Preparation Of Layered Sodium Ion Intercalation Electrode Material And Desalination Performance

Water pollution and shortage of fresh water resources have become major issues for sustainable social development,and desalination technology is an effective solution to this problem.At present,relatively traditional technologies include reverse osmosis,electrodialysis,ion exchange,distillation and freezing,but high cost,high energy consumption and secondary pollution problems are still exist.Therefore,it is extremely urgent to develop low-cost,low-energy,pollution-free and long-life desalination technologies.Capacitive deionization(CDI)is an emerging technology with potential for development in seawater desalination.CDI has two kinds of desalination mechanisms:electrostatic double layer electrostatic adsorption and Faraday reaction.Electrosorption is mainly to electrostatically adsorb ions on the surface of carbon electrode or inside the electrode material,while Faraday adsorption is mainly carried out by reversible deintercalation of ions in the electrode material by Faraday reaction.In this thesis,the sodium ion electrode material was used as the negative electrode to capture sodium ion,the porous carbon material was used as the positive electrode to adsorb chloride ion,and the hybrid capacitor desalination(HCDI)device was constructed.The assembly mode and the desalination performance of the process parameters were studied.Due to the introduction of the sodium storage mechanism of capacitors,the desalination performance and charge efficiency are greatly improved.This paper is mainly divided into two parts:1.The two-dimensional layered carbide(MXene)was obtained by etching ternary carbide Ti2AlC with etchant LiF and HCl.Results show that as-obtained MXene is composed of major crystal phase Ti2CTx and secondary phase Ti3C2Tx.As-etched samples have accordion-like morphology.The electrochemical performance was tested in a 1 M NaCl solution,and a redox peak appeared between the potential window and-1-0 V,indicating a sodium ion deintercalation reaction mechanisms.The effects of two-electrode assembly modes(AC//AC,MXene//MXene and MXene//AC)on desalination performance were investigated.The desalination capacity of MXene//AC asymmetrical electrodes is approach to 36.23 mg g-1 and the charge efficiency reaches 99%in NaCl solution with an initial concentration of 50 ppm.After 5 cycles of adsorption-desorption,no obvious decline in the solution conductivity is observed,which indicates that the MXene electrode has good stability in consecutive electrosorption-desorption cycling.2.Layer structured NaxCoO2(0.52<x<0.75)with tuning sodium contents was prepared by a facile sol-gel and chemical deintercalation method and used them as faradaic electrode materials.Results show that the Co-O interlayer spacing increases as the sodium content decreases.The Co4-content increases resulting to an increasement of oxygen vacancy content.NaxCoO2(x=0.75,0.65,0.52)with different sodium content was used as the negative electrode,and AC was used as the positive electrode to constitute a HCDI device,Capacitance deionization performance was tested in NaCl solutions with different voltages(0.8 V?1.0 V?1.2 V and 1.4 V)and conductions(100 ?S cm-1?500 ?S cm-1 and 1000 ?S cm-1).When the solution conduction is 1000 ?S cm-1,the working voltage is 1.4 V,the desalting capacity of Na0.75CoO2,Na0.65CoO2 and Na0.52CoO2 reached 41.82 mg g-1,72.03 mg g-1 and 104.45 mg g-1,respevtively.It is found that the Na0.52CoO2 electrode has the highest removal capacity among all samples.After 7 cycles of adsorption-desorption,no obvious decline in the solution conductivity is observed,which indicates that the NaxCoO2(x=0.75,0.65,0.52)electrode has good stability in consecutive electrosorption-desorption cycling.