|M.Sc Student||Landau Elena|
|Subject||Metallocorroles as Catalysts for Energy Relevant Processes|
|Department||Department of Chemistry||Supervisor||Professor Zeev Gross|
|Full Thesis text|
Finite amount of fossil fuel and their rapid consumption are only partial reasons for the growing attention to the development of energy conversion technologies like fuel cells, in which oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) have an important role. The best catalysts for these reactions are based on Pt， but the low abundance and high cost of this metal raises serious concerns regarding the feasibility and availability of platinum for large scale production. The consequential quest for low-cost alternatives to platinum catalysts led to intensive developing efforts regarding non-precious metal catalysts, among them transition metal complexes of corroles.
This thesis describes the effort to improve the already very active metallocorrole catalysts by electropolymerization of the appropriate monomers. The hypothesis was that the polymeric structure will lead to higher concentration of active sites, and that the short distance between them will result in cooperative effects. For fulfilling this task, a series of new cobalt (III) corroles were prepared, which differ from each other by the number of aniline moieties present on the meso-carbon atoms of the corrole. All complexes were fully characterized by a variety of spectroscopic methods . The cyclic voltammetry (CV) method was used for electropolymerization of these metal complexes on electrodes in organic solvent. The same method was used to explore the ability of the modified electrodes catalysts for reduction of H and O2 and to compare their efficiency to each other, relative to bare glassy carbon (GC) electrode and to solubilized metallocorroles. Successful electropolymerization was obtained when at least two aniline groups were present on the corrole ring.
Exploration of catalytic activity of the modified electrodes regarding ORR was performed in 0.1 M H2SO4. In Argon saturated solution no catalytic activity was observed. When the solution was saturated with oxygen cathodic peaks appeared at 0.3 V and 0.4 V onset potentials for poly-Co-dianiline and poly-Co-trianiline coated GC electrodes, respectively. No catalytic activity was observed with the bare GC electrode, even in the presence of solubilized Co-complexes, under the same experimental conditions,
Oxygen reduction reactions are most frequently characterized by two competing reaction, the direct four electron reduction to water and the two electron reduction to peroxide. Among other factors the preferred pathway depends also on the surface configuration of the catalyst. To determine which pathways is preferred and compare the surface morphology influence, the rotating ring disk electrode methodology was applied. The poly-Co-trianiline GC coated electrode was compared with a differently modified GC electrode: the obtained onset potentials were 0.72 V and 0.55 V, respectively. Percentage of H2O2 generated during ORR and the total electron transfer number for both electrodes were calculated. The results showed that the poly-Co-trianiline modified electrode is more efficient for ORR than the other electrode. This finding supports the hypothesis.
Opposite results were obtained for the hydrogen evolution catalysis: the modified electrodes were less active towards HER than the bare GC electrode and solubilized metallocorroles.