Tailoring NiO–SrCO3 nanocomposites via fuel-controlled combustion synthesis for enhanced supercapacitor performance

Abstract

The electrochemical performance of transition metal oxide (TMO)-based supercapacitor electrodes depends on their morphology, composition, crystal structure, and porosity. Solution combustion synthesis offers a versatile approach to tailoring these physical and electrochemical properties, as the characteristics of the resultant nanoparticles are influenced by the choice of fuel used in the process. In the current study, we investigated the influence of different fuels – citric acid, urea, and glucose – on the morphology, composition, crystal structure, and functionality of nickel oxide–strontianite nanocomposites synthesised via a solution combustion method. The X-ray diffraction investigations confirmed the formation of a nanocomposite consisting of a cubic phase of NiO along with an orthorhombic phase of SrCO₃. Variations in the type of fuel employed during the synthesis lead to notable changes in particle morphology and size distribution. These structural differences profoundly impact the electrochemical properties of the synthesized materials. Electrochemical performance was assessed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode system with 1 M KOH electrolyte. The electrodes were fabricated by drop-casting the nanoparticles over the Toray carbon sheet. The C_s values obtained from CV curves recorded at 5 mV s⁻¹ were ∼5.9, 39.5, and 131.89 F g⁻¹ for electrodes prepared using citric acid, glucose, and urea, respectively. The redox peaks confirmed a pseudocapacitive charge storage mechanism, involving both faradaic reactions and electrical double-layer capacitance, where an increase in pseudocapacitance (C_pseudo) directly enhances energy storage efficiency. The Trasatti analysis carried out using CV data recorded at different scan rates reveals that, among the electrodes, the electrode fabricated using citric acid-synthesised nanoparticles (NiO–SrCO₃@citric acid) shows the lowest C_pseudo contribution at 71.1%, followed by NiO–SrCO₃@glucose at 90.5%, while NiO–SrCO₃@urea offers the highest pseudocapacitance of 94.8%. The study demonstrates that the nanocomposites, particularly the one synthesised with urea, hold promise as efficient electrode materials for supercapacitors.