Role of polymeric surfactant in the synthesis of cobalt molybdate nanospheres for hybrid capacitor applications

Abstract

The role of Pluronic F127, a triblock copolymer, i.e. poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) PEO–PPO–PEO, adsorbed on cobalt molybdate (CoMoO₄), and its influence on the physico-chemical properties have been investigated. As a surfactant, Pluronic F127 is able to alter the surface properties of CoMoO₄ during synthesis. Through a facile synthesis at 300 °C, F127 adsorbs at the interface and self-assembles into a micellar aggregate, resulting in the formation of CoMoO₄ nanospheres. A cluster of nano-particles with an average size of 250 nm is obtained when F127 is added to CoMoO₄, while rod-shaped particles (1 μm) are obtained in the absence of F127. The surfactant-assisted CoMoO₄ is associated with enhanced pore accessibility and electronic conductivity, having a dual role in potential applications. The objective of this study is to test the as-synthesized CoMoO₄ with regard to application in energy storage by tuning the surface properties. The hybrid capacitor (F127 added to CoMoO₄ vs. activated carbon) showed an excellent electrochemical performance with a specific capacitance of 79 F g⁻¹ and an energy density of 38 W h kg⁻¹ in 2 M NaOH electrolyte, which was much higher than that for pure CoMoO₄ (23 F g⁻¹). The long-term cycling stability of the modified CoMoO₄ was tested and it was found to retain almost 80% of its initial capacity after 2000 cycles. The results obtained suggest that F127-modified CoMoO₄ would be a suitable candidate for fabricating a cost-effective energy storage device.