Improved electrochemical performance of graphene oxide via copper ion cross-linking and plasma functionalization

Abstract

The electrochemical performance of graphene oxide (GO) is restricted by π–π stacking and other intermolecular interactions, hindering electrolyte access to the densely packed GO layers. Herein, the stacking of GO sheets is effectively prevented, and a nearly three-dimensional (3D) structure is constructed through the cross-linking of Cu²⁺ with GO. This cross-linking, via Cu²⁺ interactions with epoxy and carboxyl groups, results in a higher specific surface area after freeze-drying, achieving enhanced electrochemical properties. Furthermore, characterization results demonstrate that oxygen plasma processing can efficiently tailor the oxygen-containing groups of GO without damaging its structure, thereby creating more cross-linking sites. Subsequently, to restore the conductivity, GO is reduced via argon (Ar) plasma treatment while preserving most of the electrochemically active oxygen-containing groups. As a result, electrochemical performance optimization for Cu–GO is attained by synergistically utilizing Cu²⁺ cross-linking and plasma technology, and the entire process is very simple, facilitating scalable production. Cu–GO can deliver a specific capacitance of 235 F g⁻¹ at 1.5 A g⁻¹, representing a 197% increase compared to that of pure GO, excellent rate performance with a capacitance retention of 93% at 15 A g⁻¹ and long-term cycling stability with no capacitance decay after 60 000 cycles. The assembled all-solid-state symmetric supercapacitor demonstrates an outstanding energy density of 8.1 W h kg⁻¹ and impressive cycling stability with no capacitance decay after 10 000 cycles, showing promising application potential.