Spray-Coated W₁₈O₄₉/Ti₃C₂T_x MXene Electrodes for High-Performance Electrochromic Energy Storage Devices

Smart windows, capable of modulating near-infrared (NIR) and visible light, have gained significant attention for enhancing indoor comfort and privacy while integrating energy storage functionalities. Transition metal oxides, particularly tungsten oxides, are widely used in electrochromic applications, but often suffer from limitations such as low coloration efficiency (C.E.) and slow response times. This study explores the incorporation of Ti₃C₂T_x MXene into oxygen-deficient tungsten oxide (W₁₈O₄₉) to enhance electrochromic and energy storage performance. By optimizing solvothermal synthesis through solvent variation, a 5 wt.% Ti₃C₂T_x-W₁₈O₄₉ composite (5MX-WO) is developed, exhibiting superior electrochromic properties with 72% optical modulation at 700 nm, rapid switching speeds (6.5 s coloration, 5.6 s bleaching), high C.E. (≈182 cm² C^-1 at 700 nm), and areal capacitance of 25 mF cm^-2 at 0.5 mA cm^-2. The presence of Ti₃C₂T_x facilitates enhanced electronic and ionic transport pathways, contributing to optimal electrochromic behavior. A complementary electrochromic device (CECD) of size ≈5 × 5 cm² is fabricated using 5MX-WO as the working electrode and spray-coated NiO as the counter electrode. The device achieved 61% optical modulation at 850 nm, fast response times, and excellent cyclic stability over 1000 cycles. These findings underscore the potential of W₁₈O₄₉/Ti₃C₂T_x composites for next-generation electrochromic energy storage systems.