Concurrently increasing specific energy and suppressing self-discharge of electrochemical capacitors by complexing carbon nanotubes with redox active units-containing charged copolymers

Specific energy and self-discharge are two important performances of electrochemical capacitors. In this work, we have fabricated the composite electrodes by complexing the negatively charged carboxylated multi-walled carbon nanotubes (cMWCNT) with the redox active units-containing positively charged random copolymers. 2,2,6,6-Tetramethylpiperidinyl- N -oxyl and viologen are employed as model redox active units to exemplify the strategy of the concurrent increase of specific energy and suppression of self-discharge of a two-electrode device. The slower hydrogen and oxygen evolution reactions compared with the reactions of the redox active units lead to an increased electrolyte decomposition window, thereby giving rise to an increase in specific energy. On the other hand, the complexation between the cMWCNT and the copolymers suppresses both the redox shuttling and the cross-diffusion of the redox active units-containing polymer chains, leading to an improved performance of self-discharge. Based on the complexation between carbon nanotubes and redox active units-containing charged copolymers, this work provides a convenient and universal strategy to concurrently increase specific energy and suppress self-discharge of electrochemical capacitors.