Article pubs.acs.org/JPCC
Enhanced Coloration Efficiency for Electrochromic Devices based on Anodized Nb2O5/Electrodeposited MoO3 Binary Systems David D. Yao,† Rozina A. Rani,† Anthony P. O’Mullane,‡,§ Kourosh Kalantar-zadeh,*,† and Jian Zhen Ou*,† †
School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, Australia School of Applied Sciences, RMIT University, Melbourne, Victoria, Australia
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S Supporting Information *
ABSTRACT: There is a continuous quest for developing electrochromic (EC) transition metal oxides (TMOs) with increased coloration efficiency. As emerging TMOs, Nb2O5 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, MoO3 was electrodeposited onto Nb2O5 nanochannelled films as homogeneously conformal and stratified α-MoO3 coatings of different thickness. The EC performance of the resultant MoO3 coated Nb2O5 binary system was evaluated. The system exhibited a coloration efficiency of 149.0 cm2 C−1, exceeding that of any previous reports on MoO3 and Nb2O5 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-MoO3 coating, and a high surface-tovolume ratio, while the Nb2O5 nanochannelled templates provided stability and low impurity pathways for charge transfer to occur.
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INTRODUCTION Nanostructured transition metal oxides (TMOs) have received significant attention for their incorporation into a variety of applications in recent years. Their unique features such as high optical transparency, tunable energy bandgaps, and large surface-to-volume ratio as well as uniform and efficient access for physical and chemical interactions across their whole volume are largely associated with the merits of zero-, one-, and two-dimensional (0D, 1D, and 2D) morphologies.1,2 Combining nanostructured TMOs with complementary features has been shown to promote enhanced charge separation, surface absorption, and structure stability as well as to facilitate bandgap engineering.3−5 These features are critical for the development of devices that are reliant on nanostructured components such as dye-sensitized solar cells,6,7 sensors,8 batteries,9−11 electrochromic and smart windows,5,12 as well as in electrochemical applications13 and optical-based systems.14 Niobium pentoxide (Nb2O5) has drawn increasing attention as an emerging TMO with excellent potential as an electrochromic (EC) material.15,16 Past research has shown that nanostructured Nb 2 O 5 6,17,18 is applicable to EC applications with unique performance attributes such as multicolor capabilities19 and long-term cyclic stability.20 Nb2O5 has been reported to show coloration efficiencies (CEs) of
