Fabrication Of Graphene-based Composite Electrode Materials For Capacitive Deionization

The water crisis is one of the biggest crises humans face in this century.In order to solve the water crisis,vigorous development of water treatment technology has become one of the inevitable choices.Capacitive deionization?CDI?technology is an emerging water treatment technology in recent years.The advantages of low energy consumption,high efficiency,no pollution and regeneration ability make it a great promising technology.The key factor of the capacitive deionization technology is the electrode material.The existing electrode materials are mainly activated carbon,carbon aerogel and so on,but they cannot meet the requirements of large-scale application of capacitive deionization.As an emerging carbon material,graphene has many excellent characteristics.Its high conductivity and high theoretical specific surface area meet the expectations of capacitive deionization for electrode materials.However,graphene has poor hydrophilicity,low practically available specific surface area,and easy agglomeration seriously hinders its practical application.It is an effective way to solve these problems to construct graphene-based composites by surface or interface modification of graphene.A series of work has been carried out on the preparation of graphene-based composite electrode materials and their capacitive deionization performance.The main work is as follows.?1?N and P co-doped three-dimensional porous carbon/graphene composite CDI electrode materials were prepared by using chitosan and phytic acid as nitrogen and phosphorus sources respectively,and graphene oxide as conductive additives.Through a series of analysis and characterization,it is found that N and P co-doped materials have obvious hierarchical pore and through"pore-in-pore"morphology,and the contents of N and P in N and P co-doped materials are both higher than that in N and P separately doped samples.In addition,N,P co-doped three-dimensional porous carbon/graphene composite electrode materials have significantly improved conductivity and wettability.This work provides theoretical guidance for the design and application of high efficiency CDI electrode materials.?2?Prussian blue/graphene composite CDI electrode material was prepared by chemical reaction between Fe Cl₃ and K₃Fe?CN?₆ using graphene as conductive additive and P123 as a dispersing additive.It was found that the addition of graphene significantly improved the electrical conductivity of the material.Prussian blue closely attached to graphene,which reduces the interfacial resistance between graphene and Prussian blue.This is helpful to exploit the capacity advantage of Prussian blue and increase the deionization capacity of the material.The Prussian blue/graphene composite electrode material obtained a high deionization capacity of69.3 mg/g in 500 mg/L Na Cl aqueous solution,1.2 V voltage and 60 m L/min flow rate,and has good regeneration performance.This work provides a theoretical guidance for the design and application of ultra-high capacity capacitive deionization electrode materials.?3?Mo S₂/graphene composite CDI electrode material was prepared by hydrothermal method using ammonium molybdate tetrahydrate and thiourea as raw materials and graphene oxide as conductive agent.Through controlled the ratio of graphene oxide,Mo S₂/graphene got high volumetric specific capacity and high gravimetric specific capacity simultaneously.Through a series of analysis and characterization,it was found that additive amount of graphene oxide can effect the morphology of Mo S₂/graphene obviously.Graphene oxide provides nucleation sites for the formation of Mo S₂ and improve the electrical conductivity of the material after being reduced thermally.The high volumetric specific capacity of 15.2 mg/cm³ and high gravimetric specific capacity of 20.5 mg/g are obtained in 500 mg/L Na Cl aqueous solution,1.2 V voltage and 60 m L/min flow rate.The good chemical stability is proved by 10 000 cycles of constant current charging and discharging.The regeneration test showed that the electrode material has good regeneration ability.The CDI mechanism of Mo S₂/graphene was revealed by in situ Raman measurements.It was found that the phase transition from 2H phase to 1T phase occurred during deionization,and part of 1T phase changed back to 2H phase during deionization.This work provides theoretical guidance for the design and application of CDI electrode with high volumetric and gravimetric capacity.