Decoding Potassium Ion Desolvation States for Enhanced Electric Double-Layer Capacitance in Actual Porous Carbon

Porous carbon (PC) electrodes store energy mainly via electric double-layer formation, governed by ion adsorption on pore surfaces and strongly influenced by ion desolvation states in PC, potassium ions can exist in five distinct desolvation states, denoted as [K(H₂O)_0-4]⁺. However, the mechanisms and thermodynamics and kinetics of individual desolvation states remain poorly understood. In this study, a methodology is developed to resolve and characterize the distinct desolvation states of ions within structurally realistic PCs. The corresponding desolvation energies and diffusion barriers of fully desolvated, partially desolvated, and fully solvated ion species are quantitatively determined. To enhance the electric double-layer capacitance(EDLC) of PC, a comprehensive design strategy is established based on a dual thermodynamic-kinetic optimization principle. This approach enables the identification of appropriate types and concentration windows of oxygen groups that synergize with specific ion desolvation states. The optimized PC achieved a specific capacitance of 273 F g^-1, representing the highest value reported for coal-derived PC electrodes. The proposed methodology provides an integrated analytical and design framework for the development of aqueous supercapacitors and metal-ion battery carbon electrodes, and offers mechanistic insights into catalytic and adsorption-separation processes occurring in aqueous environments confined within carbon nanopores.