Microwave-assisted sol-gel synthesis of mesoporous NiO-decorated silica nanostructures utilizing biogenic silica source for supercapacitor applications

Abstract

Developing efficient and sustainable energy storage materials is essential for supercapacitor technology. This study presents a microwave-assisted sol-gel synthesis of nickel oxide-decorated SiO2 nanostructures employing rice husk as a silica source for supercapacitor application. Rice husk, an abundant agricultural waste, was utilized as a cost-effective and environmentally friendly precursor for silica synthesis. Sol-gel synthesis assisted by microwaves allowed rapid and controlled formation of the silica nanostructure via alkaline extraction with NaOH, acidification with acetic acid, and capping with PEG. Likewise, nickel precursor with an appropriate concentration was introduced during the formation of silica nanostructures, leading to NiO-decorated silica nanostructures. XRD, FTIR, BET, FESEM, EDS, and HRTEM analysis demonstrated that NiO was decorated on the silica nanostructure distinctly depending on the concentration of nickel precursor. The electrochemical studies using 2 M KOH electrolyte revealed that the maximum specific capacitance of RH-SiO2, NiO@RH-SiO2-1, and NiO@RH-SiO2-2 was found to be 102 F/g, 405 F/g, and 506 F/g at a current density of 0.5 A/g with superior energy density and power density. It is also found that the electrode exhibits high-capacitance retention and good cycle stability after 5000 cycles. The obtained result revealed that when the nickel precursor concentration was increased, the specific capacitance was also increased because high nickel precursor concentration leads to the formation of NiO species which can serve as reactive surfaces for carrier transport. Moreover, the asymmetric supercapacitor (ASC) was fabricated using NiO@RH-SiO2-2 and it provides an excellent energy density of 31.25 Wh kg−1 at a power density of 745 W kg−1 with long-term cyclic stability (96.4% specific capacitance retention after 10,000 cycles). Based on these results, NiO-decorated silica nanostructures can be a promising electrode material for supercapacitor applications.