Preparation Of High Specific Surface Area Biochar From Marine Biomass And Its Electrochemical Performance

Supercapacitors have attracted much attention because of their excellent performances such as high power density,long cycle life,and fast charge and discharge speed,and electrode materials are the main factors affecting their performance and cost.In the current research,some biochars have low electrochemical surface area due to low specific surface area and single pore structure.The electrochemical performance is not outstanding,and many scholars use modified methods to adjust the biochar structure.In order to achieve good results,many research efforts have paid a high cost and precious time.Recently,we found that some biomass raw materials have good microstructure and surface elements.If they can be used,no additional modifiers are needed,which can greatly reduce the processing cost during the synthesis process.The characteristics of reproducibility and greenness and no pollution are becoming increasingly prominent today,especially in line with the concept of sustainable development.In this paper,six kinds of biomass that are the most representative in different fields are selected as raw materials,namely agricultural waste-rice husk(RH),urban waste-sludge(SD),forestry waste-phoenix leaves(PL),marine energy waste-kelp(KL),undaria pinnatifida(UP)and enteromorpha prolifera(EP)to prepare biochar without adding any modifiers.By examining the structural characteristics and electrochemical performance of the biochar prepared,it is expected to find supercapacitor electrode materials with excellent performance and explore its energy storage mechanism.The main findings are as follows:(1)The structural difference and electrochemical performance difference of biochar prepared by different biomass sources were studied.The results show that the specific surface area and pore size of the three marine-based biochars are significantly better than rice husk char,sludge charcoal and sycamore leaf charcoal.The specific surface areas of the three marine-based biochars are 1140 m2 g-1,822 m2 g-1 and 621 m2 g-1,respectively.The pore structure is mainly micropores,with a small amount of mesopores.The rich pore size distribution is beneficial to increase the active sites and accelerate the diffusion of electrolyte ions,thereby improving the electrochemical performance.Under the three-electrode system,the electrochemical performance of three marine-based biochars is significantly better than rice husk charcoal,sludge charcoal,sycamore leaf charcoal,and five commercial activated carbons,and has good application prospects.The results show that the biochar materials prepared by marine biomass have high specific surface area and outstanding electrochemical performance,which proves that without the addition of external modifiers,direct carbonization of biomass can obtain biochar materials with excellent performance.The green preparation of biochar provides a theoretical basis.(2)The surface structure and electrochemical performance of marine-based biochar before and after washing the raw materials were analyzed,and the energy storage mechanism of marine-based biochar was studied.From the structural characterization analysis of the three groups of biochar,it can be seen that the surface salt of the biomass raw material is greatly reduced after being washed;compared with the biochar prepared without the raw material being washed:the pore structure of the surface becomes narrower and less;graphitization The degree is weakened;the specific surface area is reduced.By analyzing its electrochemical performance,it was found that the specific capacitance of the biochar electrode after washing the raw materials was significantly reduced,and the electrochemical performance was significantly weakened.Based on the above research,it is proposed that the reason for the excellent electrochemical performance of marine-based biochar is mainly due to the in-situ activation of surface salts,which enables it to have a larger specific surface area and a higher degree of graphitization,accelerate electron transmission,and increase the electrode The contact area between the material and the electrolyte provides abundant active sites,promotes its electrochemical performance,and provides a reference for the green preparation of high-performance supercapacitor electrode materials.