Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt‐free and Fe‐free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high‐performance nitrogen‐coordinated single Co atom catalyst is derived from Co‐doped metal‐organic frameworks (MOFs) through a one‐step thermal activation. Aberration‐corrected electron microscopy combined with X‐ray absorption spectroscopy virtually verifies the CoN4coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half‐wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe‐based catalysts and 60 mV lower than Pt/C ‐60 μg Pt cm−2). Fuel cell tests confirm that catalyst activity and stability can translate to high‐performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well‐dispersed CoN4active sites embedded in 3D porous MOF‐derived carbon particles, omitting any inactive Co aggregates.
Fe‐N‐C single‐atom catalysts (SACs) are emerging as a promising class of electrocatalysts for the oxygen reduction reaction (ORR) to replace Pt‐based catalysts. However, due to the limited loading of Fe for SACs and the inaccessibility of internal active sites, only a small portion of the sites near the external surface are able to contribute to the ORR activity. Here, this work reports a metal–organic framework‐derived Fe‐N‐C SAC with a hierarchically porous and concave nanoarchitecture prepared through a facile but effective strategy, which exhibits superior electrocatalytic ORR activity with a half‐wave potential of 0.926 V (vs RHE) in alkaline media and 0.8 V (vs RHE) in acidic media while maintaining excellent stability. The superior ORR activity of the as‐designed catalyst stems from the unique architecture, where the hierarchically porous architecture contains micropores as Fe SAC anchoring sites, meso‐/macro‐pores as accessible channels, and concave shell for increasing external surface area. The unique architecture has dramatically enhanced the utilization of previously blocked internal active sites, as confirmed by a high turnover frequency of 3.37 s−1and operando X‐ray absorption spectroscopy analysis with a distinct shift of adsorption edge.
more » « less- Award ID(s):
- 1742828
- PAR ID:
- 10445013
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 18
- Issue:
- 30
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for the oxygen reduction reaction (ORR). Here we report a composite ORR catalyst consisting of ordered intermetallic Pt-alloy nanoparticles attached to an N-doped carbon substrate with atomically dispersed Fe–N–C sites, demonstrating substantially enhanced catalytic activity and durability, achieving a half-wave potential of 0.923 V ( vs. RHE) and negligible activity loss after 5000 cycles of an accelerated durability test. The composite catalyst is prepared by deposition of Pt nanoparticles on an N-doped carbon substrate with atomically dispersed Fe–N–C sites derived from a metal–organic framework and subsequent thermal treatment. The latter results in the formation of core–shell structured Pt-alloy nanoparticles with ordered intermetallic Pt 3 M (M = Fe and Zn) as the core and Pt atoms on the shell surface, which is beneficial to both the ORR activity and stability. The presence of Fe in the porous Fe–N–C substrate not only provides more active sites for the ORR but also effectively enhances the durability of the composite catalyst. The observed enhancement in performance is attributed mainly to the unique structure of the composite catalyst, as confirmed by experimental measurements and computational analyses. Furthermore, a fuel cell constructed using the as-developed ORR catalyst demonstrates a peak power density of 1.31 W cm −2 . The strategy developed in this work is applicable to the development of composite catalysts for other electrocatalytic reactions.more » « less
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Abstract To produce efficient ORR catalysts with low Pt content, PtNi porous films (PFs) with sufficiently exposed Pt active sites were designed by an approach combining electrochemical bottom‐up (electrodeposition) and top‐down (anodization) processes. The dynamic oxygen‐bubble template (DOBT) programmably controlled by a square‐wave potential was used to tune the catalyst morphology and expose Pt active facets in PtNi PFs. Surface‐bounded species, such as hydroxyl (OH*, *=surface site) on the exposed PtNi PFs surfaces were adjusted by the applied anodic voltage, further affecting the dynamic oxygen (O2) bubbles adsorption on Pt. As a result, PtNi PF with enriched Pt(111) facets (denoted as Pt3.5 %Ni PF) was obtained, showing prominent ORR activity with an onset potential of 0.92 V (vs. RHE) at an ultra‐low Pt loading (0.015 mg cm−2).
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Abstract To produce efficient ORR catalysts with low Pt content, PtNi porous films (PFs) with sufficiently exposed Pt active sites were designed by an approach combining electrochemical bottom‐up (electrodeposition) and top‐down (anodization) processes. The dynamic oxygen‐bubble template (DOBT) programmably controlled by a square‐wave potential was used to tune the catalyst morphology and expose Pt active facets in PtNi PFs. Surface‐bounded species, such as hydroxyl (OH*, *=surface site) on the exposed PtNi PFs surfaces were adjusted by the applied anodic voltage, further affecting the dynamic oxygen (O2) bubbles adsorption on Pt. As a result, PtNi PF with enriched Pt(111) facets (denoted as Pt3.5 %Ni PF) was obtained, showing prominent ORR activity with an onset potential of 0.92 V (vs. RHE) at an ultra‐low Pt loading (0.015 mg cm−2).
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