Ti ₃ C ₂ T _x MXene‐Hydrous Tungsten Oxide Hybrid for Aqueous Multivalent Ion‐Based Smart Windows With Dual‐Band Control and Energy Storage

Abstract Multifunctional electrochromic devices have gained significant attention in recent years for their potential application in dual‐band smart windows with integrated energy storage, an attractive concept for future green buildings with reduced energy consumption. However, the performance is often constrained by conventional electrolytes. Moreover, the low electrical conductivity and limited transparency of electrodes, which typically function within a single band only, remain a bottleneck due to these material limitations. This study focuses on developing a visible and NIR dual‐band electrochromic supercapacitor using a novel MXene/WO 3 ·H 2 O hybrid electrode, fabricated via a simple solution‐based method and using an aluminium ion‐based multivalent aqueous electrolyte. The incorporation of 2D MXene into the electrochromic 2D‐like WO 3 ·H 2 O matrix enhances charge transport kinetics, while multivalent cations further boost performance by enabling multiple electrons transfer redox reactions. Owing to these synergistic effects, the electrode exhibits outstanding electrochromic properties, including fast switching (≈3 s) and high optical modulation (≈51% visible, ≈82% NIR), indicating excellent solar thermal regulation, along with high stability and energy storage performance (60 mF cm −2 ). This work demonstrates the cost‐effective fabrication of multifunctional electrochromic energy storage devices that offer promising prospects for sustainable smart window technologies.