Sucrose pyrolysis assembling carbon nanotubes on graphite felt using for vanadium redox flow battery positive electrode

In the present paper, multi-walled carbon nanotubes (MWCNTs) are successfully assembled on graphite felt (GF) using sucrose pyrolysis method for the first time. The in situ formed pyrolytic carbon is chosen as the binder because it is essentially carbon materials as well as CNTs and GF which has a natural tendency to achieve high bonding strength and low contact resistance. The MWCNTs/GF electrode is demonstrated to increase surface area, reduce polarization, lower charge transfer resistance and improve energy conversion efficiency comparing with GF. This excellent electrochemical performance is mainly ascribed to the high electro-catalytic activity of MWCNTs and increasing surface area

Activated Charcoal Modified Graphite Felts Using for Positive Electrodes of Vanadium Redox Flow Battery

In the present paper, a composite electrode material was developed for vanadium redox flow batteries (VRFBs). Activated charcoal particles were evenly immobilized on the graphite felt (GF) via a sucrose pyrolysis process for the first time. The in site formed pyrolytic carbon is used as the binder, because it is essentially carbon material as well as GF and activated charcoal, which has a natural tendency to realize good adhesion and low contact resistance. The activated charcoal decorated GF electrode (abbreviated as the composite electrode) possesses larger surface area (13.8 m(2) g(-1)), more than two times as GF (6.3 m(2) g(-1)). The oxygen content of composite electrode is also higher (7.0%) than that of GF (4.8%). The composite electrode was demonstrated to lower polarization and increase the reversibility toward the VO2+/VO(2)(+)redox couple according to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge-discharge cycling test was conducted with a single VRFB cell. The results indicate that the cell with composite electrode presents higher charge-discharge capacity, larger electrolyte utilization efficiency (EU), and higher energy conversion efficiency (79.1%) compared with that using GF electrode. The increasing electrochemical performances of composite electrodes are mainly ascribed to the high electrochemical activity of activated charcoal particles and increasing superficial area.</p

Preparation and Electrochemical Properties of High Purity Mixed-Acid Electrolytes for High Energy Density Vanadium Redox Flow Battery

All-vanadium redox flow battery (VRFB) is a large-scale electrochemical energy storage technology with numerous potential applications because of its inherent safety and long service life. In previous years, a novel mixed-acid electrolyte system, vanadium electrolytes with mixture of sulfuric acid and hydrochloric acid, has been developed by the Pacific Northwest National Laboratory (PNNL) to increase vanadium solubility, which can effectively raise the electrolyte energy density from 25 Wh/L to 40 Wh/L. To further improve mixed-acid VRFBs, in present work, high purity mixed-acid electrolytes were prepared using a novel direct dissolution - electrochemical reduction process from high purity vanadium oxytrichloride (VOCl3). And the purity and electrochemical properties were investigated, comparing with common mixed-acid electrolytes and regular sulfate electrolytes prepared from metallurgical grade vanadium pentoxide. It was found that the novel process demonstrated a great potential for the low cost and high efficiency production of high purity electrolytes with excellent electrochemical properties for mixed-acid VRFBs. Comparing the traditional high purity electrolytes preparation process, the present novel method will dramatically cut the cost by more than 90 percent, which will considerably facilitate the commercial application of high performance and high density VRFBs.</p

Selective hydrolysis of trace TiCl4 from VOCl3 for preparation of high purity V2O5

Given the strong demands for high purity vanadium products dedicated for all-vanadium redox flow battery (VRFB), numerous preparation technologies have been developed. One of them, the chloride process that using vanadium oxytrichloride (VOCl3) as purification intermediate presents distinct technical advantages. The intermediate is readily purified via distillation process to remove most of the impurities. However, the trace titanium tetrachloride (TiCl4) is difficult to be removed, due to close saturated vapor pressures. In present work, based on thermodynamic calculation and analyses, we found that TiCl4 reacts with water significant preferentially to form the corresponding oxide, compared with VOCl3. Then we proposed a novel method to remove trace TiCl4 from VOCl3 by selective hydrolysis - distillation. The related experiments were conducted and validated the feasibility of the innovative process. Vanadium pentoxide (V2O5) with purity higher than 99.99 wt% (4N) was further prepared from the purified VOCl3 by precipitation calcination. (C) 2017 Elsevier B.V. All rights reserved.</p

Sucrose pyrolysis assembling carbon nanotubes on graphite felt using for vanadium redox flow battery positive electrode

In the present paper, multi-walled carbon nanotubes (MWCNTs) are successfully assembled on graphite felt (GF) using sucrose pyrolysis method for the first time. The in situ formed pyrolytic carbon is chosen as the binder because it is essentially carbon materials as well as CNTs and GF which has a natural tendency to achieve high bonding strength and low contact resistance. The MWCNTs/GF electrode is demonstrated to increase surface area, reduce polarization, lower charge transfer resistance and improve energy conversion efficiency comparing with GF. This excellent electrochemical performance is mainly ascribed to the high electro-catalytic activity of MWCNTs and increasing surface area. (c) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Effect of different modification methods on fluidized bed hydrogen reduction of cohesive iron ore fines

