Enhanced electrochemical performance of multilayer WO3/MnO2 thin films via sputtering on graphene substrate for high-stability supercapacitors

Abstract

Hybrid approaches provide a promising pathway to integrate the advantageous properties of carbon-based and metal oxide-based electroactive materials, thereby enhancing the energy and power density of supercapacitors (SC). In this work, we have developed a composite SC electrode featuring a multilayer (WO₃/MnO₂) metal oxide assembly fabricated via sputtering and supported on a flexible graphene sheet. The optimized four-layer (4 LBL) structure, with its tailored composition and surface morphology, enhances electrical conductivity, increases the number of active electrochemical sites, and reduces the charge transport distance. Owing to these carefully engineered structural features, the proposed 4 LBL@graphene nanostructure exhibits significantly improved electrochemical performance, achieving a high gravimetric specific capacitance of 494.2 F g⁻¹ at a scan rate of 5 mV s⁻¹ and excellent rate capability. The flexible symmetric SC device based on 4 LBL@graphene operates stably within a potential window of 0.8 V, delivering a specific energy of 44 Wh kg⁻¹ at a specific power of 521 W g⁻¹, along with a low solution resistance of 2.40 Ω. Furthermore, the device demonstrates outstanding cycling stability, retaining 89% of its initial capacitance after 10 000 charge–discharge cycles at a specific current of 10 A g⁻¹, as well as excellent mechanical flexibility. Overall, the electrochemical performance of the 4 LBL@graphene device surpasses that of previously reported symmetric SC, highlighting the strong potential of such hybrid nanostructures for next-generation high-performance energy storage applications.