Electrochemical Behavior of H[sub 2]O in Nonaqueous Electrolyte

Abstract

The electrochemical behavior of trace quantities of water (1–30 mM) in LiClO4‐normalpropylene carbonate solutions was studied via chronopotentiometric and cyclic voltammetric techniques. It was observed that, with platinum electrodes, the chronopotentiometric constant increased with increasing current density up to a constant limiting value at high current densities. Analysis of the cyclic voltammetric results showed analogous behavior. The reaction product of H2O reduction was inferred to be a porous, insoluble film of normalLiOH . This layer apparently acts to block part of the electrode surface thereby increasing the effective current density, decreasing Τ and hence iΤ½ . From the concentration dependence of iΤ½ and of ip/v½ it was further inferred that strong complexes were formed between water and Li+ ion which decreased the activity coefficient of H2O . Current reversal subsequent to the reduction step showed an oxidation step which may be associated with an adsorbed film of atomic hydrogen on the platinum surface.

Electrochemical analysis of trace amounts of water in propylene carbonate electrolytes

“…They postulated that water in low concentration (below 0.1M) serves only as a proton donor and is not reduced cathodically, providing that the electrolyte contains an alkali metal salt. This is in contradiction to the work reported previously [2][3][4], in which the cathodic peak due to water reduction was reported.…”

“…The blocking layer included both KOH and potassium glycolate, products of the decomposition of PC. Unlike the reaction studied by Dey [3], and by Burrows and Kirkland [4], this reaction was found to be irreversible. The height of this cathodic peak was used to estimate water content of the solution.…”

“…Burrows and Kirkland [4] studied the reduction of water in the same system at lower concen- trations {20-500 ppm, ,.., 0.01-0.1M). In voltammetric experiments the anodic and cathodic peaks for water appeared at 1.3 V and 2 V vs. Li/ Li+, which is in the same potential range vs. SCE as found by Dey [3].…”

Impedance of Lithium Electrodes in a Propylene Carbonate Electrolyte

“…1 and 2 deduced from the SEI model. Taking l+(jw RC) [12] where a is the depression parameter. It is also related to the angle 8 = an/2 between the radius of the semicircle and the real axis in the complex plane.…”

“…9 The kinetic properties of the surface layer have been studied by means of stationary polarization, 1 0,ll cyclic voltammetry, 12 potentiostatic and galvanostatic pulse techniques, 13 and electrode-impedance spectroscopy.…”