Batteries

Research

Jump to: Review

21 pages, 7323 KiB

Open AccessArticle

Operational Experience of 5 kW/5 kWh All-Vanadium Flow Batteries in Photovoltaic Grid Applications

by Enrique García-Quismondo, Ignacio Almonacid, Maria Ángeles Cabañero Martínez, Veselin Miroslavov, Enrique Serrano, Jesús Palma and Juan Pedro Alonso Salmerón

Batteries 2019, 5(3), 52; https://doi.org/10.3390/batteries5030052 - 3 Jul 2019

Cited by 31 | Viewed by 11346

Abstract

The purpose of this work was to analyse and characterize the behavior of a 5 kW/5 kWh vanadium battery integrated in an experimental facility with all the auxiliary equipment and determine whether it would be possible to ascertain the most appropriate application for [...] Read more.

The purpose of this work was to analyse and characterize the behavior of a 5 kW/5 kWh vanadium battery integrated in an experimental facility with all the auxiliary equipment and determine whether it would be possible to ascertain the most appropriate application for storage of electricity in photovoltaic (PV) grid applications. The battery has been in operation for 9–10 months. During this time the battery has achieve a full cycle efficiency of approximately 65%. A slight reduction in efficiency is the result of the constant auxiliary power consumption from pumps amounting to 8–9% of rated power, meanwhile the stack is quite efficient showing a cycle efficiency of 73%.The operation of the pumps has been adjusted to fix the current density applied together with the state of charge in order to reduce unnecessary consumption related to the energy required for pumping. According to the results obtained, the intended improvement in global efficiency for the system has not been achieved by this proposed strategy. However, the flow factor evolution selected at this stage needs further optimization in order to establish a trade-off between the concentration overpotential and a detrimental loss in energy due to pumping. Therefore, one should be able to improve system performance through a better configuration of flow factors in order to reach total system efficiencies of 70–75% required for achieving a commercially viable product. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

25 pages, 3837 KiB

Open AccessArticle

A One-Dimensional Stack Model for Redox Flow Battery Analysis and Operation

by John L. Barton and Fikile R. Brushett

Batteries 2019, 5(1), 25; https://doi.org/10.3390/batteries5010025 - 22 Feb 2019

Cited by 37 | Viewed by 12781

Abstract

Current redox flow battery (RFB) stack models are not particularly conducive to accurate yet high-throughput studies of stack operation and design. To facilitate system-level analysis, we have developed a one-dimensional RFB stack model through the combination of a one-dimensional Newman-type cell model and [...] Read more.

Current redox flow battery (RFB) stack models are not particularly conducive to accurate yet high-throughput studies of stack operation and design. To facilitate system-level analysis, we have developed a one-dimensional RFB stack model through the combination of a one-dimensional Newman-type cell model and a resistor-network to evaluate contributions from shunt currents within the stack. Inclusion of hydraulic losses and membrane crossover enables constrained optimization of system performance and allows users to make recommendations for operating flow rate, current densities, and cell design given a subset of electrolyte and electrode properties. Over the range of experimental conditions explored, shunt current losses remain small, but mass-transfer losses quickly become prohibitive at high current densities. Attempting to offset mass-transfer losses with high flow rates reduces system efficiency due to the increase in pressure drop through the porous electrode. The development of this stack model application, along with the availability of the source MATLAB code, allows for facile approximation of the upper limits of performance with limited empiricism. This work primarily presents a readily adaptable tool to enable researchers to perform either front-end performance estimates based on fundamental material properties or to benchmark their experimental results. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

19 pages, 4689 KiB

Open AccessArticle

Vanadium Oxygen Fuel Cell Utilising High Concentration Electrolyte

by Mandar Risbud, Chris Menictas, Maria Skyllas-Kazacos and Jens Noack

Batteries 2019, 5(1), 24; https://doi.org/10.3390/batteries5010024 - 19 Feb 2019

Cited by 20 | Viewed by 13135

Abstract

A vanadium oxygen fuel cell is a modified form of a conventional vanadium redox flow battery (VRFB) where the positive electrolyte (VO²⁺/VO₂⁺ couple) is replaced by the oxygen reduction (ORR) process. This potentially allows for a significant improvement in [...] Read more.

