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Degree

Doctor of Philosophy, Case Western Reserve University, Chemistry, 1993.

Abstract

The objective of this thesis research has been to study the electrochemical and electrocatalytic properties of lithiated nickel oxide. The major reaction studied in the present research was O₂ reduction. Lithiated nickel oxide was used both as the catalyst for O₂ reduction and as a catalyst support for platinum. The properties of transition metal macrocycles as O₂ reduction catalysts were also examined on lithiated nickel oxide and other oxides. The first part of this work involved the synthesis of different forms of lithiated nickel oxides, including mosaic crystals with (100) faces, air-grown films and powder samples. The physical and chemical properties of these samples were characterized, including surface morphology, surface area and conductivity. The intrinsic electrochemical properties were also studied, using cyclic voltammetry both in acid and alkaline solution. The second part of this work involved the examination of O₂ reduction on lithiated nickel oxide at different temperatures. In alkaline solution, O₂ reduction proceeds at significant rates on this electrocatalyst but does not do so in acid solution. At room temperature, O₂ reduction proceeds via a two electron reduction pathway, with peroxide as the product. At elevated temperatures, O 2 reduction becomes much more active, and a nearly four electron reduction process was achieved when the temperature approached to ∼200°C. The third part of this work involved the examination of lithiated nickel oxide as a catalyst support for Pt. At room temperature on single crystal-like mosaic crystal electrodes, it was found that the Pt/(Li)NiO junction plays an inhibiting role in the electrochemical reduction process due to the p-type character of (Li)NiO. However, at elevated temperatures and on powdered samples (having more defects on the surfaces), lithiated nickel oxide shows promising performance as a support for Pt. The fourth part of this work involved the study of the behavior of the O₂ reduction catalyst CoTsPc (cobalt tetrasulfonated phthalocyanine) on lithiated nickel oxide. It was found that CoTsPc does not irreversibly adsorb on lithiated nickel oxide and other oxides in contrast to graphite. The well-defined solution-phase redox couples of CoTsPc were found on tin-doped indium oxide (ITO) electrode, while some of these redox couples (e.g. ligand oxidation) could not be observed on (Li)NiO due to the p-type semiconducting properties. RDE studies showed that CoTsPc in solution phase is still O₂ reduction active and the reduction process follows a two-electron pathway, producing peroxide. In conclusion, lithiated NiO is a good catalyst for O₂ reduction at elevated temperatures and is a promising catalyst support for Pt.

Subject Headings

Chemistry, Physical

Keywords

Oxygen reduction lithiated nickel oxide catalyst catalyst support

Advisor

Ernest B. Yeager

Pages

203p.

Document number: case1057093196
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1057093196

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