Fig a shows cyclic voltammograms of

3.3. Electrochemical characterization of MG/Co4(PW9)2 n films
The cyclic voltammograms for a single MG/Co4(PW9)2 bilayer obtained at different scan rates in Ibuprofen 4.0 CH3COOH/CH3COONa, are shown in Fig. 4. Methyl green is not electroactive in the potential range studied so, the electrochemical responses are attributed to the immobilized Co4(PW9)2 and correspond to W-centred reduction processes (WVI → WV) with E1/2 (1) = −0.658 and E1/2 (2) = −0.843 vs. Ag/AgCl, scan rate 0.050 V s−1. At pH 4.0 CH3COOH/CH3COONa buffer solution, the free POM (Figure S3, SI) revealed one well defined W-centred reduction process with E1/2 (2) = −0.820 V vs Ag/AgCl, which is similar to the corresponding process in the immobilized Co4(PW9)2; the reduction process at less negative potential, that is observed in the immobilized POM at E1/2 (1) = −0.658, is not well defined in the free POM.
Fig. 4. Cyclic voltammograms of MG/Co4(PW9)2 bilayer in pH 4.0 CH3COOH/CH3COONa at different scan rates: 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12 and 0.15 V s−1 (a); Plots of log ip vs. log ν (b).Figure optionsDownload full-size imageDownload as PowerPoint slide