A vanadium oxygen fuel cell is a modified form of a conventional vanadium redox flow battery (VRFB) where the positive electrolyte (VO²⁺/VO₂⁺ couple) is replaced by the oxygen reduction (ORR) process. This potentially allows for a significant improvement in energy density and has the added benefit of overcoming the solubility limits of V (V) at elevated temperatures, while also allowing the vanadium negative electrolyte concentration to increase above 3 M. In this paper, a vanadium oxygen fuel cell with vanadium electrolytes with a concentration of up to 3.6 M is reported with preliminary results presented for different electrodes over a range of current densities. Using precipitation inhibitors, the concentration of vanadium can be increased considerably above the commonly used 2 M limit, leading to improved energy density. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

16 pages, 1506 KiB

Open AccessArticle

Optimal Charging of Vanadium Redox Flow Battery with Time-Varying Input Power

by Md. Parvez Akter, Yifeng Li, Jie Bao, Maria Skyllas-Kazacos and Muhammed Fazlur Rahman

Batteries 2019, 5(1), 20; https://doi.org/10.3390/batteries5010020 - 10 Feb 2019

Cited by 35 | Viewed by 14020

Abstract

The battery energy storage system has become an indispensable part of the current electricity network due to the vast integration of renewable energy sources (RESs). This paper proposes an optimal charging method of a vanadium redox flow battery (VRB)-based energy storage system, which [...] Read more.

The battery energy storage system has become an indispensable part of the current electricity network due to the vast integration of renewable energy sources (RESs). This paper proposes an optimal charging method of a vanadium redox flow battery (VRB)-based energy storage system, which ensures the maximum harvesting of the free energy from RESs by maintaining safe operations of the battery. The VRB has a deep discharging capability, long cycle life, and high energy efficiency with no issues of cell-balancing, which make it suitable for large-scale energy storage systems. The proposed approach determines the appropriate charging current and the optimal electrolyte flow rate based on the available time-varying input power. Moreover, the charging current is bounded by the limiting current, which prevents the gassing side-reactions and protects the VRB from overcharging. The proposed optimal charging method is investigated by simulation studies using MATLAB/Simulink. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

12 pages, 5664 KiB

Open AccessArticle

Degradation Phenomena of Bismuth-Modified Felt Electrodes in VRFB Studied by Electrochemical Impedance Spectroscopy

by Jonathan Schneider, Eduard Bulczak, Gumaa A. El-Nagar, Marcus Gebhard, Paul Kubella, Maike Schnucklake, Abdulmonem Fetyan, Igor Derr and Christina Roth

Batteries 2019, 5(1), 16; https://doi.org/10.3390/batteries5010016 - 23 Jan 2019

Cited by 23 | Viewed by 9554

Abstract

The performance of all-V redox flow batteries (VRFB) will decrease when they are exposed to dynamic electrochemical cycling, but also when they are in prolonged contact with the acidic electrolyte. These phenomena are especially severe at the negative side, where the parasitic hydrogen [...] Read more.

The performance of all-V redox flow batteries (VRFB) will decrease when they are exposed to dynamic electrochemical cycling, but also when they are in prolonged contact with the acidic electrolyte. These phenomena are especially severe at the negative side, where the parasitic hydrogen evolution reaction (HER) will be increasingly favored over the reduction of V(III) with ongoing degradation of the carbon felt electrode. Bismuth, either added to the electrolyte or deposited onto the felt, has been reported to suppress the HER and therefore to enhance the kinetics of the V(II)/V(III) redox reaction. This study is the first to investigate degradation effects on bismuth-modified electrodes in the negative half-cell of a VRFB. By means of a simple impregnation method, a commercially available carbon felt was decorated with Bi

_{2}

O

_{3}

, which is supposedly present as Bi(0) under the working conditions at the negative side. Modified and unmodified felts were characterized electrochemically using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode setup. Surface morphology of the electrodes and composition of the negative half-cell electrolyte were probed using scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (TXRF), respectively. This was done before and after the electrodes were subjected to 50 charge-discharge cycles in a battery test bench. Our results suggest that not only the bismuth catalyst is dissolved from the electrode during battery operation, but also that the presence of bismuth in the system has a strong accelerating effect on electrode degradation. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

24 pages, 9008 KiB

Open AccessArticle

Investigations on a Mesoporous Glass Membrane as Ion Separator for a Redox Flow Battery

by Ioannis Michos, Zishu Cao, Zhi Xu, Wenheng Jing and Junhang Dong

Batteries 2019, 5(1), 6; https://doi.org/10.3390/batteries5010006 - 5 Jan 2019

Cited by 11 | Viewed by 7921

Abstract

This article reports extensive studies of a Vycor^® porous glass (VPG) membrane as an ion separator for an all-vanadium redox flow battery (VRFB). The VPG membrane had an average pore size of 4 nm and porosity of ~28%. The VPG ion separator [...] Read more.

