Preparation Of Vanadium Carbonitride Modified Graphite Felt By Shale Vanadium-rich Liquids And Its Application As Negative Electrode For Vanadium Redox Flow Battery

Vanadium redox flow battery（Vanadium battery）is an important large-scale energy storage device,which plays an active role in peak load shifting and clean energy storage.As the electrode material of vanadium redox flow battery（VRFB）,the low electrocatalytic activity of graphite felt restricts the improvement of VRFB’s energy efficiency.Vanadium carbonitride is expected to improve the electrocatalytic performance of the electrode material because of its chemical stability and electrocatalytic activity.Compared with NH₄VO₃,V₂O₅,and V₂O₃,shale vanadium-rich liquids can shorten the process and reduce the cost of preparing vanadium carbonitride,which is beneficial to its application in VRFB.Because of this,shale vanadium-rich liquids were used to prepare the precursors of vanadium carbonitride by hydrothermal method using oxalic acid as a reducing agent and dispersant.Then the precursors were used to prepare vanadium carbonitride by carbothermal nitriding reaction.Finally,vanadium carbonitride modified graphite felt composite electrode material was prepared by a coating method.The vanadium carbonitride/graphite felt composite electrode material as a negative electrode improves the energy efficiency of VRFB.Main research contents and conclusions:（1）Na_xV₂O₅,VO₂,and their mixture were chosen as the target vanadium source to prepare vanadium carbonitride by thermodynamic analysis.The precursors ofδ-Na_xV₂O₅/acetylene black,VO₂（B）/acetylene black,andδ-Na_xV₂O₅/VO₂（B）/acetylene black were prepared by hydrothermal reaction using simulated vanadium-rich liquids as raw materials,acetylene black as a carbon source,oxalic acid as a reducing agent and dispersant.The yields of the three precursors reached 98.17%,93.22%,and88.47%,respectively,by exploring the effects of vanadium concentration,initial p H of vanadium-rich liquids,a dosage of oxalic acid,reaction temperature,and reaction time on the phase and yield of the precursors.The implementation of the above novel process has achieved remarkable beneficial effects:the vanadium sources and carbon sources in the precursors have been thoroughly mixed,the reaction temperature of the subsequent preparation of vanadium carbonitride is significantly reduced,and the reaction time is greatly shortened.The dispersion mechanism of the vanadium sources and carbon sources was proposed by comparing the structural properties of the vanadium sources and the precursors.Compared to the traditional methods for precursors of vanadium carbonitride,our method has a shorter process and avoids the generation of ammonia nitrogen wastewater and ammonia gas.（2）Vanadium carbonitride prepared by VO₂（B）/acetylene black performed good electrocatalytic activity for the V³⁺/V²⁺coupled reaction.The optimum conditions for preparing vanadium carbonitride by VO₂（B）/acetylene black are as follows:1150°C of reaction temperature,one hour of reaction time,0.55 of C/V ratio,200 cm³·min^-1of nitrogen flow rate.The structural characterization of the product shows that vanadium carbonitride is a nanoparticle with a particle size of 200～500 nm.The product’s surface contains V-C-H,V-C-O-H,V-N-H,and V-N-O-H.A three-electrode test system studied the electrocatalytic performance of vanadium carbonitride for the V³⁺/V²⁺coupled reaction.Cyclic voltammetry results showed that the oxidation peak current density reached 2.02 m A·cm^-2and the peak potential difference was 96 m V,indicating that vanadium carbonitride showed good electrocatalytic activity for the V³⁺/V²⁺coupled reaction.The functional groups such as V-C-H,V-N-H,V-C-O-H,and V-N-O-H on the vanadium carbonitride surface enhanced vanadium ions’adsorption,and the chemical bonds such as V-C and V-N strengthened the electron transfer in the redox reaction process.（3）The effects of binder addition,conductive agent addition,and vanadium carbonitride loading on vanadium carbonitride/graphite felt composite electrode material performance was studied.The results showed that introducing vanadium carbonitride into graphite felt could improve the electrocatalytic activity of the electrode material and the energy efficiency of VRFB.The electrocatalytic activity of the vanadium carbonitride/graphite felt composite electrode material prepared under the optimal conditions was significantly higher than that of the conventional graphite felt electrode material for the V³⁺/V²⁺coupled reaction in the three-electrode system,and the oxidation peak and reduction peak current densities reached 151.10 m A·cm^-2and-195.90 m A·cm^-2,respectively.The vanadium carbonitride/graphite felt composite electrode material can maintain a stable phase and surface structure after cyclic catalysis for the V³⁺/V²⁺redox reaction.The single cell was assembled with vanadium carbonitride/graphite felt composite electrode material as the negative electrode,and the battery performance was tested.The results showed that when the current density was 50 m A·cm^-2,the discharge capacity,voltage efficiency,and energy efficiency of the battery was 1.48 Ah,85.62%,and 80.02%,respectively.Compared with the conventional graphite felt assembled battery,it increased by 11.49%,5.02%,and3.57%,respectively.Based on the above three aspects of research:the preparation of the precursors by oxalic acid hydrothermal method using shale vanadium-rich liquids as raw materials;preparation and electrochemical properties of vanadium carbonitride;preparation and properties of vanadium carbonitride/graphite felt composite electrode material.In this paper,vanadium carbonitride/graphite felt composite electrode material was prepared by a short process of using shale vanadium-rich liquids and used as the negative electrode to improve VRFB’s energy efficiency.