To meet the requirement for the high-ranked positive electrode materials having auspicious pseudocapacitive features for potential application in energy storage devices, the suitable designs of unique core−shell heterostructures featuring mixed transition metal oxide and layered double hydroxide (LDH) are highly needed and have been progressing expeditiously in recent years. Herein, 3D hierarchical zinc−nickel−cobalt (ZNCO)@Co−Ni-LDH (LDH-1 and LDH-2) core−shell nanostructured arrays on Ni foam as a pseudocapacitive electrode are prepared by using a facile hydrothermal and metal−organic framework (MOF) assisted coprecipitation method. FE-SEM images show that the core 1D ZNCO and shell 2D Co−Ni-LDH are well interconnected to form 3D porous and hierarchical ZNCO@Co−Ni-LDH core−shell nanostructures, leading to the fast and efficient transmission/transfer of both electrolyte ions and electrons, due to the higher electroactive surface areas and enhanced electrical conductivity. In a three-electrode system, the ZNCO@Co−Ni-LDH-2 electrode material delivers excellent electrochemical performance with higher specific capacitance of 2866 F g −1 at 1 A g −1 with ultrahigh capacitance retention of 68.35% at a higher current density of 10 A g −1 and excellent life span of 89% capacitance retention after 8000 cycles. Moreover, the sandwiched asymmetric supercapacitor (ASC) device using ZNCO@Co−Ni-LDH-2 as the positive electrode and N-doped graphene hydrogel (NGH) as the negative electrode exhibits superior specific capacitance (178 F g −1 at 1 A g −1 ), outstanding rate capability (70.22% at 10 A g −1 ), excellent life span (91.2% after 8000 cycles at 10 A g −1 ), and very high energy density (63.28 W h kg −1 at power density of 796.53 W kg −1 ).
The design and development of an economic and highly active non-precious electrocatalyst for methanol electrooxidation is challenging due to expensiveness of the precursors as well as processes and non-ecofriendliness. In this study, a facile preparation of core-shell-like NiCo2O4 decorated MWCNTs based on a dry synthesis technique was proposed. The synthesized NiCo2O4/MWCNTs were characterized by infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and selected area energy dispersive spectrum. The bimetal oxide nanoparticles with an average size of 6 ± 2 nm were homogeneously distributed onto the surface of the MWCNTs to form a core-shell-like nanostructure. The NiCo2O4/MWCNTs exhibited excellent electrocatalytic activity for the oxidation of methanol in an alkaline solution. The NiCo2O4/MWCNTs exhibited remarkably higher current density of 327 mA/cm2 and a lower onset potential of 0.128 V in 1.0 M KOH with as high as 5.0 M methanol. The impressive electrocatalytic activity of the NiCo2O4/MWCNTs is promising for development of direct methanol fuel cell based on non-Pt catalysts.
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