Unraveling the Effect of Cation Types on Electrochromic Properties of Titanium Dioxide Nanocrystals

Abstract

Electrochromic (EC) devices have been regarded as promising candidates for energy-saving smart windows, next-generation displays, and wearable electronics. Monovalent ions such as H+- and Li+-based electrolytes are the benchmark insertion ions for EC devices but have serious limitations such as high cost, instability, and difficulty to handle. Seeking multivalent electrolytes is an effective alternative way to prepare high-performance EC devices; unfortunately, the related reports are currently limited to tungsten oxide EC materials. Herein, for the first time, we investigate the EC properties driven by different valence cationic (i.e., Li+, Zn2+, and Al3+) electrolytes in the titanium dioxide system. It is found that the initial optical modulation ranges of TiO2 nanocrystal (NC) films in Li+, Zn2+, and Al3+ electrolytes are 76.8%, 77.4%, and 77.3%, respectively. After 250 cycles, the optical contrast of these films in Zn2+ electrolyte decreased by only 2.3%, much lower than that in benchmark Li+ electrolyte of 10.1% and Al3+ electrolyte of 59.1%. Density functional theory calculation indicates that the potential barriers of Li+, Zn2+, and Al3+ in TiO2 are 0.59, 0.55, and 0.74 eV, respectively, which makes TiO2 NCs show good EC properties in Zn2+ electrolytes. This work unravels the effect of different valence cations on the electrochromic properties of titanium dioxide NCs, which may provide some new directions for the development of excellent EC devices with long-term stability and durability.