Self-assembly of NiMoO4 nanoparticles on the ordered NiCo2O4 ultra-thin nanoflakes core-shell electrode for high energy density supercapacitors and efficient oxygen evolution reaction

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The scrupulous design and construction of self-ordered binder-free core-shell electrodes with numerous active sites has drawn massive attention in the field of supercapacitors and oxygen evolution reaction. We demonstrate a powerful and environment friendly two-step electrochemical engineering of the highly ordered two-dimensional NiCo2O4 nanoflakes trapped with NiMoO4 nanoparticles on Ni foam. The vertically self-assembled NiCo2O4 nanoflakes offer easiest paths for the ion and electron transport. Moreover, the synergistic effect between nanoflakes and nanoparticles provide large active surface area for electrochemical energy storage and oxygen evolution electrocatalysis. Compared to NiCo2O4 nanoflakes NiCo2O4/NiMoO4 core-shell electrode exhibited an enhanced electrochemical performance having an excellent specific capacitance (3705 F g-1 at 1.5 A g-1), high rate capability (95.1% for 20-fold increase of the current density), and a stable cycle life (94.6% for 5000 charge-discharge cycles). Moreover, it showed an overpotential of 400 mV at a current density of 50 mA cm-2, Tafel slope of 150 mVdec-1, and 100% of stability for 5 h of continuous operation in alkaline medium. Moreover, as-fabricated NiCo2O4/NiMoO4//NiCo2O4/NiMoO4 symmetric supercapacitor delivered highest energy density of 76.45 Wh kg-1 and cycle life of 88% after 5000 cycles. Thus, present study demonstrates sustainable engineering approach to fabricate highly ordered two-dimensional heterostructures for various electrochemical applications.