Characterization of charged film of fluorocarbon polymer (Nafion) and blended fluorocarbon polymer (Nafion)/Collodion composite membranes by electrochemical methods in the presence of redox substances

In order to get a better understanding regarding the structure of charged film of membranes, two kinds of the composite Collodion membrane (C), and Nafion one (N) were prepared and characterized by systematic and comparative studies. The Nafion (fluorocarbon polymer) and Collodion blended with Nafion in the ratio of (CN5:5) composite solutions were used to produce thin membrane films on Au electrodes. The present study indicated that better diffusion coefficient of redox substances can be achieved by blending the Nafion solution with ionic group to Collodion solution compared Nafion only. Diffusion coefficient of MV2+ and FcDM in the blended Nafion/Collodion showed higher values compared to that Nafion. The uptake of neutral species of ferrocenedimethanol (FcDM), positively charged species of methyl viologen (MV2+) and negatively charged of potassiumferrocyanide, [Fe(CN)6]4− ions were studied by cyclic voltammetry (CV), chronopotentiometry (CP) and chronocoulometry (CC). The diffusion coefficient values of MV2+ of the blended composite, CN5:5 membranes are about twice (0.43 × 10−6 cm2/s) that of Nafion based membrane (0.27 × 10−6 cm2/s). While the diffusion coefficients of FcDM of the blended, CN5:5 and Nafion based membranes are in the order of 2.4 and 1.8 × 10−6 cm2/s, respectively. This means that the diffusion of positively charged species, MV2+ was decreased in the membrane matrix compared to neutral species, FcDM. It also indicates that the concentrations of the MV2+ are higher than that of the neutral species, FcDM, in both blended (CN5:5) and Nafion membranes. This may attributed to the existence of interaction between SO3− functional groups of fluorocarbon polymer and MV2+ that led to mobility restriction of MV2+compared to neutral FcDM one, i.e. diffusion of MV2+ was decreased. It was found that the negatively species, [Fe(CN)6]4− exist in surface of the blended membrane (CN5:5) slightly, but not in Nafion one due to the electrostatic repulsion effect between SO3− functional groups of flourocarbon polymer and negatively species, [Fe(CN)6]4−. This means that diffusion of [Fe(CN)6]4− species was not clearly observed. As a whole, the blended membranes indicated membrane performance comparable to the commercial ion-exchange membranes.