Surface immobilisation of the sandwich type Na 14[Fe 4(Ox) 4(H 2O) 2(SbW 9O 33) 2]·60H 2O polyoxometalate

Abstract

A functionalised Fe-substituted Keggin Na 14[Fe 4(C 2O 4) 4(H 2O) 2(SbW 9O 33) 2]·60H 2O type POM termed “Fe 4Ox 4” 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 Fe III/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 Fe 4Ox 4 layers and cationic Ru II metallodendrimers with poly(diallyldimethylammonium chloride) (PDDA) employed as an initial base layer. Stable redox couples associated with both the Fe III/II and tungsten-oxo framework, for the Fe 4Ox 4 POM, and the Ru III/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 H 2O 2 at pH 6.5.