Robust MnO 2 -WO 3 Complementary Electrochromic Device Enabled by Reversible Electrodeposition of MnO 2 .

Reversible electrodeposition and dissolution of manganese oxide (MnO ₂ ) represent an emerging electrochromic system. However, challenges such as "dead MnO ₂ " formation, limited optical modulation across a narrow wavelength range, and difficulties in scaling up have significantly hindered the development of MnO ₂ reversible electrodeposition-based electrochromic windows. In this work, we introduced Fe ²⁺ /Fe ³⁺ mediator ions into the electrolyte to suppress the Jahn-Teller effect, thereby preventing the formation of "dead MnO ₂ " and achieving stable and reversible MnO ₂ deposition/dissolution. Furthermore, by employing WO ₃ 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 cm ² .