Controlling the Active Sites of Sulfur‐Doped Carbon Nanotube–Graphene Nanolobes for Highly Efficient Oxygen Evolution and Reduction Catalysis |
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Authors: | Abdelhamid M. El‐Sawy Islam M. Mosa Dong Su Curtis J. Guild Syed Khalid Raymond Joesten James F. Rusling Steven L. Suib |
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Affiliation: | 1. Department of Chemistry, University of Connecticut, Storrs, CT, USA;2. Institute of Materials Science, University of Connecticut, Storrs, CT, USA;3. Department of Chemistry, Faculty of Science, Tanta University, Tanta, Egypt;4. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA;5. Photon Science Directorate, Brookhaven National Laboratory, Upton, NY, USA;6. Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT, USA |
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Abstract: | Controlling active sites of metal‐free catalysts is an important strategy to enhance activity of the oxygen evolution reaction (OER). Many attempts have been made to develop metal‐free catalysts, but the lack of understanding of active‐sites at the atomic‐level has slowed the design of highly active and stable metal‐free catalysts. A sequential two‐step strategy to dope sulfur into carbon nanotube–graphene nanolobes is developed. This bidoping strategy introduces stable sulfur–carbon active‐sites. Fluorescence emission of the sulfur K‐edge by X‐ray absorption near edge spectroscopy (XANES) and scanning transmission electron microscopy electron energy loss spectroscopy (STEM‐EELS) mapping and spectra confirm that increasing the incorporation of heterocyclic sulfur into the carbon ring of CNTs not only enhances OER activity with an overpotential of 350 mV at a current density of 10 mA cm?2, but also retains 100% of stability after 75 h. The bidoped sulfur carbon nanotube–graphene nanolobes behave like the state‐of‐the‐art catalysts for OER but outperform those systems in terms of turnover frequency (TOF) which is two orders of magnitude greater than (20% Ir/C) at 400 mV overpotential with very high mass activity 1000 mA cm?2 at 570 mV. Moreover, the sulfur bidoping strategy shows high catalytic activity for the oxygen reduction reaction (ORR). Stable bifunctional (ORR and OER) catalysts are low cost, and light‐weight bidoped sulfur carbon nanotubes are potential candidates for next‐generation metal‐free regenerative fuel cells. |
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Keywords: | bifunctional catalysts metal‐free catalysis oxygen evolution reaction oxygen reduction reaction nanolobes |
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