Study On Modification Of Graphite Felt For Iron-chromium Redox Flow Battery

As a kind of new large-scale energy storage equipment with low cost,iron-chromium redox flow battery is widely used in the field of solar energy,wind energy and other green renewable energy.Electrode is one of the key materials of iron-chromium redox flow battery,among which graphite felt is widely used as the electrode of iron-chromium redox flow battery because of its high specific surface area,stable chemical properties and lower price.However,the low hydrophilic and electrochemical activity of the graphite felt electrode results in serious efficiency and capacity attenuation of iron-chromium redox flow battery,which limits its further commercial application.Therefore,it is necessary to modify the graphite felt electrode for iron-chromium redox flow battery.In this paper,the selection and modification of electrode materials for iron-chromium redox flow batteries were studied.The electrode material suitable for iron-chromium redox flow battery was determined.The electrode material was activated by introduced Zirconium phosphate?ZrP?as surface catalyst and silicic acid decomposed into SiO₂.The influence of active electrode material on the performance of iron-chromium redox flow battery was investigated.The result shows that:In order to clarify the role of carbon felt?CF?and graphite felt?GF?in iron-chromium redox flow battery,this experiment compared the polyacrylonitrile-based carbon felt and graphite felt found that: The physical-chemical parameters of graphite felt and carbon felt after the thermal activated at 500 ? for 5 h is affected significantly by their graphitization degree.Cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?manifest that GF and CF before and after the thermal activation have different electrocatalytic activities through the specific surface area,C=O group,and the graphitization degree.Therefore,GF is a more promising electrode material for ICRFBs application than CF.In order to simplify the preparation process of active graphite felt electrode,this paper found that: The electrochemical performance of iron-chromium redox flow battery can be effectively improved by introducing proper amount of ZrP on the graphite felt surface.Active graphite felt with different ZrP introducing amounts were obtained by introducing 1 mg/cm²,3 mg/cm² and 5 mg/cm² on the graphite felt surface,respectively.SEM results showed that ZrP was successfully introduced into the fiber surface.The active electrode with 3 mg/cm²?TGF-ZrP-3?has good electrochemical performance due to the right amount of phosphate group,good conductivity and hydrophilicity.At the current density of 60 mA/cm² to 120 mA/cm²,iron-chromium redox flow batteries assembled with TGF-ZrP-3 electrode have higher efficiency and more stable capacity than other batteries.Compared with TGF,at 120 mA/cm² current density,with TGF-ZrP-3 graphite felt as electrode material,iron-chromium redox flow battery voltage efficiency was improved by 3.95 %.In order to further improve the electrochemical activity and stability of graphite felt electrode,this paper found that: The silicic acid etches the graphite felt in hot air to form pores,which enlarges the effective specific surface area of the felt and provides more reactive sites.Simultaneously,the SiO₂ generated by the thermal decomposition of silicic acid not only has electrocatalytic activity but also hinders the further oxidation etching of the graphite felt by hot air.However,the SiO₂ also results in the oxidation sites caused by hot air more concentrated of the graphite felt.A large amount of the oxygen functional groups are formed on the surface of graphite felt,which enhances its wettability and electrochemical activity.At a current density of 120 mA/cm²,an iron-chromium redox flow battery assembled with graphite felts etched by 50 wt% silicic acid as the electrodes has an energy efficiency and voltage efficiency of 79.66 % and 86.27 %,the capacity of iron-chromium redox flow battery assembled with SiO₂-TGF-2 is 15.55 Ah/L and 14.60 Ah/L,respectively.The capacity decay rate is only 0.46 % per cycle.