Enabling directional ion transport over graphene electrode surfaces for kilohertz electrochemical capacitors

Abstract

The filtering capacitor is an electrochemical energy storage device, which can realize signal stabilization from alternating current to direct current in the modern electronic circuits. Traditional filtering capacitor, an aluminum electrolytic capacitor is usually limited by the bulky and rigid configuration. The graphene-based electrochemical capacitor with a fast frequency response has the potential to be the next-generation filtering capacitor. Kilohertz electrochemical capacitor with alternating current line-filtering performance requires the microstructural engineering of graphene electrodes to facilitate effective electrolyte ion permeation. Vertically-oriented graphene electrode-based electrochemical capacitor by microstructural engineering provides a significant solution for improving the filtering performance, but the underlying mechanism by which the vertical orientation endows graphene electrodes with the fast frequency response is still not clear. Therefore, a fundamental understanding of this mechanism must be developed and improved to ensure the design of superior kilohertz electrochemical capacitors for effective filtering. Here, a vertically-oriented graphene macroporous membrane is prepared to enable directional ion transport over the electrode surface at high frequencies, which is demonstrated by all of the electrochemical analysis, line scanning, schematic illustration and finite element analysis simulation results. Compared with those based on conventional horizontally-oriented and unordered graphene macroporous membrane electrodes, the vertically-oriented electrode-based electrochemical capacitor exhibits excellent filtering performance. Furthermore, it can convert arbitrary alternating current waveforms to straight signals. This work advances the understanding of the mechanism underlying the kilohertz frequency response and enables directional ion transport over the surface of vertically-oriented graphene electrodes, providing new insight into the search for future kilohertz filtering capacitors.