Sodium‐Substituted Tungsten Oxide Nanoflowers: An Efficient Electrode Enhancing the Pseudocapacitive Storage in Aqueous Asymmetric Supercapacitors

Abstract Electrode materials engineering at the nanoscale is essential to improve the electrochemical performance for next‐generation energy storage devices. Herein, a novel approach of sodium substitution in the tungsten oxide matrix is highligting the enhancement of the pseudocapacitor performance of the electrode in an aqueous asymmetric supercapacitor. The sodium‐substituted tungsten trioxide (NWO) and pristine tungsten oxide (PWO) nanoflowers prepared by a single‐step hydrothermal process has presented. The tetragonal crystal structure and nanoflower morphology has maintained even after Na substitution. The electrochemical properties of PWO and NWO have investigated with three‐electrode setups in 1 M H₂SO₄ aqueous electrolyte. The specific capacitance of PWO and NWO exhibits 104 F g⁻¹ and 476 F g⁻¹ at 1 A g⁻¹, respectively. Furthermore, an aqueous asymmetric supercapacitor (AAS) of NWO demonstrates a specific capacitance of 41 F g⁻¹, an energy density of 13 W h kg⁻¹, and a power density of 3750 W kg⁻¹. An excellent stability of AAS has achieved with 100 % capacitance retention from 1000 to 5000 cycles. The sodium substitution significantly enhanced the pseudocapacitive behavior, attributed to enhanced electroactive sites, conductivity, surface area, and chemical stability. It shows the potential of NWO nanoflowers as a promising candidate for next‐generation supercapacitor devices.