From synthetic montroseite VOOH to topochemical paramontroseite VO2 and their applications in aqueous lithium ion batteries

Kirkendall effect induced ultrafine VOOH nanoparticles and their transformation into VO2(M) for energy-efficient smart windows

Vanadium dioxide (VO2) has received widespread attention for application in energy-efficient smart windows because of its distinct thermochromic property in the near-infrared region during the reversible metal-insulator phase transition. In this study, lepidocrocite VOOH ultrafine nanoparticles (NPs) with a diameter less than 30 nm were prepared by a mild and efficient hydrothermal method, and the Kirkendall effect played a vital role in the growth of the VOOH NPs. It was found that VOOH could be transformed into VO2via a subsequent annealing treatment during which the size and morphology of VOOH are well preserved even though the annealing temperature is up to 500 °C. The ultrafine VO2 NPs are crucial for achieving excellent nanothermochromic performance with a luminous transmittance (Tlum) up to 56.45% and solar modulation ability (ΔTsol) up to 14.95%. The environmental durability is well improved by coating VO2 NPs with an SiO2 shell as confirmed via progressive oxidation and acid corrosion experiments. Meanwhile, the Tlum of the VO2@SiO2 film is further increased from 56.45% to 62.29% while the ΔTsol remained unchanged. This integrated thermochromic performance presents great potential for the development of VO2-based smart windows.

Operando crystal-amorphous transformation cathode for enhanced zinc storage

Aqueous zinc-ion batteries have obtained broad attention due to their high safety, eco-friendliness, and low cost. However, they are still in the developing stage considering the limited candidate of high-performance cathode materials. Furthermore, the intrinsic storage zinc mechanism is also needed to uncover. Here, we propose an operando crystal-amorphous transformation of tunnel-type VOOH and the obtained amorphous V2O5 serves as a high-performance zinc-ion battery cathode. In-situ X-ray diffraction corroborates the unique operando crystal-amorphous transformation of VOOH during the initial charging process. X-ray photoelectron spectroscopy and transmission electron microscopy further demonstrate the element valence evolution and the lattice structure change, respectively. The operando electrochemical crystal-amorphous transformation allows the obtained amorphous V2O5 to achieve the high capacity of ∼ 350.7 mAh g-1, rate performance (151.2 mAh g-1 at 6.4 A g-1), energy and power densities (137 Wh kg-1 at 6831 W kg-1), unveiling a promising approach of cathode materials via operando crystal-amorphous transformation to achieve the enhanced zinc storage.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

Autogenous growth of the hierarchical V-doped NiFe layer double metal hydroxide electrodes for an enhanced overall water splitting

NiFe layer double metal hydroxide nanosheets (NiFe LDHs) have been extensively investigated as one of the best promising candidates to construct efficient bifunctional catalysts. In this research, element (vanadium) doping into NiFe LDHs grown in nickel foam were synthesized by the one-step method and applied in overall water splitting. The content and structure of the composites were adjusted to regulate the catalyst's electronic structure and reduce the onset potential and achieved unprecedented electrocatalysis for OER and HER. The V-NiFe-LDH/NF showed perfect OER and HER activities with low Tafel slopes of 31.3 and 89.8 mV dec-1, and small overpotentials of 195 and 120 mV at 10 mA cm-2 in 1.0 m KOH solution, respectively. Electrochemical analysis indicated that the efficient catalytic activity of V-NiFe-LDHs/NF mainly benefited from V doping, which optimized the electronic structure and produce defects, thereby resulting in an enhanced conductivity, facile electron transfer, and adequate active sites.

One-step hydrothermal synthesis of cobalt-vanadium based nanocomposites as bifunctional catalysts for overall water splitting

Designing low-cost and high-active bifunctional catalysts for overall water splitting has attracted increasing research interest. Herein, the brilliant overall water splitting performance of cobalt-vanadium bimetal-based nanocomposites is explored. Co-V based nanocomposites are synthesized through a one-step hydrothermal method, in which the cobalt species is introduced into the lepidocrocite VOOH and further cobalt vanadium oxide is formed. The additive level of cobalt is optimized and the corresponding effect on electrocatalytic activity is also investigated in this work, systematically. The targeted catalyst (denoted as Co0.2-VOOH) exhibits a unique sheet-like morphology, resulting in the high exposure of catalytically active sites. When used as the bifunctional catalyst, Co0.2-VOOH can achieve a current density of 10 mA cm-2 at the overpotentials of 210 mV for water oxidation and 130 mV for hydrogen generation, respectively. Notably, it only requires low cell voltages of 1.57 and 1.74 V to drive the catalytic current densities of 10 and 100 mA cm-2 during the water splitting process. This work significantly indicates that cobalt-vanadium based materials are promising alternatives for overall water splitting.

VO2(D) hollow core–shell microspheres: synthesis, methylene blue dye adsorption and their transformation into C/VOxnanoparticles

Hollow core–shell VO₂(D) microspheres were fabricated and they exhibited excellent MB adsorption ability; and the regenerated C/VO_xnanoparticles showed enhanced adsorption performance and good reusability.

