Nitrogen doped CNT structures as co-Catalysts for Oxygen Reduction

Palaniappan Subramanian, Department of Biological Chemistry, Ariel University, Ariel, Israel
Asaf Cohen, Department of Biological Chemistry, Ariel University, Ariel, Israel
Daniel Nessim, Department of Chemistry, Bar Ilan University, Ramat Gan, Israel
Eti Teblum, Department of Chemistry, Bar Ilan University, Ramat Gan, Israel
Alex Schechter, Department of Biological Chemistry, Ariel University, Ariel, Israel

Oxygen reduction catalysts (ORC) are critical materials in the development of fuel cells and metal air batteries. Current state of the art, Pt-based catalysts are very costly and demonstrate limited long term stability. It has been reported that carbonization of macrocyclic transition metals molecules (e.g. Iron/Cobalt phthalocyanine) can lead to the formation of highly active ORC.  Although the origin of this activity is not clear, it was suggested that mixed metal-nitrogen and metal-carbon structures formed in the carbonization process are involved in the catalytic active site. However, the density of the active sites in these materials is too low for practical air electrodes. In this context, we have developed a simple and rapid procedure to prepare nitrogen-doped vertically aligned carbon nanotube carpets (VA-NCNTs). The VA-NCNTs were obtained by nitrogen plasma treatment of vertically aligned multi-walled carbon nanotube carpets (VA-CNTs) grown on stainless steel substrate by chemical vapour deposition. This novel electrochemical interface reduces oxygen in lower over potential under basic condition (onset of -0.12 V vs.Ag/AgCl at pH 13) when compared to untreated VA-CNTs condition (onset of -0.22 V vs.Ag/AgCl at pH 13). The robustness of these nanostructures and ease of formation makes VA-NCNTs a promising non-platinum oxygen reduction catalyst that could be employed during real time alkaline fuel cell operation.