Research On The Synthesis And Capacitive Deionization Performance Of Biomass Carbon Based Composite Porous Materials

Biomass is a high-quality material for the preparation of porous carbon materials due to the abundant resources and environmental friendliness.Derived porous carbon prepared from biomass has advantages such as rich pore structure and large specific surface area.In addition to the stable structure and good cyclic stability,biomass-derived porous carbon occupies an important position in the field of electrochemical energy storage.Based on this property,graded porous carbon materials were prepared by hydrothermal pre-carbonation and activation using biomass grapefruit peel as the carbon source.Metal sulphide composites were further prepared on porous carbon substrates using hydrothermal methods to improve the specific capacitance of the materials.Biomass graded porous carbon materials were applied to capacitive deionization technology to investigate the practical application in desalination systems.The main content is as follows:(1)The biomass graded porous carbon materials were obtained by hydrothermal pre-carbonation and KOH activation in steps with pomelo peel as the carbon source and KOH as the activator,respectively.The pore structure mainly dominated by microporous with a co-existence of mesopores and macropores as well as the specific surface area of 1595.01 m~2 g^-1 and the pore volume of 0.75 cm~3 g^-1.The effects of different ratios of activator,activation temperature and time on the morphology,structure and electrochemical properties of the porous carbon were investigated.The prepared materials were used as supercapacitor electrode materials and tested in a three-electrode system in 6 M KOH electrolyte.The porous material showed a specific capacitance of 401.2 F g^-1 at a current density of 0.5 A g^-1 which benefiting from a large specific surface area.The capacitance retention rate was 96.2%after 5000 charge/discharge tests at a current density of 10 A g^-1,demonstrating excellent cycling stability.(2)The layered flower-like NiCo₂S₄@BGPC electrode material was successfully prepared on a substrate of biomass graded porous carbon(BGPC2-700-2)using a two-step hydrothermal method.The crystal structure,elemental composition,morphological characteristics and pore structure of the material were analytically characterized using XRD,XPS,EDS,SEM and BET,and its pseudo-capacitance behavior was investigated.In the three-electrode system,the NiCo₂S₄@BGPC composite electrode material with a sulphuration time of 8 h exhibited a large specific capacitance(1322.5 F g^-1)at a current density of 1 A g^-1.To verify the practical application of NiCo₂S₄@BGPC materials,both the NiCo₂S₄@BGPC//NiCo₂S₄@BGPC symmetrical supercapacitor and the NiCo₂S₄@BGPC//AC asymmetric supercapacitor displayed the good capacitive performance and cycling property during the two-electrode system tests,meaning the potential application of NiCo₂S₄@BGPC in the commercial electrochemical energy storage region.(3)The efficient removal of salt ions from the aqueous environment based on capacitive deionization technology is of great significance in securing the cleaning of freshwater resources.Biomass-derived porous carbon was selected as the CDI module electrode material for desalination experiments.The desalination capacities of the BGPC materials prepared at different activation times were compared separately.The results showed that the BGPC2-700-2electrode material exhibited the highest salt adsorption capacity of 29.25 mg g^-1 and the maximum salt adsorption rate of 0.745 mg g^-1 min^-1 during electrochemical adsorption of Na⁺(initial Na Cl concentration of 500 mg L^-1,operating voltage of 1.2 V and flow rate of 40%).The desalination capacity of BGPC2-700-2 was also investigated at different initial Na Cl concentrations(200,500 and 1000 mg L^-1).It was found that the salt adsorption capacity of the BGPC2-700-2 electrode increased equally with increasing initial concentration,with a salt adsorption capacity of 39.47 mg g^-1 at 1000 mg L^-1,showing a strong capacitive adsorption capacity.It has excellent potential for practical applications.