Dehydration of Cations Inducing Fast Ion Transfer and High Electrical Capacitance Performance on Graphene Electrode in Aqueous Electrolytes

Abstract

We fabricated single-layer graphene as an ideal two-dimensional electrode for evaluating fundamental mechanism of ion transfer into a capacitance system and conducted cyclic voltammetry and molecular dynamics simulations to evaluate its capacitive performances in different aqueous electrolytes solutions of KCl, NaBr, NaCl, NaF, and LiCl. The system of KCl electrolyte had the highest areal capacitance at various scan rates and the fast ion diffusion coefficient. The highest capacitance and the fast ion diffusion were also observed from the molecular dynamics simulations. Cationic mobility especially influenced capacitance performance, whereas those capacitance performances were inactive for anionic mobility. Those are the result of direct contact of K+ ions with graphene interfaces by dehydration. The comparison analyses indicated the guides for efficient capacitance by ion dynamics during charging cycles. These results therefore improve our understanding of ion dynamics during charging and will contribute to the development of energy storage applications of electric double-layer capacitors.

Sequential and simultaneous ion transfer into carbon nanopores during charge–discharge cycles in electrical double layer capacitors

“…[13][14][15][16][17][18] Faster diffusion of K + ions associated with their desolvation on graphene and conical electrodes leads to high EDLC performance. 19,20 Furthermore, solvent dynamics has been reported to affect the EDLC performance in a narrow pore. 19 However, inuence of ion dynamics is still not well understood, and differences in the pore structure lead to discrepancies between experiments and simulations.…”