A Study of the Electrical Double Layer

Peacock, James M (1953) A Study of the Electrical Double Layer. PhD thesis, University of Glasgow.

Abstract

The thesis is divided into four sections. A. The introduction traces the development of electrical double layer theory and outlines the essentials of the Helmholtz, Gouy-Chapman, and Stern concepts. The ideal polarised electrode is then considered, and the application of electrocapillarity techniques to the structural elucidation of the metal-solution interface is discussed. Modifications and extensions of the Stern theory described by Grahame are then introduced, and finally the principal experimental methods of double layer investigation are summarised. B. This is the main section of the work. It describes first an accurate alternating current bridge system designed to measure the differential capacity of the interface at a dropping mercury cathode in contact with a solution of some indifferent electrolyte. Thereafter the results obtained by this method are presented. Capacity data for aqueous N/10 potassium chloride are reported. The minimum value of 16.7 muF/cm2. is in good agreement with 16.1 muF/cm2. determined by Grahame. The effects on capacity of the addition of trace concentrations of a number of surface active substances, i.e., gelatin, eosin, methyl red, and pyridine were then investigated, and finally, pseudo capacities obtained in the presence of small concentrations of salts such as cadmium chloride, were used to determine the effects of the reagents already mentioned, on reversible reduction of the cation. The remaining part of this section is concerned with a systematic examination of capacity phenomena in some non aqueous solvents. Electrocapillarity measurements, using a capillary electrometer method were also made. Minimum capacities of 6.84 and 11.46 muF/cm2. were found for anhydrous acetic and formic acids respectively. The supporting electrolytes were 1 molal ammonium acetate and 1 molal ammonium formate. Although the high decomposition potential of sulphuric acid restricted capacity determinations, a value of 17.75 muF/cm2. for 98% (w/w ) acid is reported at -0.6 volt v. a mercury pool reference electrode. Surface charge densities have been derived both from electrocapillarity differentiation and capacity integration, and electrocapillarity curves have been determined by a further integration. Capacity and electrocapillarity data for water, anhydrous methanol, ethanol, n-propanol and pyridine with 1 molal lithium chloride as supporting electrolyte are presented. Some of the experimental work was carried out by the late Dr. J. C. James just prior to his death and so it was thought to be appropriate to complete the work and to extend it to other systems. Thus, surface charge densities and electrocapillarity curves for the non aqueous solvents above have been derived from capacity integration. The minimum capacity values for water, methanol, ethanol, n-propanol, and pyridine were found to be 16.25, 9.50, 8.00, 8.00, and 5.75 muF/cm2. The effects of cation variation for a given anion in methanol were determined by comparison of cathodic capacities for 1 molal lithium, sodium, potassium, and ammonium iodides. The same trends as in aqueous solution were found, but the effects were much more pronounced. C. A double layer capacity investigation of the system Cu/Cu++ was carried out by two different methods. The electrolyte was 0.5 M copper sulphate -1N sulphuric acid. An alternating current bridge system similar to that already mentioned was first used. The results were found to be frequency dependent, but a minimum capacity of 55 muF/cm2. at 10,000 cycles per second is reported. The second method employed an oscillographic technique designed to present cathodic double layer charging curves, the slope of which measures capacity. The oscillograms obtained were initially linear prior to electrolysis, but the slopes were highly susceptible to current density variations. The effects on the capacity of the copper system of trace concentrations of gelatin and thiourea were also investigated. D. The last section reports work of a different nature, viz. , the ion association which occurs between cations and dicarboxylate anions in aqueous solution. This was studied by potentiometric, conductometric, and spectrophotometric methods. Equilibrium constants are given, and the significance of these results is discussed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Physical chemistry
• Date of Award: 1953
• Depositing User: Enlighten Team
• Unique ID: glathesis:1953-79098
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 11:43
• Last Modified: 05 Mar 2020 11:43
• URI: https://theses.gla.ac.uk/id/eprint/79098