Open-circuit potential of a Pt electrode immersed in different aqueous solutions

The aim of this study is to investigate the multi-day behavior of the electromotive force (EMF) between Pt and reference Ag/AgCl, KClsat. electrodes immersed in various aqueous systems (deionized water, 1 × 10−3 M H2SO4 solution and 0.15 M KCl solution) at 32 °C and also at ambient temperature, without oxygen removal and redox species introduction. The control test of EMF behavior in the presence of redox species was performed with cyanide complexes of Fe2+ and Fe3+ ions at ambient temperature. In experiments with deionized water, systems were protected against the influence of daylight and static electricity. The results have shown diurnal oscillations of EMF in all investigated systems with amplitudes in the range ≈ 1 to 25 mV depending on applied experimental conditions. EMF oscillations in deionized water were independent on the applied temperature and yielded amplitudes of 15–25 mV in daylight regime, and only a few mV when protected from its influence. The effect of electrostatic electricity was not observed. Diurnal EMF oscillations with the amplitudes ≤ 5 mV were observed individually in 0.15 M KCl solution, redox system and after 4 days of investigation in H2SO4 solution. Results presented in this work pointed out that the behavior of Pt–oxygen electrode is specific and very complex, even in the simplest system such as deionized water. To investigate the origin of the observed EMF oscillations and the application of Pt–oxygen electrode in in situ multi-day dynamics studies under open-circuit potential condition, additional theoretical and experimental methods and particularly electrochemical ones, must be applied.