Surfactant integrated nanoarchitectonics for controlled morphology and enhanced functionality of tungsten oxide thin films in electrochromic supercapacitors

This research focuses on tungsten oxide (WO3) as a promising material, and the study investigates the electrodeposition of WO3 thin films on fluorine-doped tin oxide (FTO) coated glass substrates using three different surfactants: cationic hexamethylenetetramine (HMTA), anionic sodium dodecyl sulfate (SDS), and non-ionic polyethylene glycol (PEG). The X-ray diffraction analysis confirms that the resulting thin films exhibit amorphous structures. Raman analysis supports the identification of the pure WO3 phase based on the stretching and vibrational modes observed in the colored and bleached states. The X-ray photoelectron spectroscopic study examines the influence of cathodic and anodic potentials on the formation of oxidized and reduced tungsten species in surfactant-aided WO3 thin films. Field emission scanning electron microscopy is utilized to investigate the impact of different surfactants on the morphology of WO3 thin films, revealing the formation of porous, clumped, and dense nanogranules on the film surface. Electrochromic energy storage investigations highlight the superior performance of the W-PEG (polyethylene glycol assisted WO3) thin film, which exhibits efficient lithium-ion accommodation and desirable bifunctional characteristics. The optimized W-PEG sample demonstrates excellent electrochromic performance, including high optical modulation (84.39 %), good reversibility (98 %), and high coloration efficiency (117.95 cm2/C). Supercapacitive measurements reveal a high areal capacitance of 44.1 mF/cm2 at a current density of 0.1 mA/cm2, as well as an energy density of 0.024 mWh/cm2 at a power density of 0.1 mW/cm2, with 85 % capacitive retention over 8000 consecutive galvanostatic charge-discharge cycles. Furthermore, the application potential of nanogranular WO3 for electrochromic energy storage is demonstrated through the successful illumination of a red and green light-emitting diode (LED) using fully colored electrochromic supercapacitor devices (4 × 3 cm2), highlighting their energy storage capability.