Construction Of Novel Three-Dimensional Ti-Based Electrode Materials And Their Performance For Capacitive Deionization

Desalination of seawater or brine is an effective way to resolve the the shortage of freshwater issues.For the low-carbon and sustainable development in current society,capacitive deionization（CDI）has attracted great attention in the field of desalination technology owing to its simple operation,economic and green.As one of the important components of the CDI system,the electrode material is the development core of improving the desalination capacity and reducing the cost of CDI system.At present,the carbon electrode materials suffer from the problems of low desalination capacity and poor cycle regeneration ability,which seriously limits the practical process of CDI.Therefore,the development of electrode materials with fast desalination rate,high desalination capacity and excellent cycling ability have become an important task for scientific researchers.Due to high theoretical capacity,abundant reserves on the earth,low-cost and environment-friendly,titanium-based electrode materials have broad application prospects in the field of capacitive deionization.However,the titanium-based electrode materials posses sluggish kinetics.To address this problem,our developed a series of Ti-based electrode materials with multi-stage structure and composite components,and exhibit excellent desalination performance.At the same time,the preparation mechanism and construction strategy of Ti-based electrode materials were studied.Based on the in-depth analysis of the structure-performance structure-activity relationship,a new type of high performance Ti-based electrode material was developed.Besides,this work may also endow the multiple promising application of multi-stage structure titanium matrix composites.The specific research contents this paper include the following points:1.To simplify the conventional preparation process of titanate/carbon composite material and improve the interface interaction,NH₂-MIL-125 is proposed to construct the 3D NTO/N-C-2 composite electrode material.The effect of hydrothermal reaction time on the morphology and electrochemical property of composites were issused.This unique structure and synergistic effect among the components,which could improve the conductivity of the material,enhance the contact area of electrode/electrolyte and provide abundant active sites for electrochemical reaction.Moreover,the high specific surface area and abundant pore structure of MOFs derivatives materials are conducive to the full exposure of active sites.Thus,the 3D NTO/N-C-2 stump has excellent desalination potential.The CDI results shows that the 3D NTO/N-C-2 stump electrode has a better CDI performance compared with NTO-2 nanorods electrode.A desalination capacity of 59.3 mg·g^-1in 1000 mg·L^-1Na Cl solution at 1.4 V is achieved.And long-life cyclability over 20 loops with 95%capacity retention at 1.4 V.This work provides a simple and efficient method for constructing hierarchical structure titanium-based electrode materials.2.Despite the great advantages of hollow materials as electrode for CDI electrode,one apparent conmmon drawback which is often criticized is their compromised volumetric energy density.Here,hollow red cell-like 3D RHNa₂Ti₃O₇/N-C-6 was successfully prepared via hydrothermal treatment of hollow red cell-like 3D Ti O₂/N-C-60 precursor（RHTi O₂/N-C-60）,which was obtained optional chemistry etching of NH₂-MIL-125 by using tannin,and followed by in situ carbonization strategy.The prepared RHNa₂Ti₃O₇/N-C-60 exhibited excellent desalination performance.Such excellent desalination performance was mainly attributed to the hollow structure inside,which effectively shortened the ion diffusion distance and provided sufficient electrode/electrolyte contact area,ensured the desalination capacity.In addition,the nitrogen-rich carbon not only protects the Na₂Ti₃O₇nanoparticles from the harsh environment of the solution and stabilizes the cycling performance but also can enhance the conductivity of materials.Moreover,the rich channels and good conductivity in hollow structure could be easy for the penetration of electrolyte,ensuring the rapid transmission of charges and ions throughout the whole electrode,which maximizes the utilization of active materials.As a result,RHNa₂Ti₃O₇/N-C-60delivers a high desalination capacity of 66.8 mg·g^-1and favorable cycling stability over20 cycles,significantly exceeding those of CDI electrodes derived from single Na₂Ti₃O₇.This work provides theoretical guidance for the design and application of high desalination capacity CDI electrode materials.3.NaTi₂（PO₄）₃（NTP）,a promising cathode materials for CDI,is limited by the poor conductivity.Herein,we report a feasible dual strategy to optimize the crystal structure and conductive characteristics of NTP.A new 3D Fe-doped NaTi₂（PO₄）₃/N-C（NTFP/N-C）electrode was designed and successfully synthesized by sol-gel reaction and anneal treatment of Ti O₂/N-C,which was obtained by pyrolysis NH₂-MIL-125.It proved that doping of iron element create oxygen vacancy and thus enhance the electrical and ionic conductivities,which is beneficial to increase the active site numbers of the adsorption reaction and enhance the desalination rate.In addition,the constructed NTFP/N-C composite with N-doped porous carbon could improve the conductivity.Due to the the synergistic effect of NTFP and N-doped carbon,the obtained NTFP/N-C composite displayed an extraordinary desalination performance including a maximum desalination rate(25.1 mg·g^-1·min^-1),an ultrahigh desalination capacity of 104.4 mg·g^-1and a stable cycling desalination ability.The mixed-transition-metal typed electrode materials yields high desalination rate and high removal capacity,which opens a new horizon towards the commercialization of CDI technologies.