Unlocking the energy storage potential of polypyrrole via electrochemical graphene oxide for high performance zinc-ion hybrid supercapacitors

Abstract Safe and low-cost zinc-ion hybrid supercapacitors using neutral aqueous electrolytes are promising for large scale and high power energy storage. A key challenge for Zn-ion hybrid supercapacitors is to increase their energy density without sacrificing the high power performance. Herein, we report a Zn-ion hybrid supercapacitor using a polypyrrole/electrochemical graphene oxide (PPy/EGO) composite cathode and aqueous 1 M ZnCl2 or ZnBr2 electrolytes. The Zn-PPy/EGO system with an operating cell voltage from 0.5 to 1.5 V exhibited high energy and high power densities of 117.7 and 72.1 Wh kg−1 at 0.34 and 12.4 kW kg−1, respectively, outperforming the Zn-ion hybrid supercapacitors using carbon cathodes. This high performance is because of the facilitated electronic and ionic transport in the PPy/EGO composite. In brief, the EGO prepared via the electrochemical method we recently reported has good structure integrity and is easily reduced; the porous PPy/EGO composite from co-electrodeposition benefits fast ion diffusion in pores; the small, monovalent halides anions in the zinc halides electrolytes are highly mobile in bulk PPy for fast solid-phase anion insertion/de-insertion. Electrochemical characterization and ex-situ X-ray photoelectron spectroscopy confirmed the anion-dominated charge storage mechanism of PPy/EGO cathode in Zn-PPy/EGO system.