Tunable-pH Environment Induced by Local Anchor Effect of High Lewis Basicity Conductive Polymers toward Glycerol Upgrading Assisted Hydrogen Evolution

Hybrid organic/inorganic composites with the organic phase tailored to modulate the local chemical environment at the transition metal-based catalyst surface arise as an enchanting category of catalysts for electrocatalysis. A fundamental understanding of how the conductive polymers of different Lewis basicities affect the reaction path is, however, still lacking to guide rational catalyst design. Herein, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(vinyl alcohol) (PVA) manifesting different Lewis basicities are compared for their regulatory roles on the hydrogen evolution reaction (HER) and glycerol electrooxidation (GOR) pathways regarding local proton coverage. Concerted efforts from in situ Raman and DFT theoretical calculations unveil that conductive polymer/V2O5 surface with tunable local pH regulated by Lewis acidity/basicity. As a result of the tailored chemical environment, the restructured V2O5/PANI/NF composite demonstrates a low overall potential of 1.55 V at the partial current density of 50 mA cm-2 for formate. The glycerol upgrading assisted hydrogen evolution device composed of V2O5/PANI/NF exhibits excellent electrochemical performance at a maximal Faraday efficiency of 82%, ranking among state of the art.

Effect of microplate size on the semiconductor–metal transition in VO2 thin films

The degree of changes in resistivity (Δρ) becomes more prominent as the VO2 film microplate size grows, which is primarily attributed to a reduced probability of electron scattering with decreasing grain boundary density.

V2O5/vertically-aligned carbon nanotubes as negative electrode for asymmetric supercapacitor in neutral aqueous electrolyte

Development of aqueous asymmetric supercapacitors (ASCs) is often limited by low specific capacitance of negative electrodes. Herein, a composite electrode with tiny vanadium pentoxide (V₂O₅) nanoparticles homogeneously decorated in vertically-aligned carbon nanotube arrays (VACNTs) is prepared by supercritical CO₂ impregnation and subsequent annealing, and used as binder-free negative electrode for aqueous ASCs. Owing to its unique three-dimensional (3D) hierarchical nanostructure, the V₂O₅/VACNTs (VN) electrodes exhibit an ideal specific capacitance of 284 F g^-1 in the potential range of -1.1 to 0 V vs SCE at 2 A g^-1 and outstanding cycling stability in the Na₂SO₄ aqueous solution. An aqueous ASC device possessing wide potential range of 1.7 V was constructed with pure VACNTs and VN-350 as the positive and negative electrodes, respectively. The ASC delivers a high energy density of 32.3 Wh kg^-1 at a power density of 118 W kg^-1 and satisfactory cycling life with capacitance retention of 76% after 5000 cycles.

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.

A polypyrrole-adorned, self-supported, pseudocapacitive zinc vanadium oxide nanoflower and nitrogen-doped reduced graphene oxide-based asymmetric supercapacitor device for power density applications

Herein, a distinctive approach has been implemented for exploiting a typical battery material zinc vanadium oxide (ZV) as a supercapacitor electrode material.

Electrochemically Generated γ-Lix V2 O5 as Insertion Host for High-Energy Li-Ion Capacitors

In this study, we explored the feasibility of using electrochemically generated γ-Li_x V₂ O₅ as an insertion-type anode in the lithium-ion capacitor (LIC) with activated carbon (AC) as a cathode. Along with the native form of V₂ O₅ , their carbon composites are also used as the electrode material which is prepared by high-energy ball milling. The electrochemical pre-lithiation strategy is used to generate the desired γ-phase of V₂ O₅ (γ-Li_x V₂ O₅ ). Under the optimized mass loading conditions, the LICs are assembled with γ-Li_x V₂ O₅ as anode and AC as a cathode in the organic medium. Among the different LICs fabricated, AC/γ-Li_x V₂ O₅ -BM50 configuration delivered an energy density of 33.91 Wh kg^-1 @ 0.22 kW kg^-1 with excellent capacity retention characteristics. However, a dramatic increase in energy density (43.98 Wh kg^-1 @0.28 kW kg^-1 ) is noted after the electrolyte modification with fluoroethylene carbonate. The high temperature performance of the assembled LIC is also studied and found that γ-Li_x V₂ O₅ phase can be used as a potential battery-type component to construct high-performance hybrid charge storage devices.

Phase-pure VO2 nanoporous structure for binder-free supercapacitor performances

Vanadium oxides are anticipated as a high-performance energy storage electrode due to their coupled double layer and pseudo-capacitative charge storage mechanism. In the present work, we investigated the influence of different structural phases of as-grown VO₂ nanoporous structure and corresponding oxidation states on the supercapacitor performance. This nanoporous structure facilitates fast ion diffusion and transport. It is shown that stoichiometric monoclinic VO₂, with V oxidation state of +4, provides superior charge storage capacity with a capacitance value of 33 mF/cm², capacitance retention of 93.7% and Coulombic efficiency of 98.2%, to those for VO₂ structures with mixed oxidation states of V⁵⁺ and V⁴⁺. A comparable high energy density is also recorded for the sample with all V⁴⁺. Scanning Kelvin probe microscopy results clarify further the formation of space charge region between VO₂ and carbon paper. These key findings indicate the potentiality of binder-free single phase monoclinic VO₂ porous structure towards the next-generation micro-supercapacitor application.