Electrode double layer measurements and voltammetry of some organosulfur compounds in sulfolane Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3r074x481

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  • A new pulse method for measuring differential double layer capacitances has been developed in this work. The technique is based on the determination of the cell time constant which, for an ideally polarized test electrode-solution interface, is composed of the double layer capacitance and solution resistance. By applying small step voltage changes to a cell, an exponentially decaying current due to the charging of the double layer is observed. A propagation of errors analysis indicated that when the charging current had decayed to 50-25% of its peak value the maximum relative precision in the double layer capacitance could be achieved. The pulse capacitance technique was implemented using a three-electrode potentiostat of conventional design built with integrated circuit operational amplifiers. The instrumentation and technique were tested on cell circuit RC analogs and the accuracy of the capacitance measurements was within the precision of the measurement themselves, ± 3%. Double layer capacitance measurements made on a Hg-1. 0 M KC1 interface yielded results that agreed within experimental error with the accepted literature values. The method was used to determine the double layer capacitancepotential curves for interfaces formed between electrodes of various materials and solutions of 0.10 M tetraethylammonium perchlorate in sulfolane. The simple RC model of the double layer was not applicable for these interfaces and a more complex model for the double layer was assumed which allowed for a small faradaic current to flow. Except for a capacity hump anodic of the potential of zero charge, the capacitance-potential curve for mercury in sulfolane is similar in shape to those obtained for the electrode in other nonaqueous solvents. The value of the capacity maximum is about 30 μf/cm². The capacity-potential curve was integrated by numerical summation to give the surface charge density and interfacial tension relative to the maximum value as a function of electrode potential. The parabolic relationship between interfacial tension and electrode potential was checked and found to agree closely with results obtained from polarographic drop time measurements. Capacitance-potential curves were also measured for gold, glassy carbon, and platinum. The double layer capacitances for these electrodes were usually higher than for mercury and had larger faradaic current corrections. Some of the advantages of the capacitance technique over the AC bridge technique are that the method is applicable to solutions of both high and low conductivities and that correction in the capacitance determination can be made for a non-ideally polarized interface. The technique can be implemented using instrumentation commonly used for fast scan voltammetry, thus not requiring a special instrument useful only for double layer capacitances. The voltammetric potential ranges accessible in sulfolane with tetrathylammonium perchlorate supporting electrolyte are very large. The range available with mercury is +0.1 to -3.3 v, while for gold, glassy carbon, and platinum the ranges are +1.2 to -3.2, +1.3 to -3.3 and +1.6 to -3.0 v as measured with respect to a silver-silver ion reference electrode in the solvent. Voltammetric waves were observed for n-butyl mercaptan, -sulfide, -disulfide and phenyl disulfide. The substances gave reasonably well-defined peaks with characteristic peak potentials. Anodic waves were observed for the mercaptan and sulfide on gold, glassy carbon and platinum electrodes. Cathodic waves were observed for butyl disulfide. All electrode reactions involving the aliphatic sulfur compounds appeared irreversible. Phenyl disulfide could be reversibly reduced on mercury.
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  • File scanned at 300 ppi (Monochrome, 256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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