Surface Immobilization of a Tetra-Ruthenium Substituted Polyoxometalate Water Oxidation Catalyst Through the Employment of Conducting Polypyrrole and the Layer-by-Layer (LBL) Technique

A tetra Ru-substituted polyoxometalate Na10[{Ru4O4(OH)2(H2O)4}(γ-
SiW10O36)2] (Ru4POM) has been successfully immobilised onto glassy carbon
electrodes and indium tin oxide (ITO) coated glass slides through the employment of
a conducting polypyrrole matrix and the layer-by-layer (LBL) technique. The resulting
Ru4POM doped polypyrrole films showed stable redox behavior associated with the Ru
centres within the Ru4POM, whereas, the POM’s tungsten-oxo redox centres were not
accessible. The films showed pH dependent redox behavior within the pH range 2−5
whilst exhibiting excellent stability towards redox cycling. The layer-by-layer assembly
was constructed onto poly(diallyldimethylammonium chloride) (PDDA) modified
carbon electrodes by alternate depositions of Ru4POM and a Ru(II) metallodendrimer. The resulting Ru4POM assemblies
showed stable redox behavior for the redox processes associated with Ru4POM in the pH range 2−5. The charge transfer
resistance of the LBL films was calculated through AC-Impedance. Surface characterization of both the polymer and LBL
Ru4POM films was carried out using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning
electron microscopy (SEM). Initial investigations into the ability of the Ru4POM LBL films to electrocatalytically oxidise water at
pH 7 have also been conducted.