Hybrid methyl green/cobalt-polyoxotungstate nanostructured films: Self-assembly, electrochemical and electrocatalytic properties

Hybrid {MG/Co(PW9)2}n multilayer films were successfully prepared and exhibit W-based electrocatalytic activity towards reduction of nitrite and iodate anions. •Layer-by-layer hybrid films {MG/Co(PW9)2}n were sucessfully prepared.•UV–vis was used to monitor film build-up and showed regular stepwise film growth.•XPS confirmed sucessfull {MG/Co(PW9)2}n film fabrication.•Films showed excellent electrocatalytic activity towards nitrite and iodate reduction. Hybrid multilayer films were prepared by alternately depositing cationic dye methyl green (MG) and anionic sandwich-type polyoxometalate K10[Co4(H2O)2(PW9O34)2] (Co(PW9)2) via electrostatic layer-by-layer (LbL) self-assembly method. Film build-up was monitored by UV–vis spectroscopy which showed a regular stepwise growth. X-ray photoelectron spectroscopy data confirmed the successful fabrication of the hybrid films with MG-Co(PW9)2 composition and scanning electron microscopy images revealed a completely covered surface with a non-uniform distribution of the molecular species. Electrochemical characterization of films by cyclic voltammetry revealed two tungsten-based reduction processes in the potential range between −0.9 and −0.5V due to WVI→WV in Co(PW9)2. Studies with the redox probes, [Fe(CN)6]3−/4− and [Ru(NH3)6]3+/2+, revealed that not only the electrostatic attractions or repulsions have effects on the kinetics of the probe reactions, but also the film thickness. Additionally, the {MG/Co(PW9)2}n multilayer films exhibit efficient W-based electrocatalytic activity towards reduction of nitrite and iodate.