Electrowetting-driven capacitance enhancement dependent on charge carrier and nanopore size

Enhancing the specific capacitance of supercapacitors requires a deeper understanding of their charge storage mechanisms. While recent studies have primarily focused on micropore-dominant activated carbons (ACs) and monovalent ions, a more comprehensive and systematic exploration remains underexplored. In this work, we developed microporous and mesoporous AC electrodes with pore size distributions centered at 1.4 nm (AC14) and 3.7 nm (AC37), respectively. These electrodes were systematically evaluated in various electrolyte systems containing monovalent or multivalent cations and sulfate anions as charge carriers. A key finding of this study is the dual role of electrowetting: it quantitatively increases the accessible active surface area and qualitatively enhances capacitance by facilitating the formation of Stern layer-dominated electric double layers. Furthermore, under conditions that promote sufficient electrowetting, multivalent ion charge carriers exhibit a stronger charge-neutralizing effect compared to monovalent ions, resulting in significantly enhanced specific capacitance. These results highlight the critical importance of multivalent charge carriers and mesopores, suggesting the need for targeted research to optimize these parameters for improved charge storage performance. This study offers a novel framework for advancing electrochemical systems beyond conventional strategies, such as increasing surface area or reducing ion-electrode distances. • Microporous and mesoporous activated carbons (AC) were successfully fabricated. • Unconventional dual-ion adsorption behaviors were observed in high-performance ACs. • Electrowetting boosts charge storage in both magnitude and mechanism. • The electrowetting response depends strongly on charge-carrier type and AC pore size. • Multivalent electrolytes paired with mesoporous AC deliver the best supercapacitor performance.