Cathodic electrodeposition of amorphous tungsten oxide dihydrate film for dual-band electrochromic modulation

Recent advances in hydrated tungsten oxides (WO3·nH2O, n = 1, 2) have highlighted their potential for dual-band electrochromic applications. However, achieving both high optical modulation and robust cycling stability remains a challenge. This study presents a cost-effective and straightforward cathodic electrodeposition method to fabricate amorphous tungsten oxide dihydrate (WO3·2H2O) films using a precursor solution primarily composed of monomeric diperoxotungstate. The open framework and interlayer structural water in WO3·2H2O enable exceptional dual-band electrochromic performance at super-low switching potentials (−0.5 V for full coloration and 0.5 V for full bleaching) in a 1.0 M LiClO4/propylene carbonate (LiClO4/PC) electrolyte. Key features include high optical modulation (∼92% at 633 nm and ∼86% at 1100 nm), fast response times (17.5 s for bleaching and 18.1 s for coloration at 633 nm; 5.0 s for bleaching and 7.1 s for coloration at 1100 nm), high coloration efficiencies (204.2 cm2 per C at 1100 nm and 72.3 cm2 per C at 633 nm), and exceptional cycling stability (retaining 94% of initial optical modulation after 2000 cycles and 76% after 10 000 cycles at 633 nm). The interlayer water in WO3·2H2O plays a critical role in facilitating pseudocapacitive Li+ intercalation, enabling control over optical properties across the visible and near-infrared (NIR) regions while maintaining structural integrity. Additionally, the scalability of the method was demonstrated through the successful fabrication of large-area films (10 cm × 10 cm) and prototype electrochromic devices.