Oxygen reduction catalysts for polymer electrolyte fuel cells from the pyrolysis of various transiti
JOURNAL OF NEW MATERIALS FOR ELECTROCHEMICAL SYSTEMS Volume: 2 Issue: 4 Pages: 243-251 Published: OCT 1999
Various transition metal(II) acetates (Cr, Mn, Fe, Co, Ni, and Cu) have been adsorbed on perylenetetracarboxylic dianhydride (PTCDA) then pyrolyzed at 900 degrees C in Ar : H-2 : NH3 ambient. For each material, the electrocatalytic activity for the reduction of oxygen has been measured by rotating disk electrode. The catalytic activity increases according to the following sequence: Mn- < Cr- < Co- < Fe-based materials. For each metal, the electrocatalytic activity rises quickly with the metal content up to about 5000 ppm, then saturates. Ni- and Cu-based materials do not catalyse the electroreduction of oxygen. The performance of the catalysts have also been tested in H-2/O-2 fuel cells at 80 degrees C. For the Cr-, Mn, Fe- and Co-based catalysts, XPS measurements at the N1s edge indicate the occurrence of an interaction between pyridinic type nitrogens and the metal in an oxidized state. A similar but less important interaction is also observed for nitrile type nitrogens. These interactions do not exist for Ni and Cu-based materials.