Preparation Of Vanadium-based Electrodes For Hybrid Capacitive Deionization

With the rapid development of human society,the scarcity and pollution of fresh water resources have become more and more severe.Practice has proved that an effective method to alleviate the freshwater crisis is to use seawater desalination technologies to convert abundant seawater or brackish water into freshwater for people to recycle.Capacitive deionization?CDI?is an emerging desalination technology based on the electrochemical mechanism,which is characterized by high efficiency,well stability,environmental friendliness and energy-saving process.The desalination process of CDI is based on the electrode materials to remove salt ions in water under the effect of applied electrical field.In the actual operation,the structure and physical and chemical properties of electrode materials often seriously restrict the desalination performance of CDI.Therefore,the research and exploitation of electrode materials are the significant foundation for promoting the development of CDI technology.This dissertation focuses on the research of new and efficient CDI electrode materials.The composite comprised of NH₄V₄O₁₀ and reduced graphene oxide(NH₄V₄O₁₀/rGO)and porous Na₂VTi?PO₄?₃ are prepared respectively.These two electrode materials are applied in CDI with the use of hybrid capacitive deionization?HCDI?.The desalination performance of as-prepared electrode materials is investigated.The research contents and main conclusions of this dissertation are as follows:?1?NH₄V₄O₁₀/rGO?NHVO/rGO?was synthesized by a simple one-step hydrothermal synthesis method.And this composite was used as a cathode material of CDI for the first time and coupled with active carbon electrode to establish a hybrid capacitive deionization system?NHVO/rGO-HCDI?for exploring its storage property of Na⁺in aqueous solution.Graphene can provide a well 3D conductive network for NH₄V₄O₁₀,which can effectively improve the performance of electron transfer on the surface of it.Compared with NHVO-HCDI,therefore,NHVO/rGO-HCDI exhibited excellent NaCl removal capacity of 20.1 mg/g?101.6%higher than NHVO-HCDI?and charge efficiency of 72.9%?13.9%higher than NHVO-HCDI?at an applied cell voltage of 1.2 V and well cycle stability with capacity retention rate of 71.5%after 100 cycles at an applied cell voltage of 0.8 V in 500 mg/L NaCl solution.?2?Porous Na₂VTi?PO₄?₃ was prepared through an annealing process with the use of polystyrene spheres?PS?served as a template.Porous Na₂VTi?PO₄?₃?p-NVTP?was used as a cathode material of CDI for the first time and coupled with active carbon electrode to establish a hybrid capacitive deionization system?p-NVTP//HCDI?for exploring its storage property of Na⁺in aqueous solution.The unique porous structure existed in p-NVTP can greatly reduce the diffusion resistance of Na⁺in it.Therefore,compared with NVTP//HCDI,p-NVTP//HCDI possessed excellent NaCl removal capacity of 19.8 mg/g?24.5%higher than NVTP//HCDI?and charge efficiency of 75.7%?18.1%higher than NVTP//HCDI?at an applied cell voltage of 1.2 V and well cycle stability with capacity retention rate of 80.6%after 50 cycles at an applied cell voltage of 0.8 V in 500 mg/L NaCl solution.