The Vanadium Redox Battery

Vanadium half-cell Cell Stack Vanadium half-cell 

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Skyllas-Kazacos M, Peng C, Cheng M. Evaluation of precipitation inhibitors for supersaturated vanadyl electrol3des for the vanadium redox battery. Electrochem Solid-State Lett 1999 2 121-2. 

Sukkar T, Skyllas-Kazacos M. Water transfer behaviour across cation exchange membranes in the vanadium redox battery. J Membr Sci 2003 222 235 7. 

The vanadium redox battery stands for a whole family of batteries in which the active material is exclusively stored in the electrolyte. The electrode material does not participate in the electrochemical reactions but only acts as acceptor or donator of... 

The vanadium redox battery uses also a cell stack of bipolar plates and separate tanks for the positive and the negative electrolytes, similar to the design of Fig. 1.39. (cf., e.g. Fig. 7.9 in Ref. 76). An ion exchange membrane is used as separator in each cell. 

Other redox systems were also proposed in the past, such as the zinc/alkaline sodium ferricyanide [NajFeCCN) H2O] couple, and initial development work was performed. However, none of these efforts proved successful, mainly because of difficulties resulting from the efficacy and resistance of the ionic exchange membranes, until the development of the vanadium redox battery, by the University of New South Wales, Australia, in the late 1980s. Almost concurrently with this, development work started on VRBs at Sumitomo Electric Industries (SEI) of Osaka, Japan. Starting in the mid-1990s, VRB development has also been conducted at Mitsubishi Chemical s Kashima-Kita facility, although at a lower level of effort than at SEI. 

The calculated density values used in the above model were based on the molality of vanadium (III) sulphate and excess sulphuric acid. Nevertheless, these concentration units are not commonly used to report the composition of vanadium solutions used in the vanadium redox battery. Hence, the data were re-fitted to the above model but using the molar concentration of the vanadium ions and the total molar concentration of the sulphate ions [S04 ]t as shown in Equation 10.3. These concentration units are most frequently used to report the properties of the vanadium solutions. The calculated coefficients are shown in Table 10.4. 

The properties of the negative half-cell solutions are critical in the design and optimisation of the vanadium redox battery, especially for low-temperature operation where the solubilities of V(ll) and V(in) sulphates will influence the maximum practical vanadium ion concentration in the VRB electrolyte. The selected composition of the VRB electrolyte will determine the solution properties such as density, viscosity and conductivity and these in turn are also influenced by temperature. 

Redox flow batteries, under development since the early 1970s, are stUl of interest primarily for utility load leveling applications (77). Such a battery is shown schematically in Figure 5. Unlike other batteries, the active materials are not contained within the battery itself but are stored in separate tanks. The reactants each flow into a half-ceU separated one from the other by a selective membrane. An oxidation and reduction electrochemical reaction occurs in each half-ceU to generate current. Examples of this technology include the iron—chromium, Fe—Cr, battery (79) and the vanadium redox cell (80). 

One of the most important requirements that must be met is the membrane s ability to prevent excessive transfer of water from one half cell to the other. The preferential transfer of water can be a problem in the vanadium battery as one half-cell (the negative half cell in the case of cation exchange membranes) is flooded and becomes diluted, while the other becomes more concentrated, adversely affecting the overall operation of the cell. Most of the membranes show good initial water transfer properties, but their performance deteriorates with exposure to the vanadium solutions. Sukkar et al. ° evaluated various polyelectrolytes to determine whether they could improve the selectivity and stability of the membranes in the vanadium redox cell solutions. Both the cationic and anionic polyelectrolytes evaluated improved the water transfer properties of the membranes, although upon extended exposure to the vanadium electrolyte the modified membranes did not maintain their improved water transfer properties. The solvent based Nuosperse 657 modified membrane displayed exceptional properties initially but also failed to maintain its performance with extended exposure to the vanadium solutions. 

