Theoretic Insights into Porous Carbon-Based Supercapacitors

Supercapacitors, or more specifically electric double-layer capacitors, (EDLCs) store electrical energy by adsorbing ionic species to the inner surfaces of porous electrodes. Porous carbons are the most commonly used electrodes, while ionic liquids, organic electrolytes, and aqueous electrolytes are used as charge carriers. Approximating the porous carbon as a slit pore and ions as charged hard spheres, we address the differential capacitance and layering of the ionic-liquid/carbon interface and the dependence of the capacitance on the pore size from a classical density functional theory (CDFT) perspective. We further introduce the solvent into the electrolyte to model the organic electrolyte EDLC. We demonstrate that the CDFT is uniquely amenable to the investigations of the electrochemical behavior of confined electrolytes given its applicability to electrodes with a wide distribution of pore sizes, ranging from ionic dimensionality to mesoscopic scales.