The Effect of Lithiation on the Electrochromism of Sol‐Gel Derived Niobium Oxide Films

Abstract

Niobium oxide films are promising cathodic electrochromic materials that in certain aspects can compete with the more frequently studied WO 3 films. The films reported here were prepared using the sol-gel route from a NbCl, precursor. The electrochromic properties were pronounced for crystalline films heat-treated at 500°C exhibiting transmittance changes between the colored and bleached states of 60% in the ultraviolet (UV) and 80% in the visible and near-infrared spectral regions. The reversibility of electrochromic changes of thick niobium oxide films (d > 250 nm) was enhanced by lithiation.

Sol‐gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism

“…17 cm 2 /C. As it was already observed [23], the incorporation of Li + improves the kinetics and the coloration efficiency increased to approx. 23 cm 2 /C up to a molar ratio Li/Nb = 0.1 for the crystalline layers sintered between 500 and 600 • C.…”

“…Schmitt [18], using the same configuration with a 125 nm thick Nb 2 O 5 and a 240 nm thick CeO 2 − TiO 2 counter electrode measured also a very small Li insertion (< 0.25 mC/cm 2 after switching between −2.5 V and +1 V during 120 s) with a corresponding change in optical density at 500 nm lower than 0.01 ! Only Orel et al [23][24][25] succeeded to observe a transmission change between 60% and 33% using a sol-gel SnO 2 : Sb(7%) : Mo10% layer as counter electrode (IS) switching between −4.0 V(!) and +2.0 V during 120 s. Due to the very high negative applied potential, the cell had a very poor stability, less than 500 cycles.…”

Electrochromic glazing

“…Lithiation of Nb2O5 through the addition of a lithium salt to the precursor solution enhances the EC kinetics -in particular the bleach rate and reversibility for lithium intercalation. This was shown for both the amorphous and crystalline material 41 . In comparison to WO3 niobium oxide requires higher potentials for color and bleach and has slower EC kinetics.…”

Electrochromic Properties of Sol-gel Coating of Nb2O5 and Nb2O5:Li+

“…Also Nb2O5 films were prepared by the sonocatalytic method 12 . In order to improve the bleaching process, Macek et al 15 have prepared films of Nb2O5 doped with lithium salt (LiCF3SO3) according to Barros Filho et al 16 procedure. These sols were obtained by the solubilization of NbCl5 in propanol for 24 h, and the addition of glacial acetic acid and LiCF3SO3.…”