This article reports extensive studies of a Vycor^® porous glass (VPG) membrane as an ion separator for an all-vanadium redox flow battery (VRFB). The VPG membrane had an average pore size of 4 nm and porosity of ~28%. The VPG ion separator exhibited higher proton diffusivity but lower conductivity than the Nafion^® 117 membrane because the former is intrinsically nonionic. The VRFB equipped with the VPG ion separator (VPG-VRFB) exhibited much better stability during long-term cyclic operation than the VRFB equipped with the Nafion-117 membrane (Nafion-VRFB) because the ionic Nafion membrane could be contaminated by vanadium ions exchanged into the water channels. This increases its area specific resistance, while the VPG does not have ion exchange capacity and hence has less vanadium ion contamination. The VPG-VRFB was found to outperform the Nafion-VRFB in energy efficiency (EE) during long-term cyclic operation although the former underperformed the latter in the initial period of continued operation. The VPG ion separator also showed markedly better thermal stability and temperature tolerance than the Nafion membrane as indicated by the significantly smaller losses of EE and discharge capacity for the VPG-VRFB than for the Nafion-VRFB after operating at 45 °C. The outstanding temperature tolerance of the VPG ion separator is due primarily to its rigid and non-swelling pore structure and nonionic nature, which are highly resistant to thermal distortion and vanadium ion contamination. The excellent temperature tolerance of the VPG may be useful for applications where temperature control is difficult. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

11 pages, 5293 KiB

Open AccessArticle

Monitoring the State of Charge of the Positive Electrolyte in a Vanadium Redox-Flow Battery with a Novel Amperometric Sensor

by Isabelle Kroner, Maik Becker and Thomas Turek

Batteries 2019, 5(1), 5; https://doi.org/10.3390/batteries5010005 - 5 Jan 2019

Cited by 19 | Viewed by 8071

Abstract

Vanadium redox-flow batteries are a promising energy storage technology due to their safety, long-term stability, and independent adjustability of power and capacity. However, the vanadium crossover through the membrane causes a self-discharge, which results in a capacity shift towards one half cell. This [...] Read more.

Vanadium redox-flow batteries are a promising energy storage technology due to their safety, long-term stability, and independent adjustability of power and capacity. However, the vanadium crossover through the membrane causes a self-discharge, which results in a capacity shift towards one half cell. This leads to a gradual decrease in its efficiency over time. Capacity balancing methods for compensation of this effect require a reliable online state of charge (SoC) monitoring. Most common methods cannot provide exact values of the individual concentration of each species in both electrolytes. In particular, the state of the positive electrolyte cannot yet be precisely determined. In this work, an amperometric SoC monitoring is proposed as a new approach. First, the suitability of the principle is investigated with a rotating disc electrode (RDE). Then, a sensor based on a gas diffusion layer (GDL) is developed and tested in the positive electrolyte. The dependencies between oxidative current and V(IV)-concentration are examined as well as those between reduction current and V(V)-concentration. Using both relationships, a reliable measurement of all relevant concentrations is possible. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

11 pages, 1770 KiB

Open AccessCommunication

Towards Production of a Highly Catalytic and Stable Graphene-Wrapped Graphite Felt Electrode for Vanadium Redox Flow Batteries

by Seyedabolfazl Mousavihashemi, Sebastián Murcia-López, Mir Ghasem Hosseini, Joan Ramón Morante and Cristina Flox

Batteries 2018, 4(4), 63; https://doi.org/10.3390/batteries4040063 - 3 Dec 2018

Cited by 5 | Viewed by 6663

Abstract

Despite the appealing features of vanadium redox flow batteries as a promising energy storage solution, the polarization losses, among other factors, prevent widespread applications. The dominant contribution to these polarization losses is the sluggish (even irreversible) electron-transfer towards reactions, leading to large over-potentials [...] Read more.

