Synthetic Membranes for Aqueous Organic Redox Flow Batteries (AORFBs): towards High Conductive and Selective Ion Channels

Aqueous organic redox flow batteries (AORFBs) have emerged as a leading electrochemical technology for grid-scale energy storage, using water-based electrolytes to deliver inherent safety and cost efficiency. High-performance ion exchange membranes promote the battery performance, including energy/power densities, operational durability, and Coulombic/energy efficiencies. This review examines recent advances in ion channel engineering for AORFB membranes, focusing on chemical synthesis strategies, structural optimization approaches, and ion channel architecture evolution. We analyze characterization methodologies for diverse membrane types, their corresponding cell performance, and design principles. We highlight conductivity-permeability relationships across membrane architectures, particularly microphase separation, microporous channels, and dual-ion configurations, establishing fundamental structure-property correlations. These insights provide a strategic roadmap for future ion channel design in membranes, advancing practical frameworks for high-performance AORFBs.

Abstract

Aqueous organic redox flow batteries (AORFBs) have emerged as one of the most promising electrochemical technologies for large-scale energy storage due to their use of water-based electrolytes, offering safety and cost advantages over organic solvent-based systems. AORFBs utilize organic molecules derived from earth-abundant elements, enabling tunable properties such as solubility, stability, and redox potential at the molecular level. These features enable improvements in energy and power densities, operational lifetimes, and efficiency metrics in the battery system. However, the lack of suitable ion exchange membranes limits the energy efficiency, power density, and long-term cycling stability. Membrane design for AORFBs faces challenges in balancing conductivity and permeability, requiring precise control over ion transfer channel size, quantity, and interconnection. This review summarizes recent advances in AORFBs membrane design, focusing on ion channel engineering through chemical and microstructural adjustments. We highlight the impact of these designs on membrane conductivity, permeability, and overall cell performance, aiming to provide a practical framework for developing superior membranes for future grid-scale AORFBs applications.

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