Films formed by the electrooxidation of p-aminophenol (p-APh) in aqueous medium: What do they look like?

The purpose of the present study was to clarify the occurrence or absence of film formation during the electrooxidation of p-aminophenol (p-APh, a very simple and useful molecule) in aqueous medium. The results here described were based on data collected from the initial stage of the electrooxidation process with an in situ quartz crystal microbalance and with in situ spectroelectrochemical measurements in the visible range and FT-IR. Film formation upon the electrooxidation of p-APh was found to occur in the entire pH range (2–12) investigated. Of particular interest were the films obtained at the pH values of 4, 6, and 8. The main factor for film formation was charge-transfer complex precipitation, which was totally dependent on pH. The films formed at pH 6 or 8 tended to be thicker, but showed smaller charge retention. Those generated at pH 4 showed greater charge retention, despite their smaller thickness. In the case of films produced at pH 4, greater charge retention appeared to correlate with a greater number of phenyl-N-phenyl bonds than of phenyl-O-phenyl ones, whereas an equal number of phenyl-N-phenyl and phenyl-O-phenyl bonds appeared to result in films with a lower capability for charge retention.