Preparation of non-precious metal catalysts for PEMFC cathode from pyrolyzed vitamin B12

In this study, the effect of non-precious metal catalysts in the form of pyrolyzed Vitamin B12 that is supported by carbon black on oxygen reduction reaction (ORR) is examined. Pyrolysis was carried out at temperatures of 300 degrees C (py-B12/C-300), 500 degrees C (py-B12/C-500), 700 degrees C (py-B12/C-700) and 900 degrees C (py-B12/C-900) in an N-2-atmosphere. The ring-rotating disk electrode technique revealed that the electron-transfer numbers of py-B12/C-300, py-B12/C-500, py-B12/C-700 and py-B12/C-900 are 3.02, 3.42, 3.90 and 3.57, respectively: py-B12/C-700 exhibits near four-electron transfer. The X-ray absorption spectra demonstrate that during the pyrolysis, as the Co oxidation state of py-B12-700 is changed from Co(III) to Co(II), the Co coordination number changes from 6 to 4, suggesting that the structure is a square-planar Co-N-4 chelate. However, the Co-N-4 chelate is decomposed as the pyrolysis temperature increases to 900 degrees C, resulting in a loss of ORR activity. The H-2-O-2 PEMFC that uses py-B12/C-700 provides excellent performance, substantially outperforming py-CoTMPP/C. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.