Redox flow battery types

In redox flow batteries such as Zn/Cl2 and Zn/Br2, carbon plays a major role in the positive electrode where reactions involving Cl2 and Br2 occur. In these types of batteries, graphite is used as the bipolar separator, and a thin layer of high-surface-area carbon serves as an electrocatalyst. Two potential problems with carbon in redox flow batteries are (i) slow oxidation of carbon and (ii) intercalation of halogen molecules, particularly Br2 in graphite electrodes. The reversible redox potentials for the Cl2 and Br2 reactions [Eq. (8) and... 

Another type of redox flow battery that utilizes carbon electrodes and soluble reactants involving vanadium compounds in H2S04 is under evaluation [38,39] ... 

Each type of fuel cell tends to be specific to a given manufacturer and information on the construction is highly proprietary. Ogawa and Shimizaki [66] studied the effects of carbonization and surface treatment conditions on the performance of redox flow battery using PAN based carbon fibers. 

Other Types of Typical Redox Flow Batteries. 74... 

Based on the occurrence of phase transition, redox flow batteries can be classified as a true system or a hybrid system. In a true system, active species dissolve in the electrolytes all the time, and no second phase other than liquid is formed on the electrode. For a hybrid system, at least one kind of active species is insoluble solid or gas. In the next chapter, we will introduce different types of redox flow batteries using this method. 

OTHER TYPES OF TYPICAL REDOX FLOW BATTERIES... 

As mentioned in early sections, redox flow batteries can be classified into different types based on electrochemical reactions occurring at the electrodes. Divided and undivided reactor configurations of redox flow batteries are shown in Figure 11. 

The electrode materials for redox flow batteries can be classified into two-dimensional (2D) and three-dimensional (3D) types. CF is conunonly used as a 3D electrode, while carbon cloth, carbon black, and AC are 2D electrodes. Typically, in a sodium polysulfide/bromine RFB, CF, carbon cloth, carbon black, and AC are main electrode materials for an aqueous bromide/bromine couple, and AC, metal foam, and CF are main electrode materials for a negative half-cell. 

The co-laminar flow principles of microfluidic electrochemical cells enable mixed media operation, in contrast to traditional types of fuel cells aud redox flow batteries operating under all-acidic or all-alkaline conditions imposed by the membranes. The unique mixed media capability allows independent tuning of half-cell conditions for optimization of reaction kinetics and cell potential. In nuxed media conditions, the open-circuit cell voltage can be increased by shifting the reversible... 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

There are three types of zinc-flow batteries (belonging in general to the group of flow or redox batteries) which have been studied intensively two of them are similar with respect to the reactants involved, the... 

Flow cells (also redox flow cells, flow batteries) are similar to batteries, except that the electrodes are catalysts for the chemical reaction, which occurs as a microporous membrane allows ions to pass from one electrolyte solution to another. Among flow cells are types that use zinc and bromine, vanadium in two types with different states, or polysulfide and bromine as the pairs of electrolytes. The advantages of flow cells are that they are capable of a large number of cycles, and the electrolytes can be replenished. 

Other types of batteries have been introduced to serve specific needs (electric vehicles, electricity storage for grid support, etc.). For this discussion, we have chosen to focus on sodium-sulfur (Na-S) batteries and nickel-chloride-based batteries, which are both so-called high temperature battery systems, and lastly redox flow systems. 

There are three types of zinc-flow batteries (belonging in general to the group of flow or redox batteries) which have been studied intensively two of them are similar with respect to the reactants involved, the zinc/chlorine [(—) Zn/HCl, ZnCl2/Cl2 (+)] and the zinc/bromine [(—) Zn/HBr, ZnBr2/Bt2 (+)] batteries the third one uses an alkaline electrolyte and potassium ferricyanide as active cathode material [(-) Zn/NaOH/K3[Fe(CN)6[(+)] [192]. 

The Daniell cell illustrates the basic features of an electrochemical cell. Electrochemical cells always involve a redox reaction. Oxidation occurs at the cathode of the cell and reduction takes place at the anode. Electrons always flow from the anode to the cathode. Electrochemical cells come in many arrangements. To gain an appreciation for the variety of electrochemical cells, consider all the types of batteries available. 

Electrons created in the oxidation reaction at the anode of a voltaic cell flow along an external circuit to the cathode, where they fuel the reduction reaction taking place there. We use the spontaneous reaction between zinc and copper as an example of a voltaic cell here, but you should realize that many powerful redox reactions power many types of batteries, so they re not limited to reactions between copper and zinc. 

There are two types of electrochemical cells. A galvanic or voltaic cell produces electric current from a spontaneous reaction, whereas an electrolytic cell has an external current source, such as a battery, to drive a nonspontaneous reaction. Reactions in electrochemical cells are redox reactions since they involve a transfer of electrons from a reducing agent to an oxidizing agent. The reduction reaction withdraws electrons from one electrode, the positive electrode or cathode. The oxidation reaction supplies electrons to the other electrode, the negative electrode or anode. Current flows via an external circuit from the anode to the cathode. 

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