Layer-by-layer self-assembly and electrocatalytic properties of poly(ethylenimine)-silicotungstate multilayer composite films

Hybrid multilayer films composed of poly(ethylenimine) and the Keggin-type polyoxometalates SiW₁₁O₃₉ ]^{8 -} ( SiW₁₁ ) {\left {{\hbox{Si}}{{\hbox{W}}_{{11}}}{{\hbox{O}}_{{39}}}} \right]^{{8} - }}\left( {{\hbox{Si}}{{\hbox{W}}_{{11}}}} \right) and SiW₁₁Co^II( H₂O )O₃₉ ]^{6 -} ( SiW₁₁Co ) {\left {{\hbox{Si}}{{\hbox{W}}_{{11}}}{\hbox{C}}{{\hbox{o}}^{\rm{II}}}\left( {{{\hbox{H}}_2}{\hbox{O}}} \right){{\hbox{O}}_{{39}}}} \right]^{{6} - }}\left( {{\hbox{Si}}{{\hbox{W}}_{{11}}}{\hbox{Co}}} \right) were prepared on glassy carbon electrodes by layer-by-layer self-assembly, and were characterized by cyclic voltammetry and scanning electron microscopy. UV-vis absorption spectroscopy of films deposited on quartz slides was used to monitor film growth, showing that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of bilayers. Cyclic voltammetry indicates that the electrochemical properties of the polyoxometalates are maintained in the multilayer films, and that the first tungsten reduction process for immobilized SiW₁₁ and SiW₁₁Co is a surface-confined process. Electron transfer to Fe( CN )₆ ]^{3 - /4 -} {\left {{\hbox{Fe}}{{\left( {\hbox{CN}} \right)}_6}} \right]^{{3} - /{4} - }} and Ru( NH₃ )₆ ]^{3 + /2 +} {\left {{\hbox{Ru}}{{\left( {{\hbox{N}}{{\hbox{H}}_3}} \right)}_6}} \right]^{{3} + /{2} + }} as electrochemical probes was also investigated by cyclic voltammetry. The (PEI/SiW₁₁Co)_n multilayer films showed excellent electrocatalytic reduction properties towards nitrite, bromate and iodate.