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
Summary
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
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