Despite the appealing features of vanadium redox flow batteries as a promising energy storage solution, the polarization losses, among other factors, prevent widespread applications. The dominant contribution to these polarization losses is the sluggish (even irreversible) electron-transfer towards reactions, leading to large over-potentials (poor rate capability). In particular, the positive half-cell reaction suffers from a complex mechanism since electron- and oxygen-transfer processes are key steps towards efficient kinetics. Thus, the positive reaction calls for electrodes with a large number of active sites, faster electron transfer, and excellent electrical properties. To face this issue, a graphene-wrapped graphite felt (GO-GF) electrode was synthesized by an electrospray process as a cost-effective and straightforward way, leading to a firm control of the GO-deposited layer-by-layer. The voltage value was optimized to produce a homogeneous deposition over a GF electrode after achieving a stable Taylor cone-jet. The GO-GF electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in order to elucidate the electrocatalytic properties. Both analyses reflect this excellent improvement by reducing the over-potentials, improving reversibility, and enhancing collected current density. These findings confirm that the GO-GF is a promising electrode for high-performance VRFB, overcoming the performance-limiting issues in a positive half-reaction. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

14 pages, 1871 KiB

Open AccessArticle

Verification of Redox Flow Batteries’ Functionality by Electrochemical Impedance Spectroscopy Tests

by Daniel Manschke, Thorsten Seipp, Sascha Berthold and K. Andreas Friedrich

Batteries 2018, 4(4), 58; https://doi.org/10.3390/batteries4040058 - 6 Nov 2018

Cited by 8 | Viewed by 7342

Abstract

The state-of-the-art functionality test of classic redox-flow-stacks measures the current–voltage characteristic with the technical electrolyte. This research paper aims to simplify the validation of redox flow batteries’ functionality by conducting electrochemical impedance spectroscopy (EIS) on redox flow stacks. Since the electrolyte used in [...] Read more.

The state-of-the-art functionality test of classic redox-flow-stacks measures the current–voltage characteristic with the technical electrolyte. This research paper aims to simplify the validation of redox flow batteries’ functionality by conducting electrochemical impedance spectroscopy (EIS) on redox flow stacks. Since the electrolyte used in the batteries is usually toxic and aggressive, it would be a significant simplification to verify the functionality with an alternative, non-toxic fluid. EIS measurements on batteries with larger sized electrodes, multiple cells, and different fluids were performed. It was demonstrated that all impedances are repeatable, thereby validating this procedure as a qualification method for full-size and complex batteries with an alternative fluid. EIS measurements were able to detect deliberately manipulated cells. This research uses three different analysis methods for the acquired data to identify errors. The respective approaches are, firstly, (1) a comparison of the Nyquist plots; secondly, (2) a comparison of the Bode plots; and thirdly, (3) a comparison of the calculated characteristic values of the equivalent circuits. The analysis found that all methods are suitable to detect errors in the batteries. Nevertheless, the bode-plot comparison method proves to be especially advantageous, because it enables a quantitative statement. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

11 pages, 2359 KiB

Open AccessArticle

Conversion of Spent Coffee Beans to Electrode Material for Vanadium Redox Flow Batteries

by Vida Krikstolaityte, Oh En Yao Joshua, Andrei Veksha, Nyunt Wai, Grzegorz Lisak and Tuti Mariana Lim

Batteries 2018, 4(4), 56; https://doi.org/10.3390/batteries4040056 - 1 Nov 2018

Cited by 22 | Viewed by 7478

Abstract

This study presents the application of pyrolyzed spent coffee beans as a potential electrode material to replace commercial bipolar graphite plate in vanadium redox flow batteries (VRB). The results indicate that the biochar obtained from spent coffee beans shows relatively good electrochemical charge [...] Read more.

This study presents the application of pyrolyzed spent coffee beans as a potential electrode material to replace commercial bipolar graphite plate in vanadium redox flow batteries (VRB). The results indicate that the biochar obtained from spent coffee beans shows relatively good electrochemical charge transfer kinetics of vanadium redox reactions as well as generates higher energy and voltage efficiency in a static cell test when compared to TF6 bipolar graphite plate. Additionally, the biochar was activated via steam at various activation times to increase its surface area, and their effect on the kinetics of the electrochemical reactions was investigated. The activated carbon did not exhibit any improvement neither in electron transfer kinetics nor in the battery efficiency, despite their increased surface area. The performed studies demonstrate that the biochar obtained from spent coffee beans can be a low-cost electrode material for VRB with improved performance characteristics. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

