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

Abstract

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 NiCo2O4 nano-sheets grown on Ni-foam are coated with an ultrathin layer of MoS2 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 MoS2 coated Co3O4 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 (NiCo2O4) for this application. The thinner and well-connected nano-sheets of NiCo2O4 provides the more interface between the electrode and the electrolyte whereas an optimal thickness of MoS2 helps to maximize the performance of the device. The high areal capacitance (2445 mF cm−2), enhanced rate capability of the optimized NiCo2O4-MoS2 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.