Construction And Properties Regulation Of Biomass-derived Carbon Materials With Multi-morphology

Porous carbon materials with outstanding physical and chemical properties,such as high specific surface area,abundant porosity,excellent stability,good electrical conductivity and low density,have potential applications in the fields of energy storage and conversion.Traditional porous carbon materials are mainly fabricated from fossil resources,which suffer from resource depletion and environmental pollution,and are not the path of sustainable development.Thus,from the concept of sustainable development,using the abundant,renewable,environment-friendly biomass to replace fossil resources for the fabrication of porous carbon materials should be an ideal way.In this paper,a series of novel and efficient biomass-derived porous carbons were fabricated via the regulation of their physical and chemical structures(e.g.pore structure,specific surface area,heteroatom doping,metal doping,etc.),and applied in supercapacitors and zinc-air batteries.The specific contents are as follows:1.In this work,an N-doped porous carbon was fabricated from renewable cellulose by a sol-gel method,and followed a solution impregnation process with urea as nitrogen source.Typically,the pore structure and specific surface area of the porous carbon can be effectively controlled by such sol-gel process,while the nitrogen doping content can be regulated by changing the concentration of urea solution.The as-prepared carbon revealed high specific surface area,reasonable pore size distribution,controllable nitrogen doping content(0.68-7.64wt%)and partial graphitized structure,thus resulting in excellent supercapacitor performances with high specific capacitance(193 F g^-1),good rate capability,outstanding cycling stability as well as high energy density.2.A hierarchical porous carbon was synthesized from biomass(i.e.rice straw)through the carbonization and bio-template processes.The intrinsic silica acting as an in-built biotemplate can not only ensure well-distribution of the template in the biomass,but also prevent the framework from excessive shrinkage and collapse during carbonization.The biomass-derived hierarchical porous carbon displayed high porosity,reasonable pore distribution and high specific surface area(1909 m²g^-1),which were beneficial to ion transfer and charge storage.In addition,the nitrogen and oxygen self-doping can improve the surface accessibility of the carbon and generate additional pseudocapacitance,thus improving the electrochemical performances.Due to its excellent porous structure and heteroatoms doping,the porous carbon had a specific capacitance high up to 357 F g^-1and an energy density of 29.3 Wh kg^-1at the power density of 900 W kg^-1.3.A compressible and elastic carbon aerogel with tracheid-like structure was prepared from cellulose nanofibers(CNFs)and lignin through a directional freezing casting strategy.The flexible CNFs entangled and assembled into an interconnected framework,while lignin with high thermal stability and favorable stiffness restricted the severe crimp of CNFs and prevented the framework from severe structural shrinkage during annealing,thus resulting in elastic tracheid-like structure.The obtained carbon aerogel exhibited excellent mechanical performances,including high compressibility(up to 95%strain)and outstanding fatigue resistance(with a stress retention of 79.1%after 30000 cycles at 50%strain).It also revealed high sensitivity(5.16 k Pa^-1)at a wide working pressure range of 0-16.89 k Pa and can detect human biosignals accurately.Moreover,the carbon aerogel can be assembled into a flexible and free-standing all-solid-state symmetric supercapacitor that revealed satisfactory electrochemical performances(energy density of 8.6 Wh kg^-1)and mechanical flexibility(without significant capacitance change at different bending angles).4.A series of cost-effective and sustainable S modified M-N₄(M represented metal atoms,e.g.,Fe,Cu,Co)single atom catalysts were fabricated using papermaking by-product(i.e.lignosulfonate)as multi-functional precursor(chelating agent,carbon and sulfur source)through hydrothermal treatment and pyrolysis.Taking Fe as example,the coordination between Fe and lignosulfonate and the cooperated N doping guaranteed the formation of Fe-N₄active sites.In addition,the self-doping sulfur can adjust the charge distribution around Fe-N₄sites and promote the release of intermediates in oxygen reduction reaction(ORR),thus boosting the catalytic performances.Owing to its the sulfur-modification Fe-N₄active site,high specific surface area and partial graphitization structure,the resultant catalyst exhibited excellent ORR(initial potential of 1.01 V and half-wave potential of 0.876 V)and oxygen evolution reaction(OER)performances.The Zn-air battery using the catalyst as a cathode material exhibited high specific capacity of 798.7 m Ah g^-1and energy density of 941.7 Wh kg^-1,as well as long-term stability.