Aqueous Hybrid Flow Battery Based On Anthraquinone Polymer Anode

Developing and utilizing renewable energy sources such as solar energy and wind energy to alleviate dependence on traditional fossil fuels is a benign strategy to achieve environmental restoration and sustainable economic development.Cost-effective energy conversion and storage technologies are urgently needed to overcome the intermittency and volatility of solar and wind power.Among many energy storage technologies,redox flow battery（RFB）is one of the most promising technologies due to its unique structure,low cost,high flexibility and high safety,which has great application potential in the field of renewable energy storage.However,traditional flow batteries based on inorganic redox species has been limited by their toxicity,corrosivity and cost.Organic redox materials have many advantages,such as low cost,environmental friendliness and the ability to regulate their electrochemical characteristic by molecular structure design.Therefore,in recent years,flow batteries based on organic redox materials have received extensive research attention.In addition,hybrid flow battery（HFB）pairing a solid-state electrode with a flow electrode was proposed to improve the energy density of RFB.Electroactive anthraquinone compounds/polymers are expected to be ideal energy storage materials for flow batteries because of their excellent electrochemical reversibility,fast multi-electron transfer reaction kinetics,environmental friendliness,and the possibility of mass production.In this dissertation,we synthesized an electro-active anthraquinone-based pyrrole polymer that was utilized as anode material to assemble hybrid flow batteries by combining with different flow cathodes.The full cell performance and cycling stability were systematically investigated.The main contents of this dissertation are as follows:（1）A novel conjugated polymer,Poly（N-anthraquinoyl pyrrole）（e-PAQPy）,containing redox-active anthraquinone units was prepared by electrochemical polymerization.The structure and physical properties of e-PAQPy were further characterized by nuclear magnetic resonance（NMR）,liquid chromatography（LC）and gel permeation chromatography（GPC）.The electrochemical properties of e-PAQPy in aqueous solution were studied by electrochemical method.e-PAQPy exhibited reversible electrochemical kinetics and high cyclic stability in acidic systems.The standard equilibrium potential of e-PAQPy was 0.064 V（vs SHE）in 0.5M H₂SO₄.（2）The physical and electrochemical properties of a high potential organic active electrolyte,violuric acid（VA）were systematically studied.The solubility of VA in acidic aqueous solution is about 0.05 M.VA and its oxidation state have very long half-life in aqueous solution system,which reveals its high chemical stability.The standard potential of VA in acidic solution is 1.137 V（vs SHE）,while in neutral solution it is about0.961 V（vs SHE）.Moreover,VA showed good electrochemical reversibility in both acidic and neutral electrolyte systems.On this basis,we combined e-PAQPy anode and VA flow cathode to design and construct e-PAQPy//VA acid HFB.The single-cell performance and cycle stability were investigated,and the possible mechanism of battery performance degradation was explored.（3）e-PAQPy//4,4-BPTS acid HFB was designed and constructed with e-PAQPy as solid anode and 4,4-dihydroxy biphenyl sulfonate（4,4-BPTS）as flow cathode.The single cell performance and cycle stability were further investigated.The experimental results show that e-PAQPy anode exhibits excellent rate performance and high cycle stability in 2 M H₂SO₄.e-PAQPy//4,4-BPTS battery has an open circuit voltage of about 0.9V and a discharge specific capacity of 124 m Ah g^-1 at0.2A g^-1,which is about 62.7%of its theoretical specific capacity,indicating its high material utilization rate.The power density of the battery at 100%SOC reached 2.92 w g^-1.In addition,after 100charge-discharge cycles,the battery capacity is basically unchanged,revealing its extremely excellent cycle stability.（4）e-PAQPy//K₄Fe（CN）₆ alkaline HFB was designed and constructed with e-PAQPy as solid anode and K₄Fe（CN）₆ as flow cathode.e-PAQPy//K₄Fe（CN）₆ battery has a discharge specific capacity of 103.6m Ah g^-1 at 2A g^-1,which is about 52.4%of its theoretical specific capacity.In addition,the battery also shows good rate performance and high cycle stability.（5）Sulfonated Poly（N-anthraquinoyl pyrrole）（e-PAQPyS）were synthesized by introducing water-soluble sulfonic groups on and Poly（N-anthraquinoyl pyrrole）through sulfonation reaction.In 1 M H₂SO₄,e-PAQPyS showed good electrochemical reversibility and excellent stability.