially resolving method, we observe that upon heating in an atmosphere of NH3 and O2 the spatial homogeneity of the VOx layer is removed at 800 K and a pattern consisting of macroscopic stripes develops; at elevated temperatures this pattern transforms into a pattern of circular VOx islands. Under reaction conditions the neighboring VOx islands become attracted by each other and coalesce. Similar processes of pattern formation and island coalescence are observed in catalytic CO oxidation. Reoxidation of the reduced VOx catalyst proceeds via surface diffusion of oxygen adsorbed onto Rh(111). A pattern consisting of macroscopic circular VOx islands can also be obtained by heating a Rh(111)/VOx catalyst in pure O2.

Island Ripening via a Polymerization-Depolymerization Mechanism.

In catalytic methanol oxidation on ultrathin vanadium oxide layers on Rh(111) (Θ_{V}≈0.2 monolayer equivalent) we observe a 2D ripening of the VO_{x} islands that is controlled by the catalytic reaction. Neighboring VO_{x} islands move under reaction conditions towards each other and coalesce. The motion and the coalescence of the islands are explained by a polymerization-depolymerization equilibrium that is sensitive to gradients in the adsorbate coverages.

Ionic liquid intercalated V2O5 nanorods: synthesis and characterization

In this work, ionic liquid (IL) intercalated V2O5 (IL-V2O5) nanorods have been synthesized through the IL-assisted hydrothermal method using imidazolium-based functionalized IL at 130 ∘C for 3 days. The structure and morphology of the obtained product was characterized using various techniques. X-ray diffraction pattern reveals the intercalation of IL at 2 𝜃=7∘ in orthorhombic V2O5. The Fourier transform infrared spectrum shows a band at 1044 cm−1, which could be assigned to stretching vibration of terminal vanadyl (V =O), sensitive to cation intercalation between vanadium oxide layers. UV–vis absorption spectrum of IL-V2O5 nanorods and calcined V2O5 nanoparticles show a maximum absorbance at 402 and 420 nm, respectively. The morphology of the product was investigated by scanning electron microscopy and transition electron microscopy (TEM). TEM analysis reveals the nanorods with thickness of 30–50 nm.

Lattice Breathing Inhibited Layered Vanadium Oxide Ultrathin Nanobelts for Enhanced Sodium Storage.

Operating as the "rocking-chair" battery, sodium ion battery (SIB) with acceptable high capacity is a very promising energy storage technology. Layered vanadium oxide xerogel exhibits high sodium storage capacity. But it undergoes large lattice breathing during sodiation/desodiation, resulting in fast capacity fading. Herein, we develop a facile hydrothermal method to synthesize iron preintercalated vanadium oxide ultrathin nanobelts (Fe-VOx) with constricted interlayer spacing. Using the Fe-VOx as cathode for SIB, the lattice breathing during sodiation/desodiation is largely inhibited and the interlayer spacing is stabilized for reversible and rapid Na(+) insertion/extraction, displaying enhanced cycling and rate performance. This work presents a new strategy to reduce the lattice breathing of layered materials for enhanced sodium storage through interlayer spacing engineering.

High Performance Pillared Vanadium Oxide Xerogel Cathode for Lithium Ion Batteries

Lithium ion batteries commonly utilize layered oxide materials as the cathode, where lithium is intercalated and deintercalated between the layers in the crystal structure during cycling. The repeated lithium insertion and extraction can cause stress on the material, leading to fracture. Additionally, the extent of lithiation may cause phase changes in the layered structure that are sometimes irreversible. These changes to the material cause capacity loss and reduce the battery cycle life. This research focuses on nanostructuring layered oxides to enhance their cyclability and power capabilities. In particular, vanadium oxide xerogels were modified by adding pillaring molecules between the layers to increase the interlayer spacing. Vanadium oxide xerogels possess attractive capacities but suffer from significant capacity fade due to distortion of the crystal structure. We hypothesize that the pillars will enhance thermal and mechanical stability by reducing the strain on the structure and increasing lithium ion mobility, thereby increasing the cycle life and high rate capacities. Aluminum Keggin ions were used as pillaring agents for the vanadium oxide xerogels. X-ray diffraction showed an interlayer spacing increase from 1.14 to 1.32 nm after pillaring, consistent with the size of the keggin ions (~1.3 nm), while still maintaining the layered V2O5 xerogel crystalline structure (Figure 1). Elemental analysis indicated an aluminum loading of 9 wt% in the pillared material. The pillared materials also demonstrate increased thermal stability and rate capabilities during cycling in coin cells, with capacities over 60% higher than those of the unpillared V2O5 xerogel. Additionally, the pillared materials retained more capacity during cycling at C/2. Pillaring the layered vanadium oxide xerogels improved both capacity retention and battery lifetime. Figure 1. Diffraction patterns for V2O5 xerogel (a), pillared V2O5 xerogel (b), and pillared V2O5 xerogel after heat treatment in either air (c) or nitrogen (d). The dotted line is intended as a guide for the eye. Figure 1

