The Influence of Fluorine-Containing Surfactants and Polymers on Regularities of Lead Dioxide Electrodeposition

Abstract

Electrochemical synthesis allows one to influence the composition and properties of materials by changing the conditions of electrolysis and electrolyte composition. Lead dioxide due to the simplicity of its electrochemical synthesis, high corrosion resistance and relatively low cost is widely used in electrocatalysis, electroplating, lead-acid batteries, etc. The inclusion of fluorine-containing compounds in the metal oxide matrix provides antistatic, anti-adhesive, anti-corrosion properties, and at the same time the materials retain the properties of metal oxide: high electrical conductivity, resistance to mechanical wear and good adhesion to the substrate.In this work, the regularities of lead dioxide electrosynthesis in the presence of fluorine-containing surfactants with different fluor-carbon chain lengths and polyelectrolytes in the electrolyte were investigated.Electrodeposition was studied in 0.11 M CH3SO3H + 0.01 M Pb (CH3SO3)2. The surfactant was added to the deposition electrolyte in the form of aqueous solutions with a concentration of 3×10-4 M. Determination of current efficiency and partial oxidation current (IPb(II)) was performed by the method described in detail previously [1].The kinetic regularities of PbO2 electrodeposition are satisfactorily described in a four-stage mechanism applied to a wide range of electrolytes (both nitrate and methanesulfonate), including those containing ionic additives, colloidal TiO2 and polyelectrolytes [2,3]. As a rule, at low anodic polarizations (E <1.6 V) the reactions will take place with kinetic control, while at high polarizations the delivery of Pb2+ ions to the electrode surface will be the rate-determining stage. It was found that the addition of surfactants and polyelectrolytes in different ways affect the kinetics of electrodeposition of lead dioxide, without changing the mechanism of the process.The basis of the surface effects is the adsorption of additives on the electrode surface. The adsorption on the electrode of methanesulfonate and fluoride ions significantly affects the rate of the discharge-ionization stage. This effect is due to a number of factors that lead to changes in the concentration of reacting particles in the surface layer and the activation energy of the electrode process. Since the value of surface charge is positive, a decrease in the value of the potential in the plane of localization of the activated complex will increase the rate of the charge transfer stage, which is observed in practice in solutions containing short-chain perfluoroalkyl surfactants and low concentrations of Nafion® polymer. During the adsorption of a polyelectrolyte or anionic surfactant on the surface of the electrode, the value of such potential can not only decrease significantly, but even become negative due to recharging of the electric double layer. This possibility is indicated by the change in the electrokinetic potential of PbO2 from positive to negative by adding anionic surfactants and polymers to the electrolyte.The inhibition parameter reflects both the electrostatic and chemical interaction of the activated complex with the adsorption layer, which leads to an increase in the activation energy of the charge transfer stage. Increasing the volume concentration of the additive in the electrolyte leads to an increase in the degree of filling of the electrode surface, which will cause a decrease in the rate of the charge transfer stage due to blocking of active centers on the electrode surface.Since the process of formation of lead dioxide takes place together with the reaction of oxygen evolution, the dependences of PbO2 current efficiencies (CE) on the electrodeposition potential were investigated to assess the influence of surfactants on the lead dioxide electrodeposition.In the low polarizations area, the PbO2 CE remains virtually unchanged, close to 100%. In this area, the deposition process is controlled by kinetic stages. If the additive does not inhibit the deposition of lead oxide, CE is close to 100% and is almost independent of the current density. In the next part of the curve the process of electrodeposition of oxide occurs under mixed control. On the descending part of the dependence CE decreases due to the increase in the reaction rate of oxygen evolution when the limiting current of electrodeposition of oxide is observed (diffusion control). References A. Velichenko, T. Luk’yanenko, O. Shmychkova, L. Dmitrikova, Electrosynthesis and catalytic activity of PbO2-fluorinated surfactant composites, J. Chem. Technol. Biotechnol., 95, 3085, (2020). A. Velichenko, T. Luk’yanenko, N. Nikolenko, O. Shmychkova, P. Demchenko, R. Gladyshevskii, Composite electrodes PbO2-Nafion®, J. Electrochem. Soc., 167, 063501 (2020).O. Shmychkova, T. Luk’yanenko, A. Velichenko, Lead dioxide electrocrystallization from nitrate and methanesulfonate electrolytes: The influence of various dopants on initial stages, ECS Transactions, 77, 1617 (2017).