The combination of a polymer-based 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) catholyte and a zinc anode, together with a cost-efficient size-exclusion membrane, builds a new type of semi-organic, "green," hybrid-flow battery, which features a high potential range of up to 2 V, high efficiencies, and a long life time.

Hybrid-flow batteries are a suitable storage technology for "green" electricity generated by renewable sources such as wind power and solar energy. Redox-active organic compounds have recently been investigated to improve the traditional metal-and halogen-based technologies. Here we report the utilization of a 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) derivative that is in particular designed for application in semiorganic zinc hybrid-flow batteries. The TEMPO derivative is synthesized and electrochemically characterized via cyclic voltammetry and rotating disc electrode measurements. This derivative features a high solubility in aqueous electrolytes; thus, volumetric capacities above 20 Ah L −1 are achieved. The fabricated hybrid-flow batteries feature over 1100 consecutive charge−discharge cycles at constant capacity retention, and current densities up to 80 mA cm −2 are applied.

The combination of 2,2,6,6-tetramethylpiperidinyl-N-oxyl and phenazine yields an organic redox-active material for redox-flow battery applications. This combined molecule (combi-molecule) features a redox voltage of 1.2 V and facilitates the utilization of aqueous electrolytes. It was synthesized from cost-efficient starting materials, electrochemically characterized and applied as charge-storage material in a symmetric aqueous redox-flow battery.

The utilization of boron-dipyrromethene (BODIPY) as active group for the charge storage process in a battery application is reported. Two BODIPY-containing copolymers were synthesized and electrochemically characterized. The polymers feature redox processes at 0.7 V and −1.5 V vs AgNO3/Ag, which enable the application in a redox-flow battery setup.

A poly(TEMPO methacrylate)-poly(styrene) block copolymer was utilised as catholyte in polymer/zinc hybrid flow batteries.

Organic polymer-based batteries represent a promising alternative to present-day metal-based systems and a valuable step toward printable and customizable energy storage devices. However, most scientific work is focussed on the development of new redox-active organic materials, while straightforward manufacturing and sustainable materials and production will be a necessary key for the transformation to mass market applications. Here, a new synthetic approach for 2,2,6,6tetramethyl-4-piperinidyl-N-oxyl (TEMPO)-based polymer particles by emulsion polymerization and their electrochemical investigation are reported. The developed emulsion polymerization protocol based on an aqueous reaction medium allowed the sustainable synthesis of a redox-active electrode material, combined with simple variation of the polymer particle size, which enabled the preparation of nanoparticles from 35 to 138 nm. Their application in cell experiments revealed a significant effect of the size of the active-polymer particles on the performance of poly(2,2,6,6-tetramethyl-4-piperinidyl-N-oxyl methacrylate) (PTMA)-based electrodes. In particular rate capabilities were found to be reduced with larger diameters. Nevertheless, all cells based on the different particles revealed the ability to recover from temporary capacity loss due to application of very high charge/discharge rates.

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Despite a continuous effort to develop novel materials for organic polymer-based batteries, their commercial success is still hampered by the demanding synthesis and the high costs of these materials. To overcome these issues, we developed poly(naphthotriazolequinonestyrene) (pNTQS), the first redox-active polymer bearing naphthotriazolediones, and have demonstrated its promising characteristics for an application in organic batteries. The polymer is effectively synthesized using a straightforward cycloaddition reaction followed by a free-radical polymerization. The electrochemical investigations of this new material reveal a two-electron storage capability, and an electrolyte system optimized for use in Li−organic batteries was established. Coin cells comprising pNTQS as active electrode material reveal an excellent capacity of 135 mAh g −1 , which exceeds most of the commonly applied polymer-based materials, while a capacity loss of only 30% over 1000 cycles was observed.