Electrochemical Synthesis of Amorphous VO2 Colloids and Their Rapid Thermal Transforming to VO2(M) Nanoparticles with Good Thermochromic Performance

Amorphous VO2 (a‐VO2) colloids were synthesized by electrochemical anodic oxidation of metallic vanadium. It was found that the a‐VO2 colloids have a cotton‐like morphology composed of very small clusters, and that the crystallization temperature of the a‐VO2 colloids can be adjusted either by the electrolyte of the anodic oxidation or/and the dispersion agent of the colloids. VO2(M) nanoparticles (NPs) (and a NP film) with an average size of about 50 nm can be obtained by a rapid thermal annealing of the a‐VO2 colloids at 310 °C under air, which is beneficial for practical applications. The VO2(M) NP film shows an obvious metal–semiconductor transition with a resistance less than 10 Ω in the metallic state. An integral visible transmittance of 40.7 %, a solar transmittance modulation of 9.4 %, and a resistance modulation in the order of 5×104 were realized in the VO2(M) NP film. Perfect film: A VO2(M) nanoparticle film obtained by rapid thermal annealing of amorphous VO2 colloids from electrochemical anodic oxidation of metallic vanadium (see figure) shows an integral visible transmittance of 40.7 %, a solar transmittance modulation of 9.4 %, and a resistance modulation in the order of 5×104.