Modification Of Graphite Felts And Their Application For Organic Flow Batteries

Redox flow battery（RFB）can be readily scaled up and independent control of stored energy and power,and is often used in large energy storage systems.In RFB,in order to enhance the catalytic activity of graphite felt（GF）electrodes,methods of decorating metals,metal oxides,conductive polymers or carbon nanomaterials on the surface of GF have been proposed and examined.In this thesis,cyclic voltammetric electrodeposition was used to decorate highly catalytic and binder-free MnO₂ nano-particle,which were applied for2,5-dihydroxy-1,4-benzoquinone（DHBQ）/K₄Fe（CN）₆ flow batteries.MnO₂nanoparticles significantly enhanced the mass transfer and reaction activity of the electrode surface.The contact angle measurement showed that the hydrophilicity of the electrode increased significantly.We conducted a series of studies on the electrodeposition conditions for MnO₂,including scan rate and scan cycles.The graphite felt electrode with a scan rate of 10 m V/s and electrodeposited 20 circles of MnO₂ nanoparticles showed the best electrochemical performance for the redox reaction of DHBQ.At a current density of 100 m A/cm²,the first-cycle energy efficiency of the battery using GF-MnO₂ reached 58.6%,which was 3.0%higher than the battery using the pristine GF electrode.Secondly,we prepared polyaniline（PANI）decorated graphite felt by cyclic voltammetric electrodeposition,and studied the electrochemical performance of GF-PANI for DHBQ/K₄Fe（CN）₆ flow battery.At a current density of 100 m A/cm²,the first-cycle voltage efficiency（VE）of the battery using GF-PANI was 15.6%lower than that of the battery using the pristine GF electrode.This may be due to the deprotonation of PANI under strong alkaline conditions,resulting in a decrease in conductivity.Furthermore,we prepared a polyaniline-based nitrogen-doped carbon layer decorated graphite felt electrode（GF-C）for the all-vanadium flow battery.Batteries using GF-C showed high discharge capacity during the cycle test.At a current density of 80 m A/cm²,the first-cycle energy efficiency of the battery using GF-C reached 80.5%,which was an increase of 2.5%compared with the battery using the pristine GF electrode.In addition,we studied the influence of different solutions on the constant voltage electrodeposition of Ag on graphite felt.The Ag decorated graphite felt electrode exhibited poor electrochemical performance for the DHBQ redox reaction.This may be caused by the increase in side reactions and polarization caused by Ag.Batteries using Ag decorated graphite felt electrodes showed low discharge capacity during the cycle test.At a current density of 100 m A/cm²,the energy efficiency of the battery using Ag decorated graphite felt at the first cycle was 49.41%,which was 6.15%lower than that of the battery using the pristine GF electrode.