Thermochromic Hydrogel Smart Window for Iron-Chromium Flow Batteries: Dual Band Modulation and Efficient Energy Storage

X Zeng and KR Chen and RC Zhou and MY Li and X Zhou and Z Wang and W Qiu and YP Liu and Y Zhou and Q Xu, CHEMISTRY-A EUROPEAN JOURNAL, 31, e01867 (2025).

DOI: 10.1002/chem.202501867

This study introduces the HydroTherm-Flow Smart Window (HTF Window), the first groundbreaking integration of thermochromic windows and Fe-Cr redox flow batteries (Fe-Cr RFBs), achieving dual functionalities of dynamic solar modulation-via dual-band (visible + near-infrared, NIR) modulation-and high-efficiency energy storage in a single component. Leveraging tunable hydroxypropyl cellulose (HPC) hydrogels, it enables ultrafast optical switching and autonomous nighttime opacity, overcoming the slow response and privacy limitations of conventional thermochromic systems. By repurposing the window as a compact electrolyte reservoir, it reduces the RFB spatial footprint while enhancing ionic conductivity by 30% via hydrogel "ion highways," achieving 77% energy efficiency with a 40% reduction in the solar heat gain coefficient. Molecular dynamics simulations reveal interactions between hydrogels and electrolytes, where chloride ion networks and encapsulation structures enhance battery discharge capacity. Addressing intermittent renewable energy grids and global carbon neutrality goals, the HTF Window stores surplus solar/wind energy to balance building-grid demand, reduces annual heating, ventilation, and air conditioning (HVAC) energy consumption by 25% across climates, and stabilizes electrolyte temperature via waste heat recovery to minimize thermal loads. With a projected 20 + year lifespan, it offers a scalable, universal solution for net-zero buildings, bridging sustainable infrastructure and global decarbonization imperatives.

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