Temperature Dependence of the Kinetics of Ozone Reduction on the Platinum Surface
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TEMPERATURE DEPENDENCE OF THE KINETICS OF OZONE REDUCTION ON THE PLATINUM SURFACE G. O. Tatarchenko
UDC 620.191
We study the redox processes in ozonized sulfuric acid solutions at different temperatures. It is shown that the changes in the effective activation energy within a potential range of 0.75 V are connected with the transition from the ozone reduction via the active forms of oxygen, e.g., hydroxide ions or hydrogen peroxide, to its direct reduction on the metal. It is also discovered that the ozone reduction through hydrogen peroxide is improbable at low temperatures. Keywords: ozone, ozone-oxygen depolarization, redox processes, effective activation energy, platinum electrode.
The kinetics and mechanism of reaction of ozone electroreduction depend on the nature of the electrodeelectrocatalyst (i.e., on its surface, electronic, or chemical structures) and the state of its surface (the presence of intermediate or foreign particles tightly adsorbed on the surface). Oxygen-containing particles formed on the
surface in the course of discharge of water molecules or OH − ions and tightly bound with it, affect the reactions of ozone, molecular oxygen, and hydrogen peroxide especially strongly [1]. Only taking into account the simultaneous influence of these factors, it is possible analyze the mechanism of oxygen reduction and establish the factors catalytically affecting the reaction of ozone electroreduction. Changing the surface concentration of active centers and the strength of bonding of the adsorbed oxygen-containing particles, one can affect the electrocatalytic properties of anodic materials. The investigations of the influence of temperature are of great theoretical and practical interest for the processes running in time. Thus, the activation of oxygen reduction with increase in temperature is determined by various factors: on the one hand, the solubility of oxygen in 10% sulfuric acid decreases according to the linear law [2]
C = − 0.103t + 7.18 (cm 3 /liter) ,
(1)
and, on the other hand, the temperature dependence of the diffusion coefficient is described by the formula
D = Ae −Q / RT (cm 2 /sec) ,
(2)
i.e., this quantity varies according to an exponential law. As shown in [3], the solubility of ozone in solutions of sulfuric acid (higher than 5%) obeys Henry’s law, and this law is preserved as temperature increases. Technological Institute of the East-Ukraine V. Dahl National University, Severodonetsk, Ukraine; e-mail: [email protected]. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 49, No. 2, pp.126–130, March–April, 2013. Original article submitted November 26, 2012. 276
1068-820X/13/4902–0276
© 2013
Springer Science+Business Media New York
TEMPERATURE DEPENDENCE OF THE KINETICS OF OZONE REDUCTION ON THE PLATINUM SURFACE
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Fig. 1. Polarization curves for platinum taken in nonozonized (a) and ozonized (b) 10% H 2SO 4 solutions: (1) 3°С, (2) 20, (3) 40, and (4) 60°С.
The low solubility of ozone in water [4] is explained by its specific solvation with the solvent, i.e., by
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