10 pages, 1630 KiB

Open AccessCommunication

Effect of Operating Temperature on Individual Half-Cell Reactions in All-Vanadium Redox Flow Batteries

by Ruediger Schweiss, Christian Meiser and Dana Dan

Batteries 2018, 4(4), 55; https://doi.org/10.3390/batteries4040055 - 1 Nov 2018

Cited by 11 | Viewed by 6613

Abstract

Systematic steady-state measurements were performed in order to investigate the effect of operating temperature on the individual half-cell reactions in all vanadium redox flow cells. Results confirm that the kinetic losses are dominated by the negative half-cell reaction. Steady-state polarization and AC impedance [...] Read more.

Systematic steady-state measurements were performed in order to investigate the effect of operating temperature on the individual half-cell reactions in all vanadium redox flow cells. Results confirm that the kinetic losses are dominated by the negative half-cell reaction. Steady-state polarization and AC impedance measurements allowed for extraction of kinetic parameters (exchange current densities, activation energy) of the corresponding half-cell reaction. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

16 pages, 3768 KiB

Open AccessArticle

Characterisation of a 200 kW/400 kWh Vanadium Redox Flow Battery

by Declan Bryans, Véronique Amstutz, Hubert H. Girault and Léonard E. A. Berlouis

Batteries 2018, 4(4), 54; https://doi.org/10.3390/batteries4040054 - 1 Nov 2018

Cited by 37 | Viewed by 11660

Abstract

The incessant growth in energy demand has resulted in the deployment of renewable energy generators to reduce the impact of fossil fuel dependence. However, these generators often suffer from intermittency and require energy storage when there is over-generation and the subsequent release of [...] Read more.

The incessant growth in energy demand has resulted in the deployment of renewable energy generators to reduce the impact of fossil fuel dependence. However, these generators often suffer from intermittency and require energy storage when there is over-generation and the subsequent release of this stored energy at high demand. One such energy storage technology that could provide a solution to improving energy management, as well as offering spinning reserve and grid stability, is the redox flow battery (RFB). One such system is the 200 kW/400 kWh vanadium RFB installed in the energy station at Martigny, Switzerland. This RFB utilises the excess energy from renewable generation to support the energy security of the local community, charge electric vehicle batteries, or to provide the power required to an alkaline electrolyser to produce hydrogen as a fuel for use in fuel cell vehicles. In this article, this vanadium RFB is fully characterised in terms of the system and electrochemical energy efficiency, with the focus being placed on areas of internal energy consumption from the regulatory systems and energy losses from self-discharge/side reactions. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Graphical abstract

10 pages, 2254 KiB

Open AccessArticle

Variable Porous Electrode Compression for Redox Flow Battery Systems

by Nicholas Gurieff, Victoria Timchenko and Chris Menictas

Batteries 2018, 4(4), 53; https://doi.org/10.3390/batteries4040053 - 22 Oct 2018

Cited by 18 | Viewed by 6816

Abstract

Vanadium redox flow batteries (VRFBs) offer great promise as a safe, cost effective means of storing electrical energy on a large scale and will certainly have a part to play in the global transition to renewable energy. To unlock the full potential of [...] Read more.

Vanadium redox flow batteries (VRFBs) offer great promise as a safe, cost effective means of storing electrical energy on a large scale and will certainly have a part to play in the global transition to renewable energy. To unlock the full potential of VRFB systems, however, it is necessary to improve their power density. Unconventional stack design shows encouraging possibilities as a means to that end. Presented here is the novel concept of variable porous electrode compression, which simulations have shown to deliver a one third increase in minimum limiting current density together with a lower pressure drop when compared to standard uniform compression cell designs. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

9 pages, 2695 KiB

Open AccessCommunication

Novel Approaches for Solving the Capacity Fade Problem during Operation of a Vanadium Redox Flow Battery

by Arjun Bhattarai, Purna C. Ghimire, Adam Whitehead, Rüdiger Schweiss, Günther G. Scherer, Nyunt Wai and Huey Hoon Hng

Batteries 2018, 4(4), 48; https://doi.org/10.3390/batteries4040048 - 1 Oct 2018

Cited by 38 | Viewed by 8571

Abstract

The vanadium redox flow battery (VRFB) is one of the most mature and commercially available electrochemical technologies for large-scale energy storage applications. The VRFB has unique advantages, such as separation of power and energy capacity, long lifetime (>20 years), stable performance under deep [...] Read more.

