Journal
JOURNAL OF POWER SOURCES
Volume 213, Issue -, Pages 169-179Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jpowsour.2012.04.029
Keywords
Alkaline fuel cell; Oxygen reduction reaction; Non-noble electrocatalyst; Cu; Fe; X-ray absorption spectroscopy
Funding
- Office of Hydrogen, Fuel Cells and Infrastructure Technologies of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Science Foundation [CHE-1129417]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1129417] Funding Source: National Science Foundation
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We synthesized two single-core Fe-N-x/C and Cu-N-x/C electrocatalysts and a bi-core CuFe-N-x/C composite electrocatalyst using iron and copper phthalocyanine-based precursors and a high-temperature pyrolysis method. The morphology, structure, and activity toward the oxygen reduction reaction (ORR) in alkaline media were evaluated for each electrocatalyst by transmission electron microscopy (TEM), X-ray Diffraction (XRD), and the rotating ring-disk electrode (RRDE) method. Although the Cu-N-x/C catalyst showed lower catalytic activity than Fe-N-x/C, the presence of Cu enhanced the ORR performance of bi-core CuFe-N-x/C, as compared to single-core Fe-N-x/C. To fully understand the synergistic effect between Cu and Fe on this enhancement, high resolution X-ray photoelectron spectroscopy (HR-XPS) and soft X-ray absorption spectroscopy (XAS) was employed to study the electronic structure of as-synthesized electrocatalysts. The HR-XPS analysis showed that metal-nitrogen bonding was maintained and that the oxidation states of Fe and Cu were influenced by the presence of the second metal in the bi-core catalyst. The XAS data revealed that a fraction of an electron was transferred from Fe to Cu, which may help to lower the kinetic barrier during the ORR process. Based on our experimental results and four different models, we briefly discuss ORR mechanisms on these metallic catalysts. Published by Elsevier B.V.
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