Overscreening-Driven Modulation of Ion Adsorption and Desorption in Conductive MOF Electrodes by Charging Rates.

Abstract

Elucidating the charging mechanism plays an intrinsic and critical role in the development of high-performance supercapacitors; however, a deep understanding of how this mechanism varies under different charging rates remains challenging. In this study, we investigate the charging mechanism of conductive metal-organic framework (c-MOF) electrodes in ionic liquids, combining electrochemical quartz crystal microbalance and constant-potential molecular dynamics simulations. Both experimental and modeling results reveal a transition of the ion adsorption and desorption modes from anion dominance at low charging rates to ion-exchange governance at high charging rates, significantly reducing the contribution of anions to the capacitance. The dynamic structures of in-pore ions suggest that this transition stems from variations in the overscreening strength, which leads to different ion responses between the central and surface regions of c-MOF pores under polarization. This work could lay the foundation for optimizing supercapacitor design, especially under high charging rates.