Two-Dimensional Orthopyroxene Enstatite Silicate Mineral for Supercapacitor Application

This paper discusses the structural properties of orthopyroxene, specifically Enstatite [(Mg,Fe)2Si2O6] silicate, named here as “En-silicate”. En-silicates are exfoliated using a scalable liquid-phase exfoliation technique, producing mostly thin sheets of approximately 2 nm thickness. The bonding characteristics of orthopyroxene are characterized by FTIR spectroscopy, where a combination of covalent and ionic bonding, with strong Si–O covalent bonds and weaker Mg–O and Fe–O ionic bonds, was observed. The high surface area of these 2D silicates stores charges on the surface of the silicate layers or in the interlayer spaces, which makes them ideal for supercapacitor application. This work investigates the charge-storing capacity using 2D En-silicate as the positive electrode and activated carbon as the negative electrode in a hybrid asymmetric supercapacitor. The dominance of surface ion adsorption kinetics and the strong cyclic stability of En-silicate give rise to an excellent capacitive property. The highest specific capacitance obtained was 303 F g–1 at 5 mV s–1 with 280 F g–1 at 1 A g–1 for the 3 M KOH aqueous electrolyte. The fabricated asymmetric device shows a specific energy of 18 Wh kg–1 at 1600 W kg–1 with an aqueous KOH electrolyte.