Fast-switching dual-cathode electrochromic smart windows for year-round building energy savings

For dual-band electrochromic smart windows to achieve widespread adoption, challenges such as slow switching, poor stability, and high power consumption must be addressed. This study introduces a polyviologen|zinc mesh|WO3 ⋅ 2H2O electrochromic energy storage device (EESD) with a PEDOT: PSS layer to enhance conductivity and prevent polyviologen degradation. By utilizing a dual-cathode design, the EESD enables fast switching and operates in four distinct modes—transparent, visible colored, near-infrared colored, and fully colored—allowing adaptive light regulation (320–2500 nm) to optimize energy efficiency across different seasons and times of day. Its self-operating and energy recovery features achieve zero energy consumption while maintaining functionality similar to conventional glass. Simulations indicate that a large-scale deployment across the U. S. can save 66. 87 billion MWh, amounting to 7. 35 trillion, and reduce CO2 emissions by 66. 94 billion tons. With its rapid switching, long-term durability, and scalability, this device presents significant economic and environmental advantages for real-world applications. Electrochromic materials are promising for smart windows, though challenges such as slow switching, poor stability, and high power consumption must be addressed. Here, the authors report a dual-cathode electrochromic energy storage device that enhances conductivity and stability.