Bromine/polysulphide RFB

The early research of RFB systems was mainly carried out in the United States and Japan. NASA built the first 1 kW true RFB system with an Fe/Cr redox couple in the 1970s [11]. In this system, an aqueous solution of ferric-ferrous is employed as the positive reactant redox couple, and the negative reactant is a solution of chromos-chromic couple, with hydrochloric acid as a supporting electrolyte in most cases. Because of the poor kinetics of the chromium redox reaction, a serious deterioration of RFBs was observed after a long period of time moreover, a relatively low open circuit potential was also obtained. These drawbacks limited its practical application. In the following years, several RFB systems were evaluated, but none of them was developed on a commercial scale until the bromine/polysulphide RFB and vanadium system was invented [4]. In this section, in addition to these two systems, we will also introduce new progress in tme RFB systems. 

A bromine/polysulphide RFB was patented by Remick in 1984 [12], but it was not widely acknowledged until Regenesys Technology commercialized this system in the 1990s [13]. From then on, considerable progress has been made to meet the standards for commercial application several testing and commercial facilities for different series were built [14]. 

For example, Figure 3 [15] shows a bromine/polysulphide RFB in Columbus, Mississippi, located east of Columbia Air Force Base. The TVA-Regenesys plant was buUt by Regenesys and TVA Public Power Institute, and its design capacity was to store up to 120 MW-h of energy. Once fully charged, it is able to provide power to 7,500 homes for 10 h or more. 

The electrolytes of the bromine/polysulphide RFB are sodium bromide on the positive side and sodium polysulphide on the negative side. These two reactants are abundant and fully soluble in water. The cost of this type of RFB is also reasonably low. 

The standard open circuit potential of bromine/polysulphide RFBs reaches 1.515 V, but in practical applications, it depends on many factors, including electrode material, electrolyte composition, operating temperature, and state of charge. 

Although bromine/polysulphide RFBs have several commercial applications, many technical challenges still exist, including [4] ... 

These drawbacks restrict bromine/polysulphide RFBs from becoming a widely com-merciahzed technology. In addition, increasing their economic efficiency and decreasing their cost are also necessary. 

---