Water adsorption on polycrystalline vanadium from ultra-high vacuum to ambient relative humidity

We have studied the reaction of water vapor with a polycrystalline vanadium surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) which allows the investigation of the chemical composition of the vanadium/water vapor interface at p(H2O) in the Torr range. Water dissociation on the vanadium surface was studied under isobaric conditions at p(H2O) ranging from 0.01 to 0.50Torr and temperatures from 625K to 260K, i.e. up to a relative humidity (RH) of ~15%. Water vapor exposure leads to oxidation and hydroxylation of the vanadium foil already at a pressure of 1×10−6Torr at 300K (RH~4×10−6%). The vanadium oxide layer on the surface has a stoichiometry of V2O3. Initial adsorption of molecular water on the surface is observed at RH>0.001%. Above a RH of 0.5% the amount of adsorbed water increases markedly. Experiments at increasing temperatures show that the water adsorption process is reversible. Depth profile measurements show a thickness for the vanadium oxide layer of 3–5 mono layers (ML) and for vanadium hydroxide of 1–1.5 ML over the whole RH range in the isobar experiments. The thickness of the adsorbed water layer was found to be in the sub-ML range for the investigated RH's.

Vanadium Oxide Polycrystalline Nanorods and Ion-Exchanged Nanotubes for Enhanced Lithium Intercalation

In this work we investigate two alternative methods to remove amine molecules from as-synthesized vanadium oxide nanotubes (VONTs). Thermal treatment results in the formation of polycrystalline nanorods (poly-NRs) and ion exchange reactions with NaCl result in the formation of Na-VONTs. The removal of amine molecules is confirmed by monitoring the inorganic and organic phase changes and decomposition, respectively, using electron microscopy, IR spectroscopy and X-ray diffraction analyses. We compare the electrochemical performance of as-synthesized VONTs, poly-NRs and Na-VONTs. This work demonstrates that the presence of amine molecules within the layers of vanadium oxide impedes the intercalation of lithium ions, and that their removal results in a significant improvement in electrochemical characteristics. Out of the three vanadium oxide nanostructures investigated, poly- NRs exhibit the most promising results for practical use as a cathode material.

Insertion study of alkali metal cations into layered vanadium oxide foam

The reaction of inorganic ions (Li+, Na+, and K+) with the lamellar material of composition (V2O5)(C16H33NH2)1.3 under reflux conditions in alcohol-water mixed medium results in the rapid and quantitative displacement of the surfactant to form inorganic ions intercalated vanadium oxides. The products were characterized by employing powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), thermogravimetric/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM). FTIR and thermal studies showed the displacement of surfactants by inorganic ions during ion-exchange process. The XRD peaks observed at lower and wider 2θ angles reflect the interlayer separation and crystallinity of the host vanadium oxide framework.

