Project description:We studied the half-cell performance of a slurry-based vanadium redox flow battery via the polarization and electrochemical impedance spectroscopy methods. First, the conductive static mixers are examined and lower ohmic and diffusion resistances are shown. Further analyses of the slurry electrodes for the catholyte (VO2+-VO2 +) and anolyte (V3+-V2+) are presented for the graphite powder slurry containing up to 15.0?wt.% particle content. Overall, the anolyte persists as the more resistive half-cell, while ohmic and diffusion-related limitations are the dominating resistances for both electrolytes. The battery is further improved by the addition of Ketjen black nanoparticles, which results in lower cell resistances. The best results are achieved when 0.5?wt.% Ketjen black nanoparticles are dispersed with graphite powder since the addition of nanoparticles reduces ohmic, charge transfer and mass diffusion resistances by improving particle-particle dynamics. The results prove the importance of understanding resistances in a slurry electrode system.
Project description:The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally crosslinked polyvinyl alcohol-silica (PVA-SiO2) membranes for the vanadium redox flow battery (VRFB). Hygroscopic, proton-storing metal oxides such as SiO2, ZrO2 and SnO2 were coated on the membranes via the acid-catalyzed sol-gel strategy. The membranes of PVA-SiO2-Si, PVA-SiO2-Zr and PVA-SiO2-Sn demonstrated excellent oxidative stability in 2 M H2SO4 containing 1.5 M VO2+ ions. The metal oxide layer had good influence on conductivity and zeta potential values. The observed trend for conductivity and zeta potential values was PVA-SiO2-Sn > PVA-SiO2-Si > PVA-SiO2-Zr. In VRFB, the membranes showcased higher Coulombic efficiency than Nafion-117 and stable energy efficiencies over 200 cycles at the 100 mA cm-2 current density. The order of average capacity decay per cycle was PVA-SiO2-Zr < PVA-SiO2-Sn < PVA-SiO2-Si < Nafion-117. PVA-SiO2-Sn had the highest power density of 260 mW cm-2, while the self-discharge for PVA-SiO2-Zr was ~3 times higher than Nafion-117. VRFB performance reflects the potential of the facile surface modification technique to design advanced membranes for energy device applications.
Project description:This paper contains a vanadium redox flow battery stack with an electrode surface area 40 cm2 test data. The aim of the study was to characterize the performance of the stack of the original design. The dataset include three series of galvanostatic charge-discharge cycling in the potential region 8-16 V with current densities 75, 150 and 200 mA/cm2 for 100 cycles. Coulomb, voltaic, energy efficiencies and capacity utilization coefficient are also provided for all three series.
Project description:It is important to study the effect of Fe(III) on the positive electrolyte, in order to provide some practical guidance for the preparation and use of vanadium electrolyte. The effect of Fe(III) on the thermal stability and electrochemical behaviour of the positive electrolyte for the vanadium redox flow battery (VRFB) was investigated. When the Fe(III) concentration was above 0.0196 mol l-1, the thermal stability of V(V) electrolyte was impaired, the diffusion coefficient of V(IV) species decreased from (2.06-3.33) × 10-6 cm2 s-1 to (1.78-2.88) × 10-6 cm2 s-1, and the positive electrolyte exhibited a higher electrolyte resistance and a charge transfer resistance. Furthermore, Fe(III) could result in the side reaction and capacity fading, which would have a detrimental effect on battery application. With the increase of Fe(III), the collision probability of vanadium ions with Fe(III) and the competition with the redox reaction was aggravated, which would interfere with the electrode reaction, the diffusion of vanadium ions and the performance of VRFB. Therefore, this study provides some practical guidance that it is best to bring the impurity of Fe(III) below 0.0196 mol l-1 during the preparation and use of vanadium electrolyte.
Project description:Carbon electrodes are one of the key components of vanadium redox flow batteries (VRFBs), and their wetting behavior, electrochemical performance, and tendency to side reactions are crucial for cell efficiency. Herein, we demonstrate three different types of electrode modifications: poly(o-toluidine) (POT), Vulcan XC 72R, and an iron-doped carbon-nitrogen base material (Fe-N-C + carbon nanotube (CNT)). By combining synchrotron X-ray imaging with traditional characterization approaches, we give thorough insights into changes caused by each modification in terms of the electrochemical performance in both half-cell reactions, wettability and permeability, and tendency toward the hydrogen evolution side reaction. The limiting performance of POT and Vulcan XC 72R could mainly be ascribed to hindered electrolyte transport through the electrode. Fe-N-C + CNT displayed promising potential in the positive half-cell with improved electrochemical performance and wetting behavior but catalyzed the hydrogen evolution side reaction in the negative half-cell.
