Temperature dependence of the Tafel slope. The reduction of bromate in alkaline media

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 1993-12, Vol.361 (1), p.193-201
• Main Authors: Schwarz, M., Kirowa-Eisner, E., Gileadi, E.
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/0022-0728(93)87054-Y

The temperature dependence of the transfer coefficient of bromate reduction at pH > 12 is studied in several supporting electrolytes (0.1–1 M LiCl, NaCl, KCl, CsCl) in the temperature range 0–90° at the dropping mercury electrode. The transfer coefficient is found to be independent of temperature. The treatment of the raw current—potential data includes correction for the ohmic drop in solution, calculation of the activation controlled current density from the ratio I/ I d through Koutecky's tabulated χ values and diffuse-double-layer correction according to Frumkin's theory. The Tafel lines are linear over four to six decades of activation current density. Strong emphasis is placed on accuracy. A small but definite dependence of the transfer coefficient on the cation of the supporting electrolyte is found (0.61, 0.64, 0.67 and 0.67 for Li +, Na +, K + and Cs + respectively). The diffuse double-layer effects are suitably accounted for by Frumkin's theory. The corrected reaction rates for the individual electrolytes, except for CsCl, are independent of ionic strength. A negative apparent enthalpy of activation is observed with all electrolytes along the polarographic wave.