| Presently Pt and Pt alloys are widely used as anode and cathode materials in Proton Exchange Membrane (PEM) Fuel Cells. Despite a cathodic over potential loss of 20%, Pt and Pt alloys are still preferred for their resistance towards corrosion in acidic media. Pt however, being an expensive metal of low abundance, it is of interest for researchers to develop a corrosion resistant non noble metal substitutes. Development of selective oxygen reduction non noble catalyst is also of interest for Direct Methanol Fuel Cells (DMFC), where methanol cross over and oxidation of methanol at the cathode remains an impeding factor for its commercialization.; In the last few years, several transition metal compounds have been proposed as oxygen reduction reaction (ORR) selective catalyst. Prominent among them are macrocycle based metal containing porphyrin system, chevrel phase type compounds (e.g., Mo4Ru2Se8) and other transition metal chalcogenides. Co based macrocyclic compounds have shown improved activity towards oxygen reduction. However, in addition to their expensive nature, such macrocyclic compounds are highly instable in acidic media. The objective of the present study is to generate MN4 structures from low cost organic precursors with improved activity and stability. Co and Fe based metal catalysts from nitrogen donating organic compounds were synthesized and characterized. Electrochemical characterization was performed in rotation ring disc electrode (RRDE) and fuel cell test conditions. The catalysts synthesized exhibit, four electron reduction of molecular oxygen and improved activity in comparison with other state of art non precious metal catalysts. The effect of metal wt%, metal: nitrogen ratio, heat treatment temperature and nature carbon substrate on the activity and mechanism of oxygen reduction reaction were studied and optimized. Influence of different surface groups on carbon such as N, O and S were studied with the objective of improving the activity and stability of the non noble metal catalysts. The obtained catalysts show comparable performance with ETEK 20% Pt/C catalysts under RRDE test conditions.; On the other hand, toxic materials like hexavalent chrome passivates and cadmium coatings are widely used for corrosion protection of steel. In the present work, novel silica based coatings were prepared by electroless method and surface activation process. Through electroless method, naturally available hemimorphite form of zinc disilicate is reproduced. An adsorption-condensation mechanism was proposed to explain the silica deposition. The nanostructured silica coating showed comparable or better performance than hexavalent chrome passivation. The corrosion performance of sample prepared through surface activation showed two times higher performance than electroless silica and hexavalent chrome. |
