Preparation Of Novel Structured Carbon Materials For Capacitive Deionization

The shortage and pollution of fresh water resources have increasingly become one of the urgent problems in the world.Traditional seawater desalination technologies,such as distillation,reverse osmosis,and electrodialysis are commonly used to solve the shortage of fresh water resources.However,these technologies have been hindered by the problems of large energy consumption,complicated operation,and secondary pollution.In recent years,capacitive deionization(CDI)has become an emerging technology in the field of seawater desalination due to its low energy consumption and environmental friendliness.The principle of CDI is based on the accumulation of ions at the surface of porous electrodes by forming electric double layer(EDL)under electric field.The CDI performance largely depends on the structure of the electrode material.At present,carbon materials are widely used as CDI electrode materials due to their large specific surface area,suitable pore structure distribution,and good electrical conductivity.However,it is still a challenge to design and synthesize electrode materials with a rational structure based on deep understanding of their structure-dependent CDI performance.This paper focuses on the preparation of carbon materials with novel structure,and the investigation of the relationship between material structure and CDI performance.(1)SiO2 and resorcinol-formaldehyde resin were used as a template and carbon source respectively to prepare carbon nanocages(CNC)as CDI electrode materials through hydrothermal and carbonization steps.CO2 treatment during the carbonization process can simultaneously adjust the shell thickness and pore structure.For the first time,we used CNC as CDI electrode material and optimized its structure.The optimized specific surface area of CNC was up to 2257.5 m2 g-1.Compared with typical carbon sphere(CS)electrode,CNC electrodes have higher specific capacitance,faster charge and discharge rates,and lower internal resistance.In a solution with an initial concentration of 250 mg L-1 NaCl and a voltage of 1.4 V,the salt removal capacity of the CNC electrode was 17.5 mg g-1.Moreover,we used finite element simulations to reveal the relationship of electrode structure and performance.On the one hand,due to the unique cage structure of the CNC,the transmission rate of ions in the electrode is greatly improved.On the other hand,the inner and outer sides of the shell provide enough active sites for rapid adsorption and desorption of ions(2)By precisely controlling the ratio of SiO2,resorcinol and formaldehyde,we have prepared hollow carbon bowl(HCB)with small cavity and thin carbon shell.This structure inherits the advantages of hollow carbon spheres(HCS)and overcomes the disadvantage of ineffective space occupation caused by the large cavity.In addition,the HCB electrode has a large specific surface area,a low internal resistance and a high electrical conductivity.For CDI applications,the weight desalination capacity(SACG)of HCB was up to 21.8 mg g-1 with a rapid adsorption and desorption rate.In addition,HCB has an excellent volume desalination capacity(SACV)of 3.6 mg cm-3.The experimental results firmly demonstrate the structural advantages of HCB in CDI applications.The smaller cavities and ultra-thin carbon shells not only shorten the transmission distance of ions,but also increase the electrode packing density.This work not only proves that CNC and HCB are potential electrode materials,but also discusses the relationship between structure and performance from a new perspective.The obtained materials and results can be certainly extended to other fields such as electrocatalysis,electronics,and energy storage and conversion.