Zr-induced structural modulation of monoclinic WO₃ nanostructures for aqueous supercapacitors

Chemical synthesis plays an important role in determining the structural and electrochemical properties of metal oxide nanomaterials for energy-storage applications. Herein, Zr-incorporated monoclinic WO₃ nanostructures were directly grown on carbon cloth using a simple chemical bath deposition method and investigated as binder-free electrodes for aqueous supercapacitors. The effect of Zr concentration on the morphology, structure, composition, and electrochemical response of WO₃ was systematically examined. Among the investigated samples, the optimized 5% Zr-WO₃ electrode exhibited improved electrochemical performance compared with pristine WO₃ in 1 M H₂SO₄ within a potential window of 0 to -0.4 V vs. Ag/AgCl. The optimized electrode delivered a specific capacitance of 840 F g^-1 at 8 A g^-1, corresponding to a 5.6-fold improvement over pristine WO₃. The enhanced charge-storage behavior is attributed to the modified local electronic environment, accessible nanostructured morphology, and improved electrode/electrolyte interaction after Zr incorporation. A symmetric aqueous supercapacitor device assembled using identical optimized electrodes achieved an energy density of 24 Wh kg^-1 at a power density of 5500 W kg^-1 and showed stable cycling behavior under aqueous operating conditions. In addition, the device was able to power multiple light-emitting diodes, indicating its practical applicability. This work highlights controlled Zr incorporation as a feasible approach for tuning WO₃-based binder-free electrodes for electrochemical energy-storage applications.