Rationally controlled synthesis of Ni–Cu–Zn oxide hollow structures for high-performance supercapacitors

Abstract

Designing electrodes with rational components and structures can remarkably boost their electrochemical properties. Hybrid metal oxide electrodes with hollow structures show advantages for electrochemical energy storage. Herein, we present a simple synthetic route for the preparation of Ni–Cu–Zn oxide yolk–shell sphere (YSS) and hollow sphere (HS) structures as supercapacitor electrodes. A solvothermal method is first employed to obtain the precursors with YSS and HS structures by controlling the reaction time. The resulting precursors are then converted into Ni–Cu–Zn oxide YSS and HS structures, followed by calcination in air. The compositional and structural features of both Ni–Cu–Zn oxide structures make them suitable for supercapacitor applications. Particularly, the Ni–Cu–Zn oxide HS structures deliver a high capacity of 1114.2 C g⁻¹ at 2.0 A g⁻¹ and a capacity of 774.4 C g⁻¹ at 20 A g⁻¹ while maintaining 92.5% capacity retention after 10 000 cycles. Furthermore, an asymmetric supercapacitor was constructed using Ni–Cu–Zn oxide HS and activated carbon (AC), exhibiting an energy density of 58.9 Wh kg⁻¹ at a power density of 1500 W kg⁻¹ and excellent cycling stability. In general, this work not only offers a promising material for supercapacitor electrodes but also provides a simple method to prepare hollow-structured hybrid metal oxides.