Study On Capacitive Deionization Of Hierarchical Porous Carbon Aerogel And Energy Storage Performance Of Fe_1-xS@RGO

Water scarcity and energy crisis are the two main global issues in addition to food,which affect millions of people worldwide.It is thus essential to develop environmentally friendly and efficient desalination technologies and energy conversion/storage systems.To this end,this thesis mainly carried out research in the following two areas.?1?Capacitive deionization?CDI?technique.Compared with conventional technologies,e.g.reverse osmosis and thermal evaporation,CDI is one of the most promising and environmentally friendly desalination technique because it has outstanding benefits such as high energy efficiency,low cost,easy regeneration and non-secondary pollution.The working mechanism of CDI is based on the formation of electric double-layer?EDL?at the CDI electrode/solution interface.When a low direct current potential?typically in the range of 1.0?1.4 V?is applied to the porous CDI electrodes,ions in saline water flowing over the CDI electrodes are adsorbed to the oppositely charged CDI electrodes,forming EDL therein.Based on this mechanism,it is crucial to develop new electrode materials with high EDL capacitance for high performance CDI.Currently,porous carbon materials are the most widely used CDI electrode materials.However,the porous carbon materials contain abundant micropores,closed pores,dead-end pores.Although they contribute a large portion to the surface area,this portion surface area is difficult for ions to access.Moreover,pure porous carbon materials often have a poor wettability,being difficult to be well wetted by the solution.To offer a large EDL capacitance for CDI,the ideal electrode materials should possess a large specific surface area,suitable pore size distribution,high wettability,and high conductivity.This thesis reports a nitrogen-doped hierarchical porous carbon aerogel?N-HPCA?for high-performance CDI.?2?Electrochemical energy storage.Owing to the abundant resources of Ni and Fe elements,aqueous Ni/Fe battery has emerged as an attractive electrochemical energy storage device.However,the performance of the Ni/Fe ba ttery is largely limited by the low specific capacity and poor discharge rate capacity of the Fe electrodes.To address these challenges,a series of strategies have been developed,including exploring new iron electrode materials,constructing inorganic/c arbon hybrid electrode materials,and adding additives to electrolyte or anode materials.Herein,this thesis reports a new composite Fe_1-xS nanoparticles and reduced graphene oxide(Fe_1-xS@rGO composite)as anode material for high performance Ni/Fe batteries.The main research contents of the thesis are outlined as follows:?1?This thesis has successfully fabricated nitrogen-doped hierarchical porous carbon aerogel?N-HPCA?using commercial chitosan as the carbon source for high performance CDI.The obtained N-HPCA possess a highly interconnected hierarchical porous structure and abundant mesopores ranging from 2-5 nm,providing a large specific surface area of 2405 m² g^-1 for the adsorption and efficient transport of ions.Meanwhile,N-doping largely enhances the conductivity and surface wettability of the carbon material.Consequently,the N-HPCA delivers a high specific capacitance(263F g^-1 in 6 mol dm^-3 KOH solution and 153 F g^-1 in 0.5 mol dm^-3 NaCl solution),enabling an outstanding electrosorption capacity of 17.9 mg g^-1 in 500 mg dm^-3 NaCl solution.Moreover,the N-HPCA electrode also demonstrates good cycle stability,without obvious attenuation in electrosorption capacity upon 5 CDI cycles.?2?This thesis has successfully fabricated the composite of Fe_1-xS nanoparticles and reduced graphene oxide(Fe_1-xS@rGO composite),using Fe₂O₃@rGO as the precursor and thioacetamide?TAA?as the S source,as anode material for high performance Ni/Fe batteries.In the composite,the highly conductive rGO sheets wrap the Fe_1-xS particles,creating a compact sheet-particle interface and thereby greatly improving the conductivity of the anode electrode.Moreover,the rGO sheets can effectively prevent the aggregation/dissolution of the Fe_1-xS particles.Consequently,the resultant Fe_1-xS@rGO electrode delivers a specific capacity of ?320,282,270 and 120 mAh g^-1 at a current density of 0.3,0.6,1,and 10 A g^-1,respectively,exhibiting high specific capacity and high rate capacity.Moreover,the Fe_1-xS@rGO electrode exhibits a long cycling stability,with 83.3% of initial capacity retained after 100 cycles at 1 A g^-1.