Electrochromic and pH-Sensitive Multilayer Films Based on Nickel-Substituted Dawson-Type Polyoxometalate

An ultrathin multilayer film consisting of polyoxometalate cluster α - K 8 [ P 2 W 17 O 61 Ni II ( H 2 O ) ] ∙ 18 H 2 O ( P 2 W 17 Ni ) and polyallyl amine hydrochloride (PAH) was fabricated on quartz and indium tin oxide substrates by layer-by-layer self-assembly. The multilayer films, ( P 2 W 17 Ni ∕ PAH ) n , were characterized by UV-visible spectra, cyclic voltammetry, chronoamperometry, atomic force microscopy, and in situ spectroelectrochemical measurements. The multilayer film exhibits both suitable response time and low operation potential due to the presence of nickel-substituted polyoxometalate, providing valuable information for exploring the possible application of polyoxometalate-based electrochromic materials. Further, P 2 W 17 Ni embedded in a self-assembled polyelectrolyte matrix can also be used as a pH sensor because of the pH dependence of its electrochemical response.