Coupled H+/anion transport through polyaniline membranes

Direct measurements of the H+ transport through polyaniline (PAN) membrane separating two aqueous solutions were conducted. It was demonstrated that Fick’s law could not describe the H+ transport through PAN membrane. It was found that the transport of H+ from acidic to neutral solution through PAN membrane (∼30 μm thickness) reaches its maximum steady state value after relatively long time. Time lag was 400 min at pH = 2 in the donor solution. This time lag value showed a strong dependence on the donor H+ concentration and decreased at lower pH. The steady state transport rate was less than 1.0 × 10−9 mol/s cm2 if the H+ concentration in the donor solution was less than 0.5 M, but then it increased sharply at higher [H+] to the level above 1.0 × 10−8 mol/s cm2. A kinetic model, taking into account coupled H+/anion transport, ion interactions with PAN polymer chains and their structural changes, is proposed. The large value of the time lag is explained on the basis of the idea about slow structural changes in the film during the H+ induced doping.