1. Octahedral spinel electrocatalysts for alkaline fuel cells.
- Author
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Yao Yang, Yin Xiong, Holtz, Megan E., Xinran Feng, Rui Zeng, Chen, Gary, DiSalvo, Francis J., Muller, David A., and Abruña, Héctor D.
- Subjects
ALKALINE fuel cells ,SCANNING transmission electron microscopy ,FUEL cells ,ELECTROCATALYSTS ,OXYGEN reduction - Abstract
Designing high-performance nonprecious electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) has been a key challenge for advancing fuel cell technologies. Here, we report a systematic study of 15 different AB
2 O4 /C spinel nanoparticles with well-controlled octahedral morphology. The 3 most active ORR electrocatalysts were MnCo2 O4 /C, CoMn2 O4 /C, and CoFe2 O4 /C. CoMn2 O4 /C exhibited a half-wave potential of 0.89 V in 1 M KOH, equal to the benchmark activity of Pt/C, which was ascribed to charge transfer between Co and Mn, as evidenced by X-ray absorption spectroscopy. Scanning transmission electron microscopy (STEM) provided atomic-scale, spatially resolved images, and high-energy-resolution electron-loss near-edge structure (ELNES) enabled fingerprinting the local chemical environment around the active sites. The most active MnCo2 O4 /C was shown to have a unique Co-Mn core–shell structure. ELNES spectra indicate that the Co in the core is predominantly Co2.7+ while in the shell, it is mainly Co2+ . Broader Mn ELNES spectra indicate less-ordered nearest oxygen neighbors. Co in the shell occupies mainly tetrahedral sites, which are likely candidates as the active sites for the ORR. Such microscopic-level investigation probes the heterogeneous electronic structure at the single-nanoparticle level, and may provide a more rational basis for the design of electrocatalysts for alkaline fuel cells. [ABSTRACT FROM AUTHOR]- Published
- 2019
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