Advances in covalent organic frameworks and membranes composed of polymers of intrinsic microporosity for a next-generation redox flow battery

Abstract

Redox Flow Batteries (RFBs) have drawn attention in flexible electrochemical energy storage technology, which can integrate renewable energy sources into the electrical grid. RFBs store energy externally in liquid electrolytes containing redox-active species. Ion Exchange Membranes (IEMs) are critical components inside RFBs. Their ion conductivity, selectivity, robustness, stability, and cost have direct impact on the overall performance, efficiency, and commercial viability of a RFB system. Covalent Organic Frameworks (COFs) and Polymers of Intrinsic Microporosity (PIMs) are promising alternatives to conventional Nafion membranes. This review presents a comprehensive overview of membrane functionality within RFBs, discusses critical performance criteria, and compares traditional and advanced membrane materials. It delves into the recent progress in synthesis and fabrication strategies of COF- and PIM-based membranes, evaluates their electrochemical properties and structural advantages, and outlines the key challenges associated with their scale-up and integration into practical systems. Finally, the review identifies future research directions toward the rational design of next-generation IEMs that can enable efficient, durable, and cost-effective RFB technologies for large-scale energy storage.