Robust MnO2–WO3 Complementary Electrochromic Device Enabled by Reversible Electrodeposition of MnO2

Reversible electrodeposition and dissolution of manganese oxide (MnO₂) represent an emerging electrochromic system. However, challenges such as "dead MnO₂" formation, limited optical modulation across a narrow wavelength range, and difficulties in scaling up have significantly hindered the development of MnO₂ reversible electrodeposition-based electrochromic windows. In this work, we introduced Fe²⁺/Fe³⁺ mediator ions into the electrolyte to suppress the Jahn-Teller effect, thereby preventing the formation of "dead MnO₂" and achieving stable and reversible MnO₂ deposition/dissolution. Furthermore, by employing WO₃ as the counter electrode, we developed a complementary electrochromic device based on ion insertion and metal oxide deposition. This complementary system exhibits color neutrality in the colored state and high optical contrast across the entire visible spectrum, with an average optical modulation of 67.3%, excellent cycling stability (85.0% retention after 3000 cycles), and capability to switch uniformly over areas as large as 100 cm².