Experimental and Modeling Studies on Redox Flow Batteries

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Given growing populations and industrialization and the shift toward renewable energy, the need for energy storage systems has never been higher. These systems store surplus energy during certain periods and discharge it on demand at other times, enabling the electrical grid to better integrate renewables with base load energy and be more robust to disturbances. Unfortunately, few storage methods are currently available and so less than 10% of the total delivered electric power worldwide comes via energy storage. Electrochemical methods are well poised to fill this gap due to their pollution-free operation, fast response, high efficiency, flexibility, portability and low maintenance. Among these methods, redox flow batteries (RFB) stand out. The electrodes are contained in separate compartments as in other batteries. Unlike conventional batteries, the reactants are dissolved in liquid electrolytes stored in external tanks and pumped continuously through their compartments where the redox reactions occur. These features give RFBs advantages over other batteries independent control of energy and power, inherent safety, fast and reversible redox reactions, no solid-state effects, easy thermal management, no overheating, no electrolyte breakdown and long lifetimes. However, two main factors have hindered their adoption high installed cost and durability concerns. This research program focuses on improving the performance and durability while reducing the cost of two relatively new systems zinc-cerium and vanadium-cerium RFBs. The Ce3+/Ce4+ reaction operates at the positive electrode in both RFBs, while Zn/Zn2+ and V2+/V3+ operate at the negative electrodes. These systems are very promising since they attain higher cell voltages and potentially much higher energy and power than other RFBs. The proposed research will include i) bench-scale experiments aimed at suppressing parasitic side reactions and enhancing cell performance and durability and ii) development of a comprehensive model for each battery. Novel aspects of the research are the use of mixed acids in both compartments, replacement of expensive Pt positive electrodes with highly active modified carbon materials, replacement of conventional Nafion membranes with anion exchange membranes and use of a zero-gap flow-through cell for the V-Ce RFB. Given their advantages and the lack of viable alternatives, the Zn-Ce and V-Ce RFBs are poised for a breakthrough in energy storage technology, provided the key challenges addressed in this program are overcome. Canada has played an important role in RFB development via the operation of demonstration units and venture capital investment. Success in the proposed research will help maintain Canada's prominence in this sector. The four graduate students involved in the research will learn a broad suite of cutting-edge experimental and modeling skills that will enable them to pursue successful careers in academia or the energy/manufacturing sectors.