Bi-functional electrochromic supercapacitor based on hydrothermal-grown 3D Nb₂O₅ nanospheres

The design and development of novel cathodic materials with suitable crystal structure and nanostructure is an essential basis for both electrochromism and electrochemical energy storage devices. In this study, Niobium oxide (Nb₂O₅) thin films as high-performance cathodic materials were synthesized using a facile hydrothermal method. The influence of the precursor concentration on the structural, morphological, electrochromic, and energy storage properties was investigated successfully. The X-ray diffraction analysis confirmed the highly crystalline orthorhombic nature of Nb₂O₅ thin films. Nanostructured Nb₂O₅ nanospheres effectively improved the charge transportation and mobility of charge carriers. Nb₀₁ thin film most effectively accommodated lithium ions and facilitated the desired bifunctional performance. An electrochromic supercapacitor (ESC) of Nb₀₁ composition showed the highest optical modulation of (76.92%), excellent reversibility of (98%), high coloration efficiency (CE) (98.75 cm² C⁻¹), and high-energy storage capacity (93.33 C cm⁻²). The fully colored ESC devices (4 × 5 cm²) have lightened a red and yellow light-emitting diode (LED) which confirms the energy storage level with the color changing ability of the 3D Nb₂O₅ nanospheres as a potential application in ESC.