Fabrication Of Carbon Material Electrode For Capacitive Deionization Performance

During the development of human society,the water crisis has become a major issue that restricts the development of many countries.The earth has huge reserves of water,but freshwater for human use is scarce.97.3%of Earth’s water is composed of seawater and highly salinized water,and freshwater resources that can be used directly account for only 2.7%of the total water resources.This part of water is in the form of deep groundwater or continental glaciers.To use desalination technology to prepare fresh water from seawater and brackish water to solve the contradiction between supply and demand of fresh water,which has become a global focus and research hot spots.Capacitive desalination（CDI）,as a highly efficient and cost-effective desalination technology,has made up for the above shortcomings of traditional desalination technologies.The water and salt content after desalination is low or moderate.CDI is a kind of low-pressure,membrane-free desalination process that uses circulating capacitor structure to treat seawater or brackish water by attracting and storing the positive and negative ions in the solution through the electric double layer of the electrodes.High-performance electrode materials are the key of CDI technology.At present,carbon materials are considered as ideal CDI electrode materials due to their high specific surface area and good conductivity.In this paper,we mainly introduce the preparation of three different carbon composite electrodes,and the morphology and size of the micro-nano structure are systematically analyzed.On this basis,the electrochemical performance of the material is further tested and the materials are assembled into a CDI device.Capacitive desalination tests are conducted to test the performance of the material used in the CDI.The main research contents and conclusions are as follows:（1）Carbon nanofibers containing reduced graphene oxide（RG）and carbon nanotubes（CNTs）were prepared via electrospinning and carbonization.The addition of carbon nanotubes was found to be embedded within the inner fibers and graphene sheets,which are beneficial to provide more defects and mesopores.Without any binder,the tri-component nanofibers were directly used as CDI electrodes,which showed a desalination capacity of 13.6 mg g^-1 in a 500 mg L^-1 NaCl solution with a remarkable cyclic stability and 98%capacitance retention after 1000 cycles of charging-discharging.The presence of reduced graphene oxide and carbon nanotubes was found to effectively improve conductivity and electrosorption efficiency.Such a tri-component carbon nanofibrous sheet may be useful for making high performance electrodes for various CDI applications.（2）In this study,we prepare a carbon aerogel using electrospun polyacrylonitrile nanofibers and graphene oxide as precursor.By freeze-shaping and subsequent carbonization,the aerogel obtained showed strong interconnection between the carbon nanofibers and graphene.The assembly of 1D carbon nanofibers and 2D graphene sheets allows the aerogel to possess a unique porous structure with increased electron transfer rate.The carbon aerogel electrode prepared from s-PAN/GO-30 showed an electrosorption capacity as high as 15.7 mg g^-1 in 500 mg L^-1 NaCl solution and excellent electrosorption stability over 100 times of adsorption-desorption cycles.（3）In order to improve the adsorption capacity of Na ion and Cl ion,N-doped porous carbon nanotube composites were prepared by electrospinning and self-etching using polyacrylonitrile（PAN）and zinc acetate as raw materials.While obtaining the N doped porous carbon nanofibers（PCNF-N）with the optimal pore size,we continue to dope LiNO₃ into the spinning solution to obtain Li⁺-doped porous carbon nanofiber composites（Li⁺/PCNF-N）.The results show that PCNF-N not only has a high specific surface area and rich nitrogen content,but also enhance the conduction of electrons.PCNF-N composites have better cyclic stability,excellent specific capacitance(218.4 F g^-1)and perfect electrosorption capacity(16.7 mg g^-1).Further doping with Li⁺can form an additional diffusion layer,which helps to adsorb and store more Cl^-.