Porous Carbon Material based on Biomass Prepared by MgO Template Method and ZnCl2 Activation Method as Electrode for High Performance Supercapacitor

Qingyang Sun, Northeastern Electric Power University, College of Chemical Engineering, Jilin 132012, China
2019 International Journal of Electrochemical Science  
Here, we use cotton as a biomass material, MgO as a templating agent, and ZnCl2 as an activator to prepare a biomass-based porous carbon material. As a pore generator, MgO is incorporated into cotton carbon by absorbing a solution of Mg(NO3)2 in cellulose fibers, subsequent drying and carbonization processes. After removing the MgO template by acid leaching, a biomass-based porous carbon material having a low cost and a high specific surface area is prepared. ZnCl2 has the functions of
more » ... nctions of dehydroxylation and dehydration during the activation process, so that hydrogen and oxygen in the raw material are released in the form of water vapor to form a porous structure. Moreover, ZnCl2 is transferred to ZnO during the activating process. The ZnO particles in the obtained material are removed by acid washing, and then these remained voids contribute additional porosity in internal structure. The experimental results show that the activated carbon material prepared by using MgO as the template agent ZnCl2 as the activator has a specific surface area of up to 1990 m 2 g -1 . In the three-electrode system test, the current density is 1 A g -1 and the capacitance is 240 F g -1 . When the current density is 20 A g -1 , the specific capacitance is 173 F g -1 , and the capacitance retention rate is 71%. In addition, the assembled symmetric supercapacitors were tested in 6M KOH aqueous solution and 1M Na2SO4 aqueous solution, respectively. The energy density in the alkaline system is 5.7 Wh kg -1 . The energy density in the neutral electrolyte is 12.5 Wh kg -1 and the cycle stability is 89%. 2 Compared with other energy storage devices, it has the advantages of high power density, fast charge and discharge speed, and high cycle stability [3] . Electrode materials are an important part of supercapacitors, mainly including carbon materials [4], metal oxides [5], conductive polymers [6], conductive polymers and mental oxides have been used to increase the specific capacitance via a variety of reversible oxidation states for highly efficient redox charge transfer [7] . But the practical application of the pseudocapacitive material is constrained by its high price, instability of circulation and low electrical conductivity [8] . In contrast, carbon materials have the advantages of excellent electrical properties, good cycle stability, and high specific surface area, and are therefore one of the most commonly used electrode materials [9] . Carbon electrode materials include activated carbon [10], carbon fiber [11] , and carbon nanotubes [12] . Among them, activated carbon materials have become the main material for the fabrication of supercapacitor storage electrodes due to their low-cost production process [13] . Precursors for the preparation of carbon materials are quite extensive, such as coal [14] , but due to the shortage of fossil energy, a low-cost and sustainable raw material is needed as a precursor [15] . Therefore, the development of biomass as a precursor of carbon materials with structurally controllable high-performance carbon materials has received extensive attention [16] . So far, scholars have carried on an extensive research of carbon materials in nature, a potential electrode materials for supercapacitors. Lotus stems [17] , wild rice stem [18] , fungus [19] , and cotonier strobili [20] are regarded as potential precursors for the synthesis of activated carbons. It is well known that Cotton, one of the most significant agricultural commodities, is cultivated and produced widely [21] . Cellulose is a major component of cotton. Cellulose contains a large amount of carbon and is sintered at high temperature to carbon under nitrogen protection [22, 23] . The addition of a template agent during the carbon burning process can make the arrangement of the pores of the carbon material more orderly, increase the number of pores, increase the specific surface area of the carbon material, and thereby cause accelerate the rate of movement of anions and cations from the positive to the negative electrodes in the electrolyte [24] . Thereby improving the electrochemical performance. The addition of an activator can increase the number of pores of the carbon material, and the increase in the number of pores can also cause the migration of anions and cations to both electrodes more quickly, increase the charge transfer rate, and thus have better conductivity [25, 26] . At present, Chunyu Zhu, used cotton to prepare a porous carbon material with a specific surface area of 1260 m 2 g -1 by using the MgO template method and applied it to a lithium ion battery [27] . In this paper, cotton fiber is used as carbon source, MgO is used as template and ZnCl2 is used as activator. Cotton-based porous activated carbon is prepared by simple chemical activation one-step method. For comparison, the dried absorbent cotton was directly carbonized and the material immersed only in the ZnCl2 solution and only immersed in Mg(NO3)2 was carbonized and comparatively analyzed.
doi:10.20964/2019.01.50 fatcat:i23eau24qje3nnhik7np27xdpa