Proton migration and water diffusion in polyaniline

Abstract

Proton migration and water diffusion in films of polyaniline (PANI) on various metals was measured using the evolution of hydrogen and oxygen. For both reactions Tafel lines are obtained which are typical for the underlying metal, and the polyaniline film has only a small influence. Hence, the reactions take place at the metal/polymer interface but not on the polymer surface. From very small or negligible resistances of the film we can estimate a lower limit of conductivity K H+ ⩾ 2 × 10 −5 Ω −1 cm −1. In the case of palladium, the postulated hydrogen absorption in the metal can be proved with a hydrogen permeation cell. On polymer-covered gold electrodes, the formation and reduction of gold oxide takes place with a small additional overvoltage which verifies the good proton conductivity of the film. The five-fold increase of the oxide charge indicates a strong degree of roughening of the electrode surface during the PANI formation. Finally, the conclusions are justified by the gas evolution with current densities exceeding 20 mA cm −2. Then a fast bubble formation at the metal/film interface destroys the film. From this observation an upper limit of the diffusion coefficient of gas molecules, D, of 10 −5 cm 2 s −1 can be estimated.