Aqueous WO₃ electrochromic devices suffer from harmful Mn³⁺ byproducts generated during the Mn²⁺/MnO₂ anodic reaction. Here, we address this issue by simply adjusting the electrolyte acidity. Our results show that increasing the electrolyte pH significantly suppresses Mn³⁺ formation. The optimized device achieves an optical modulation of over 70% in the visible region (380–780 nm), with a colored-state transmittance approaching 0%, and retains more than 90% of its modulation after 12 hours. A prototype smart window based on this device effectively regulates solar radiation, and simulations indicate that it can save up to 37.9% of air-conditioning energy consumption compared to conventional Low-E glass in tropical regions. This work provides a straightforward electrolyte design strategy to inhibit side reactions and enhance the performance of electrochromic devices.
 

Smart window,Mn3+,Mn2+/MnO2 reaction,WO3-based electrochromic device