Research On Novel Organic Electroactive Materials For Pyridinium-Based Flow Batteries

Clean energy power generation directly incorporated into the grid will have a huge impact on the stability of the existing power system due to its discontinuous and unstable characteristic,which needs to be equipped with an energy storage system for effective consumption.Aqueous flow batteries have the advantages of intrinsic safety,capacity and power decoupling,deep charge and discharge,long cycle life,low cost of long-term energy storage,etc.,and are one of the important technologies for large-scale energy storage.For capacity batteries,Electroactive materials are the key bottleneck restricting the practical application of flow batteries.Therefore,novel electroactive materials have received extensive attention.Organic electroactive molecules have the advantages of high abundance of constituent elements,wide sources,low cost potentially,and easy modulation of structure and properties.They can get rid of the dependence on non-ferrous metal resources and are expected to be used in next-generation flow batteries.In this paper,the design and synthesis of new organic electroactive materials and their application in flow batteries are carried out to address the key issue of low energy density of aqueous organic flow batteries.The main results are as follows:（1）Novel triazine pyridineium salt electroactive molecular research.Taking the triazine ring as the dense electron storage unit and the pyridinium salt ring as the radical stabilizing unit,a new type of tripyridine salt triazine（（TPy Tz）Cl₆）electroactive molecule that can store six electrons was successfully constructed.By using nuclear magnetic resonance spectroscopy,electron paramagnetic resonance spectroscopy,Raman spectroscopy,ultraviolet-visible-near-infrared spectroscopy,DFT theoretical calculation and other means,the structural evolution of（TPy Tz）Cl₆ multi-electron storage process was studied,and its multi-electron storage mechanism was elucidated.Using（TPy Tz）Cl₆ as the negative electrode and matching ferrocene derivative Fc NCl as the positive electrode,the assembled flow battery achieved a high specific capacity of 33.0 Ah L^-1 and a high peak power density of 273 m W cm^-2.The above battery performance is better than those of the reported pyridinium salt electroactive molecules,which provide a new design concept for the development of new ultra-high-capacity organic electroactive molecules.（2）Research on a novel thermoelectric conversion based on pyridyl biradical spin state conversion.The two-electron reduction product of（TPy Tz）Cl₆ is a diradical（TPy Tz）^??4+.The energy gap between its polarized singlet and triplet states(～2 k J mol^-1)can match the low-grade thermal energy（<100℃）.Basing on the thermal conversion behavior of（TPy Tz）^??4+biradical spin states,a novel thermoelectric conversion flow battery is proposed.The ground state and excited state of the（TPy Tz）^??4+diradical were determined by in-situ variable-temperature nuclear magnetic resonance spectroscopy.The distribution of the triplet state of the（TPy Tz）^??4+diradical was determined by in-situ variable-temperature electron paramagnetic resonance spectroscopy.The cyclic voltammetry test verified that（TPy Tz）^??4+diradicals have different formal potentials at different temperatures.The thermoelectric conversion mechanism based on（TPy Tz）^??4+diradical spin state transition was verified.This work builds a new type of flow battery system for build a new type of flow battery system for heat/electricity conversion and provides a new perspective for the recovery and utilization of low-grade thermal energy.