Oxidation Of VO2 Research Articles

Theoretical study of a highly fault-tolerant and scalable adaptive radiative cooler

Abstract Conventional static radiative coolers have an unadjustable cooling capacity, which often results in overcooling in low temperature environment. Therefore, there is a great need for an adaptive dynamic radiative cooler. However, such adaptive coolers usually require complex preparation processes. This paper proposes an adaptive radiative cooler based on a Fabry–Perot resonant cavity. By optimizing the structural parameters of the radiative cooler, this adaptive radiative cooler achieves a modulation rate of 0.909 in the atmospheric window band. The net radiative cooling performance difference between low and high temperatures is nearly eight times. Meanwhile, the device is easily prepared, has a high tolerance, and can effectively prevent W–VO2 oxidation. This study provides new insights into adaptive radiative cooling with potential for large-scale applications.

Facile fabrication of VO2/SiO2 aerogel composite films with excellent thermochromic properties for smart windows

In order to improve the solar modulation ability and near-infrared shielding performance of VO2-based films, in this work, VO2/SiO2 aerogel composite films have been fabricated by a facile mechanical ball-milling method. It has been clarified that the solar modulation efficiency (ΔTsol) of the composite film can be increased by 187.5% (from 6.4% to 18.4%) by introducing SiO2 aerogel into the composite film when the visible light transmittance (Tlum) is about 40%, which can be ascribed to the synergistic effect of Rayleigh scattering effect of SiO2 aerogel and the good dispersion of the particles. The VO2/SiO2 aerogel composite particles not only have excellent dispersion, but also the SiO2 aerogel can effectively slow down the oxidation of VO2 and improve the oxidation resistance of VO2. In particular, the universality of the Rayleigh scattering effect of SiO2 aerogel is demonstrated, which can act together with the doping effect of Mg2+ ions to further improve the thermochromic properties of VO2 films. This study provides a new idea for improving the thermochromic properties of VO2 films and meanwhile is of great significance in promoting the practical application of VO2 films in the field of smart windows.

Voltage-induced phase transition of VO2@SiO2 nanoparticles

As a typical metal oxide with a strong electronic correlation, vanadium dioxide (VO2) has great application potential in over-pulse protection, new storage devices, and field-effect switches. However, its chemical instability and low dispersibility have restricted its application in these areas. The synthesis of VO2@shell nanoparticles may improve VO2's oxidation resistance. Herein, VO2@SiO2 core-shell nanoparticles with different coating thicknesses are synthesized via the Stöber method. The coated VO2's oxidation temperature is 45 °C higher than that of the uncoated sample. However, the phase-transition temperature of the coated samples remains unaffected (68 °C). A VO2@SiO2 composite material is prepared by mixing VO2 with a polyvinyl pyrrolidone matrix. When the SiO2 coating thickness is less than 3 nm, the composite material undergoes temperature and electro-induced phase transitions. As a result of temperature changes and high voltage application, the resistance of the material can suddenly change. Moreover, the material resistance increases with increasing coating thickness. When the thickness of the material exceeds 3 nm, the room temperature resistance of the material sharply increases. The temperature-induced phase transition of the composite material is not clearly observed. In addition, repeated electro-induced phase transition cannot occur. The nonlinear coefficient of the electro-induced phase transition of the VO2@SiO2 composite material filled with coated particles is improved, particularly when the coating thickness exceeds 2 nm. Our results indicate that SiO2 coating can improve both oxidation resistance and electro-induced phase transition performance of VO2. The optimal coating thickness was between 2 and 3 nm. These findings are of great importance to promote the practical applications of VO2.

