✍ Scribed by J. Jansta; F.P. Dousek; J. Říha
No coin nor oath required. For personal study only.
Over the last few years, a series of papers appeared dealing with electrochemical phenomena in aprotic electrolytes among others also in connection with high energy batteries. In a previous paper 1 we quoted several representative opinions on the necessary degree of exclusion of water, and stated that only few authors were aware of the strong influence trace amounts of water had on the electrochemical processes they studied. An attempt towards a more complete quantitative treatment of the electrochemical activity of water in aprotic solvents has so far only been made by Dey z and Burrows and Kirkland 3, both of them dealing with a solution of LiC104 in propylene carbonate (PC) with a water content exceeding 18 ppm. In the second more advanced paper, the authors demonstrated that water was reduced on a Pt surface, the reduction being accompanied by blocking of the electrode surface with an insoluble film of LiOH. The technique worked out by the authors even permitted an approximate estimate of water concentration to be made.
On the E-I curve obtained in the driest electrolyte they were able to prepare, the authors found several cathodic and anodic peaks. In our previous paper 1 we were able to demonstrate that on a stationary Pt electrode in K+-PC electrolyte in the region of potentials more positive than that of potassium deposition, E-I curves were smooth only in a highly dried electrolyte. In fact, tens of ppm of water were sufficient to induce the formation of fiat cathodic peaks and to slow down or eventually to stop the deposition of potassium.
We were successful not only in excluding almost completely active hydrogen from the K÷-PC solution but also in storing the electrolyte for prolonged periods of time without recontamination 4. This enabled us to prepare a series of synthetic solutions of a varying very low concentration of water by deliberately adding small quantities of electrolyte of a known water content to the highly dried one. It would, therefore, have been possible to follow quantitatively the influence of water in concentrations far below 20 ppm, were it not for an increasing irreproducibility of E-I curves accompanying the increase in water content. The present paper describes the influence of water content on E-I curves obtained with Pt, Au, Ag, Ni and Cu electrodes in the concentration range 0 to 100 ppm in 0.5 M KPF 6 in PC, and the technique employed to overcome the difficulties due to poor reproducibility.
📜 SIMILAR VOLUMES
Requirements for the degree of exclusion of water of the so-called non-aqueous electrolytes depend largely on the electrochemical systems under consideration and there is therefore no unique definition with regard to limits. The electrochemistry of alkali metals is understandably extremely sensitive