Direct Patterning of TiO ₂ Nanotube Bundle Platforms for Viologen‐Enhanced Electrochromism

Abstract The development of precise, rapid, and scalable fabrication methods for patterned electrochromic nanostructures represents a critical challenge in advancing next‐generation optoelectronic devices. This study presents an innovative hybrid approach that integrates a modified 3‐dimensional (3D) printing platform with high‐speed breakdown anodization (1 mm s ⁻¹ ) in chloride‐based aqueous electrolytes to achieve direct patterning of TiO ₂ nanotube bundles on Ti substrates. Systematic optimization reveals that anodization voltages of 15–60 V produce well‐defined nanotube bundles with diameters of 20–40 nm within seconds, demonstrating significant advantages over traditional fluoride‐based systems through lower operational voltages and faster processing times. These high‐surface‐area nanotube bundle platforms provide effective scaffolds for subsequent viologen functionalization, resulting in dramatic enhancement of electrochromic properties with viologen‐anchored TiO ₂ nanotube bundles exhibiting remarkable reflectance modulation (Δ R ) of 56.2% compared to pristine TiO ₂ (Δ R : 12.7%) and enhanced charge density (20.5 to 40.9 mC cm ⁻² ) and excellent cycling stability (88.5% retention after 100 cycles). This integrated, programmable anodization strategy offers a versatile and scalable pathway for fabricating advanced electrochromic devices with promising applications in adaptive displays, smart windows, and next‐generation optoelectronic systems.