INFLUENCE OF ANIONS ON OXYGEN OZONE EVOLUTION ON PBO2/SPE AND PBO2/TIELECTRODES IN NEUTRAL PH MEDIA/

The formation of O-2/O-3 on PbO2 from the electrolysis of water in neu tral solutions is shown here to present some analogies and some differ ences with respect to the same process in acid media. The electrolyte composition affects the current efficiency for O-3 formation (n) and t he cell potential (E) of a Membrel type electrochemical assembly. An i mprovement in n and a decrease in E is observed upon addition of relat ively low amounts of Na4SO4 or NaClO4 in pure water. We observe no eff ect of NaNO3 on either parameters. In agreement with literature data i n acid solutions, F- causes an increase in both n and E. The results o f electrochemical kinetic investigations with electrodes of PbO2 elect rodeposited on Ti confirm the above data. Current-potential curves con structed from measurements in NaNO, show a region of Tafel linearity w ith slopes of 2RT/F and RT/F in the low and high currents range, respe ctively. Addition of Na2SO4 and NaClO4 to NaNO3 has an effect on the p rocess at more positive potentials only: the RT/F slope decreases towa rd a value of RT/2F as the concentration of the ''foreign'' salt is in creased. As an explanation of the observed behaviour, the possibility is advanced that a step following the discharge of water is rate deter mining at high positive potentials with the adsorption of intermediate s described by Temkin conditions. The composition of the electrolyte i s expected to influence the yield of ozone formation by affecting the coverage and free energy of adsorbed oxygen intermediates.