Methanol permeability and proton conductivity of Nafion membranes modified electrochemically with polyaniline

Nafion membrane was modified with polyaniline by electrochemical methods, including constant current, constant potential and potential cycling. The methanol permeability and the proton conductivity of the Nafion membranes with and without modification were determined by the electrochemical oxidation of the permeated methanol and electrochemical impedance spectroscopy, respectively. It is found from FTIR results that the polyaniline formed by electrochemical method is in emeraldine state. With the modification of polyaniline, the methanol permeability of the Nafion membrane is reduced by one decade but there is only a slight decrease in proton conductivity. The power density output of direct methanol fuel cell using polyaniline-modified Nafion membrane is 40% larger than that using pure Nafion membrane. The modification with polyaniline is better than that with polypyrrole. The methanol permeability of the polyaniline-modified Nafion is about half of that of the polypyrrole-modified Nafion but the proton conductivity of the former is higher than the later.