Limiting current increase of oxidation of ferrocyanide anions in water and electrolyte solutions during freezing

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Vol. 401; no. 1; pp. 163 - 169
• Main Authors: Tanaka, Kazuko, Hasebe, Tooru
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.01.1996; Elsevier Science
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; Ferrocyanide anions; Freezing; General and physical chemistry; Kinetics and mechanism of reactions; Limiting current; Oxidation; Oxidation; Limiting current; Ferrocyanide anions; Freezing; Water; Limiting electric current; Hexacyanoferrates; Transition metal; Experimental study; Inorganic compound; Operating conditions; Alkali metal Chlorides; Platinum; Non electrolyte solution; Microelectrode; Aqueous solution; Diffusion coefficient; Electrochemical reaction; Disk electrode
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/0022-0728(95)04259-8

Normal pulse voltammograms of the oxidation of ferrocyanide to ferricyanide were investigated in water and aqueous solutions of various electrolytes at temperatures above and below the freezing point of the solvent using a platinum microdisc electrode. A significant increase in the limiting current was observed on freezing, particularly in water without added electrolyte, and, in most cases, current vs. t −1 2 plots gave a straight line, suggesting a diffusion-controlled mechanism. The concentration of ferrocyanide in the liquid phase localized at the electrode area in partially frozen solution was estimated from the slope by applying the diffusion coefficient of the ion in complete liquid at the freezing point or in the supercooled state, and this was compared with the concentration averaged in the bulk determined from the free induction decay (FID) signals of 1H-NMR measured under similar conditions to those of voltammetry. The degree of concentration determined from the limiting current was much higher than that estimated from the FID signals, particularly just before freezing was complete. Such a result indicates that a liquid microphase which concentrates solutes exists at or near the electrode in low temperature freezing solutions.