Exploring the Capacitive Behavior of Carbon Functionalized with Cyclic Ethers: A Rational Strategy To Exploit Oxygen Functional Groups for Enhanced Capacitive Performance

Abstract

The presence of oxygen functional groups (OFGs) on a carbon surface is a double-edged sword in electric double-layer capacitors (EDLCs) because of their mixed influences on capacitance. Critical problems of common OFGs are greatly decreased electrical conductivity, steric hindrance limiting the migration of ions, and promoted self-discharge via faradaic reactions. To explore a new breakthrough to these long-standing problems, carbon electrodes selectively functionalized with cyclic ether groups (CEGs) are investigated with in-depth spectroscopic and electrochemical analyses. The in-plane CEGs embedded in the graphene matrix are greatly advantageous over conventional out-of-plane OFGs for EDLC performance because they can boost capacitance via pseudocapacitance while substantially minimizing all of the negative effects of traditional OFGs. This study also reveals that preserving the original sp(2) carbon network during surface functionalization is crucial to maximizing the benefits of OFGs. These new insights call for the development of elaborate surface engineering strategies that can introduce functionalities with no significant damage to pi-conjugation.