Study On Electrochemical Behavior Of Carbon-based Electric Double Layer In A Multi-scale Embedded Capacitor Model

Supercapacitor has high power density and cycle stability.The improvement of its technology is mainly due to the continuous development of electrode materials.Based on Helmholtz theory,this paper provides a simple way to explain the formation mechanism of double electric layer of carbon with wide pore distribution.Firstly,the focus is shifted from the traditional material preparation process innovation to the internal structure design of hierarchical porous carbon.Several mainstream hierarchical porous carbon models are summarized and compared,and the structure model is linked with specific capacitance.Finally,several models are integrated,and a multi-scale hierarchical porous carbon embedded model is proposed,which mainly defines the interaction between pore structure and electrolyte ions.Secondly,according to the different chemical properties and activation mechanism of activators,five types of carbon were synthesized through pyrolysis and followed activation using chestnut shell as biomass precursor and H₃PO₄,Zn Cl₂,K₂CO₃,and KOH as activators.Pore structure information was obtained by scanning electron microscopy and N₂ adsorption-desorption with non local density functional theory.The results show that the pore forming ability and etching degree of alkali metal compounds?KOH and K₂CO₃?are better than that of H₃PO₄ and Zn Cl₂ when activated at 750?.In the electrochemical test,although ABC-KOH will show great capacitance due to its ultra-high micropore content,the IR drop produced in practical application can not be ignored.Therefore,it is of great significance to control the specific surface area and pore diameter of appropriate electrode materials.The development of reasonable hierarchical porous carbon will be the mainstream of electrode materials in the future.Finally,based on the experimental data of biochar electrode,a multi-scale embedded capacitor model is proposed to simulate the capacitance of carbon material with wide pore distribution.The model can be applied to sandwich-type micropores and spherical mesopores,while the macropores are described by the classical parallel plate capacitor model.The parameters in the model include pore curvature and electrolyte ion concentration,and the ion solvated layer related to the interface properties is clarified.By analyzing the effect of pore curvature and the density of solvent molecules on the relative permittivity of the electrode electrolyte interface and the thickness of the double layer,the screening effect of carbon materials on electrolyte ions was revealed.The capacitance measured by constant current charge discharge method is in good agreement with the simulation value,which shows that the parameters in the model can reasonably predict the capacitive behavior of layered porous carbon.The capacitance measured by constant current charge discharge method is in good agreement with the simulation value,which shows that the parameters in the model can reasonably predict the capacitance behavior of layered porous carbon.