Enhanced Coloration Efficiency for Electrochromic Devices based on Anodized Nb₂O₅/Electrodeposited MoO₃ Binary Systems

There is a continuous quest for developing electrochromic (EC) transition metal oxides (TMOs) with increased coloration efficiency. As emerging TMOs, Nb 2 O 5 films, even those of ordered anodized nanochannels, have failed to produce the required EC performance for practical applications. This is attributed to limitations presented by its relatively wide bandgap and low capacity for accommodating ions. To overcome such issues, MoO 3 was electrodeposited onto Nb 2 O 5 nanochannelled films as homogeneously conformal and stratified α-MoO 3 coatings of different thickness. The EC performance of the resultant MoO 3 coated Nb 2 O 5 binary system was evaluated. The system exhibited a coloration efficiency of 149.0 cm 2 C –1, exceeding that of any previous reports on MoO 3 and Nb 2 O 5 individually or their compounds. The enhancement was ascribed to a combination of the reduced effective bandgap of the binary system, the increased intercalation probability from the layered α-MoO 3 coating, and a high surface-to-volume ratio, while the Nb 2 O 5 nanochannelled templates provided stability and low impurity pathways for charge transfer to occur.