Soft-template assisted morphology tuning of NiMoO4 for hybrid supercapacitors

Abstract

The electrochemical performance of electrode materials depends on various physicochemical properties like particle size, morphology, porosity, etc. of materials. Herewith, a facile surfactant assisted hydrothermal route using cetyltrimethylammonium bromide (CTAB) and hexamethylenetetramine (HMT) is used to successfully synthesize nanostructured nickel molybdate (NiMoO4) with various morphologies. It is found that NiMoO4 possesses different morphologies when synthesized by using these surfactants. With change in morphology, there is a significant increase in diffusion coefficient for sample synthesized with CTAB. It is interesting to note that NiMoO4 synthesized by using CTAB exhibit a high specific capacitance of 947 F g−1 when cycled at 1 A g−1 in 1 M KOH solution as compared to that of 322 F g−1 (synthesized without CTAB), which can be ascribed to its flower-like shape with uniform porosity. Both Ni2+/Ni3+ and Mo6+/Mo4+ redox couples are involved in the capacitive characteristic of NiMoO4, as found from the XPS study. Additionally, a hybrid supercapacitor has been assembled using NiMoO4 as positive electrode and reduced grapgene oxide (rGO) as negative electrode, which can exhibit 107 F g−1 with an operating voltage of 1.6 V with excellent cycling stability of maintaining 94 % capacitance retention after 6000 cycles in 1 M KOH solution. The hybrid supercapacitor can possess an energy density of 37.7 Wh kg−1 and a power density of 8 kW kg−1. Thus, this study enables the importance of tuning the morphology to enhance the capacitance property of transition metal oxide based electrode materials for supercapacitor applications.