Elucidating the Importance of Pore Structure in Determining the Double-Layer Capacitance of Nanoporous Carbon Materials

Porous carbon is a common electrode material used, in electrochemical double-layer capacitors, in which energy is stored by physical adsorption of electrolyte ions on the carbon's surface, forming an electrical double layer (EDL). However, due to the complex nanoporous network of carbon materials, it is difficult to characterize the EDL structure. This work demonstrates that the understanding of the EDL structure in nanoporous carbon materials can be improved by defining the pore shapes using ultrahigh resolution scanning electron microscopy (SEM). The SEM images reveal a continuous network of curved pores. This characterization, along with the experimentally determined surface areas and pore sizes, enabled the investigation of the applicability of various models describing the EDL configuration. This study found that, by using the microscopic information to characterize the 3-D nanostructure and select the appropriate models for the pore shape, it is possible to predict a porous carbon material's experimental capacitance within +/- 8%. This updated approach may be used to identify ideal pore structures and top-performing carbon materials. It is clear that using ultrahigh resolution SEM images to understand the relationship between pore shape, EDL structure, and capacitance provides valuable insight into the complexity of energy storage in nanoporous carbon materials.