Substitutional doping of WO₃ for Ca-ion based supercapacitor

In the present work, we analyzed the effect of doping (Bi, Hf, and Nb) on the performance of tungsten oxide (WO₃) based supercapacitor. Through substitutional doping, the properties were altered to enhance its electrochemical charge storage performance. The doped samples were tested in different electrolytes (H⁺, Li⁺, Na⁺, Ca²⁺ and Al³⁺). The cyclic voltammetry, galvanostatic charge–discharge, and EIS studies were performed to identify the best suitable anode material for the fabrication of asymmetric supercapacitor. Nb:WO₃ yielded the highest specific capacitance (C_sp) of 782 Fg⁻¹ in Ca electrolyte. An asymmetric device with Nb:WO₃ as anode and MnO₂ as a cathode using an aqueous Ca ion electrolyte exhibited a high potential window of 2 V and capacitance of 126 Fg⁻¹. The factors responsible for performance of electrode material in different electrolytes were identified through experimental results, theoretical calculations, and relevant simulations. The effect of doping on WO₃ crystal structure and electronic properties along with their binding nature/interaction with different electrolyte ions were first postulated through density functional theory (DFT) calculations.