Fast switching Prussian blue film by modification with cetyltrimethylammonium bromide

A novel process is developed for the preparation of Prussian blue (PB) film, involving its electrodeposition from its precursor solution, containing additionally the surfactant, cetyltrimethylammonium bromide (CTAB); the film is denoted as CTAB-modified PB film. The present approach allows for mitigating the energy barrier of redox reactions between Prussian blue and its reduced state, Everitt’s salt. The absorbance spectra of the CTAB-modified PB exhibit a maximal optical difference at 690 nm. The transmittance changes (ΔT) of CTAB-modified PB film and unmodified PB film were measured in the electrolyte of 0.5 M KCl and 0.01 M HCl at 690 nm. It reveals that CTAB-PB film took 4.2 and 2.4 s for darkening (oxidation) and bleaching (reduction), respectively, for 44.2% transmittance change (ΔT), whereas the unmodified film required 35 and 55 s for 42.1% of ΔT. By an electrochemical quartz crystal microbalance (EQCM) analysis, it is observed that the insertion and extraction of potassium ions and water molecules at the interface of the CTAB-modified PB film and the electrolyte solution are faster than those of the unmodified PB film. Also, during the potential cycling of the CTAB-modified PB film, it was found to be stable, with reference to the stability of the unmodified PB film.

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► Prussian blue (PB) thin films were modified with cetyltrimethylammonium bromide (CTAB).
► CTAB-modified PB film has much shorter response times than those of unmodified PB.
► CTAB-modified PB film has less charge transfer resistance than that of unmodified PB.
► EQCM analysis was employed to observe the ion insertion/extraction into and out of the film.
► CTAB-modified PB film improves stability, with reference to that of unmodified PB.