High‐Performance Dual‐Band Electrochromic Smart Windows Based on Amorphous Tungsten Oxide Hydrate Films and Aluminum Ion Electrolytes

Abstract It is reported that by introducing structural water into amorphous tungsten oxide and using multivalent Al³⁺ as electrolyte ions, the tungsten oxide hydrate films exhibit dramatically enhanced dual‐band EC performance. The structural water triggers the surface reduction of tungsten at a relatively low reduction potential, which governs the selective regulation of NIR light. The fast electrochemical kinetics and negligible structural destruction during the surface redox process enable fast and ultrastable NIR regulation. Increasing the reduction potentials, the Al³⁺ intercalates into the lattice, accompanied by injection of electrons, resulting in the formation of polaron absorbing visible light. The high charges and small radius of Al³⁺, and the enlarged ion diffusion channels by structural water synergistically facilitate the ion insertion/extraction, leading to enhanced EC performance in the visible light region. The tungsten oxide hydrate film is used as a working electrode to pair with an electrocatalytic counter electrode, with the presence of redox couples in Al³⁺ based electrolyte, to form a full EC device that exhibits NIR selectivity of 0.66, and cycling stability of 20 000 cycles in NIR region and 8000 cycles in visible region, which enables to design and fabricate large‐size high‐performance dual‐band EC smart window for controllable management of solar heat and light.