The Performance Of Polyacrylonitrile-based Graphite Felt Composite Electrode For VRFB

Renewable energy sources such as wind energy,solar energy and ocean energy are the most important alternative energy sources for fossil energy,but these renewable energy sources have inherent problems of unstable energy output.In order to solve the problem of unstable output of renewable clean energy,an energy storage system must be developed.The all-vanadium redox flow battery(VRFB),as an important chemical energy storage system,has the characteristics of high reliability,long service life,and flexible system design.Polyacrylonitrile(PAN)-based graphite felt is the most widely used electrode material for VRFB,but the poor hydrophilicity and low electrocatalytic activity of PAN-based graphite felt hinders the large-scale development of all-vanadium redox flow batteries.In order to improve the performance of PAN-based graphite felt electrodes,this paper proposed two electrode modification methods to improve the hydrophilicity and electrocatalytic activity of PAN-based graphite felt electrodes,thereby improving the overall performance of the battery.The details are as follows:(1)Using dopamine as the nitrogen source,the doped amine self-polymerization reaction was used to prepare a nitrogen-doped graphite felt composite electrode through the methods of self-polymerization and high temperature carbonization.Through physical and electrochemical performance analysis of the prepared composite electrode research was carried out,and the results indicated that compared with the untreated graphite felt electrode,the performance of dopamine modified PAN-based graphite felt composite electrode had been significantly improved.Thanks to the introduction of nitrogen-containing functional groups,the reversibility of the electrochemical reaction on the electrode surface was significantly enhanced,and the number of active sites was increased,so that the energy efficiency of the battery was improved by 5.9%compared to untreated graphite felt.After 50 charge-discharge cycles,the energy efficiency of the battery equipped with dopamine modified PAN-based graphite felt composite electrode remained above 74%.The method of using dopamine to modify the electrode had the advantages of mild reaction conditions and good environmental compatibility.The study of the performance of the PAN-based graphite felt composite electrode modified by dopamine provides a theoretical basis for the modification of the electrode of the all-vanadium flow battery.(2)Carboxylated multi-walled carbon nanotubes co-doped with sulfur and nitrogen were prepared using thiourea as the sulfur source and nitrogen source.Sulfur-nitrogen co-doped carboxylated multi-walled carbon nanotubes were used as composite catalysts to modify graphite felt electrodes.The synergistic effect of sulfur-nitrogen co-doped and carboxylated multi-walled carbon nanotubes was used to significantly improve the performance of graphite felt electrodes.Comparative analysis of the electrodes before and after modification in various aspects and angles showed that the modified graphite felt electrode had an increase of 2.3701m2/g compared to the segmented untreated graphite felt electrode,and had higher electrocatalytic activity.The electrochemical kinetics process on the surface was significantly accelerated,and the redox reaction speed was improved,so that the energy efficiency of the battery equipped with the sulfur-nitrogen blended multi-walled carbon nanotube/graphite felt composite electrode was increased by 6.62%.In this paper,sulfur-nitrogen co-doped carboxylated multi-walled carbon nanotubes were used as catalysts to modify graphite felt electrodes,which effectively improved the performance of graphite felt electrodes and provides new ideas for the modification of all vanadium flow battery electrodes.