Comparing Novel PGM-Free, Platinum, and Alloyed Platinum Catalysts for HT-PEMFCs

Abstract

Electrochemical Impedance Spectroscopy (EIS) constitutes a well-established method for characterizing the losses in a polymer electrolyte membrane fuel cell (PEMFC). However, without further analysis, the EI spectrum yields only quantitative insight into the mechanism and contribution of each of the losses in the fuel cell. The distribution of relaxation times (DRT) method allows the quantification of each process contributing to the performance loss in the cell. The application of aforementioned methods for various catalysts allows the explanation of performance differences of the investigated catalysts based on the respective contribution of each major loss mechanism. We tested a platinum (Pt) catalyst, a platinum-cobalt (Pt3Co) alloy catalyst, and a platinum group metal (PGM) free iron-nitrogen-carbon (Fe-N-C) catalyst and found that the Oxygen Reduction Reaction (ORR) is not the dominant loss factor. Against our expectation, the mass transport loss in the PGM-free catalyst is severely dominating. The higher performance of the alloy catalyst can be explained by both, an improved mass transport and a lower ORR resistivity.