Enhancing Capacitance of High-Rate Electric Double-Layer Capacitors with CO ₂ -Activated Mesoporous Carbon Gel Electrodes

Electric double-layer capacitors (EDLCs) store charge by adsorbing ions at the electrode–electrolyte interface, offering fast charge–discharge rates, high power density, minimal heat generation, and long cycle life. These characteristics make EDLCs ideal for memory backup in electronic devices and power assistance in electric and hybrid vehicles, where rapid energy response and high-power delivery are critical. However, their energy density remains lower than that of batteries, requiring improvements in capacitance and operating voltage. Activated carbon with high surface area is commonly used as the electrode material, but its microporous structure limits ion transport at high rates, reducing power performance. This limitation is especially critical in automotive motor drive systems. Recent research has shifted toward mesoporous carbon materials, which improve ion diffusion and accessibility. In this study, resorcinol–formaldehyde carbon cryogels (RFCCs) with controlled mesoporous architectures were synthesized and applied as EDLC electrode materials, in combination with organic electrolytes that provide a wider electrochemical window. A CO₂-activated RFCC (RFCC-CO₂) demonstrated the most balanced electrochemical performance, combining high surface area and interconnected mesoporous networks. Characterization using scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area analysis confirmed the hierarchical porous structure. Electrochemical evaluations through cyclic voltammetry (CV) and constant current charge–discharge measurements demonstrated that RFCC-CO₂ achieved high specific capacitance and excellent rate capability. These results point to the importance of mesopore engineering in addressing ion transport limitations in conventional carbon materials and highlight RFCC-CO₂ as a promising electrode candidate for EDLCs in regenerative braking and other fast-response electric mobility applications.