Modification of porous graphite coins with tungsten oxide nanoparticles for photo-supercapacitor applications

Supercapacitors are energy storage systems that utilize either an electrical double layer or reversible Faraday reactions on or near the surface of the electrode to store energy. They are classified into two main types based on the energy storage mechanism: Electric Double Layer Capacitors (EDLC) and Pseudo Capacitors (PC) [1-6]. Photo supercapacitors use the electrochemical and electronic properties of supercapacitors along with solar energy for fast and efficient charging and discharging. Due to these unique features, optical supercapacitors present themselves as a suitable solution for optical energy storage [2-3]. Carbon allotropes like graphite, graphene, and carbon nanotubes exhibit double-layer capacitive behavior due to their high surface areas and electrostatic interactions with ions inside their pores which can be used as appropriate substrates in photo-supercapacitors. Metal oxides such as, MnO₂, Co₃O₄, and conductive polymers like polyaniline and polypyrrole possess quasi-capacitive behavior as well as excellent photo-electronic characteristic because they store charge through surface redox reactions [4]. Experimental, Synthesis of tungsten oxide-graphite coin In this work, under optimal conditions (considering electrochemical performance and mechanical strength) 0.8 g of commercial graphite powder, 0.02 g of commercial Zinc-metal powder were uniformly mixed. Coins with a diameter of 13 mm and a thickness of 3 mm were prepared by a press machine. Then, coins were put in 1.0 M H2SO4 solution for 2 h to selectively dissolve Zinc-metal from the structure of the coin. Finally, the coins were washed with distilled water and placed at 80 0C for one day. Electrodeposition of tungsten oxide onto the graphite coin was carried out under potentiostatic conditions at a constant potential of -0.48 V vs. saturated Ag/AgCl electrode for the duration of 200s in the three-electrode cell using graphite coin as a working electrode. platinum foil (9.0 cm2) as an auxiliary electrode and an Ag/AgCl electrode as a reference. The electrolyte for Electrodeposition of tungsten oxide was 25 mM Na2WO4.2H2O and 0.03 M hydrogen peroxide aqueous solution with PH ¼ 1.0 [5]. Results show that the porous tungsten oxide/graphite sample shows excellent photo_capacitive behaviour in presence of light, attributing to porous structure of graphite, photoelectronic behaviour of WO3 and synegistic effect between graphite and WO3.