Project description:In order to increase the chemical stability of polybenzimidazole (PBI) membrane against the highly oxidizing environment of a vanadium redox flow battery (VRFB), PBI/Nafion hybrid membrane was developed by spray coating a Nafion ionomer onto one surface of the PBI membrane. The acid-base interaction between the sulfonic acid of the Nafion and the benzimidazole of the PBI created a stable interfacial adhesion between the Nafion layer and the PBI layer. The hybrid membrane showed an area resistance of 0.269 Ω cm2 and a very low vanadium permeability of 1.95 × 10-9 cm2 min-1. The Nafion layer protected the PBI from chemical degradation under accelerated oxidizing conditions of 1 M VO2 +/5 M H2SO4, and this was subsequently examined in spectroscopic analysis. In the VRFB single cell performance test, the cell with the hybrid membrane showed better energy efficiency than the Nafion cell with 92.66% at 40 mA cm-2 and 78.1% at 100 mA cm-2 with no delamination observed between the Nafion layer and the PBI layer after the test was completed.
Project description:In order to evaluate the performance of the anion exchange membranes in a vanadium redox flow battery, a novel anion exchange polymer was synthesized via a three step process. Firstly, 1-(2-dimethylaminoethyl)-5-mercaptotetrazole was grafted onto poly(pentafluorostyrene) by nucleophilic F/S exchange. Secondly, the tertiary amino groups were quaternized by using iodomethane to provide anion exchange sites. Finally, the synthesized polymer was blended with polybenzimidazole to be applied in vanadium redox flow battery. The blend membranes exhibited better single cell battery performance in terms of efficiencies, open circuit voltage test and charge-discharge cycling test than that of a Nafion 212 membrane. The battery performance results of synthesized blend membranes suggest that those novel anion exchange membranes are promising candidates for vanadium redox flow batteries.
Project description:In the title compound, {[Nd(3)(C(7)H(3)NO(4))(3)(OH)(3)]·H(2)O}(n), the Nd(III) atom is eight-coordinated by the three O atoms of three asymmetrically ?(3)-bridging hydroxide groups, by four carboxyl-ate O atoms of four different pyridine-2,5-dicarboxyl-ate (2,5-pydc) ligands, and by the N atom of a 2,5-pydc ligand. Six Nd atoms are connected by six hydroxide groups, forming an [Nd(6)(?(3)-OH)(6)] cluster unit of symmetry -3 and a slightly compressed octa-hedral geometry. Adjacent [Nd(6)(?(3)-OH)(6)] clusters are connected by the 2,5-pydc ligands, via O and N atoms, forming chains along the c axis. The remaining O atoms of the 2,5-pydc ligands link these chains into a three-dimensional framework. A disordered water molecule, located on a threefold rotation axis at the opposite side of the [Nd(6)(?(3)-OH)(6)] cluster and exposed to each of the three Nd atoms, completes the structure.
Project description:Proton exchange membrane is the key factor of vanadium redox flow battery (VRB) as their stability largely determine the lifetime of the VRB. In this study, a SPEEK/MWCNTs-OH composite membrane with ultrahigh stability is constructed by blending sulfonated poly(ether ether ketone) (SPEEK) with multi-walled carbon nanotubes toward VRB application. The carbon nanotubes disperse homogeneously in the SPEEK matrix with the assistance of hydroxyl group. The blended membrane exhibits 94.2 and 73.0% capacity retention after 100 and 500 cycles, respectively in a VRB single cell with coulombic efficiency of over 99.4% at 60 mA cm-2 indicating outstanding capability of reducing the permeability of vanadium ions and enhancing the transport of protons. The ultrahigh stability and low cost of the composite membrane make it a competent candidate for the next generation larger-scale vanadium redox flow battery.
Project description:Conducting Nafion/SiO₂ composite membranes were successfully prepared using a simple electrostatic self-assembly method, followed by annealing at elevated temperatures of 240, 270, and 300 °C. Membrane performance was then investigated in vanadium redox flow batteries (VRB). These annealed composite membranes demonstrated lower vanadium permeability and a better selectivity coefficient than pure Nafion membranes. The annealing temperature of 270 °C created the highest proton conductivity in the Nafion/SiO₂ composite membranes. The microstructures of these membranes were analyzed using transmission electron microscopy, small-angle X-ray scattering, and positron annihilation lifetime spectroscopy. This study revealed that exposure to high temperatures resulted in an increase in the free volumes of the composite membranes, resulting in improved mechanical and chemical behavior, with the single cell system containing composite membranes performing better than systems containing pure Nafion membranes.