A research team at Xi'an Jiaotong University (XJTU) led by Professor Song Jiangxuan has made new breakthroughs in aqueous flow batteries.

They adopted the double-conjugation design control strategy of the substituent structure, and successively grafted an amide group with p-π electron interaction and an imidazolium group with π-π electron interaction on the 4-substituted position of the TEMPO core structure-piperidine ring, and obtained a novel "conjugated" TEMPO molecule (MIAcNH-TEMPO) with highly stable oxidation and reduction states.

 By using in situ Raman spectroscopy, UV-Vis spectroscopy, electron paramagnetic resonance techniques and density functional theory calculations, the authors confirmed the high stability of the oxidized and reduced states of the molecule and the change of the FuKui function of the molecules' electrophilic and nucleophilic attacks.

The results show that the p-π and π-π double conjugation effects brought about by the grafting of amide and imidazolium groups can significantly promote the uniform distribution of electrons at the N-O radical end (O1-N2) in TEMPO-like molecules.

More importantly, this change effectively inhibits the electrophilic and nucleophilic aggression of species such as H+ or OH- in the aqueous solution to the reduction and oxidation states of the molecule, and greatly improves the stability of the TEMPO molecule in the battery charge-discharge cycle.

This strategy can effectively improve the stability of the oxidized and reduced states of nitrogen-oxygen radicals during electrochemical charge-discharge processes, and broaden design and research possibilities for organic active key materials.

The research was published in the internationally renowned journal Angew. Chem. Int. Ed. under the title Conjugate-Driven Electron Density Delocalization of Piperidine Nitroxyl Radical for Stable Aqueous Zinc Hybrid Flow Batteries. (Link to the paper: https://onlinelibrary.wiley.com/doi/10.1002/anie.202115908 )

Assistant Professor Fan Hao of the School of Materials Science and Engineering is the first author, Professor Song Jiangxuan is the only corresponding author, and the State Key Laboratory for Mechanical Behavior of Materials of Xi'an Jiaotong University is the only corresponding author unit.

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