Executive Summary :
Objective: The main objective of this proposal is to develop high-energy density, low cost, environmentally benign redox flow batteries with the fundamental understanding of their structure-composition-performance relationships.
1. To design of aqueous flow battery which involves low cost and environmentally benign alkaline metal /metal ion pair (Mg & Al) as anolyte and halides (triiodide/iodide (I3-/I-)) redox pair as catholyte with an achievement of high cell voltage ? 3 V.
2. To study the effect of electrolyte concentration and influence of the additives for the stability of the electrochemical interface wherein high reversibility is ensured.
3. To investigate of robust, low cost and highly conductive ion exchange membrane for alkaline metal-iodine RFBs to enhance cycling ability.
4. To demonstration of a fully functional prototype of alkaline metal-halogen RFBs (100 W) by utilizing the knowledge gained to design best combination of redox couples.
Summary: The proposal describes the mechanisms that involve the investigation of high energy density, low cost and environmentally benign alkaline based redox flow batteries (RFBs) for bulk storage of electricity. Among the various redox chemistries, few significant and reliable systems includes zinc-bromine, all vanadium iron-chromium, polysulfide-bromine and soluble lead acid batteries with the known critical challenges such limited energy density, materials instability, solubility of the electrolyte and overall cost of the systems. In this regard, the development of high performance RFBs is highly desirable. In general, there are two ways to enhance the energy density (i) concentration of the electrolyte (ii) number of electron involved in the redox species (iii) the cell voltage. Fine tuning the cell voltage with designing new redox couple is one of the feasible and effective approaches to enhance the overall energy density. Further, non-aqueous RFBs (Li-ion and Li-Sulfur batteries with flow technology) have been proposed due to the wide electrochemical window by utilizing the organic solvents. Moreover, the scaling up of non- aqueous RFBs remains a great challenge. Thus, revisiting the aqueous flow battery with significant change in the redox chemistries and design of the system becomes very important. In principal, it is not possible to obtain high redox voltage in aqueous electrolyte due to water electrolysis. Thanks to the Pourbaix diagram, the pH value of an aqueous electrolyte has a great influence of redox potential of electrodes. Inspired by this idea, the low hydrogen evolution potential in alkaline medium can be combined with high oxygen evolution potential in acidic medium. This new RFB can exhibit almost double the cell voltage of conventional aqueous RFB enhancing the energy density. Here alkaline metal hydroxides (Mg & Al) are coupled with iodine redox pair to achieve the cell voltage close to 3 V.