Electrochemical behaviour of self-assembly multilayer films based on iron-substituted α-Keggin polyoxotungstates

Ultrathin multilayer films containing metal-substituted polyoxometalates, [PW11FeIII(H2O)O39]4− (PW11Fe) or [SiW11FeIII(H2O)O39]5− (SiW11Fe), and poly(ethylenimine) (PEI) were prepared by the electrostatic layer-by-layer self-assembly method on a glassy carbon electrode. The multilayer films were characterized by cyclic voltammetry and scanning electron microscopy and UV–Vis absorption spectroscopy on a quartz slide was used to monitor film growth. Cyclic voltammetry indicates that the electrochemical properties of the polyoxometalates are completely maintained in the multilayer films, and the influence of scan rate on the voltammetric features showed that the first tungsten reduction process for immobilized PW11Fe and SiW11Fe is a surface-confined process. Studies with [Fe(CN6)]3−/4− as electrochemical probe showed that their permeability depends on the thickness of the multilayer films, if the outermost layer is negatively charged. Additionally, the (PEI/SiW11Fe)n multilayer films showed electrocatalytic properties towards nitrite reduction.