Manganese Dioxide/Water Hyacinth Based Activated Carbon Nanocomposite for Electrochemical Supercapacitor

Abstract

Using electrode materials that are inexpensive, abundant, renewable, and ecologically benign for clean energy sources like Supercapacitor (SCs) is an efficient way to build a sustainable future. This study is aimed at the synthesis, characterization, and electrochemical SCs performance testing of a manganese dioxide (MnO2) nanostructure and it’s composite with activated carbon (MnO2/AC). In the green synthesis of MnO2 and MnO2/AC nanocomposite, Eichornia crassipes (water hyacinth) leaf extract was employed as reducing and capping agents, and its stem part was used as the precursor to prepare activated carbon (AC) through the chemical activation method in self-generated atmospheric conditions. The biosynthesized MnO2 and MnO2/AC nanocomposite were characterized using TGA-DTA, X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-Vis spectroscopy, Brunauer-Emmett-Teller (BET) analysis, and FT-IR spectroscopy. XRD analysis identified the formation of the δ–MnO2 phase structure with crystallite sizes of 2.75 nm, 2.22 nm and 2.78 nm for metal to plant extract ratios of 1:3, 1:1, and 3:1 nanostructures (NS), respectively. The band gap energy changed from 1.51 to 1.37 eV, with the corresponding BET specific surface area (SSA) values of 498 m 2 g -1 and 601 m 2 g -1 for MnO2 and when it was composited with AC, respectively. SEM micrograms and FT-IR analysis revealed the presence of MnO2 and it’s composite in a cluster of spherical NS with an oxygenic functional group-rich surface. A three-electrode system with an IVIUM electrochemical workstation was employed to measure their SCs performances in a 6M KOH aqueous electrolyte. The result showed that an excellent specific capacity (Cs) of 224 F g-1 was obtained using MnO2/AC nanocomposite as compared to the capacitance of individual components WH3 (75 F g -1 ) and Mn (1:1) (108 F g-1 ) samples of activated carbon and MnO2, respectively, at 3 A g-1 current density. It also showed its original capacitance retention of 95% after 2000 galvanostatic charge discharge (GCD) cycles. Thus, green synthesized MnO2 NS and its composite with AC, derived from water hyacinth stem are a promising for use as electrode materials in electrochemical SCs.