Abstract

In this work, mesoporous ZnCo2O4 electrode material with necklace-type nanowires was synthesized by a simple hydrothermal method using water/ethylene glycol mixed solvent and subsequent calcination treatment. The ZnCo2O4 nanowires were assembled by several tiny building blocks of nanoparticles which led to the growth of necklace-type nanowires. The as-synthesized ZnCo2O4 nanowires had porous structures with a high surface area of 25.33 m2 g−1 and with an average mesopore of 23.13 nm. Due to the higher surface area and mesopores, the as-prepared necklace-type ZnCo2O4 nanowires delivered a high specific capacity of 439.6 C g−1 (1099 F g−1) at a current density of 1 A g−1, decent rate performance (47.31% retention at 20 A g−1), and good cyclic stability (84.82 % capacity retention after 5000 cycles). Moreover, a hybrid supercapacitor was fabricated with ZnCo2O4 nanowires as a positive electrode and activated carbon (AC) as a negative electrode (ZnCo2O4 nanowires//AC), which delivered an energy density of 41.87 Wh kg−1 at a power density of 800 W kg−1. The high electrochemical performance and excellent stability of the necklace-type ZnCo2O4 nanowires relate to their unique architecture, high surface area, mesoporous nature, and the synergistic effect between Zn and Co metals.

Highlights

  • An electrochemical supercapacitor is one of the most effective techniques to store electrical energy, owing to its high power density, high charge/discharge rate, long operation time, higher rate capability, mechanical stability, and environmental friendliness [1,2]

  • The ZnCo2O4//activated carbon (AC) hybrid supercapacitor (HSC) device delivered a high specific capacitance of 117.7 F g−1 at a current density of 1 A g−1, and retained 64.23 % even at a high current density of 5 A g−1 (75.6 F g−1), displaying outstanding rate performance (Figure 8d)

  • Mesoporous necklace-type ZnCo2O4 nanowires were synthesized by a simple one-pot hydrothermal method and subsequent annealing process in air

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Summary

Introduction

An electrochemical supercapacitor is one of the most effective techniques to store electrical energy, owing to its high power density, high charge/discharge rate, long operation time, higher rate capability, mechanical stability, and environmental friendliness [1,2]. Cubic spinel ZnCo2O4 is a promising energy storage material, owing to its various valence states, excellent electrochemical redox properties, better electrical conductivity, low cost, non-toxicity, and different morphologies [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35]. Bhagwan et al, prepared ZnCo2O4 nanoparticles via a combustion method for supercapacitors, showing a high specific capacitance of 843 F g−1 at a current density of 1 A g−1 [26]. Due to the high surface area, mesoporous structure, unique architecture, and synergistic effect, asprepared necklace-type ZnCo2O4 nanowires delivered a high specific capacity (439.6 C g−1 at a current density of 1 A g−1), excellent rate performance (208.0 C g−1 at 20 A g−1), and outstanding cyclic stability (84.82 % capacity retention after 5000 cycles). A hybrid supercapacitor (HSC) device was fabricated with ZnCo2O4 nanowires as a positive electrode and activated carbon (AC) as a negative electrode (ZnCo2O4 nanowires//AC), which delivered an energy density of 41.87 Wh kg−1 and a maximum power density of 4000 W kg−1

Results and Discussion
Experimental
Conclusions

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