Optimizing catalyst loading in non-noble metal electrocatalyst layer to improve oxygen reduction reaction activity

Carbon-supported non-noble metal catalysts with Fe as the metal and tripyridyl triazine (TPTZ) as the ligand (Fe-TPTZ/C), synthesized through a heat treatment process at 900 degrees C, were employed to coat an electrode surface and form catalyst layers in order to optimize their catalyzed ORR activity. The formed catalyst layers containing different catalyst loads of 100, 200, 300, 400, 500, and 600 mu g.cm(-2) were tested using both rotating disk electrode and rotating ring disk electrode techniques. It was found that as the electrode catalyst loading increased, the ORR activity rose monotonically in the loading range of 100 to 500 mu g.cm(-2), then reached a saturation point with higher catalyst loading, indicating that raising the electrode catalyst loading could effectively improve the catalyst's ORR activity. In addition, the overall ORR electron transfer numbers for Fe-N-x/C catalysts were found to be in the range of 3.7-3.9 at different loadings, suggesting that the ORR process was mainly dominated by a four-electron transfer pathway to produce water. (C) 2011 Published by Elsevier B.V.