Hydrothermal Synthesis and Thermochromic Property of VO₂/Graphene Composite Powders

VO₂ powders and VO₂/graphene composite powders were prepared by using hydrothermal reaction and thermal treatment with vanadyl oxalate solution as the vanadium source, sodium tungstate as the dopant and graphene oxide as the additive. With the assistance of XRD, DSC and TEM analyses, the effects of hydrothermal reaction conditions, doping amount and graphene oxide addition on structure and morphology, phase transition temperature and thermochromic properties the powders were systematically studied. Within the experimental temperature range, property of the hydrothermal reaction product is independent on the hydrothermal temperature, but is directly related to the hydrothermal time. The phase transitions of VO₂(D) and VO₂(B) to VO₂(M) during the thermal treatment occurred at 300 ℃ and 550 ℃, respectively. Tungsten doping resulted in reduction in thermochromic temperature and thermal hysteresis temperature difference of the VO₂ powders. With increasing content of graphene oxide, the thermochromic temperature first decreased and then increased, while the variation trend of thermal hysteresis temperature difference is the opposite. With the doping concentration of 9 at.% and graphene oxide content of 1 wt.%, the doped VO₂/graphene composite powder exhibited a thermochromic temperature of 34.5 ℃ and a thermal hysteresis temperature difference of 7.7 ℃.