Ion/electron coupled transport through polyaniline membrane: fast transmembrane redox reactions at neutral pH

Different oxidizing and reducing agents can be separated by a solid polymer membrane, but they still react. The possibility to conduct this type of transmembrane redox reactions coupled with electroneutral electron/chloride countertransport is demonstrated here for polyaniline (PANI) membrane doped with camphor sulfonic acid (CSA). For the 80 microm film, the transmembrane reaction rate can be as high as 5 x 10 (-8) mol/(cm (2) s) with FeCl 3 as the oxidizing and ascorbic acid as the reducing agents, which is approximately 25 times higher than described by us earlier with HCl-doped PANI membrane. Both solutions separated by the membrane with CSA can have pH near neutral, which is impossible with HCl-doping. Advanced kinetic mechanism of electron/ion coupled transport including chloride equilibrium at the interface is proposed, and major kinetic parameters are estimated. Interfacial redox rate constants (cm/s) are compared with the rate constants determined for polarized membranes by electrochemical methods and also with usual first and second order rate constants in the bulk volume. Possibility to conduct different redox reactions between substances which are not mixed and are separated by a membrane makes this new process very attractive for chemical and environmental engineering.