Preparation Of Biomass Carbon Based Materials And Its Application In Energy Storage Devices

Due to their abundant renewable precursor sources and ever-changing macro and micro structures,biomass carbon materials have been playing an indispensable role in practical energy storage devices.Since the national mission which urge the reducing the energy consumption and carbon dioxide emissions,the research of biomass carbon material and its application has been far more valuable than ever because of its environmentally friendly characteristics of turning waste into treasure.Based on these two characteristics of biochar materials,in this paper,energy storage materials are explored from two perspectives.The phenomenon that the specific surface area of biomass precursor increases during the carbonization process due to the etching of trace elements and the removal of functional groups is called self-activation.According to the physiological characteristics of plant metabolism,a small amount of bright blue molecules was sent into the vascular bundle of Chinese cabbage by transpiration process.The blue leaves became the electrode materials with rich microporous structures by one step carbonization.When the carbonization temp is 900?,the extent of self-activation of blue cabbage was enhanced.Compared with ordinary Chinese cabbage,the specific surface area increased from 360 m~2/g to 778 m~2/g,and the specific capacitance increased from138F/g to 171F/g(sweeping speed:2 m V/s).The specific surface area increased by 116.1%and specific capacitance increased by 23.7%,respectively.And the capacity retention rate was still higher than 99%after 10000 high-rate charge-discharge cycles.Pore size distribution analysis showed that this preparation scheme specifically increased the content of micropores with diameters between 0.5 and 0.6 nm.Compared with traditional chemical activation,enhanced self-activation can selectively improve the number of micropores in specific size of materials,which provides a powerful tool for precise control of the pores of biomass carbon materials.On the basis of the enhanced self-activation scheme above,we changed the activator to improve pore structure and the utilization of specific surface area.In this case,Na₂S₂O₃ was sent into the vascular bundles of lettuce leaves by transpiration process,and decomposed into Na2SO4and Na₂S₅ at high temperature.The carbon frame was activated twice by heating in the furnace and self-exothermic heat outside the furnace,respectively.The sample carbonized at 900?had the highest specific surface area of 1854 m~2/g,while the one carbonized at 700?got the highest specific capacitance of 249 F/g at scan rate of 0.5A/g.By pore size analysis,it can be inferred that the micropores with diamets of 0.66?0.72nm have major contributions of biomass carbon electrode to double layer supercapacitance in 6M KOH.This can be explained by the cylindrical hole energy storage model.The van der Waals'radius of potassium hydrate is about 0.33nm.These ions act as the energy storage carrier.Within a certain range,the area ratio capacitance in the micro-hole energy storage model decreases sharply with the increase of the pore size.This conclusion also explains the phenomenon that the improvement of activated Chinese cabbage carbon's specific capacitance was limited after greatly improve the specific surface area in the previous work.With enhanced self-activation strategy,the certain micro-pore's content of biomass activated carbon can be controlled by the activator and the carbonization temperature.This work provides a research tool for studying the pore composition and energy storage performance of biomass carbon materials.The microstructures readily available without excessive processing of biochar materials makes them ideal candidates where carbon is used as a template for the synthesis of other derived materials.Using cotton,lettuce and onion as carbon templates,we have obtained Ti₂Al C MAX phase conductive ceramics with the micro appearance characteristics of the precursor at 1000?in molten salt environment with Al and Ti powder.The MAX phase we got remained the shape of their carbon templates which can be described as torsional bands,two-dimensional sheets and three-dimensional blocks.We believe that the formation of MAX phase by this method is the result of the simultaneous infiltration of Ti-Al alloy at multiple points.In the experiment,the infiltration rate of titanium element is observed higher than that of aluminum element.Three kinds of transition metal two-dimensional carbides(Ti₂C MXene)nanosheet clusters were obtained by Cu Cl₂ etching at 1000?and molten salt etching at 650?.Nitrogen adsorption and desorption test showed that the specific surface area of MAX phase increased by more than 50 times after etching.This indicates that etching process of MAX phase clusters still retain the grain size and arrangement mode at the time of generation without rearrangement.The material is used to build asymmetrical capacitors and exhibits standard MXene pseudocapacitance behavior.This study provides a new idea for MAX phase morphology control,low-cost green synthesis strategy of MXene.