Abstract
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.
Highlights
In the fight against climate change, green technologies are crucial and hydrogen is a promising alternative energy carrier to fossil fuels [1,2]
Different catalysts have been synthesized through heat-treatment of a carbon support impregnated by a nitrogen and metal precursor
These catalysts are investigated by different physical analysis techniques to elucidate synergistic effects of the metal ratio during synthesis
Summary
In the fight against climate change, green technologies are crucial and hydrogen is a promising alternative energy carrier to fossil fuels [1,2]. The conversion of chemical energy stored in hydrogen gas to electrical energy is a technological challenge, for which the proton-exchange membrane fuel cell (PEMFC) is a suitable prospect [3,4,5,6]. It converts hydrogen and oxygen gas to water under the production of heat and electricity [3]. These catalysts in state-of-the-art PEMFC are predominantly comprised of Pt-nanoparticles supported on carbon blacks like Vulcan. The long-term durability under operation remains a major challenge for these catalysts [3,8]
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