Preparation Of Walnut Shell-based Biomass Porous Carbon And Study Of Its Capacitive Properties

With the development of economy and society,energy consumption and accompanying environmental problems are becoming more and more serious.How to use energy efficiently is a problem that we need to solve urgently.Supercapacitor is a new type of energy storage equipment with high quality energy storage characteristics.The properties of electrode materials are closely related to the performance of supercapacitors,and they are also the research focus in the field of supercapacitors.In view of the characteristics of electrode materials for supercapacitors,this study chooses biomass solid wastes as raw materials,self-made porous carbon materials,and uses self-made carbon as electrode materials for supercapacitors to study their electrochemical properties.China is a big agricultural country.The treatment and disposal of biomass solid waste has always been the focus of our country.Utilization of biomass resources to convert it into high value-added substances is an ideal way to dispose of such solid wastes.After simple activation process,biomass solid waste can produce high-quality porous carbon materials.Carbon materials prepared from biomass solid waste can be further applied in all walks of life,which can greatly improve the added value and realize the resource utilization of solid waste.In this study,walnut shell biomass waste was used as precursor,porous carbon materials were prepared by KOH activation method.The optimum experimental conditions were determined by single factor experiments,and the best quality porous carbon materials were screened out.The optimum conditions determined are:Activation temperature 700?,activation time 1 h,mass ratio of activator to raw material 1.5:1.The saturated adsorption value of methylene blue in the optimum group was 1028.81 mg/g at 25?,which was higher than 782.12 mg/g of commercial carbon.Elemental analysis was used to study the composition changes of raw materials before and after preparation.At the same time,the basic physicochemical properties of self-made carbon and commercial carbon were compared and analyzed by means of nitrogen adsorption and desorption,thermogravimetry,X-ray diffraction and scanning electron microscopy.The carbon content of self-made carbon materials reached 59.65%,which was 13.74%higher than 45.91%of raw materials.The specific surface area is 1010.98 m2/g,average pore diameter is 3.12 nm,total pore volume is 0.60 cm3/g,and micropore proportion accounts for 40%,which means that the self-made carbon belongs to mesoporous materials.Compared with commercial carbon,self-made carbon has higher proportion of micropore,lower average pore size and higher specific surface area.It is fully explained that the precursor and activation method are suitable for the preparation of porous carbon materials.Carbon electrodes were fabricated from self-made porous carbon and compared with commercial carbon electrodes.The results show that both self-made and commercial carbon electrodes exhibit good cyclic stability.Self-made carbon electrodes have higher specific capacitance.The lower sweep speed,the higher specific capacitance.The specific capacitance reaches 130.49F/g at 10 mV/s,which is higher than 82.48 F/g of commercial carbon electrode.At the same time,Nyquist spectra of AC impedance show that both carbon electrodes exhibit good conductivity in KOH aqueous electrolyte species.The equivalent series resistance of self-made carbon electrode and commercial carbon electrode is about 0.6? and 0.8?,respectively.The self-made carbon electrode has lower impedance.It means that self-made carbon electrodes have higher energy density and lower energy loss when used in supercapacitors.Metal loading experiments on self-made carbon were carried out to prepare composite electrodes.The experimental results show that the composite electrode loaded with Cd on the surface has the most obvious capacitance enhancement effect.The specific capacitance is the highest at 10 mV/s,reaching 203.11F/g,which is 72.62 F/g higher than that of pure carbon electrode,and the increase rate is 55.65%.At the same time,Nyqusit spectra of AC impedance show that the composite electrode is similar to pure carbon electrode and consists of typical high frequency semi-circular arc and low frequency straight line.The equivalent series resistance of the composite electrode is almost unchanged from that of the pure carbon electrode,and the charge transfer impedance of the Cd-loaded composite electrode increases slightly.