Hybrid aqueous supercapacitors based on mesoporous spinel-analogous Zn-Ni-Co-O nanorods: Effect of Ni content on the structure and energy storage

Abstract

The structure and the electrochemical performance of mesoporous spinel-analogous Zn-Ni-Co-O (Zn1−xNixCo2O4; 0.2 ≤ x ≤ 0.8) nanorods are investigated. Cyclic voltammetry gives strong indication that the charge storage mechanism is governed by pore surface redox processes without significant contribution from the sub-surface charge storage. Since the size of the Zn1−xNixCo2O4 rods decreases with increasing Ni content x, the BET surface and thus the charge storage capacity increases with increasing x, namely from 266 C g−1 to 463 C g−1 at 3.12 A g−1 when increasing x from 0.2 to 0.8. Hybrid aqueous supercapacitors (HSC) are fabricated with Zn1−xNixCo2O4, activated carbon (AC) and 6 M KOH as positive electrode, negative electrode and electrolyte, respectively. The specific energy densities of HSC are in the range of 27–2 Wh kg−1 at the specific power densities range of 780–2240 W kg−1. Real-world usage of the aqueous HSC device is demonstrated by enlightening a red light-emitting diode. These outcomes show that the mesoporous spinel-analogous Zn-Ni-Co-O materials are potential candidates for next-generation electrochemical energy storage applications.