Surface immobilisation of the sandwich type Na14[Fe4(Ox)4(H2O)2(SbW9O33)2]·60H2O polyoxometalate

A functionalised Fe-substituted Keggin Na14[Fe4(C2O4)4(H2O)2(SbW9O33)2]·60H2O type POM termed “Fe4Ox4” has been successfully immobilised onto carbon electrode surfaces through the employment of conducting polypyrrole films and the layer-by-layer (LBL) technique. For the POM doped polypyrrole films the redox systems associated with the POM's tungsten-oxo framework was not apparent upon redox cycling, however a reversible redox couple associated with the FeIII/II redox system was clearly seen within the pH range 2–7. Organised multilayer assemblies were constructed by the employment of the layer by layer (LBL) technique through alternating anionic Fe4Ox4 layers and cationic RuII metallodendrimers with poly(diallyldimethylammonium chloride) (PDDA) employed as an initial base layer. Stable redox couples associated with both the FeIII/II and tungsten-oxo framework, for the Fe4Ox4 POM, and the RuIII/II for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2–7. The resulting multilayer assembly showed good stability towards redox cycling. Further investigations into the multilayer assembly were undertaken by determining it is charge transfer resistance using AC-impedance voltammetry. The layer also showed catalytic ability towards the reduction of H2O2 at pH 6.5.

► Successful surface immobilisation of Fe Polyoxometalate by layer-by-layer technique and the use of conducting polypyrrole.
► Stable and well defined redox activity of POM observed in the immobilised state.
► Catalytic properties of immobilised POM observed towards the reduction of hydrogen peroxide.