Enhanced Reactant Distribution in Redox Flow Cells

Cerium/Ascorbic Acid/Iodine Active Species for Redox Flow Energy Storage Battery

In this study, we developed a novel cerium/ascorbic acid/iodine active species to design a redox flow battery (RFB), in which the cerium nitrate hexahydrate [Ce(NO₃)₃·6H₂O] was used as a positive Ce³⁺/Ce⁴⁺ ion pair, and the potassium iodate (KIO₃) containing ascorbic acid was used as a negative I₂/I^- ion pair. In order to improve the electrochemical activity and to avoid cross-contamination of the redox pair ions, the electroless plating and sol-gel method were applied to modify the carbon paper electrode and the Nafion 117 membrane. The electrocatalytic and electrochemical properties of the composite electrode using methanesulfonic acid as a supporting electrolyte were assessed using the cyclic voltammetry (CV) test. The results showed that the Ce (III)/Ce (IV) active species presented a symmetric oxidation/reduction current ratio (1.09) on the C-TiO₂-PdO composite electrode. Adding a constant amount of ascorbic acid to the iodine solution led to a good reversible oxidation/reduction reaction. Therefore, a novel Ce/ascorbic acid/I RFB was developed with C-TiO₂-PdO composite electrodes and modified Nafion 117-SiO₂-SO₃H membrane using the staggered-type flow channel, of which the energy efficiency (EE%) can reach about 72%. The Ce/ascorbic acid/I active species can greatly reduce the electrolyte cost compared to the all-vanadium redox flow battery system, and it therefore has greater development potential.

Mass Transport Optimization for Redox Flow Battery Design

The world is moving to the next phase of the energy transition with high penetrations of renewable energy. Flexible and scalable redox flow battery (RFB) technology is expected to play an important role in ensuring electricity network security and reliability. Innovations continue to enhance their value by reducing parasitic losses and maximizing available energy over broader operating conditions. Simulations of vanadium redox flow battery (VRB/VRFB) cells were conducted using a validated COMSOL Multiphysics model. Cell designs are developed to reduce losses from pump energy while improving the delivery of active species where required. The combination of wedge-shaped cells with static mixers is found to improve performance by reducing differential pressure and concentration overpotential. Higher electrode compression at the outlet optimises material properties through the cell, while the mixer mitigates concentration gradients across the cell. Simulations show a 12% lower pressure drop across the cell and a 2% lower charge voltage for improved energy efficiency. Wedge-shaped cells are shown to offer extended capacity during cycling. The prototype mixers are fabricated using additive manufacturing for further studies. Toroidal battery designs incorporating these innovations at the kW scale are developed through inter-disciplinary collaboration and rendered using computer aided design (CAD).