Electrospun Nanofiber Composite for Stable and Scalable VO2-based Thermochromic Smart Windows: Energy and Environmental Analysis

Abstract

State-of-the-art thermochromic glazing using VO2 nanoparticles (NPs) is one of the most sustainable cost-efficient solutions for energy-saving smart windows. Prior developments have primarily focused on improving their optical performance, such as increasing the luminescence (visible) transmittance (Tlum) and solar modulation ability (ΔTsol), while lowering switching temperature (TMIT). However, the current critical issues include the low environmental stability of VO2 NPs, which determines the lifetime and lifecycle of the smart windows, and the high cost and energy-intensive manufacturing process to apply VO2. These are unsolved issues which remain key obstacles for market adoption of VO2 based thermochromic windows. Herein, we demonstrate a nanofiber (NF) based composite system, where W-doped VO2 NPs embedded in crosslinked NFs were used as the active material and refractive index matched epoxy resin was used as the protection matrix, to ensure environmental stability of W-doped VO2 NPs during the lifetime of operation. The cost-efficient, low-energy input electrospinning technique allows for precise control over the distribution of NPs in the composite, while minimizing aggregation. The room-temperature, solution-based approach offers a pathway toward cost-effective large-area fabrication. Prepared samples with excellent optical properties (Tlum ~ 67 % and ΔTsol ~ 20%) showed no decline in thermochromic performance and retained ~ 99% solar modulation ability after 1700 hours of exposure to an accelerated environmental aging test (60 °C and 95% relative humidity), and retained ~ 99% solar modulation ability over 6 months of practical exposure to an average 20 °C temperature and 74 % relative humidity in Florida, USA. The energy analysis showed potential annual energy saving of up to 27 kWh/VO2(m2) and 32 kWh/VO2(m2) for heating and cooling, respectively, and highlighted the impact of VO2 glazing with improved thermal properties and various TMIT on carbon emission reduction across the U.S. climate zones.