Brookite TiO₂ Nanorods as Promising Electrochromic and Energy Storage Materials for Smart Windows

Electrochromic smart windows (ESWs) offer an attractive option for regulating indoor lighting conditions. Electrochromic materials based on ion insertion/desertion mechanisms also present the possibility for energy storage, thereby increasing overall energy efficiency and adding value to the system. However, current electrochromic electrodes suffer from performance degradation, long response time, and low coloration efficiency. This work aims to produce defect-engineered brookite titanium dioxide (TiO₂) nanorods (NRs) with different lengths and investigate their electrochromic performance as potential energy storage materials. The controllable synthesis of TiO₂ NRs with inherent defects, along with smaller impedance and higher carrier concentrations, significantly enhances their electrochromic performance, including improved resistance to degradation, shorter response times, and enhanced coloration efficiency. The electrochromic performance of TiO₂ NRs, particularly longer ones, is characterized by fast switching speeds (20 s for coloration and 12 s for bleaching), high coloration efficiency (84.96 cm² C⁻¹ at a 600 nm wavelength), and good stability, highlighting their potential for advanced electrochromic smart window applications based on Li⁺ ion intercalation.