Hydrophilic Organic Redox-Active Polymer Nanoparticles for Higher Energy Density Flow Batteries

Hydrophilic redox-active polymer nanoparticles with different redox potentials and radii were synthesized via the dispersion polymerization to yield their stable dispersion in aqueous electrolyte media as promising catholytes and anolytes in redox flow batteries. Despite the small physical diffusion coefficient (10–9 cm2/s) of the nanosized particles, the sufficiently large coefficient for charge transfer within the polymer particle dispersion (10–7 cm2/s) was observed as a result of the fast electron propagation throughout the polymer particles. Redox flow cells were fabricated using TEMPO-, viologen-, or diazaanthraquinone-substituted polymer nanoparticles as active materials. The reversible charge/discharge over 50 cycles was achieved even at a high concentration of the redox units (1.5 M), which exceeded the limitation of the solubility of the corresponding dissolved species.