Nanocomposite Sodium Transition Metal Phosphate Prepared via Combustion Route for Hybrid Capacitor

An environmentally friendly sodium transition metal phosphate (NaMn_1/3Co_1/3Ni_1/3PO₄) has been synthesized via combustion route with carbon coating on the surface. Energy storage devices based on sodium have been regarded as an alternative to the traditional lithium-based system because they are abundant in nature, inexpensive and safe. Sodium transition metal phosphate served as an active electrode material for both aqueous and nonaqueous hybrid supercapacitors. The electrochemical behavior of phosphate vs. activated carbon in the fabricated hybrid device exhibits both faradaic and nonfaradaic processes. Reversible Na+ de-intercalation/intercalation and desorption/adsorption occur within a safe voltage window for both aqueous and nonaqueous electrolytes. The asymmetric device shows redox peaks in the cyclic voltammetry and sloping profiles in the charge-discharge curves while providing excellent capacity retention. A detailed study on the electrochemistry and materials perspective (using microscopy and surface analyses) with an emphasis on the reaction mechanism has been reported.