Novel hybrid based on a poly[Ni(salen)] film and WO3 nanoparticles with electrochromic properties

The strategy of combining electroactive polymers and inorganic nanomaterials has been widely explored in recent years in order to improve some of their properties, namely electrocatalysis and electrochromism. This report focuses on a new composite prepared through the electropolymerization of the transition metal complex [Ni(3-Mesalen)], designated as [1] in the presence of WO3 nanoparticles (NPs) and its electrochromic (EC) performance. The WO3 NPs were prepared using tungsten metal powder; their characterization indicated quasi-spherical morphology, high crystallinity and particle sizes in the range 30–40 nm. The nanocomposite WO3@poly[1] films displayed similar electrochemical responses to those of pristine poly[1] films in LiClO4/CH3CN, but higher electroactive surface coverages, an advantage of NPs incorporation in the nanocomposite. The presence of the WO3 NPs in the poly[1] matrix was assessed by X-ray photoelectron spectroscopy and scanning electronic microscopy. The nanocomposite presented similar electronic spectra to those of poly[1], indicating that the electronic structure of the pristine film is maintained in the nanocomposite, but exhibited lower ε-values for bands associated with charge transfer transitions for high oxidised states, revealing an enhanced stability towards ligand over-oxidation. The WO3@poly[1] nanocomposite showed more favourable EC properties in LiClO4/CH3CN than the pristine film. For typical coverages (Γ = 0.06-0.10 μmol cm−2) the composite showed lower switching times (τ = 1.3 − 3.6 s), higher optical contrast (ΔT ≈ 31%, an improvement of ca. 40%) and better colouration efficiencies (in the range η = 104 − 115 cm2C−1, improvement of ca. 13 − 22%).