Cobalt-based metal oxide coated with ultrathin ALD-MoS2 as an electrode material for supercapacitors

• Co 3 O 4 and NiCo 2 O 4 nanosheets are synthesized by hydrothermal technique. • An ultrathin MoS 2 is decorated on Co 3 O 4 and NiCo 2 O 4 by ALD. • Highest areal capacitance of 2445 mF cm −2 is achieved for NiCo 2 O 4 -MOS 2 . • An asymmetric supercapacitor (ASC) device is fabricated using NiCo 2 O 4 -MoS 2 //AC. • The NiCo 2 O 4 -MoS 2 //AC ASC device delivers a specific energy density of 62.32 Wh kg −1 . A novel approach of preparing a composite supercapacitor electrode consisting of ternary metal oxide nanostructure decorated with transition metal sulfide is presented. High-surface area NiCo 2 O 4 nano-sheets grown on Ni-foam are coated with an ultrathin layer of MoS 2 by atomic layer deposition (ALD) and the hybrid structure reveals superior electrochemical performance. The composite is thoroughly studied with several characterizations like XRD, Raman, XPS, SEM and TEM. A comparative study with MoS 2 coated Co 3 O 4 electrodes not only ensures the advantage of the more conducting sulfide layer in enhancing the supercapacitor performance significantly but also establishes the superiority of the ternary oxide (NiCo 2 O 4 ) for this application. The thinner and well-connected nano-sheets of NiCo 2 O 4 provides the more interface between the electrode and the electrolyte whereas an optimal thickness of MoS 2 helps to maximize the performance of the device. The high areal capacitance (2445 mF cm −2 ), enhanced rate capability of the optimized NiCo 2 O 4 -MoS 2 composite is therefore ascribed to the synergistic effect of high-surface area of the oxide nano-sheets and better electronic conductivity of the sulfide. The current study thus opens a route to combine the conventional hydrothermal synthesis of ternary oxide nanostructures with ALD grown layered transition metal dichalcogenides to achieve a superior electrode for next-generation supercapacitor.