A ubiquitous characteristic of vanadium chemistry is the fact that vanadium and many of its complexes readily enter into redox reactions. Adjustment of pH, concentration, and even temperature have often been employed in order to extend or maintain system integrity of a specific oxidation state. On the other hand, deliberate attempts to use redox properties, particularly in catalytic reactions, have been highly successful. Vanadium redox has also been successfully utilized in development of a redox battery. This battery employs the V(V)/V(IV) and V(III)AT(II) redox couples in 2.5 M sulfuric acid as the positive and negative half-cell electrolytes, respectively. Scheme 12.2 gives a representation of the battery. The vanadium components in both redox cells are prepared from vanadium pentoxide. There are two charge-discharge reactions occurring in the vanadium redox cells, as indicated in Equation 12.1 and Equation 12.2. The thermodynamics of the redox reactions involved have been extensively studied [8],... 

The book includes discussion of the vanadium haloperoxidases and the biological and biochemical activities of vanadium(V), including potential pharmacological applications. The last chapters of the book step outside these boundaries by introducing some aspects of the future of vanadium in nanotechnology, the recyclable redox battery, and the silver/vanadium oxide battery. We enjoyed writing this book and can only hope that it will prove to provide at least a modicum of value to the reader. 

New perspectives arising from isothermal oxidation. The next chapter of this book describes the greatly altered perspective of the fuel cell industry, when Grove s ideas are updated. The second chapter describes the detail of Regenesys, or ESS-RGN. This system has changed hands, as noted above, and information is available from http //www.vrbpower.com/. (The initials VRB stand for Vanadium Redox Battery, a low-power alternative to Regenesys.) The new 2005 VRB Power Systems shorthand is ESS-VRB for 2.5 to 10 MW and ESS-RGN for 10 to 100 MW. In Chapter 2 the reader will be acquainted with ESS-RGN, one of the two VRB fuel cell systems (incompressible liquid based) which can be termed complete . The redox battery uses small pumps as circulators. 

Because vanadium ions exist in four different oxidation states (as V2+, V3+, V02+ and V02+) in aqueous solution, redox couples can be formed by all vanadium ions. The emf of a vanadium redox battery is 1.4 V and the electrode kinetics are higher than those of the Fe-Cr battery. Also, the energy density of the battery can be increased due to the high solubility of vanadium salts.257 In the battery, vanadium sulfate solution is used,... 

Based on their early fundamental research of all-VRFBs, Skyllas-Kazacos et al. [25] also first developed some commercial products, for example, a 1 kW vanadium redox battery (VRB) cell stack. By employing 1.5-2 M vanadium sulphate, sulphuric acid in both half-cells, over 85% of theoretical capacity and 70-80% energy efficiency was obtained. Then in 1994, a 4 kW/12 kWh vanadium battery was evaluated in a demonstration solar house by Thai Gypsum Products Ltd. in Thailand under a license lirom the UNSW [26]. 

Zhang Q, Dong QF, Zheng MS, Tian ZW. The preparation of a novel anion-exchange membrane and its application in all-vanadium redox batteries. J Membr Sci 2012 421 232-7. 

The operational principle of a vanadium-vanadium redox flow cell (vanadium redox battery or VRB) is illustrated in Figure 12.8. 

Mostly in batteries the reacting substances are stored within the electrodes (the active material ), but there are also systems where the electrolyte participates, as in lead-acid batteries, or where the reacting substances are stored in separate tanks, e.g. Zn/Cl, Zn/Br, and vanadium redox batteries (Section 1.8.5), or as a gas in the container of nickel-hydrogen batteries (Section 1.8.3). 

Figure 1.41 Charge/discharge curves of a vanadium redox battery. The cell stack consisted of 17 cells. Constant current of 100 Ah for charging and discharging (from Ref. 80). 

Regardless of their weight and size restriction drawbacks, the vanadium-based redox battery system has a potential application as a standalone power source in a remote and unknown location where no power lines exist. In brief, the vanadium-based battery system will be best suited for special forces or covert military missions operating in a remote or hostile location where no commercial power lines exist. 