Hierarchical VOOH hollow spheres for symmetrical and asymmetrical supercapacitor devices

Hierarchical VOOH hollow spheres with low crystallinity composed of nanoparticles were prepared by a facile and template-free method, which involved a precipitation of precursor microspheres in aqueous solution at room temperature and subsequent hydrothermal reaction. Quasi-solid-state symmetric and asymmetric supercapacitor (SSC and ASC) devices were fabricated using hierarchical VOOH hollow spheres as the electrodes, and the electrochemical properties of the VOOH//VOOH SSC device and the VOOH//AC ASC device were studied by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Results demonstrated that the electrochemical performance of the VOOH//AC ASC device was better than that of the VOOH//VOOH SSC device. After 3000 cycles, the specific capacitance of the VOOH//AC ASC device retains 83% of the initial capacitance, while the VOOH//VOOH SSC device retains only 7.7%. Findings in this work proved that hierarchical VOOH hollow spheres could be a promising candidate as an ideal electrode material for supercapacitor devices.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows

Vanadium dioxide (VO₂ ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ_c ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO₂ a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τ_c , low luminous transmittance (T_lum ), and undesirable solar modulation ability (ΔT_sol ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO₂ nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO₂ nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO₂ . This Review focuses on hydrothermal synthesis, physical properties of VO₂ polymorphs, and their transformation to thermochromic VO₂ (M), and discusses the advantages, challenges, and prospects of VO₂ (M) in energy-efficient smart windows application.

In situ cathodic activation of V-incorporated NixSy nanowires for enhanced hydrogen evolution

In situ cathodic activation (ISCA) of V-incorporated Ni_xS_y nanowires supported on nickel foam (VS/Ni_xS_y/NF) can be realized in an alkaline hydrogen evolution reaction (HER) process, which provides not only clearly enhanced activity but also ultrahigh stability for HER. The ISCA process is continuous linear sweep voltammetry (LSV) on VS/Ni_xS_y/NF as a cathodic electrode with gradually enhanced HER activity. The activated VS/Ni_xS_y/NF (A-VS/Ni_xS_y/NF) demonstrates enhanced HER activity with an overpotential of 125 mV to drive 10 mA cm^-2, which is much lower than that of other samples. It may be predicted that the ISCA-derived amorphous VOOH film covering on A-VS/Ni_xS_y/NF accelerates the HER process, and NiOOH may protect active sites from decaying, leading to excellent activity and structural stability. However, for single metal sulfides, the ISCA process of nickel or vanadium sulfides is not available, implying that the synergistic effect between Ni and V of VS/Ni_xS_y/NF may be the key to drive ISCA in alkaline HER. In addition, its ultra-high stability confirms that the stable active sites and nanostructures of A-VS/Ni_xS_y/NF are derived from ISCA. Therefore, the ISCA of V-incorporated transition metal sulfides in the alkaline HER process may be a facile and promising method to obtain efficient electrocatalysts.

Hollow Porous VOx/C Nanoscrolls as High-Performance Anodes for Lithium-Ion Batteries

Novel hollow porous VO_x/C nanoscrolls are synthesized by an annealing process with the VO_x/octadecylamine (ODA) nanoscrolls as both vanadium and carbon sources. In the preparation, the VO_x/ODA nanoscrolls are first achieved by a two-phase solvothermal method using ammonium metavanadat as the precursor. Upon subsequent heating, the intercalated amines between the vanadate layers in the VO_x/ODA nanoscrolls decompose into gases, which escape from inside the nanoscrolls and leave sufficient pores in the walls. As the anodes of lithium-ion batteries (LIBs), such hollow porous VO_x/C nanoscrolls possess exceedingly high capacity and rate capability (904 mAh g^-1 at 1 A g^-1) and long cyclic stability (872 mAh g^-1 after 210 cycles at 1 A g^-1). The good performance is derived from the unique structural features of the hollow hierarchical porous nanoscrolls with low crystallinity, which could significantly suppress irreversible Li⁺ trapping as well as improve Li⁺ diffusion kinetics. This universal method of annealing amine-intercalated oxide could be widely applied to the fabrication of a variety of porous electrode materials for high-performance LIBs and supercapacitors.

Reversible phase modulation and hydrogen storage in multivalent VO2 epitaxial thin films

Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d(1) electronic configuration, and induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)-metal (HxVO2)-insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage.

Synthesis and formation mechanism of VO2(A) nanoplates with intrinsic peroxidase-like activity

In situPXRD confirmed the direct crystallization of VO₂(A) from solution after complete hydrolysis of the VO(acac)₂precursor.

Shaping cancer nanomedicine: the effect of particle shape on the in vivo journey of nanoparticles

Recent advances in nanoparticle technology have enabled the fabrication of nanoparticle classes with unique sizes, shapes and materials, which in turn has facilitated major advancements in the field of nanomedicine. More specifically, in the last decade, nanoscientists have recognized that nanomedicine exhibits a highly engineerable nature that makes it a mainstream scientific discipline that is governed by its own distinctive principles in terms of interactions with cells and intravascular, transvascular and interstitial transport. This review focuses on the recent developments and understanding of the relationship between the shape of a nanoparticle and its navigation through different biological processes. It also seeks to illustrate that the shape of a nanoparticle can govern its in vivo journey and destination, dictating its biodistribution, intravascular and transvascular transport, and, ultimately, targeting of difficult to reach cancer sites.

First investigation on charge-discharge reaction mechanism of aqueous lithium ion batteries: a new anode material of Ag2V4O11 nanobelts

Aqueous lithium ion batteries have been widely considered as promising "green" batteries due to several advantages, such as low toxicity, low cost, high safety, as well as high ion conductivity. But unlike the great effort devoted to understanding the lithium insertion/extraction process in non-aqueous lithium ion batteries, the knowledge about this in aqueous electrolytes is still lacking research at present. In this work, taking a new anode material of single-crystalline Ag(2)V(4)O(11) nanobelts as an example, we investigated the charge-discharge reaction mechanism of aqueous lithium ion batteries for the first time. A two-step reaction mechanism was proposed and it was also deduced that crystallinity loss of the electrode materials and partial irreversibility of silver oxidation are the key reasons for rapid capacity fading. We expect this work to provide a scientific platform that could help to investigate and evaluate other electrode materials in this research area.