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

Abstract

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.

Supersonically Sprayed Zn2SnO4/SnO2/CNT Nanocomposites for High-Performance Supercapacitor Electrodes

“…The capacitance of a supercapacitor arises from two different basic mechanisms: electrochemical double-layer capacitance (EDLC) and pseudocapacitance. − EDLC occurs due to the separation of electric charges at the electrode/electrolyte interface with the electrostatic adsorption/desorption of ions in the absence of Faradaic reactions . In contrast to EDLC, pseudocapacitance involves Faradaic reactions.…”

Insights into the influence of the pore size and surface area of activated carbons on the energy storage of electric double layer capacitors with a new potentially universally applicable capacitor model

“…For pores larger than 1.83 nm, we suspect an influence of the pore wall curvature on the double layer formation, which is best described with a cylindrical capacitor model as shown in Fig. 1c and d. 28,29,33,34 Although our synthesized carbon materials probably possess mainly slit shaped pores regardless of the pore diameter, the curvature of pore walls for larger pores plays a significant role in the double layer formation. Since it is not possible for two or more fully solvated ions to enter pores between 1.83 and 2.60 nm, we presume a restriction of the double layer formation, resulting in a smaller assumed double-layer thickness of 0.820 nm compared to 1.015 nm for the unrestricted double layer formation for pores larger than 2.60 nm.…”

“…They used the electrical wire and slit pore model for micropores and the cylinder and spherical model for mesopores for various activated carbons, and compared the simulated capacitance with the measured capacitance. 34 Using high resolution scanning electron microscopy (SEM) for investigation of the pore shape it was found that the activated carbon materials had curved mesopores. Furthermore, they observed the best match of simulated and measured capacitances for a combined model of slit-shaped pores for micropores and cylindrical shaped pores for mesopores, confirming the approach of Hsieh et al…”

“…43 For the optimal characterization of the porous properties of activated carbons, the method of combining carbon dioxide and nitrogen physisorption has recently been demonstrated as a legitimate method of evaluating gas physisorption data. 34,41,42,44,45 In this study, we have developed a new model that describes the dependence of capacitance on pore size. The pore sizes are divided into four ranges, based on the ion size of the electrolyte system used.…”

Mechanisms of Porous Carbon‐based Supercapacitors

“…Because nanoporous carbon materials have a complicated structure, researchers integrated electric double layer models based on the distribution of distinct pore shapes and sizes to enhance capacity prediction accuracy [34–36] . Ruben et al .…”