Advanced Electrochromic Functionality via Layered Cobalt Oxide Deposition on Tungsten Oxide Electrodes

The integration of various transition metal oxides into tungsten oxide (WO3) has been widely investigated to enhance its electrochromic (EC) performance. This approach aims to address the inherent limitations of individual metal oxides, such as poor durability, inadequate color neutrality, and restricted coloring efficiency and optical properties. The use of mixed metal oxides has emerged as a promising strategy, enabling a synergistic effect that optimizes EC performance and expands the material’s functional capabilities. In this study, we compare single-layer WO3 films with bilayer WO3/cobalt oxide (CoO) (denoted as W@C) composite films, focusing on their structural, morphological, and electrochromic properties. Both films were fabricated using the electrodeposition technique, with a consistent number of deposition cycles. Field emission scanning electron microscopy (FESEM) analysis revealed that the WO3 film presented a tightly packed arrangement of nanogranules. In contrast, the bilayer W@C composite thin film exhibited a highly interconnected and porous granular structure, with morphology evolving into larger spherical aggregates. The optimized bilayer W@C composite demonstrated exceptional electrochromic performance, achieving an optical modulation of 85.0% at 600 nm and a significantly improved coloration efficiency of 96.07 cm2/C. Stability tests confirmed its remarkable durability, showing only a 1.05% decrease in optical contrast after 5000 s of operation. Additionally, a prototype electrochromic device based on the W@C film demonstrated an optical modulation of 52.13% and outstanding long-term stability, with minimal degradation in performance.