In Situ Growth of Plasmonic Gold Nanoparticles/Polyaniline for Multicolor Electrochromic Energy Storage Films

This work reports a facile two-step electrodeposition strategy to fabricate plasmonic Au nanoparticles (AuNPs)/polyaniline (PANI) composite films that simultaneously deliver high-performance electrochromism and electrochemical energy storage. A uniform layer of AuNPs was first electrodeposited onto ITO via cyclic voltammetry by controlling the HAuCl4 concentration and cycle number. Subsequently, a thin PANI layer was deposited potentiostatically on this AuNP-coated substrate, enabling systematic tuning of nanoparticle size/packing and their coupling with PANI. The AuNPs/PANI composite film achieves superior electrochromic performance, delivering a high optical contrast of 39.6%, a high coloration efficiency of 58.33 cm2/C, and fast bleaching (∼1.1 s), together with good durability (only ∼3–4% transmittance decay at 610 nm after 400 cycles) and multicolor bistability (stable green/cyan/blue for ≥30 min without bias). 3D full electrodynamics simulations by COMSOL indicate that localized surface plasmon resonance-induced near-field enhancement occurs at the AuNPs/PANI interface. This near-field enhancement facilitates Cl– insertion–diffusion and accelerates PANI redox switching, thereby explaining the improved optical modulation and kinetics. The best enhancement–performance synergy occurs when the ratio of AuNPs diameter-to-PANI thickness is ∼1:1 (∼40 nm/∼40 nm). Additionally, the composite exhibits an areal specific capacitance of ∼25 mF/cm2, highlighting its promise for multicolor, bistable electrochromic smart windows with integrated energy storage.