Durable VO₂-Based Thermochromic Paint for Energy-Efficient Opaque Building Facades

Building energy consumption and associated carbon emissions continue to rise, motivating the development of passive and adaptive building envelope technologies. Thermochromic VO₂ is a promising candidate for temperature-responsive building thermal management. However, its practical application in buildings is limited by poor durability, while its implementation on opaque building surfaces remains underexplored and lacks systematic design guidelines. Here, we report a multifunctional, reflection-based thermochromic paint for opaque building envelopes based on tungsten (W)-doped VO₂@SiO₂ core-shell particles. The phase-transition temperature of VO₂ particles was tuned to near ambient conditions by W doping, while an amorphous SiO₂ shell significantly improved resistance to oxidation under heat and humidity. By dispersing the particles into a PDMS/epoxy matrix with SiO₂ fillers, the obtained coating simultaneously achieved a superhydrophobicity (contact angle of 151°), a strong adhesion to concrete (pull-off strength of 4.85 MPa), and high vapor permeability compared to uncoated concrete. The near-infrared reflectance modulation exhibited an approximately 1.85-fold enhancement with increasing VO₂ loading, and color-tunable paints were developed without sacrificing thermochromic functionality. Validation using a foam-concrete-coating building model demonstrated reduced surface and indoor temperatures under infrared irradiation, highlighting the energy-saving potential of the coating. Although the reflection regulation of the developed VO₂ system remains limited, this work demonstrates improved coatings with better durability and multifunctionality, as well as the feasibility of applying VO₂-based thermochromic coatings to reflection-based opaque surfaces, taking such coatings closer to practical use in building envelopes. Future work should focus on advancing the reflection modulation capability of VO₂ to achieve greater energy savings.