Polaromicrotribometric (PMT) and Spectroscopic (Infrared‐XPS) Study of the Formation and Modifications of Films Formed on a Polarized Platinum Electrode in  THF  ‐ LiClO4 Medium: I . Cathodic Polarization

Abstract

The mechanism of formation and the changes of different deposits obtained on a Pt cathode in THF-LiC104 medium are studied by means of polaromicrotribometry (PMT). Their chemical nature is determined by infrared and x-ray induced photoelectron spectroscopy (XPS). For a polarization between --1.6 and --2.5V, a thin porous homogeneous film of lithium hydroxide occurs, which is characterized by a low friction coefficient 5 = 0.7 fo, where fo is the value in the absence of polarization. Small amounts of carbon dioxide in solution react on lithium hydroxide and convert it into lithium carbonate. This chemical change provokes a strong increase in the friction coefficient ($ rises from 0.7 to 2 fo) and is marked by the appearance of a very regular stick-slip phenomenon. Under galvanostatic control and at a weak electrolysis current, the formation of lithium hydroxide and then lithium metal is successively observed. The frictian curves clearly show that Li+ ions migrate through the porous lithium hydroxide layer and are reduced on the metal surface. When electrolysis is continued over a longer period of time the lithium hydroxide layer is coated with lithium metal. At a higher current density and at a lower water concentration, a layer of metallic lithium can be obtained in the electrode surface without the prior formation of lithium hydroxide.

Polaromicrotribometric (PMT) and Spectroscopic (Infrared‐XPS) Study of the Formation and Modifications of Films Formed on a Polarized Platinum Electrode in THF ‐ LiClO4 Medium: II . Anodic Polarization

“…The chosen reagent may either be a monomer dissolved in a solvent, or the solvent itself. The THF example belongs to this latter case, and in a previous work (5) we show that several mineral films are formed on the electrode under cathodic polarization.…”

“…Reagents and solvents.--THF (Baker pure grade) and the lithium perchlorate (Fluka) were purified as previously described (5). All experiments were performed in THF-LiC104 0.3M solutions or in THF-LiC104 0.3M diphenylanthracene (DPA) 0.03M solutions which were degassed by bubbling argon through them for 15 min.…”

“…cathodic THF study, the film formation was followed m s~u Dy means of PMT. The electrolysis cell, the electrodes, and the apparatus used for friction measurements were the same as those described in the preceding work (5). The Pt working electrode was always polished with diamond paste before each experiment and rinsed in acetone.…”

“…of the electrode films was obtained as previously by means of x-ray photoelectron spectroscopy (XPS) and by multiple-reflection infrared spectroscopy. The same apparatuses were used under the same conditions as described in the preceding work (5).…”

Factors influencing the electroreductive polymerization of di‐n‐hexyldichlorosilane

“…This is due to the fact that the surface of the cathode is first passivated by a thin adherent insulating Li 2 O layer, which forms at about À1.5 V versus Ag/AgNO 3 (10 À2 M), and at moderate negative potentials prevents electron transfer from occurring. 37,38 Electron transfer happens In both cases the current yield would be the same, and probably a mixed mechanism would occur.…”