Fundamentally, both MEA-based and membraneless cells require two electrodes with an ionically conductive electrolyte between them. It is therefore proposed that a volumetric power density normalized by the essential volume of the electrochani-cal chamber, including both electrodes and the separating electrolyte, would be the most universally applicable metric for these devices. This metric captures any variations in electrolyte channel separation and electrode thickness with the only assumption being that the inlet/outlet flow field manifolds and other structural support elements are comparable between cells. With this new convention, the key microfluidic electrochemical cell technologies with the highest power densities reported to date were converted where possible and presented in Table 6.1. For comparative purposes, estimates for a typical MEA-based vanadium redox battery (VRB) [17, 18] and a DMFC [19] are also included. 

The vanadium redox flow battery (VRB) proposed by Skyllas-Kazacos and coworkers has attracted many attentions due to its long cycle life, flexible design, fast response time, deep-discharge capability, and low cost in energy storage. The VRB employs and VO +/V02 redox couples in the negative and positive... 

An equivalent circuit of shunt current. (Reprinted from /. Power Sources, 196, F. Xing, H. Zhang and X. Ma, Shunt current loss of the vanadium redox flow battery, 10753-10757. Copyright 2011, with permission from Elsevier.)... 

T. Mohammadia, S.C. Chiengb, M. Skyllas Kazacos, Water transport study across commercial ion exchange membranes in the vanadium redox flow battery, /. Membr. Sci. 133,1997,151-159. 

F. Chang, C. Hu, X. Liu, L. Liu and J. Zhang, Coulter dispersant as positive electrolyte additive for the vanadium redox flow battery, Electrochim. Acta 60,2012, 334 38. 

Physical Properties of Negative Half-Cell Electrolytes in the Vanadium Redox Flow Battery... 

See colour insert.) Photograph of an all-vanadium redox flow battery showing the electrolyte reservoirs that store the two half-ceU solutions that are pumped through the cell stack where energy is generated by the electrochemical reactions of the vanadium redox couples at inert electrodes. 

A redox battery using solutions with two different oxidation states of vanadium has recently been announced by the University of New South Wales in Sidney, Australia. When fully charged, each cell of the battery can generate a potential of about 1.5 V. A demonstration golf cart driven by the battery has been developed. Licences to industries in Thailand and Japan are underway for the production of large units for back-up power in solar houses or for peak demand in power stations. 

Developing technologies in vanadium science provide the basis for the last two chapters of this book. Vanadium(V) in various forms of polymeric vanadium pen-toxide is showing great promise in nanomaterial research. This area of research is in its infancy, but already potential applications have been identified. Vanadium-based redox batteries have been developed and are finding their way into both large-and small-scale applications. Lithium/silver vanadium oxide batteries for implantable devices have important medical applications. 

Notably, SVO can display a variety of phases, both stoichiometric and nonstoichiometric. Thus, variations in reaction conditions, starting materials, and reagent stoichiometries for the preparation of SVO can result in a wealth of products that display different structures and different properties. In addition, the variety of oxidation states available to the silver and especially the vanadium components of SVO, plus the open structure of some of the SVO materials, suggest that these materials are well suited for electron transfer applications. It is thus logical and not surprising that reports of SVO battery applications and SVO redox catalyst applications appear within similar time frames. Some reports involving the structure of SVO solids and the catalysis of organic substrate oxidation by SVO-based catalysts will be described in Section 13.2, due to their possible relevance to the SVO battery chemistry described in Section 13.3. 

Zn-bromine flow and vanadium redox flow are special cases of secondary batteries. Here, liquid electrode materials are used on one (Zn-Br flow) or both sides (V redox flow) of the electrochemical cell. In contrast to regular batteries, which are typically completely closed systems, the liquid electrode materials in flow batteries are circulated and replenished from tanks (Figure 3.5.5). Therefore, the flow batteries possess large electrodes, the effective size of which is just limited by the volume of those tanks. This partly decouples energy and power capabilities of the batteries, allowing one to optimize both separately. 

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