Fluoride-Assisted Preparation of Plasmonic Oxygen-Deficient MoO _3−x Nanowires for Dual-Band Electrochromic Smart Windows

Electrochromic materials are vital to the development of dual-band smart windows, which enable the individual control of visible and near-infrared (NIR) light transmittance. In this paper, we propose a novel single-component MoO _3−x nanowire fabricated using a simplified preparation method via a fluoride-assisted route. The incorporation of oxygen vacancies into MoO _3−x nanowire in the presence of fluoride anions has not been attempted before. Spectroscopic measurements confirm enhanced ion mobility in the MoO _3−x conduction band through the Mo ⁶⁺ substitution of Mo ⁵⁺ cations as the origin of localized surface plasmon resonance (LSPR). Oxygen vacancies greatly improve Li ⁺ diffusion in the MoO _3−x host while providing near-infrared selective modulation due to tunable LSPR absorbance in the NIR region. The MoO _3−x nanowire demonstrates excellent dual-band electrochromic performance in terms of switching speed (12.4 s and 5.4 s for coloration and bleaching between 1.0 V and 3.5 V), coloration efficiency (232.8 cm ² ·C ⁻¹ at 1080 nm and 211.7 cm ² ·C ⁻¹ at 450 nm), and electrochemical stability (91.8% at 1080 nm after 1,000 cycles). This suggests that MoO _3−x nanowire with oxygen vacancy is a promising new electrochromic material for dual-band smart windows.