A Ce^3+/4+ Redox Couple-Promoted Aqueous Zinc-Ion Hybrid Capacitor: Design Strategies and Mechanistic Insights

Aqueous zinc-ion hybrid capacitors (ZIHCs) are emerging as promising energy storage devices owing to several desirable attributes including good safety, high power density, and good stability. However, the limited energy density mainly caused by the low specific capacity of porous carbon cathodes hinders the practical application of ZIHCs. A Ce^3+/4+ redox couple-promoted aqueous ZIHC (Ce-ZIHC) is designed with the addition of Ce^3+/4+ electrolyte additives. The Ce^3+/4+ redox couple is shown to markedly increase the specific capacity of the porous carbon cathode energy and enhance the stability of Zn²⁺ stripping/plating at the Zn metal anode. Notably, the as-constructed Ce-ZIHC performs more than twice the energy density of the ZIHC with the commercial activated carbon cathode. Furthermore, the Ce-ZIHC shows a low self-discharge rate and can work stably for more than 60 000 cycles at 5.0 A g^-1. This work highlights the great potential of Ce^3+/4+ redox couple in improving the overall performance of ZIHCs toward practical application.