Novel Vanadium Oxide Polycrystalline Nanorods for Enhanced Lithium Intercalation

Over the last decade the technological advancements which have led to products such as smartphones, tablet computers and electric vehicles have been outstanding. Currently, battery technology is just about keeping up with consumer demands. In order to prevent lithium ion batteries from impeding future technological advancements every aspect of lithium ion batteries must be examined to determine how future improvements can be made. There is a tremendous amount of research being done into possible cathode materials to replace the most commonly currently used cobalt oxides [1, 2].Vanadium oxide nanotubes (VONTs) were first reported in 1998 by Spahr et al. [3] and since then there has been a great deal of research into how to fully optimise VONTs as a cathode material for lithium ion batteries [4, 5]. Typically VONTs are prepared by hydrothermal treatment of a vanadium oxide precursor mixed with a primary amine [6]. The presence of amine molecules are crucial to the formation of the VONTs as they maintain the vanadium oxide layers which scroll to form the nanotube structure [7]. While the amines are vital in the synthesis of the VONTs they are unfortunately detrimental in their electrochemical performance. It has been proposed that amine molecules occupy the majority of the possible lithium intercalation sites within the VONTs and hence are responsible for the poor cycling performance which has been reported for as-synthesised VONTs [8].In this work we investigate two alternative methods to remove amine molecules from the as-synthesised VONTs, using the nanotube structure as a ‘backbone’ or ‘starting structure’ for other polymorphs. The first method consists of annealing as-synthesised VONTs to high temperatures (≈ 600 oC) in an effort to evaporate the amines out of the vanadium oxide structure. This method results in polycrystalline vanadium oxide nanorods (poly-NRs). The second method is a two-step process. First, the as-synthesised VONTs undergo an ion exchange treatment, partially substituting amine molecules with Na+ ions to form Na-VONTs and secondly, the resulting Na-VONTs are also annealed to 600 oC.We confirm the removal of amine molecules by monitoring the inorganic and organic phase changes and decomposition, respectively, using IR spectroscopy, electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy analyses. Through detailed electrochemical investigations we compare the electrochemical performance of as-synthesised VONTs, poly-NRs, Na-VONTs and Na-VONTs after thermal treatment. We confirm that the heavy functionalization of VONTs by amine molecules can impede the intercalation of lithium ions, and that their removal results in a significant improvement in electrochemical characteristics. We will show that poly-NRs exhibit the most promising results for practical use as a cathode material. High rate capability tests demonstrate their stability at high charging rates (1C) and long term cycle life testing indicates a high level of capacity retention over 500 cycles.

Polycrystalline Vanadium Oxide Nanorods: Growth, Structure and Improved Electrochemical Response as a Li-Ion Battery Cathode Material

Thermally removing amine molecules that serve as chemical templates for vanadium oxide nanotubes is demonstrated to significantly improve the performance when tested as a cathode material in Li-ion battery cells. Capacity fading issues associated with blocked intercalation sites on the (010) faces of layered vanadium oxide that form the nanotubes are prevented. Thermal treatment of the nanotubes up to 600°C is shown to cause a specific conversion from nanotubes to polycrystalline nanorods and removal of the organic template. The conversion process was monitored by thermogravimetric analysis, X-ray diffraction, transmission electron microscopy and infra-red spectroscopy. In a potential window of 4.0–1.2 V drawing 30 μA (C/30), the nanorods show improved specific capacities of ∼280 mAh g−1 with a modest 6% capacity fade compared to ∼8 mAh g−1 with 62% capacity fade for the VONTs. The improvements in specific capacity and cycling performance are due to the successful removal of amine molecules and conversion to nanorods containing nanoscale crystals. The cathode material also demonstrated enhanced energy densities (∼700 W h kg−1) compared to composites of the same overall weight, without conductive carbon additives or polymeric binders.

Efficient Polymer Solar Cells Based on Solution‐processed Vanadium Oxide as Hole‐extracting Layer

AbstractHere we reported the fabrication of efficient polymer solar cells from regioregular poly(3‐hexylthiophene) (P3HT):fullerene derivative [6,6]‐phenyl‐C61 butyric acid methyl ester (PC61BM) mixtures, in which solution‐processed vanadium oxide (VOx) was used as a hole‐extracting layer (HEL). The obtained devices exhibited a high power conversion efficiency of 3.96%, and can be enhanced to 4.06% and 4.16%, respectively, when two types of PEDOT:PSS with different conductivities were used in conjunction with the VOx layer. All the VOx‐based devices showed a high fill factor (FF) over 70%, which was ascribed to efficient hole extracting efficiency associated with the solution‐processed VOx hole‐extracting layer. The origins of the improvement were also studied by transmission spectra, atomic force microscope (AFM), and capacitance‐voltage characteristics.