A Study of the Electrical Double Layer

Vincent, Colin A (1963) A Study of the Electrical Double Layer. PhD thesis, University of Glasgow.

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At the interface between a metal and an electrolytic solution, there is in general an array of oppositely charged particles and oriented dipoles, known as the "electrical double layer". In the present work, a study was made of the double layer for perfectly polarised systems - i.e. where charge transfer across the interface did not occur. The metallic phase was mercury, while the solution consisted of alkali metal chlorides in aqueous and non-aqueous solvents. The main purpose of the research was to devise an accurate method of measuring differential capacitance at a dropping mercury electrode and thence to investigate, for various systems, the variation of double layer capacitance with applied potential and electrode charge, so that the effect of the dielectric constant and other properties of the solvent might be assessed. The thesis is divided into four sections. After a theoretical introduction, Part 1. describes the construction of apparatus for the measurement of the double layer impedance at a dropping mercury electrode. Part 2. is an investigation of certain aspects of the double layer in aqueous solutions, while in Part 3 consideration is made of the effect of solvent variation. Since the impedance of the dropping mercury electrode, which was measured using a transformer ratio-arm bridge, varied with time, it was necessary to know the time interval between the birth of a mercury drop and the instant at which the bridge was balanced. This was achieved as set out in Part 1. by means of an electronic interval timer which measured the period between pulses emitted respectively by a "drop birth detector" and a "bridge balance detector." In Part 2. the factors determining the area of a growing mercury drop at a given time were considered and an accurate method of calculating differential capacitance per unit area was derived. Other aspects of the double layer in aqueous systems which were investigated included the effect of bridge frequency variation and the resistive component of the electrode impedance. A new method of determining differential capacitance was studied which was independent of timing and flow rate measurements. The final section of the thesis, Part 3, is mainly concerned with the results of capacitance measurements of alkali metal chloride solutions in formamide. This solvent has a very high dielectric constant, and it was therefore of interest to compare measurements in it with those for aqueous solutions and for solvents of low dielectric constant such as methanol. Three main points were noted for formamide solutions. First, while there was no capacitance maximum on the anodic side of the charge/capacitance curves such an effect did occur on the eathodic branch. Second, as the electrode charge was increased cathodically, the differential capacitance decreased. Finally, at high cathodic polarisation, the size of the cation had no effect on the differential capacitance. Explanations for these three results are suggested in terms of double layer theory and the molecular structure of formamide.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physical chemistry
Date of Award: 1963
Depositing User: Enlighten Team
Unique ID: glathesis:1963-79486
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 09:04
Last Modified: 05 Mar 2020 09:04
URI: https://theses.gla.ac.uk/id/eprint/79486

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