Construction And Performance Evaluation Of The Full Desalination Battery Based On Ag@CNTs And Na₃Fe₂（PO₄）₃@Super P Composite Electrodes

The global shortage of fresh water resources is a major challenge to ecological environment security and human survival.The traditional desalination technologies,such as thermal distillation and reverse osmosis,face problems such as high energy consumption,equipment corrosion or membrane pollution.In recent years,desalination battery with great application potential because of its advantages of environmental protection,energy saving and mild operating conditions,has been regarded as the next generation desalination technology.However,the low capacity and poor stability of chlorine and sodium storage electrode materials restrict the further improvement and future application of desalination battery.In view of the above problems,this work improves the conductivity Ag chlorine storage electrode material and the Na₃Fe₂（PO4）₃ sodium storage electrode material by coating the conductive network to improve the performance of seawater desalination.To solve the problem of poor conductivity of AgCl formed during the desalination process of Ag chlorine storage electrode material,Ag nanoparticles were anchored on the three-dimensional conductive network of carbon nanotubes（CNTs）.The Ag@10%CNTs electrode material possesses the smallest redox peak voltage difference and the most excellent charge transfer performance.In addition,compared with the Ag electrode material,the Ag@10%CNTs electrode material can not only improve the utilization rate of Ag and the conversion efficiency of AgCl to Ag,but also suppress the surface morphology change of the electrode material.Therefore,the Ag@10%CNTs electrode material exhibits the most excellent desalination performance with an initial capacity for removal salt of 120.0m Ah g^-1,the retention rate of salt removal capacity was 39.8%after 500desalination/salinization cycles.The charge efficiency of Ag@10%CNTs during desalination is also higher than that of Ag electrode material.Based on the average charge efficiency of the first ten cycles（95.6%）,the desalination capacity of Ag@10%CNTs electrode material is 250.4 mg.g^-1.To improve the capacity for removal salt of Na₃Fe₂（PO₄）₃ electrode material,the morphology of Na₃Fe₂（PO₄）₃ was controlled by turning the calcination temperature.The Na₃Fe₂（PO₄）₃ prepared at 650℃exhibits best cycle stability and highest initial capacity for removal salt(18.3 mA h g^-1),which is much higher than that of conventional capacitive deionization electrodes(ie,6.9-11.5 mAh g^-1).Aiming at the poor conductivity of Na₃Fe₂（PO₄）₃,a strategy of coating with PEDOT and carbon black（Super P）was proposed to construct conductive networks.PEDOT coating can improve the charge transport ability of Na₃Fe₂（PO₄）₃ and inhibit the dissolution of iron ions,the initial capacity for removal salt is increased to22.9 mAh g^-1,and the capacity for removal salt after 50 charge-discharge cycles is 19.0 mAh g^-1,which is 1.4 times higher than that of the bare Na₃Fe₂（PO₄）₃.Super P coating Na₃Fe₂（PO₄）₃（NFP@Super P）can significantly reduce the charge transfer resistance.The initial salt removal capacity of NFP@Super P-2 electrode material is 25.9 mAh g^-1,which is higher than that of bare Na₃Fe₂（PO₄）₃(18.3 mAh g^-1).After 600 cycles of desalination and salinization of NFP@Super P-2,the capacity retention rate was 94.6%.The desalination full battery constructed with Ag@10%CNTs and NFP@Super P-2 with a mass ratio of 1:2 has the best seawater desalination performance,and the initial salt removal capacity is 17.2 mAh g^-1.After400 cycles,the capacity retention rate of desalination full battery was76.9%.Because of the suitable working potential of NFP@Super P-2,the full desalination battery composed of NFP@Super P-2 and Ag@10%CNTs effectively suppressed the side reactions during the desalination process,and the charge efficiency was about 88%.In summary,Ag@10%CNTs chlorine storage electrode materials and NFP@Super P-2 sodium storage electrode materials with good desalination performance were prepared in this work,which solved the problem of low salt removal capacity and poor stability of Ag and Na₃Fe₂（PO₄）₃ and provided a strategy for the development of desalination batteries with excellent desalination performance.