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Transition metal electrocatalysts encapsulated into N-doped carbon nanotubes on reduced graphene oxide nanosheets: efficient water splitting through synergistic effects


Wan, Wenchao; Wei, Shiqian; Li, Jingguo; Triana, Carlos A; Zhou, Ying; Patzke, Greta R (2019). Transition metal electrocatalysts encapsulated into N-doped carbon nanotubes on reduced graphene oxide nanosheets: efficient water splitting through synergistic effects. Journal of Materials Chemistry A, 7(25):15145-15155.

Abstract

The development of efficient noble-metal free electrocatalysts is crucial for clean hydrogen production through water splitting. As carbon-based supports are expected to play a major role in low cost electrocatalysis, improved synthetic methods and a deeper understanding of their mechanisms of action are now required. To this end, we synthesized transition metal catalysts for overall water splitting encapsulated into nitrogen-doped carbon nanotubes (M–N-CNTs, M = Ni, Co, Fe) through a direct and convenient pyrolysis of bulk g-C3N4. Furthermore, the addition of reduced graphene oxide (rGO) leads to a significant dispersion of the catalytic N-CNTs. Among the obtained catalyst series, NiFe–N-CNT with rGO (NiFe–N-CNT–rGO) exhibits extremely low overpotential of 270 mV (on glassy carbon) for the oxygen evolution reaction (OER) at a current density of 10 mA cm−2. This performance is superior to most of the previously reported noble metal-free catalysts for OER. Our comprehensive study unravels that the growth of CNTs follows a “reduction–nucleation–growth” process. The thermally reduced metallic nanoparticles (NPs) serve as nucleation sites of carbon species on their surface to further promote N-CNT growth. Density functional theory (DFT) calculations reveal that the CNT walls and N-dopants in the catalysts modify the electronic structure and adjust the free energy toward the adsorption of intermediates. The one-step hydrogen evolution reaction (HER) process is influenced more strongly by N-centers when compared to the four-electron transfer OER process. The scalable and straightforward synthesis together with excellent electrocatalytic performance renders the NiFe–N-CNT–rGO hybrid catalyst quite promising for large-scale water splitting applications.

Abstract

The development of efficient noble-metal free electrocatalysts is crucial for clean hydrogen production through water splitting. As carbon-based supports are expected to play a major role in low cost electrocatalysis, improved synthetic methods and a deeper understanding of their mechanisms of action are now required. To this end, we synthesized transition metal catalysts for overall water splitting encapsulated into nitrogen-doped carbon nanotubes (M–N-CNTs, M = Ni, Co, Fe) through a direct and convenient pyrolysis of bulk g-C3N4. Furthermore, the addition of reduced graphene oxide (rGO) leads to a significant dispersion of the catalytic N-CNTs. Among the obtained catalyst series, NiFe–N-CNT with rGO (NiFe–N-CNT–rGO) exhibits extremely low overpotential of 270 mV (on glassy carbon) for the oxygen evolution reaction (OER) at a current density of 10 mA cm−2. This performance is superior to most of the previously reported noble metal-free catalysts for OER. Our comprehensive study unravels that the growth of CNTs follows a “reduction–nucleation–growth” process. The thermally reduced metallic nanoparticles (NPs) serve as nucleation sites of carbon species on their surface to further promote N-CNT growth. Density functional theory (DFT) calculations reveal that the CNT walls and N-dopants in the catalysts modify the electronic structure and adjust the free energy toward the adsorption of intermediates. The one-step hydrogen evolution reaction (HER) process is influenced more strongly by N-centers when compared to the four-electron transfer OER process. The scalable and straightforward synthesis together with excellent electrocatalytic performance renders the NiFe–N-CNT–rGO hybrid catalyst quite promising for large-scale water splitting applications.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
08 Research Priority Programs > Solar Light to Chemical Energy Conversion
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > General Chemistry
Physical Sciences > Renewable Energy, Sustainability and the Environment
Physical Sciences > General Materials Science
Language:English
Date:1 January 2019
Deposited On:07 Feb 2020 15:05
Last Modified:29 Jul 2020 14:00
Publisher:Royal Society of Chemistry
ISSN:2050-7488
OA Status:Hybrid
Publisher DOI:https://doi.org/10.1039/c9ta03213d
Project Information:
  • : FunderSNSF
  • : Grant IDCRSII2_160801
  • : Project TitlePhotocatalytic Processes at Solvated Interfaces

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