Ion Desolvation and Electric Double-Layer Formation in Confined Ultramicropores of Activation-Free Chitin-Derived...

Understanding ion transport and charge storage in confined carbon nanopores is important for the design of electric double-layer capacitors (EDLCs), but the relationship between ultramicropores, ion desolvation, and practical rate performance remains difficult to clarify. Here, chitin-derived porous carbons (CDPCs) were prepared by activation-free carbonization at 800-900 °C and evaluated as model nanoporous carbon electrodes in aqueous 6 M KOH. The CDPCs possessed moderate BET surface areas of 314-328 m2 g-1 determined from N2 adsorption isotherms, together with ultramicropores identified by CO2 adsorption analysis and sub-10 nm mesopores. Despite their relatively small BET surface areas, the CDPCs delivered high BET-area-normalized capacitances of 46.8-52.9 μF cm-2 at 0.05 A g-1 and 39.1-44.0 μF cm-2 at 1 A g-1 in a three-electrode configuration. Electrochemical impedance measurements showed that the low-frequency ion-transport response changed more strongly with electrode potential than with carbonization conditions, suggesting potential-assisted ion transport in confined ultramicropores. Because hydrated K+ ions are larger than the ultramicropores, this behavior is consistent with potential-assisted partial desolvation during electrochemical polarization. Symmetric coin-cell measurements further showed that CDPCs retained capacitances comparable to those of YP-50F, a commercially available H2O-activated carbon widely used as an EDLC electrode material, despite having much smaller BET surface areas, indicating efficient utilization of confined pore surfaces. These results suggest that the cooperative presence of ultramicropores and mesopores enables high interfacial capacitance while maintaining ion accessibility, providing design principles for nanoporous carbon electrodes in aqueous electric double-layer capacitors.