From Molecule to Stack: A Cross‐Scale Design Framework for Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (AORFBs) have emerged as promising candidates for long‐duration grid‐scale energy storage due to their decoupled power‐energy architecture and the tunability of organic redox‐active molecules. Rapid progress across molecular design, membranes, electrodes, and system engineering has produced a diverse but largely compartmentalized body of literature, in which structure‐property relationships are often analyzed in isolation. In this review, we present a cross‐scale design framework that connects molecular descriptors to interfacial processes and, ultimately, to device‐level performance constraints. We compare major classes of organic redox‐active molecules, including quinones, viologens, phenazines, nitroxide radicals, and imides, and examine how substituent engineering governs redox potential, solubility, stability, and viscosity. These molecular characteristics are then linked to electrolyte transport, membrane selectivity, and electrode kinetics, highlighting how coupled phenomena such as crossover, aggregation, and viscosity‐mass transfer limitations emerge under practical operating conditions. Building on this framework, we analyze how membrane swelling, charge‐state‐dependent partitioning, and electrode‐molecule interactions jointly determine efficiency, lifetime, and degradation pathways. We further discuss system‐level constraints arising from concentration‐dependent viscosity, mass transport limitations, and crossover‐driven state‐of‐charge imbalance. Finally, we propose deployment‐relevant benchmarking metrics and reporting practices and outline key directions for advancing molecular stability, selective membranes, and viscosity‐aware system design.