Synthesis, Electrochemistry, and Physical Studies of Graphite Electrodes with Chemically Modified surfaces and Copper Complexes with Macrocyclic Ligands

Author: Koval, Carl Anthony

Year: 1979

Degree: Dissertation (Ph.D.)

Advisors: Anson, Fred C.; Gagné, Robert R.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/smpc-8t32

Abstract

The attachment of various molecules to graphite surfaces and the electrochemistry exhibited by the attached species are discussed in Part I.

Section I-A

Aromatic compounds such as 9,10-phenanthrenequinone are irreversibly adsorbed onto pyrolytic graphite electrodes. Cyclic voltammetry is used to illustrate the differences in electrochemical reJponse between surface and solution species. Integration of the current used to oxidize or reduce the molecules on the surface affords measurement of surface concentrations, which are typically 10-10 to 10-11 moles/cm2. The use of differential pulse voltammetry to study surface electrochemistry is introduced.

Section I-B

Procedures are presented for attaching pyridinepentaammineruthenium{II) complexes to graphite electrodes by covalent bonding and irreversible ad sorption. Cyclic voltammetry and differential pulse voltammetry are used to compare the electrochemical behavior of the attached complexes and to measure surface concentrations . Different orientations of the anisotropic graphite affect the quantity of reactant that can be attached as well as the voltammetric responses. On "edge plane" pyrolytic graphite the covalently bound and irreversibly adsorbed ruthenium complexes reach coverages 0f 1.5 x 10-10 and 1.6 x 10-9 moles/cm2, respectively. The coverage for the adsorbed complex on "basal plane" graphite is 3.5 x 10-10 moles/cm2. The covalent attachment procedure is unsuccessful on this surface, presumably due to the lack of surface oxides. Attachment by irreversible adsorption yields larger quantities of complex on the electrode surface but the covalently attached complex persists on the surface for a longer time; t1/2 = 313 and 1080 min, respectively.

Section I-C

The catalytic reduction of oxygen in acidic aqueous solution at several modified pyrolytic graphite surfaces is examined using a rotating ring-disc electrode. Surfaces coated with 9,10-phenanthrenequinone and Ru(III)(edta) afford no catalysis. Adsorbed Fe(III) protoporphyrin IX catalyzes the reduction of oxygen to water at ~0.2 V. Catalytic properties of modified graphite and platinum surfaces are compared .

The synthesis, electrochemistry and physical properties of a variety of Cu(II) and Cu(I) complexes are presented in Part II. The physical studies reveal several unusual properties of the Cu(I) complexes.

Section II-A

Measurements of formal reduction potentials are compared for several inorganic systems using cyclic voltammetry, d.c. polarography, differential pulse voltammetry, and potentiometry. For the type of copper complexes being studied, d.c. polarography is judged to be the most reliable technique, especially in the electrochemical m~asurement of CO binding constants. The potential of the oxidation of ferrocene to ferricenium ion is suggested as a practical reference against which to report the potentials of other couples.

Section II-B

The synthesis of an oxo-bridged copper(II)-copper(I) mixed- valence ion and its carbon monoxide adduct is reported along with preliminary observations concerning electronic and electron paramagnetic resonance spectra of the ions.

Section II-C

More complete physical studies of the mixed-valence system introduced in Section II-B are presented. Electrochemistry is used to synthesize the copper(I)-copper(I) state of the molecule and to obtain formal reduction potentials (-0.518 V and -0.908 V) for the two copper atoms. The CO binding constant for the copper(II)-copper(I) complex is measured polarographically and found to be 2.82 x 104. All complexes are characterized by elemental analysis, infrared spectroscopy, magnetic susceptibility and electronic spectroscopy. Temperature-dependent electron paramagnetic resonance spectra of the mixed- valence complex provide an estimated intramolecular electron transfer rate of 2.2 x 1010 sec-1 at 298°K.

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