The vanadium redox flow battery (VRFB) is one of the most mature and commercially available electrochemical technologies for large-scale energy storage applications. The VRFB has unique advantages, such as separation of power and energy capacity, long lifetime (>20 years), stable performance under deep discharge cycling, few safety issues and easy recyclability. Despite these benefits, practical VRFB operation suffers from electrolyte imbalance, which is primarily due to the transfer of water and vanadium ions through the ion-exchange membranes. This can cause a cumulative capacity loss if the electrolytes are not rebalanced. In commercial systems, periodic complete or partial remixing of electrolyte is performed using a by-pass line. However, frequent mixing impacts the usable energy and requires extra hardware. To address this problem, research has focused on developing new membranes with higher selectivity and minimal crossover. In contrast, this study presents two alternative concepts to minimize capacity fade that would be of great practical benefit and are easy to implement: (1) introducing a hydraulic shunt between the electrolyte tanks and (2) having stacks containing both anion and cation exchange membranes. It will be shown that the hydraulic shunt is effective in passively resolving the continuous capacity loss without detrimentally influencing the energy efficiency. Similarly, the combination of anion and cation exchange membranes reduced the net electrolyte flux, reducing capacity loss. Both approaches work efficiently and passively to reduce capacity fade during operation of a flow battery system. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

14 pages, 3859 KiB

Open AccessArticle

The Effect of Sulfuric Acid Concentration on the Physical and Electrochemical Properties of Vanadyl Solutions

by Jamie S. Lawton, Sophia M. Tiano, Daniel J. Donnelly, Sean P. Flanagan and Thomas M. Arruda

Batteries 2018, 4(3), 40; https://doi.org/10.3390/batteries4030040 - 1 Sep 2018

Cited by 19 | Viewed by 7927

Abstract

The effects of sulfuric acid concentration in VO²⁺ solutions were investigated via electrochemical methods and electron paramagnetic resonance. The viscosity of solutions containing 0.01 M VOSO₄ in 0.1–7.0 M H₂SO₄ was measured. Diffusion coefficients were independently measured via [...] Read more.

The effects of sulfuric acid concentration in VO²⁺ solutions were investigated via electrochemical methods and electron paramagnetic resonance. The viscosity of solutions containing 0.01 M VOSO₄ in 0.1–7.0 M H₂SO₄ was measured. Diffusion coefficients were independently measured via electrochemical methods and electron paramagnetic resonance (EPR), with excellent agreement between the techniques employed and literature values. Analysis of cyclic voltammograms suggest the oxidation of VO²⁺ to VO₂⁺ is quasi-reversible at high H₂SO₄ concentrations (>5 mol/L), and approaching irreversible at lower H₂SO₄ concentrations. Further analysis reveals a likely electrochemical/chemical (EC) mechanism where the H₂SO₄ facilitates the electrochemical step but hinders the chemical step. Fundamental insights of VO²⁺/H₂SO₄ solutions can lead to a more comprehensive understanding of the concentration effects in electrolyte solutions. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

Review

Jump to: Research

62 pages, 2099 KiB

Open AccessReview

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

by Yuping Wu and Rudolf Holze

Batteries 2018, 4(3), 47; https://doi.org/10.3390/batteries4030047 - 13 Sep 2018

Cited by 45 | Viewed by 13101

Abstract

Flow batteries (also: redox batteries or redox flow batteries RFB) are briefly introduced as systems for conversion and storage of electrical energy into chemical energy and back. Their place in the wide range of systems and processes for energy conversion and storage is [...] Read more.

Flow batteries (also: redox batteries or redox flow batteries RFB) are briefly introduced as systems for conversion and storage of electrical energy into chemical energy and back. Their place in the wide range of systems and processes for energy conversion and storage is outlined. Acceleration of electrochemical charge transfer for vanadium-based redox systems desired for improved performance efficiency of these systems is reviewed in detail; relevant data pertaining to other redox systems are added when possibly meriting attention. An attempt is made to separate effects simply caused by enlarged electrochemically active surface area and true (specific) electrocatalytic activity. Because this requires proper definition of the experimental setup and careful examination of experimental results, electrochemical methods employed in the reviewed studies are described first. Full article

(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Vanadium Redox Flow Battery and Its Applications

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (16 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI