Rationally designed hierarchical ZnCo2O4/polypyrrole nanostructures for high-performance supercapacitor electrodes

Abstract

Electrodes with rationally designed hybrid nanostructures can offer many opportunities for enhanced performance in electrochemical energy storage. In this work, hierarchical ZnCo₂O₄/polypyrrole (PPy) nanostructures on Ni foam were rationally designed and successfully fabricated through a facile two-step method and were directly used as an integrated electrode for supercapacitors. The novel nanoscale morphology has been proven to be responsible for their excellent capacitive performance. When used as electrodes in supercapacitors, the hybrid nanostructures demonstrated prominent electrochemical performance with a high specific capacitance (1559 F g⁻¹ at a current density of 2 mA cm⁻²), a good rate capability (89% when the current density increases from 2 to 20 mA cm⁻²), and a good cycling ability (90% of the initial specific capacitance remained after 5000 cycles at a high current density of 10 mA cm⁻²). Moreover, the high specific energy density is 30.9 W h kg⁻¹ at a current density of 2 mA cm⁻² in a two-electrode system. The excellent electrochemical performance of hierarchical ZnCo₂O₄/PPy nanostructures can be mainly ascribed to the enhanced adherent force between electrode materials and Ni foam to hold the electrode fragments together by means of ZnCo₂O₄ nanowires, the good electrical conductivity of PPy, and the short ion diffusion pathway in ordered porous PPy nanofilms and ZnCo₂O₄ nanowires.