Bromine Catholyte Management in Redox-Flow Batteries—Safety and Durability

Bromine catholyte in redox-flow batteries (RFBs) technology is considered a promising electrochemical storage solution as a sustainable electricity storage solution due to its fast kinetics, highly reversible reactions and low chemical costs. The main bottlenecks of bromine RFBs, either coupled with hydrogen, zinc, vanadium or polysulfide, are the safety concerns of concentrated bromine, the corrosion from bromine species resulting in a high cost of system and the rapid fading of the anolyte electrode performance in the highly corrosive environment.<br/>On the catholyte side, bromine displays a high energy density when coupled with complexing agents that decrease the vapor pressure and increase the safety, either by complexing with ethyl, hexyl-pyridinium bromide or with resins.^1,2 The membrane chemistry can also be modified to reach a higher permselectivity and decrease the bromine crossover.<br/>On the anolyte side, in hydrogen-bromine RFB, the hydrogen catalyst precious group metal (PGM) is poisoned by the catholyte crossover,³ resulting in high PGM loading (~1-2 g/kW) and short lifetime (~10² hours). PGM loading can be decreased ten-fold by encapsulating the catalyst with a coating designed with a high permselectivity towards the hydrogen anolyte.⁴ The coating has been developed through conformal polymerization,⁵ carbon nanotube encapsulation,⁶ atomic layer deposition⁷ and core-shell electrospinning.⁸<br/>Herein, we shall present the electrochemistry of catholytes, the electrocatalysis of surface-modified catalysts and cycling RFBs. In an attempt to solve the safety, durability and cost issues of bromine RFBs, we have developed a general platform, including electrodes, electrolytes and membranes, with the potential to solve general poisoning and corrosion in aqueous electrolytes.<br/><br/><b>References</b><br/>(1) Saadi, K.; Kuettinger, M.; Fischer, P.; Zitoun, D. Hydrogen-Bromine Redox-Flow Battery Cycling with Bromine Complexing Agent: On the Benefits of Nanoporous Separator Versus Proton Exchange Membrane. <i>Energy Technol.</i> <b>2021</b>, <i>9</i> (2), 1–10. https://doi.org/10.1002/ente.202000978.<br/>(2) Küttinger, M.; Saadi, K.; Faverge, T.; Samala, N. R.; Grinberg, I.; Zitoun, D.; Fischer, P. Influence of Strong Bromine Binding Complexing Agent in Electrolytes on the Performance of Hydrogen/Bromine Redox Flow Batteries. <i>J. Energy Storage</i> <b>2023</b>, <i>70</i>. https://doi.org/10.1016/j.est.2023.107890.<br/>(3) Hardisty, S. S.; Samala, N. R.; Grinberg, I.; Zitoun, D. Adsorption of Bromine Complexing Agents on Platinum Electrocatalysts and Prevention through Polydopamine Coatings. <i>Int. J. Hydrogen Energy</i> <b>2022</b>, <i>47</i> (73), 31342–31349. https://doi.org/10.1016/j.ijhydene.2022.07.037.<br/>(4) Saadi, K.; Hardisty, S. S.; Tatus-portnoy, Z.; Zitoun, D. Influence of Loading , Metallic Surface State and Surface Protection in Precious Group Metal Hydrogen Electrocatalyst for H 2 / Br 2 Redox-Flow Batteries. <i>J. Power Sources</i> <b>2022</b>, <i>536</i>, 231494. https://doi.org/10.1016/j.jpowsour.2022.231494.<br/>(5) Saadi, K.; Nanikashvili, P.; Tatus-Portnoy, Z.; Hardisty, S.; Shokhen, V.; Zysler, M.; Zitoun, D. Crossover-Tolerant Coated Platinum Catalysts in Hydrogen/Bromine Redox Flow Battery. <i>J. Power Sources</i> <b>2019</b>. https://doi.org/10.1016/j.jpowsour.2019.03.043.<br/>(6) Hardisty, S. S.; Saadi, K.; Nagaprasad Reddy, S.; Grinberg, I.; Zitoun, D. Ionically Selective Carbon Nanotubes for Hydrogen Electrocatalysis in the Hydrogen–Bromine Redox Flow Battery. <i>Mater. Today Energy</i> <b>2022</b>, <i>24</i>, 100937. https://doi.org/10.1016/J.MTENER.2021.100937.<br/>(7) Hardisty, S. S.; Frank, S.; Zysler, M.; Yemini, R.; Muzikansky, A.; Noked, M.; Zitoun, D. Selective Catalyst Surface Access through Atomic Layer Deposition. <i>ACS Appl. Mater. Interfaces</i> <b>2021</b>. https://doi.org/10.1021/ACSAMI.1C20181.<br/>(8) Saadi, K.; Fan, X.; Hardisty, S. S.; Pintauro, P.; Zitoun, D. Ultralow Platinum Loading for Redox-Flow Battery by Electrospinning the Electrocatalyst and the Ionomer in Core-Shell Fibers. <i>J. Energy Storage</i> <b>2023</b>, <i>59</i>, 106430. https://doi.org/10.1016/j.est.2022.106430.