(164h) Aqueous Electrochemistry of Conducting Polymers at Low Temperatures

The cyclic voltammogram of parent polyaniline and its ring substituted derivatives can be readily obtained at temperatures as low as –65°C in aqueous acids when the ionic strength of the electrolyte is significantly increased. Under these conditions, the electrolyte does not freeze, and polyaniline can be repeatedly scanned over the entire voltage range for more than 100 cycles without any noticeable degradation (-0.2 V – 1.02 V). This permits one to comprehensively evaluate, for the first time, the “second redox peak” of the cyclic voltammogram of polyaniline, i.e., that associated with the interconversion of the half oxidized emeraldine oxidation state to the fully oxidized pernigraniline oxidation state which was not possible because of the instability of pernigraniline at higher temperatures. At –65°C, polyaniline is stable even in highly concentrated acids and cyclic voltammograms were obtained over a wide acidity range (0.001M to 7M HCl). The slope of the plot of E1/2 vs pH for both redox peaks of parent polyaniline provide important information on the number of H+ on the polymer backbone as a function of oxidation state and comparison with the 2-methyl and 2-ethyl derivatives offers some interesting trends.

Cyclic voltammogram of polyaniline at –65°C in 1M aqueous acid at high ionic strength showing no degradation even after 100 scans.