The effects of urea concentration on microstructures of ZnCo2O4 and its supercapacitor performance

The effects of urea concentration on microstructures of ZnCo2O4 during hydrothermal process and their supercapacitors performance were investigated. The sphere ZnCo2O4 oxide with nanostructure arrays was formed after hydrothermal process containing low urea concentration. The slim and curved ZnCo2O4 nanowires were formed on Ni foam due to medium urea concentration, while sharp and separated ZnCo2O4 nanostructure arrays were formed on Ni foam due to high urea concentration. The sharp and separated ZnCo2O4 nanostructure arrays on Ni foam showed the best electrochemical performance. ZnCo2O4 nanostructure arrays obtained were composed of interconnected ZnCo2O4 nanoparticles. The gaps between ZnCo2O4 nanoparticles promoted penetration of the electrolyte, which induced the high supercapacitive performance. The sharp and separated ZnCo2O4 nanostructure arrays on Ni foam had the lowest charge transfer resistance, which improved supercapacitive performance. In addition, the strong and separated ZnCo2O4 nanowires improved significantly cycle life during the charge-discharge process due to good strain accommodation of the unique structure.