Research On Carbon-based Electrodes Doped With Heterogeneous Elements For VRFB

Due to the increasing pollution caused by traditional fossil energy and the non-renewable characteristics,the research and development of clean and renewable energy（wind energy,solar energy,etc.）has received increasing attention.However,wind energy and solar power generation are volatile and unstable,which require intelligent and advanced Large-scale energy storage equipment to match them.The all vanadium redox flow battery（VRFB）is one of the most promising equipment in large-scale energy storage systems,but the pristine graphite felt（Pristine GF）as the most commonly used electrode material in vanadium batteries,has shortcomings such as small specific surface area,low electrochemical activity,and poor reaction kinetics,which severely restricts its commercial development.In this paper,carbon-based materials doped with heterogeneous elements are used as catalysts to modify the Pristine GF electrode,and a series of tests have been conducted on the redox reaction of the VO²⁺/VO₂⁺pair.In this paper,firstly,using urea as the nitrogen source,the nitrogen-doped reduced graphene oxide（N-rGO）material was successfully obtained by hydrothermal reaction method,and the N-rGO modified GF high-performance composite electrode was prepared.Through the material morphology characterization test,electrochemical performance test and single battery charge and discharge test,the physical and chemical properties of the modified GF electrode were explored.The experimental results showed that nitrogen atoms are successfully doped and reduced graphene oxide and modified on the GF electrode.The introduction of this nitrogen-containing functional group effectively improve the electrochemical catalytic activity of the GF electrode and reduce the electron transfer resistance.Under 80m A/cm² constant current density charging and discharging,the energy efficiency reache 76.08%,which are much higher than the 70.74%of Pristine GF electrode.Secondly,in order to compare with the doping of a single nitrogen atom,thiourea was used as the source of nitrogen and sulfur,and the nitrogen and sulfur co-doped reduced graphene oxide（rGO-NS）material was obtained by the hydrothermal reaction method,and rGO-NS Modified GF high-performance composite electrode was prepared.Through the tests of SEM,XPS and BET,it was found that nitrogen and sulfur atoms can be doped in the reduced graphene oxide at the same time,and can bring a higher specific surface area to the modified GF electrode,which prove that the nitrogen-containing and sulfur-containing functional groups can introduce more active sites for the GF electrode.In the cyclic charge-discharge test at different current densities,the rGO-NS/900 GF electrode showed the most excellent stability and rate.When the charge-discharge cycle was performed at a constant current density of 80m A/cm²,the energy efficiency was as high as 85.37%,9.29%higher than single nitrogen-doped GF electrode and 14.63%higher than the Pristine GF electrode,showing excellent overall performance.Finally,based on the diversity of heterogeneous elements and carbon-based materials,carboxylated multi-walled carbon nanotubes were doped with nitrogen（C-MWCNTs-PDA）using dopamine as a nitrogen source,and C-MWCNTs-PDA modified GF high-performance composite electrode were prepared.The research results showed that the nitrogen-containing functional groups introduced by dopamine effectively enhance the electrocatalytic activity of the GF electrode,and after the GF electrode are modified by the adsorption of carbon nanotubes,the electrochemical impedance of the electrode are significantly reduced.During discharge,its energy efficiency can reach 81.30%,indicating that C-MWCNTs-PDA can also be used as a catalyst to promote the VO²⁺/VO₂⁺redox reaction.