Mn-doping ensuring cobalt silicate hollow spheres with boosted electrochemical property for hybrid supercapacitors

Abstract

Recently, transition metal silicates (TMSs) have garnered significant attention as promising candidates for electrode materials in supercapacitors (SCs), especially cobalt silicate (Co₂SiO₄, CoSi) related materials. However, due to the poor conductivity and narrow potential range of CoSi, its electrochemical properties are not fully developed and far from desirable. Herein, to enhance the electrochemical properties of CoSi, hollow spheres of Mn-doped CoSi (CoMnSi) were fabricated through a hydrothermal method. The dopant Mn facilitates the formation of CoMnSi hollow spheres assembled by nanosheets and these nanosheets connect with each other to form the core-shell hollow architecture. The effect of the Mn/Co ratio on the electrochemical properties of CoSi has been investigated. CoMnSi-2 (Mn/Co = 1/9) displays the specific capacitance of 495 F g⁻¹ at 0.5 A g⁻¹, surpassing to that of CoSi (279 F g⁻¹ at 0.5 A g⁻¹) and manganese silicate (denoted as MnSi, 38 F g⁻¹ at 0.5 A g⁻¹). The CoMnSi-2//active carbon hybrid supercapacitor (CoMnSi-2//AC HSC) achieves the specific capacitance with 181 mF cm⁻² (151 F g⁻¹) at 1 mA cm⁻² and energy density with 0.644 Wh m⁻² at 2 W m⁻². The device displays a practical application by powering the LED lamp circuit bulb working for more than 25 min repeatedly. The performance achieved by CoMnSi is superior to some state-of-the-art electrode materials of TMSs. Density functional theory calculations have provided evidence that Mn-doping enhances the electronic conductivity and reduces the electron transport barrier of CoSi, boosting its electrochemical properties. This work supplies a strategy for tailoring structures of TMSs to enhance their electrochemical performance.