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.

Effect of metal dopants on the electrochromic performance of hydrothermally-prepared tungsten oxide materials

“…Moreover, it could be possible that Nb, Gd and Er ions in high concentrations block the access to the active layer, as the multivalent ions have a larger size than monovalent Li + . 42 …”

“…Moreover, it could be possible that Nb, Gd and Er ions in high concentrations block the access to the active layer, as the multivalent ions have a larger size than monovalent Li + . 42 The colouration efficiency (CE) is extracted as the slope of the line tting the linear region of the curve of the optical density of (DOD) based on eqn (3). The CE is a crucial parameter in the development of EC devices as it indicates the EC device's optical modulation capability with respect to the intercalation charge density.…”

The Progress and Outlook of Multivalent‐Ion‐Based Electrochromism

“…The superior electrochromic performance of TiO 2 nanocrystals (larger ΔT and improved cycling stability) in Zn 2þ electrolyte was ascribed to the lower potential barriers of Zn 2þ (0.55 eV) in TiO 2 compared to that of Li þ (0.59 eV) and Al 3þ (0.74 eV), showcasing the superiority of multivalent-ion-based ECD than monovalent-ion-based ECDs. [45] Nonetheless, it has been proved that the intercalation energy of ions can be reduced by doping. [37,46] W-doped TiO 2 has reduced Zn 2þ -intercalation energy to 0.86 eV, enabling improved electrochemical performance in W-TiO 2 .…”

Dual-Band Electrochromic Smart Window Based on Single-Component Nanocrystals

“…Titanium dioxide (TiO 2 ) is a common material with excellent physical and chemical stability. ,− Trizio et al found in the preparation of colloidal TiO 2 NCs that Nb 5+ doping can increase the free carrier concentration of TiO 2 NCs and make it produce obvious LSPR absorption in the NIR region. Subsequently, Dahlman et al found in the EC study of Nb-doped TiO 2 NCs that they have the ability to selectively regulate NIR and VIS light.…”