Hierarchical mesoporous flower-like ZnCo2O4@NiO nanoflakes grown on nickel foam as high-performance electrodes for supercapacitors

Herein, mesoporous ZnCo2O4@NiO nanoflakes grown on a nickel foam conductive substrate are prepared through a simple hydrothermal method combined with environmentally friendly chemical bath deposition method. The as-synthesized three-dimensional nanoflakes used as a binder-free supercapacitor electrode possess high specific surface area and shorten the ions and electron diffusion path. Electro-chemical measurements indicate that ZnCo2O4@NiO (M3) nanoflakes deliver an ultrahigh specific capacitance of 2797 F g(-1) at a current density of 1 A g(-1), and 2287.2 F g(-1) at 10 A g(-1), even 1079.2 F g(-1) at 40 A g(-1), respectively, revealing a remarkably improved rate performance. Moreover, the ZnCo2O4@NiO (M3) composite electrode exhibits superior cycling stability with-100% initial capacitance retention at the current density of 30 A g(-1) after 3000 cycles, and the coulombic efficiency remains over 97%. The first principle calculation shows that strong chemical bonds are formed between Ni (Co) and O species at the interface, which is favorable for the stabilization of the composite, resulting in a smaller interfacial polarization. The results indicate that ZnCo2O4@NiO with excellent electrochemical properties can be considered as a promising candidate for high-performance supercapacitors, and the facile architectural design strategy offers new insights in opportunities to exhibit promising potential in the field of the energy storage conversion applications. (C) 2018 Elsevier Ltd. All rights reserved.