Elucidating Synergistic Effects of Different Metal Ratios in Bimetallic Fe/Co-N-C Catalysts for Oxygen Reduction Reaction

Lowering or eliminating the noble-metal content in oxygen reduction fuel cell catalysts could propel the large-scale introduction of commercial fuel cell systems. Several noble-metal free catalysts are already under investigation with the metal-nitrogen-carbon (Me-N-C) system being one of the most promising. In this study, a systematic approach to investigate the influence of metal ratios in bimetallic Me-N-C fuel cells oxygen reduction reaction (ORR) catalysts has been taken. Different catalysts with varying ratios of Fe and Co have been synthesized and characterized both physically and electrochemically in terms of activity, selectivity and stability with the addition of an accelerated stress test (AST). The catalysts show different electrochemical properties depending on the metal ratio such as a high electrochemical mass activity with increasing Fe ratio. Properties do not change linearly with the metal ratio, with a Fe/Co ratio of 5:3 showing a higher mass activity with simultaneous higher stability. Selectivity indicators plateau for catalysts with a Co content of 50% metal ratio and less, showing the same values as a monometallic Co catalyst. These findings indicate a deeper relationship between the ratio of different metals and physical and electrochemical properties in bimetallic Me-N-C catalysts.

Automated summary

This study investigates the influence of metal ratios in bimetallic Me-N-C fuel cell oxygen reduction reaction catalysts by synthesizing and characterizing catalysts with varying Fe and Co ratios. The results show that the electrochemical properties of the catalysts depend on the metal ratio, with a Fe/Co ratio of 5:3 displaying higher mass activity and stability. Selectivity indicators plateau for catalysts with a Co content of 50% metal ratio and less, indicating a deeper relationship between different metal ratios and physical and electrochemical properties in bimetallic Me-N-C catalysts.