Hierarchical porosity and electrolyte compatibility in carbon-based supercapacitors

Abstract

Supercapacitors are pivotal for high-power energy storage, yet their energy density is governed by the complex interplay between electrode porosity and electrolyte properties. This study reveals how hierarchical porosity dictates the electrochemical performance of carbon-based electrodes—activated carbon from coconut shell (ACMag), commercial activated carbon (ACNag), and reduced graphene oxide (rGOag)—in aqueous (KOH) and deep eutectic solvent (ChClEG) electrolytes. We demonstrate that ACNag, with its hierarchical slit-shaped pores, delivers superior and stable performance (34F/g, 15.6 Ω cm2 in ChClEG). Conversely, ACMag's “ink-bottle” pores cause ion-trapping and higher resistance, while rGOag exhibits extreme electrolyte dependence, excelling in KOH (68 F/g) but failing in viscous ChClEG (8 F/g) due to inadequate porosity. By integrating electrochemical, structural (BET, SEM), and chemical (TG-FTIR-MS) analyses, we establish that optimal capacitance arises from a synergy of electric double-layer formation and surface-mediated pseudocapacitance. Quasi-elastic neutron scattering further shows efficient charge storage occurs via rapid ion diffusion or localized, surface-confined processes. Our findings prove that tailoring hierarchical slit-pores is paramount for balancing ion confinement and accessibility, providing a critical design principle for advanced supercapacitors in renewable energy and high-power applications.