Ternary WO₃–MnO₂@SiNWs hybrid electrodes for high-performance Micro-supercapacitors with enhanced energy density and stability

Advanced energy storage technologies, such as rechargeable Batteries and Micro-supercapacitors (μSCs) play a pivotal role in addressing the growing global energy demand. Improving their energy and power densities requires the development of electrode materials with well-engineered, hierarchical porous architectures. In this work, we report a facile hydrothermal synthesis of WO₃-MnO₂ composite nanostructures directly integrated onto silicon nanowires (SiNWs), which serve as a highly conductive and high-surface-area scaffold. The influence of annealing temperature on the structural, morphological, and electrochemical properties of the WO₃-MnO₂@SiNWs composite was systematically investigated. Structural characterization through X-ray diffraction (XRD) and surface analysis via X-ray photoelectron spectroscopy (XPS) confirmed the successful formation of the hybrid oxide network. Furthermore, scanning electron microscopy (SEM) revealed a homogeneous distribution of the nanostructured composite coating over the vertically aligned SiNWs, forming a porous, interconnected network favorable for ion diffusion. Energy-dispersive X-ray spectroscopy (EDX) mapping confirmed the uniform presence of W, Mn, O, and Si elements throughout the electrode, indicating successful and consistent deposition of the WO₃-MnO₂ layers. The optimized electrode exhibited excellent capacitive performance, delivering a specific capacitance (Csp) of 16.56 mF·cm−2, an energy density (Ed) of 0.0001 Wh·cm−2, and a power density (Pd) of 0.024 W·cm−2, along with long-term cycling stability retaining 84 % of its initial capacitance over 4000 charge–discharge cycles. Additionally, electrochemical impedance spectroscopy revealed a consistent Csp of 14.23 mF·cm−2 over a wide frequency range (0.01 Hz–1 MHz), indicating efficient charge transfer and low internal resistance. A solid-state symmetric μSC device constructed using WO₃-MnO₂@SiNWs electrodes further demonstrated impressive performance, achieving a maximum specific capacitance of 96 mF·cm−2 at a scan rate of 2 mV·s−1, with 85 % capacitance retention over 2300 cycles and an energy density of 0.0028 Wh·cm−2 at a power density of 0.4 W·cm−2. These remarkable electrochemical properties are attributed to the synergistic effects of multivalent WO₃ and MnO₂ species combined with the high conductivity and mechanical stability of the SiNWs framework, highlighting the potential of this composite architecture for next-generation on-chip energy storage devices.