Plasmon-Enhanced Electrochromism in Au Nanorod/WO ₃ ·H ₂ O Hybrids for High-Performance Near-Infrared Smart Windows

The development of dual-band electrochromic (EC) smart windows represents a transformative approach for next-generation energy-efficient buildings, enabling dynamic control over both visible and near-infrared (NIR) light transmittance. In this work, we present a comprehensive investigation of the morphology-dependent plasmonic-assisted enhanced performance of WO 3 ·H 2 O (WH) electrochromic films via the integration of anisotropic Au nanostructures. By precisely tailoring the shape and size of Au nanorods (Au NRs) and nanoparticles (Au NPs) at dilute concentrations, we reveal their distinct roles in enhancing EC performance through localized surface plasmon resonance (LSPR). Among the hybrids, the WH-Au NR system exhibits outstanding electrochromic characteristics, achieving 70% optical modulation at 800 nm, a high areal capacitance of 21.7 mF/cm 2, exceptional coloration efficiency (172 cm 2 /C), and superior cycling stability with 99.9% retention over 3,000 cycles. Electrochemical analysis further reveals a 4.4-fold increase in donor density and 22.85-fold enhancement in diffusion coefficient compared with pristine WH films. Importantly, the device is fabricated entirely using scalable, solution-based processing and demonstrates strong NIR modulation, offering passive indoor temperature regulation. This study not only establishes the critical influence of Au nanostructure morphology on EC functionality but also provides a possible pathway toward high-performance smart windows for sustainable architectural applications.