Synthesis Of Phenolic-based Porous Carbons With Multi-dimensions And Their Applications In Energy Storage And Environment

Porous carbon materials have been widely used in many applications,ranging from water and air purification,adsorption,and catalysis to electrodes and energy storage,owing to their unique properties including high specific surface area,large pore volume,high mechanical and chemical stability,as well as the anticorrosion and high electronic conductivity.Generally,their performances in many applications were strongly affected by the pore structures and morphologies.Nowadays,porous carbons with specific porous structures and morphologies have been developed through many methods.Especially,porous carbons based on phenolic-resin have been widely studied,and their pore structures/morphologies could be tuned by changing the precursor compositions or preparation methods.Although many efforts on the preparation of porous carbons with superior porous structures and certain morphologies have been reported,the investigation on phenolic-based porous carbons are still facing great challenges.This thesis mainly focused on the controllable synthesis of phenolic-based porous carbons with spherical,layered,and three-dimensional bulk morphologies.Their morphologies,pore structures and surface chemistries could be adjusted efficiently by varying the precursors and preparation conditions.Then,the adsorption performance and their usage as the electrode materials were further evaluated.The main results are summarized as follows:(1)Hierarchical porous carbon monoliths with a 3D framework were synthesized through a facile hydrothermal process using resorcinol-melamine-formaldehyde(RMF)as carbon precursors,and nanocrystalline celluloses(NCCs)as the structural inducing agent,followed by ambient pressure drying and carbonization.Polymerization of the RMF resin occurs around the nanorod-like NCCs dispersed homogeneously in water,which is quite beneficial for the formation of an interconnected network and supports the rigid macroporous structure.A hierarchical porous carbon monolith with modest micropores and well-developed macropores was prepared after CO2 activation at 950 ?.The obtained carbon monolith has a large specific surface area of 1O08 m2g-1 and pore volume of 0.86 cm3 g-1.It shows significant CO2 adsorption capacity of 5.2 mmol g-1 at 273 K,and high Cr(VI)ions adsorption performance with the capacity of 463 mg g-1 at 303 K.Moreover,the activated carbon monolith exhibits a high selectivity for Cr(VI)in the coexistence of several other metal ions.(2)Porous carbons with a sandwich structure were synthesized through graphene oxide template process.The growth of resorcinol-melamine-formaldehyde(RMF)happened around the surface of graphene oxide,and the thickness of the carbon coating layer could be tuned by changing the weight ratio of GO and RMF polymer.After KOH activation,the carbon nanocomposites with layered structures exhibit increased specific surface area with improved thickness.When used as electrode materials for supercapacitors,results indicating that porous carbon with higher specific surface area(1741 m2 g-1)shows higher specific capacity(231 F g-1).For comparison,KOH activation was directly applied on the polymeric composites,and results show that although the morphologies of the layered composites are severity damaged,the higher specific surface area(3048 m2 g-1)contributes greatly to a much higher specific capacity(283 F g-1).Based on the design of Li-S batteries with high performance,key parameters toward practical Li-S batteries were investigated.Results suggest that a carbon host with balanced physical parameters including surface area,pore volume,and pore size distribution provides a material foundation for building sulfur cathodes with both a high specific capacity and a good cycle stability.For binder selection,this study unambiguously demonstrates that polycations are excellent binder materials for promoting lithium polysulfides sequestration via coulombic attraction.The low weight ratio of electrolyte to sulfur is a key parameter for ensuring a high specific energy of the full Li-S cells.It also demonstrate that a lower E/S ratio is beneficial for improving cathode cycle stability,although the effect on coulombic efficiency requires further study.As an additional polysulfides sequestration strategy,metal oxide additives,particularly MgO,shows a mixed behavior in this study.(3)Silicon@carbon composites with novel structures were synthesized via a colloidal route for the first time.Surface-functionalized Si nanoparticles(SiNPs)dissolved in styrene and hexadecane are used as the dispersed phase in oil-in-water emulsions,from which yolk-shell(SiNPs@CPS)and dual-shell(SiNPs@CHD)hollow composites are produced via polymerization and subsequent carbonization.As anode materials for Li-ion batteries,the SiNPs@CHD composites demonstrate excellent cycling stability and rate performance,which is ascribed to the uniform distribution of SiNPs within the carbon hosts.When the SiNPs@CHD composites were mixed with commercial graphite,it achieved an overall capacity over 600 mAh g-1 with an areal loading higher than 3 mg cm-2,which is an improvement of more than 100%compared to the pure graphite anode.