Redox flow batteries (RFBs) are a promising technology for large scale energy storage. In RFBs power and energy are decoupled: the former depends mainly on the size of the stack while the latter on the size tanks containing the redox active species. This feature makes RFBs ideal for economical, large-scale energy storage. However, cost reductions are needed for a widespread diffusion of this technology. The required cost reductions involve two main components of the system: the electrolytes and the stack. Both need to be optimized for enabling a large-scale deployment of RFBs. RFBs are a complex system so a trade-off between cost and performances must be found for both electrolytes and stack.

This work will focus on developing and validating the use of low-cost earth-abundant redox active materials (e.g., Al, Zn, Fe, Cu, Mn, I, S) in redox flow batteries analyzing different possible solutions for redox couples and electrolytes. The doctoral thesis will start with the development of an integrated approach for the evaluation of different electrolyte solutions (combining different redox active materials, supporting electrolytes and solvents) assessing material cost and availability (with a special focus on EU-sourced materials), safety, expected performances, probability of upscaling issues (e.g., cross-over, pumping losses, etc) and other parameters in other to select the most promising solutions. This pre-selection will be refined by integrating experimental data obtained from the electrochemical and physical characterization of the electrolytes. The use of solid boosters and/or complexing agents to improve the energy density will be a fundamental step to be evaluated experimentally. The selected best candidates will be then tested in lab-scale redox flow cells customized for the specific chemistry. Membrane/separator selection or development will also be addressed during this phase. Finally, issues related to the upscaling of the technology will also be analyzed in order to assess the real potential impact of the proposed innovative solutions.