Preparation And Properties Of Silver/Carbon Chlorine Storage Electrodes For Desalination Batteries

Desalination battery is a new type of seawater desalination method,which generally consists of a sodium ion storage/release electrode and a chloride ion storage/release electrode.Compared with other desalination technologies,it has the advantages of high desalination capacity,fast electrode regeneration,low energy consumption,etc.However,the shortage of chlorine storage electrode materials has severely restricted the development of seawater desalination batteries.At present,the commonly used chlorine storage electrode materials are mainly Ag and Bi.When the Bismuth electrode is reduced from the chlorinated product BiOCl to Bi,it is very slow in kinetics and requires a significant overpotential,which results in the need for energy input during the salinization process and high energy consumption.In addition,Bismuth electrodes are toxic and not suitable for long-term use.Because of its low and stable chlorine storage voltage,the Ag electrode is the most widely used chloride ion storage/release electrode.However,Ag electrodes are expensive,and poorly conductive silver chloride is generated during the chlorine storage process,resulting in a short cycle life of the silver electrodes.These shortcomings limit the application of silver electrodes in seawater desalination batteries.Therefore,modifying the silver to improve the cycle stability of the silver electrode,thereby reducing the cost of desalination,is of great significance to the large-scale application of seawater desalination batteries.In our study,silver/carbon composites were prepared by two modification methods.The purpose is to improve the conductivity of the silver electrode in the desalination process and to improve the salt removal capacity and cycle stability of the silver electrode.In this paper,citric acid(CA)is used as the carbon source to prepare Ag@CA composite materials coated with a carbon layer.The silver/carbon material with CA:AgNO3 = 1:2(molar ratio)has a current density of 100mA/g.After 50 cycles,the capacity stabilizes at 120mg/g,which is about40% higher than the Ag electrode(73mg/g).In addition,it has a smaller polarization potential than the Ag electrode during the desalination process.It shows that the carbon-coated modified silver electrode effectively improves the electronic conductivity and cycle stability of silver.In addition,carbon nanotubes(CNTs)have excellent electronic conductivity and are often used to build electronic conductive networks to improve the electronic conductivity of materials.In this paper,Ag@CNTs composite materials were prepared by wet chemical method.Ag@CNTs(10 wt.%)has the best desalination performance.After 50 cycles,the capacity is stable at 139mg/g,which is about 47%(73mg/g)higher than the Ag electrode.Both modification methods effectively improve the salt removal capacity and cycle stability of the silver electrode.The Ag@CA and Ag@CNTs were tested at different current densities and electrolyte concentrations using a three-electrode system,and the two materials were tested in a long cycle.It was observed that Ag@CNTs had a smaller polarization than Ag@CA in the process of desalting and had a higher desalting capacity after 500 cycles of desalting.Therefore,Ag@CNTs composite materials are selected to prepare chloride ion storage electrodes,and NaTi2(PO4)3 is used to prepare sodium ion storage electrodes to construct seawater desalination batteries.The application of Ag@CNTs composite materials in seawater desalination batteries is studied.The influence of the electrode mass ratio in the battery on the salt removal performance of NaTi2(PO4)3||Ag@CNTs was studied,and the salt removal performance of the battery in different current densities and different electrolyte concentrations was studied at the optimal electrode mass ratio.The best operating parameters of the battery(current density is 100mA/g,electrolyte concentration is 1 mol/L NaCl solution).The cycle performance of the battery was tested under the best operating parameters.The initial salt removal capacity of the battery was 218mg/g,and the salt removal capacity decreased to 119mg/g after5 cycles.After 300 cycles,the salt removal rate stabilized at 90mg/g.The desalination battery equipment studied in this article is simple in structure and does not require ion exchange membranes.The operation is simple,easy to expand production,and has high practical significance.