Supervisor: Ph.D Kaido Tammeveski
Opponent: Prof. Michael Bron, Institut für Chemie, Martin-Luther-Universität Halle
The electrochemical reduction of oxygen on different nanocarbons and nanocarbon supported metallophthalocyanines and metalloporphyrins has been studied using the rotating disk electrode (RDE) method. The kinetic parameters for this reaction have been determined. The oxygen reduction reaction (ORR) was studied on carbon nanotubes purified in different acids. The RDE results showed that the acid treatment of multi-walled carbon nanotubes (MWCNTs) has strong effect on the electrocatalytic activity for ORR in acid solution and clearly demonstrated the effect of catalyst impurities remained in CNTs on the kinetics of the ORR. MWCNT and double-walled carbon nanotube (DWCNT) modified electrodes were investigated as the catalyst materials for ORR in alkaline media. The results showed that both MWCNTs and DWCNTs have excellent electrocatalytic activity towards the ORR in alkaline solution. The pH-dependence of the ORR and the effect of surfactants on this reaction was studied with MWCNT modified GC electrodes. The pH dependence of the ORR on MWCNT-modified electrodes follows the same trend as that of the unmodified GC electrode. The effect of surfactants on the reduction of O2 on MWCNT/GC electrodes was evident. The electroreduction of oxygen has been studied on different carbon nanomaterials. The results obtained in this part of research indicate that these nanocarbon materials are highly active for the reduction of oxygen in alkaline solution and this activity might be caused by native quinone-type groups on their surface. Metallophthalocyanines and metalloporphyrins were studied as non-noble metal electrocatalysts for ORR in both acid and alkaline media. It was found that metal porphyrin and phthalocyanine-based electrodes heat-treated at 800 °C yielded the highest electrocatalytic activity. Metallophthalocyanine/MWCNT catalysts were also evaluated in anion-exchange membrane fuel cell. The fuel cell performance of the membrane-electrode assemblies with Co phthalocyanine was found to be similar to the commercial Pt/C catalyst. Finally, the reduced graphene oxide (rGO) nanosheets as advanced electrocatalyst supports were prepared. Metallophthalocyanines and metalloporphyrins modified rGO exhibited excellent electrocatalytic properties for ORR in alkaline media.