Influence of fuel to oxidizer ratio on the supercapacitive properties of NiO synthesized by solution combustion method

Abstract

Porous Nickel oxide nanocrystallites were successfully synthesized by a facile single-step glycine assisted solution combustion method without a post calcination treatment. Effect of fuel to oxidizer (F/O) ratio on the combustion behaviour, crystallite size, surface characteristics, morphology, and agglomeration were thoroughly investigated. A systematic variation of crystallite size with F/O ratio was revealed from PXRD studies. BET studies showed a decrease of surface area with increase of F/O ratio. Highly porous morphology of NiO nanocrystallites synthesized at low F/O ratio (0.5) was evident from scanning electron micrograph (SEM). Transmission electron microscopy (TEM) studies showed polycrystalline nature of the material. NiO nanocrystallites exhibit high thermal stability, which was revealed from thermal analysis. The maximum specific capacitance obtained for NiO synthesized at different F/O ratios ranged from 215.6 to 99.2 C/g at 5 mV/s scan rate and 174.7 to 73.0 C/g at 10 A/g current density. Highest value of specific capacitance and lowest values of equivalent series resistance and charge transfer resistance were exhibited by NiO synthesized at low F/O ratio of 0.5. The enhanced electrochemical performance of the sample synthesized at low F/O ratio was benefited mainly from its high surface area and optimal pore size for the diffusion of ions and electrons within the electrode. An asymmetric device fabricated using NiO as the positive electrode and activated carbon derived from phyllanthus emblica as the negative electrode and 3 M KOH as the electrolyte delivered an energy density of 12 Wh/kg at a power density of 427 W/kg.