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.