✍ Scribed by F.P. Dousek; J. Říha; J. Jansta
No coin nor oath required. For personal study only.
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 in this respect and the elimination of the last traces of substances involving active hydrogen, i.e. the preparation of truly aprotic electrolytes, is without doubt an exacting operation necessitating special procedures and measures.
Various approaches to this problem have been used ; e.g. some authors 1'2 use propylene carbonate (PC) as electrolyte with a water content as high as 900 p.p.m. and state that this does not influence the electrode process studied (graphite, Pt, and Cu electrodes). Clinckspoor et al. 3 conclude that 100 p.p.m, of water does not modify E-i curves obtained in PC electrolytes with Pt, Ni, Ag, and Cu electrodes; no direct proof is given, however. Using calcium hydride, Ca'iola et al. 4'5 decreased the water content in PC electrolytes to 50-70 p.p.m, and consider this level satisfactory even for systems with alkali metals. Jasinski 6 states that traces of water interfere to some extent with the electrochemical reactions of alkali metals but remarks that only reasonably exacting purification procedures are acceptable with respect to the practical possibilities of large scale production.
However, other authors assign an importance to the last traces of water. For example Toni 7 states that about 20 p.plm. HzO considerably influenced the electrode reduction of oxygen. Gabano et al. 8 dried solutions of LiA1C14 in chloroformate ester by heating with Li metal under reflux. In this way they succeeded in excluding the last trace of impurities containing active hydrogen and demonstrated E-i curves free of any electrochemically active component in the potential range from Li deposition to + 3.5 V. In a previous study 9 we verified that E-i curves obtained with a highly-dried electrolyte of PC + KPF6 on a Pt microelectrode differed considerably from those reported elsewhere I-6.
In the present paper we give the results of a more detailed study of the PC + KPF 6 system in which impurities with active hydrogen (and simultaneously oxygen) were excluded by applying liquid K + Na alloy as described earlier 9. The electrochemical behaviour of this electrolyte is followed polarographically with a dropping mercury electrode (DME) and with E-i curves obtained with working electrodes of Pt, Au, Ni, and with a porous nickel electrode.
📜 SIMILAR VOLUMES
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 th