Abstract
One of the most important needs for the future of low-cost fuel cells is the development of highly active platinum group metal (PGM)-free catalysts. For the oxygen reduction reaction, Fe–N–C materials have been widely studied in both acid and alkaline media. However, reported catalysts in the literature show quite different intrinsic activity and in-cell performance, despite similar synthesis routes and precursors. Here, two types of Fe–N–C are prepared from the same precursor and procedure – the main difference is how the precursor was handled prior to use. It is shown that in one case Fe overwhelmingly existed as highly active single-metal atoms in FeN4 coordination (preferred), while in the other case large Fe particles coexisting with few single metal atoms were obtained. As a result, there were drastic differences in the catalyst structure, activity, and especially in their performance in an operating anion exchange membrane fuel cell (AEMFC). Additionally, it is shown that catalyst layers created from single-atom-dominated Fe–N–C can have excellent performance and durability in an AEMFC using H2/O2 reacting gases, achieving a peak power density of 1.8 W cm−2 – comparable to similar AEMFCs with a Pt/C cathode – and being able to operate stably for more than 100 h. Finally, the Fe–N–C cathode was paired with a low-loading PtRu/C anode electrode to create AEMFCs (on H2/O2) with a total PGM loading of only 0.135 mg cm−2 (0.090 mgPt cm−2) that was able to achieve a very high specific power of 8.4 W mgPGM−1 (12.6 W mgPt−1).
Highlights
Polymer electrolyte membrane fuel cells are a potentially ultralow CO2-emission energy source if fueled with renewablygenerated H2
An anion exchange membrane fuel cell (AEMFC) with best-performing FeeNeC cathode was subjected to a 105 h durability test and the degradation behavior was investigated by electrochemical techniques, post mortem 57Fe Mo€ssbauer spectroscopy, and applying a comprehensive physico-chemical model of the entire membrane electrode assembly (MEA)
While the results shown above with platinum group metal (PGM)-free cathodes are promising, they were obtained with a high PGM anode, containing itself more PGM than many reported proton exchange membrane fuel cells (PEMFCs) MEAs, and higher PGM loading than the Department of Energy (DOE) targets
Summary
Polymer electrolyte membrane fuel cells are a potentially ultralow CO2-emission energy source if fueled with renewablygenerated H2. Huang et al have achieved a peak power density of 3.5 W cmÀ2 for an AEMFC with H2/O2 gas feeds and electrodes based on PGMs [8], while UlHassan et al reported a high-performing cell with a decay rate of only ca 15 mV hÀ1 over more than 2000 h of operation [9]. These recent accomplishments have been obtained with high PGM loadings at both the anode and cathode electrodes. An AEMFC with best-performing FeeNeC cathode was subjected to a 105 h durability test and the degradation behavior was investigated by electrochemical techniques, post mortem 57Fe Mo€ssbauer spectroscopy, and applying a comprehensive physico-chemical model of the entire MEA
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