Rationally designed hierarchical ZnCo2O4/polypyrrole nanostructures for high-performance supercapacitor electrodesElectronic supplementary information (ESI) available: (Fig. S1) SEM and TEM images, and (Fig. S2) mapping images of hybrid nanostructures; the CV curves and GCD curves of PPy and ZnCo2O4 (Fig. S3); GCD curves of the PPy, ZnCo2O4, and ZnCo2O4/PPy (Fig. S4); the data of Specific capacitance (Table S1); the CV curves and GCD curves of PPy and ZnCo2O4 in a two electrode system (Fig. S5).

Electrodes with rationally designed hybrid nanostructures can offer many opportunities for enhanced performance in electrochemical energy storage. In this work, hierarchical ZnCo 2 O 4 /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 ZnCo 2 O 4 /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 ZnCo 2 O 4 nanowires, the good electrical conductivity of PPy, and the short ion diffusion pathway in ordered porous PPy nanofilms and ZnCo 2 O 4 nanowires. The synthesis procedure of ZnCo 2 O 4 /PPy composite electrodes and the electrochemical properties of the composite electrodes.