VO2/ZnO bilayer films with enhanced thermochromic property and durability for smart windows

VO2 films are widely considered as one of the most suitable material to act as smart windows. Although this system is able to function, the durability of the film has been an issue as the surface of the films may oxidize by converting V4+ to V5+. To overcome this problem, attempt is made to coat the VO2 film with ZnO, which can assist by creating a resistance layer to prevent further oxidation of VO2. Here, VO2/ZnO bilayer film was prepared by a facile method comprised of spin-coating and dip-coating process and shows excellent durability, and in particular. the solar modulation efficiency (△Tsol) maintaining ca 89.9% (from 17.8% to 16.0%) after 300 days in a humid environment, however, the △Tsol of pure VO2 film is decreased from 11.8% to 4.1%. Also, the VO2/ZnO bilayer exhibits an enhanced thermochromic property of visible transmittance (Tlum = 55.7 ± 2.1%) and △Tsol (17.1 ± 1.4%) which is 1.49 times higher than that of pure VO2 film (△Tsol = 11.5 ± 0.4%). The enhancement in the thermochromic performance and durability is probably attributed to the anti-reflection and protection of ZnO layer. Therefore, this work can provide an effective way to optimize thermochromic property for practical application of VO2-based smart windows.

Universal Algorithm for Simulating and Evaluating Cyclic Voltammetry at Macroporous Electrodes by Considering Random Arrays of Microelectrodes.

An algorithm for the simulation and evaluation of cyclic voltammetry (CV) at macroporous electrodes such as felts, foams, and layered structures is presented. By considering 1D, 2D, and 3D arrays of electrode sheets, cylindrical microelectrodes, hollow‐cylindrical microelectrodes, and hollow‐spherical microelectrodes the internal diffusion domains of the macroporous structures are approximated. A universal algorithm providing the time‐dependent surface concentrations of the electrochemically active species, required for simulating cyclic voltammetry responses of the individual planar, cylindrical, and spherical microelectrodes, is presented as well. An essential ingredient of the algorithm, which is based on Laplace integral transformation techniques, is the use of a modified Talbot contour for the inverse Laplace transformation. It is demonstrated that first‐order homogeneous chemical kinetics preceding and/or following the electrochemical reaction and electrochemically active species with non‐equal diffusion coefficients can be included in all diffusion models as well. The proposed theory is supported by experimental data acquired for a reference reaction, the oxidation of [Fe(CN)6]4− at platinum electrodes as well as for a technically relevant reaction, the oxidation of VO2 + at carbon felt electrodes. Based on our calculation strategy, we provide a powerful open source tool for simulating and evaluating CV data implemented into a Python graphical user interface (GUI).

On-line mass spectrometry study of electrochemical corrosion of the graphite electrode for vanadium redox flow battery

The electrochemical corrosion of the graphite electrode for vanadium redox flow battery is investigated by on-line mass spectrometry analysis. The results show that CO2 and CO form and evolve more preferably than O2 on the graphite anode, which lead to the electrochemical corrosion of the graphite electrode. Furthermore, the evolution rate of O2 is the highest one among evolved gases if the polarization potential becomes too positive. The oxidation of VO2+ on the graphite electrode in 2M H2SO4+2M VOSO4 hinders the carbon oxidation reaction and retards the electrochemical corrosion of the graphite electrode.

Electrochemical Oxidation of Vanadium as Studied by Electron Spin Resonance Spectroscopy

Galvanostatic oxidation of vanadium was monitored by electron spin resonance (ESR) spectroscopy. Simultaneous observation of the electrode potential together with the ESR intensity revealed that the VO2+ ion concentration increased below the potential of 0.58 V (NHE) by the continuous oxide formation. Above that potential, however, the ESR intensity decreased, indicating further oxidation of VO2+ ion to the higher valent state. The experimental results demonstrate a useful application of ESR to the study of the dissolution of vanadium metal by galvanostatic technique.

Characteristics of electron transfer reactions of early transition elements

Abstract

Accelerating effect of hydroxycarboxylic acids in the oxidation of vanadyl(IV) by potassium chlorate

The influence of citric, tartaric, sulphosalicylic and oxalic acids on the oxidation of vanadyl(IV) by chlorate is studied. The investigation is carried out in order to clarify the influence of the carboxylic acids on each stage of the homogeneous catalytic processes with vanadium(V) as catalyst. It is found that the oxidation of VO2+ is accelerated in the presence of some carboxylic acids, by a matrix mechanism. If the reaction conditions favour the formation of co-ordinatively saturated complexes, the reaction rate decreases. This is observed also when the carboxylic acid does not possess bridging groups and cannot act as a matrix.