Long-cycling organic flow batteries enabled by electronic-spatial synergistic modulation

Aqueous organic redox flow batteries (AORFBs) show promise for grid-scale energy storage but are limited by inadequate stability and solubility of active materials. Here we report an electronic-spatial synergistic modulation strategy to simultaneously enhance aqueous dissolution and electrochemical robustness of organic species, demonstrated on 4-aminophenol (PAP)-based molecules. By introducing a piperazine ring and an acetyl group at the amino site, we design 1-(4-(4-hydroxyphenyl)piperazin-1-yl)ethan-1-one (AHPP). This synergistic modulation stabilizes the oxidized state, suppresses side reactions, and boosts solubility to 1.9 molar in aqueous solution (3.8-molar electron concentration). An all-organic flow battery based on AHPP achieves 95.7% capacity retention after 5000 cycles, with stable operation across a wide temperature range. Integrating in situ spectroscopic and electrochemical analysis with computational modeling elucidates the redox chemistry of PAP-based molecules and establishes a link between intermediate stability and functional group effects. Life cycle assessment further reveals the environmental footprint of AHPP-based batteries, demonstrating considerable potential for practical grid-scale storage applications.