A peculiar cyclic voltammetric behavior of polyaniline in acetonitrile and its application in ammonia vapor sensor

A peculiar cyclic voltammetric behavior of polyaniline (PANI) film was observed in acetonitrile (ACN) solution. When the potential was scanned in a narrow potential window corresponding to the first conventional redox pair for the conversion between leucoemeraldine and emeraldine in ACN solution, splitting of the anodic peak for the oxidation from leucoemeraldine to emeraldine was observed in the cyclic voltammograms. When the low limit of the potential window was shifted to a potential negative enough, the cyclic voltammograms of PANI changed significantly, and the electrical properties of PANI film also changed due to the treatment. These peculiar behaviors were tentatively suggested to be associated with the deep reduction, accompanied by the structural changes of PANI chains due to the dedoping. It was further found that when the PANI film was treated by pre-cycling in potential windows with low limits more negative than −0.8 V, its sensitivity was significantly increased toward ammonia vapor, being little affected by the humidity. This led to a successful fabrication of a concept ammonia sensor by using the PANI film pretreated by the deep reduction.