High Performance Electrochromic Devices Based on Anodized Nanoporous Nb₂O₅

Despite the predictions, the true potential of Nb 2 O 5 for electrochromic applications has yet to be fully realized. In this work, three-dimensional (3D) compact and well-ordered nanoporous Nb 2 O 5 films are synthesized by the electrochemical anodization of niobium thin films. These films are formed using RF sputtering and then anodized in an electrolyte containing ethylene glycol, ammonium fluoride, and small water content (4%) at 50 °C which resulted in low embedded impurities within the structure. Characterization of the anodized films shows that a highly crystalline orthorhombic phase of Nb 2 O 5 is obtained after annealing at 450 °C. The 3D structure provides a template consisting of a large concentration of active sites for ion intercalation, while also ensuring low scattering directional paths for electrons. These features enhance the coloration efficiency to 47.0 cm 2 C –1 (at 550 nm) for a 500 nm thick film upon Li + ion intercalation. Additionally, the Nb 2 O 5 electrochromic device shows a high bleached state transparency and large optical modulation.