Synthesis Of Prussian Blue Analogues For High Performance Capacitive Deionization

The shortage of global freshwater resources has promoted the development of desalination technologies for seawater.Today,many desalination technologies have been widely used,including electrodialysis,reverse osmosis,and multi-stage distillation.However,these technologies have disadvantages,such as high operating cost and environmental friendliness.Capacitive Deionization?CDI?is an emerging desalination technology with the advantages of simple operation,low cost and environmental protection.Carbon materials are usually used as electrode materials for traditional CDI,which has the problems of low desalination efficiency,slow adsorption rate and short cycle life.Therefore,the development of high-performance electrodes is of great significance for CDI.Traditional carbon materials are adsorbed based on the electric double layer mechanism.The adsorption capacity is limited by the specific surface area of the material and common ions effect,which cannot meet the desalination requirements in practical applications.Faraday materials exhibit ultra-high electro-adsorption capacity.Among them,Prussian blue analogues?PBA?have higher theoretical capacity(170 m Ah g^-1)and cyclic stability due to their open framework structures with large ion channels.PBA also have adjustable morphology and other advantages,and are considered as one of the excellent materials for CDI electrodes.However,PBA synthesized by common methods have the disadvantages of low crystallinity,large crystal size,and poor conductivity.When PBA are used as a CDI electrode,its desalination capacity,rate performance and cycle life need to be improved.In order to solve the above problems,PBA is loaded on a conductive substrate.The desalination,rate performance and cycle stability of PB materials are improved by adjusting the size,distribution,crystallinity of the PBA crystal and the synergy between the crystal and the conductive substrate.At the same time,the material has high conductivity and fast ion transmission structure,which effectively solves the problem of poor conductivity and easy agglomeration of PB material.The main research contents are as follows:Experiment 1,First,a layer of Co-MOF nanosheet was loading on carbon cloth by a simple solution reaction.We used a facile self-templating method to convert Co-MOF to hollow-structured Co Fe-PB nanoarry.The transformation conditions of Co-MOF were optimized,and the morphology of Prussian blue was regulated in terms of transformation time,p H and concentration of reaction solution.The results show that a stable hollow-structured Co Fe-PB nanoarray can be prepared under the condition that the mass ratio of K₃Fe?CN?₆ to Co-MOF is 1:1 and the p H=5-6.Co Fe-PB@CC showed high electrochemical capacity(142.3 m Ah g^-1 at 0.125 A g^-1)and good reversibility?67.5%?in charge-discharge tests.The composite showed ultra-high desalination capability in CDI,and the desalination capacity was up to 108.8 mg g^-1 at 125 m A g^-1.Experiment 2,PAN fibers were prepared by electrostatic spinning,and a layer of conductive polyaniline was polymerized on the fiber surface.Then PANI/PAN was used as a template to attract Prussian blue crystals to nucleate on its surface to obtain PB/PANI/PAN nanofibers.Finally,the PAN template was dissolved to obtain a PB/PANI composite with a tubular structure.The synthesis conditions of PB were optimized,and the morphology of PB/PANI was regulated from the reaction time and the concentration of the reaction solution.The results show that the uniform and stable Prussian blue shell can be obtained under the condition that the concentration of K₃[Fe?CN?₆]and Fe Cl₃solution is 12.5 mmol L^-1 and the reaction time is 6 h.The desalination capacity of PB/PANI//AC CDI unit shows excellent desalination ability(133.3 mg g^-1 at 0.1 A g^-1),and high adsorption rate(0.49 mg g^-1 at 2 A g^-1 s^-1).Moreover,the capacity of PBA has almost no attenuation after 250 adsorption/desorption cycles at 500 m A g^-1.Finally,a concept for the recovery of the electrical energy applied for CDI process is demonstrated,the energy consumption reaches the minimum value of 0.35 kwh kg^-1 at 2 A g^-1,and the corresponding energy recovery rate is 74.7%.