Study on charge transfer reactions at multilayers of polyoxometalates clusters and poly(allylamine hydrochloride) (Grotthuss-018)

Abstract

Multilayers of anionic phosphotungstic acid (PTA) clusters and positively charged protonated poly(allylamine hydrochloride) (PAH) were assembled by layer-by-layer self-assembled method on Au electrode modified by 3-mercaptopropionic acid (3-MPA). The effect of the charge of the surface of the multilayer assembly on the kinetics of the charge transfer reaction was studied by using the redox probes [Fe(CN) 6] 3−/4− and [Ru(NH 3) 6] 2+/3+. The cyclic voltammetry experiments showed that the peak currents and peak-to-peak potential differences changed after assembling different layers on the electrode surface indicating that the charge of the surface has a significant effect on the kinetics of the studied charge transfer reactions. These reactions were studied in more detail by electrochemical impedance spectroscopy. When [Fe(CN) 6] 3−/4− was used as the redox label, multilayers that terminated with negatively charged PTA showed a high charge transfer resistance but multilayers that terminated with positively charged PAH showed lower charge transfer resistance. With [Ru(NH 3) 6] 2+/3+ as the redox label, the charge transfer resistance at multilayers that terminated with positively charged PAH was much higher than at the multilayer terminated by the negatively charged PTA. The charge transfer resistances also increased with the addition of number of layers indicating that the entire thickness of the multilayer assembly has also an effect on the kinetics of the studied charge transfer reactions and not only the electrostatic attraction or repulsion between the surface and the redox probes. The ohmic resistance of the multilayer assembly increased non-linearly with the number of layers. Assembling a layer of PAH increased the resistance more than assembling a layer of PTA.