To develop breakthrough technologies that enable a drastic reduction in CO2 emissions from the ironmaking industry, the direct reduction of iron ore fines by H2-N2 in a fluidized bed with different modification methods was investigated. The results show that powder coating could prevent the defluidization of cohesive iron ore fines through the physical spacer effect, while granulation modification with cheap cement as the binder not only inhibits the occurrence of sticking, but also greatly accelerates the reduction rate. Microstructure observations indicate that granulation modification has reconstructed the irregularly shaped iron ore fines to be spherical, consisting of small grains, and created porous channels for gas diffusion, thereby increasing the reduction rate. In addition, structure reorganization constructs nonsticking barriers on the surface using native gangue and cement, and the occurrence of defluidization is avoided. Moreover, granulation modification has been demonstrated to be an effective and general solution for efficient and stable fluidized bed reduction of iron ore fines. This makes hydrogen ironmaking through fluidized bed direct reduction technically attractive. (c) 2022 Elsevier B.V. All rights reserved

High-purity, low-Cl V2O5 via the gaseous hydrolysis of VOCl3 in a fluidized bed

Present-day all-vanadium redox flow batteries (VRFBs) generally require high purity vanadium oxide as a raw ingredient. The chlorination procedure presents distinct technical advantages with regard to preparing high purity vanadium pentoxide (V2O5) using vanadium oxytrichloride (VOCl3) as a highly pure intermediate. To efficiently prepare high purity V2O5 from VOCl3, a single-step fluidized bed chemical vapor deposition (FBCVD) method was explored in the present work. Based on thermodynamic analyses, the direct and complete conversion of VOCl3 to V2O5 is difficult, and may result in a small amount of residual Cl in the product. Consequently, the effects of temperature and the H2O/VOCl3 molar ratio on the quantity of residual Cl were assessed. The Cl concentration was found to decrease with increasing temperature or increasing H2O/VOCl3 molar ratios. Additionally, Cl was determined to be present only in the form of Cl-V bonds, while Cl-H and Cl-Cl bonds were not detected in a V2O5 product made at 200 degrees C with a H2O/VOCl3 molar ratio of 18. A Cl concentration of less than 0.05 wt% was obtained under the optimal synthesis conditions, demonstrating that the FBCVD method is a viable means of preparing high purity V2O5 via the gaseous hydrolysis of VOCl3. (C) 2019 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Influence of Oxygen Volume Percent on the Acid Solubility of Titanium Slag during the Oxidation Roasting Process

The influencing mechanism of oxygen volume percent (%VO2) on the acid solubility of the titanium slag during the oxidization at 1273K (1000 degrees C) are investigated. %VO2 has marginal effect on the phase composition evolution, but greatly affects the microstructure evolutions during the oxidation, that is, increasing %VO2 promotes Fe outward migration and further results in the formation of pores and Fe-deficient M3O5 phase, which have opposite effects on the slag solubility. Particularly, for the slag oxidized at low %VO2 (3vol%O-2), its acid solubility is bad, due to no obvious Fe outward migration happens and particles show extremely dense structure, unfavorable for the subsequent reactions. For the slag oxidized at moderate %VO2 (around 6vol%O-2), its acid solubility can be promoted, since Fe outward migration slightly happens and pores form from the original dense structure. However, for the slag oxidized at high %VO2 (21vol%O-2), since excessive Fe outward migration results in the formation of Fe-deficient M3O5 phase in the particle center, which is hard to be reduced and further leached, its acid solubility is also bad, although more pores form in such cases.</p

High-purity, low-Cl V2O5 via the gaseous hydrolysis of VOCl3 in a fluidized bed

Present-day all-vanadium redox flow batteries(VRFBs)generally require high purity vanadium oxide as a raw ingredient.The chlorination procedure presents distinct technical advantages with regard to preparing high purity vanadium pentoxide(V2O5)using vanadium oxytrichloride(VOCl3)as a highly pure intermediate.To efficiently prepare high purity V2Os from VOCl3,a single-step fluidized bed chemical vapor deposition(FBCVD)method was explored in the present work.Based on thermodynamic analyses,the direct and complete conversion of VOCl3 to V2O5 is difficult,and may result in a small amount of residual Cl in the product.Consequently,the effects of temperature and the H2O/VOCl3 molar ratio on the quantity of residual Cl were assessed.The Cl concentration was found to decrease with increasing temperature or increasing H2O/VOCl3 molar ratios.Additionally,Cl was determined to be present only in the form of Cl-V bonds,while Cl-H and Cl-Cl bonds were not detected in a V2O5 product made at 200℃with a H2O/VOCl3 molar ratio of 18.A Cl concentration of less than 0.05 wt%was obtained under the optimal synthesis conditions,demonstrating that the FBCVD method is a viable means of preparing high purity V2O5 via the gaseous hydrolysis of VOCl3