Efficient Nitrogen-doped Carbon For Zinc-bromine Flow Battery

With the development of society and technology,electrical energy has gradually played an increasingly important role as an indispensable secondary energy source for modern human production and life.Therefore,the development of energy storage technology is crucial and urgent.Flow batteries have a lot of advantages such as deep charge and discharge,modular control and breakthroughs in geographical environment,and stand out from many large-scale energy storage devices,gradually.Especially,zinc bromine flow batteries have gained more attention because of their advantages such as cheap,relatively low cost and large energy density.However,under the larger current density of the zinc-bromine flow battery system,the electrode polarization phenomenon is serious,resulting in a large amount of energy loss.Therefore,development of high-catalytic active cathode materials is a better solution.In this essay,by developing a new type of cathode material,it is intended to solve the problem of electrode polarization in a zinc-bromine flow battery system to improve the electrocatalytic activity of the cathode and the performance of the single cell.This paper explores a green and efficient method for the preparation of carbon materials,and develops an efficient carbon electrocatalyst by adjusting the temperature and time parameters of ammonia gas heat treatment.And we adopt a variety of modern physical and chemical characterization methods:scanning electron microscope,X-ray powder diffraction,Raman spectroscopy,nitrogen adsorption and desorption experiments,X-ray photoelectron spectroscopy,etc.At the same time,combined with electrochemical methods:cyclic voltammetry,electricity chemical impedance spectroscopy,etc.,we constructed the structure-effect relationship of materials.And tested in single cell test of zinc bromine flow battery,the battery data of the material was obtained.Firstly,we studied a green and efficient way to synthesize carbon materials.The carbon sphere?CS-900?was obtained by pyrolysing 0.50 M glucose at 180 ^oC for 6 hours and carbonizing at 900 ^oC for 3 hours.By adjusting the temperature and time parameters of the ammonia gas heat treatment,we finally obtained carbon materials with different nitrogen doping degrees and specific surface areas.It was found that the carbon material?CS-NH₃-1000-10?has a relatively high specific surface area and more heteroatom functional groups compared with other carbon materials when the ammonia gas treatment temperature is 1000 ^oC and the treatment time is 10 minutes.Heteroatom functional group?nitrogen/oxygen functional group?,which is conducive to the formation and exposure of more active sites,so that the material has higher catalytic activity.Secondly,from the cyclic voltammetry test results of the catalysts,it can be concluded that CS-NH₃-1000-10,which has a relatively high specific surface area and more heteroatom functional groups,has higher electrocatalytic activity.By analyzing the kinetic parameters of electrodes modified with various carbon materials,it can be seen that when the ammonia gas treatment temperature is 1000 ^oC and the treatment time is 10 minutes,the obtained carbon material has a larger exchange current.Finally,after optimizing the key materials and test conditions,the obtained electrode materials were used to assemble a zinc/bromine flow single cell for testing.At the current density of 80 m A cm^-2,the voltage efficiency?VE?of 83.0%and the Energy efficiency?EE?of 82.5%was achieved.,which is the highest value in the literature.In addition,the zinc/bromine flow single cell did not produce performance degradation after 200 cycles of charge and discharge tests,thus showing its high stability.In summary,this work provides an efficient electrode material for zinc-bromine flow batteries.