Preparation Of Biomass-based Porous Layered Carbons And Their Electrochemical Capacitive Behavior

Supercapacitors have attracted increasing attention in recent years due to their fast charge accumulation rate,long cycle durability,good reversibility and stability,thus leading to its potential application in the fields of portable electronic devices,hybrid electric vehicles and power management in smart grids.The active materials play crucial role in energy storage of supercapacitors.Among carbon-based materials,biomass-derived carbon is invariably brought into focus,because of its distinctive inherent structure,and plentiful heteroatom composition.In this article,using various biomass as precursor,we designed and developed porous carbon and composite materials with special framework via carbonization,alkali activation and hydrothermal activation method,aiming at improving its capacitance properties effectively.The contents and conclusions of researches below:(1)Fabrication of multilayered porous carbon from natural casings and its energy storage behavior study.N-enriched multilayered porous activated carbon(LPAC),using natural casings as precursor,was prepared by a gentle carbonization and subsequent KOH activation process.The influence of mass ratio of KOH to LPC on casings-derived carbon electrochemical behavior was studied.Meanwhile,the structure-activity relationship between multilayered porous structure and its capacitive performance was also analyzed.The results indicate that LPAC was of interconnected abundant porous structure and unique multilayered texture.With increase of the mass ratio of KOH to LPC,the specific surface area and average pore size of LPACs increased,but its N amount decreased sharply.The unique porous structure and big specific surface area can provide efficient electrons/ions transport channels and large contact area,and reduce greatly ion diffusion resistance to improve its energy storage ability.Furthermore,nitrogen(N)functional groups can provide extra pseudocapacitance by redox reaction.N-and O-enriched LPAC-4 exhibited the highest specific capacitance(307.5 F·g-1 at 0.5 A·g-1 in 6 M KOH solution),excellent rate performance(63.4%at 20 A·g-1)and stable cycle durability(7.1%capacitance loss after 5000 cycles).The assembled symmetric supercapacitor(LPAC-4//LPAC-4)with an extended voltage window of 1.4 V delivered a prominent energy density of 11.6 Wh·kg-1 at 297 W·kg-1.(2)Fabrication of interconnected porous multilayer carbon from reed membranes and its energy storage behavior research.Unique porous layer-stacking active carbon(RHC),using natural reed membranes as precursor,was fabricated by an easy hydrothermal treatment and following carbonization process.The effect of preparation method on reed membrance-derived carbon capacitive behavior was researched.Besides,the structure-activity relationship between multilayered porous structure and its energy storage properties was analyzed.It turned out that the layered texture of reed membranes is favorable for KOH to enter into precursor deeply to achieve uniform pore size distribution during hydrothermal process,not only making efficient use of KOH,but also relieving the stack and agglomeration of layer structure during carbonization process.Moreover,the synergistic effect between layered texture and interconnected porous structure can provide abundant active sites and shorten ion transport paths to improving electrode rate performance and cycle life.The as-obtained RHC electrode displays outstanding electrochemical performance.RHC possesses a high specific capacitance of 353.6 F·g-1 at 0.5 A·g-1,great rate capability and good cycling stability(96.4%of capacitance retention after 5000 cycles).Furthermore,the symmetric supercapacitor(RHC//RHC)has extended the operating potential to 1.4 V,and delivered a high energy density 11.6 Wh·kg-1 at power density of 210 W·kg-1 with 80%energy efficiency.(3)Synthesis of unique T-Nb2O5/EW electrode and its energy storage behavior investigation.The unique porous T-Nb2O5/EW composite was successfully synthesized through a facile hydrothermal treatment and succeeding annealing process.The impact of egg-white-derived carbon on composite electrochemical performance was studied,as well as the structure-activity relationship between porous nano-structure and its capacitive properties.The results show that egg-white can prevent Nb2O5 nano-particles stacking and agglomeration during hydrothermal treatment,thus to improve the utilization rate of active materials.What’s more,the porous and uniform texture can also offer large effective specific surface area and promote Li-ions transport quickly.The T-Nb2O5/EW displays good rate capability(51.7%capacity retention from 0.1 A·g-1 to 5 A·g-1)and excellent cycling stability(11.9%capacity loss after 1000 cycles at 0.8 A·g-1).Furthermore,the LISC(T-Nb2O5/EW//EWC),T-Nb2O5/EW as anode and EWC as cathode,demonstrated a high energy density(67.2 Wh·kg-1),power density(8750 W·kg-1)and good cycle life(82.1%capacitance retention after 3000 cycles).