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Highly efficient oxygen reduction electrocatalysts based on winged carbon nanotubes.

Cheng Y, Zhang H, Varanasi CV, Liu J - Sci Rep (2013)

Bottom Line: We found that the outer-walls of a special type of carbon nanotubes/nanofibers, when selectively oxidized, unzipped and exfoliated, form graphene wings strongly attached to the inner tubes.After doping with nitrogen, the winged nanotubes exhibited outstanding activity toward catalyzing the ORR through the four-electron pathway with excellent stability and methanol/carbon monoxide tolerance.While the doped graphene wings with high active site density bring remarkable catalytic activity, the inner tubes remain intact and conductive to facilitate electron transport during electrocatalysis.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemistry, Duke University, Durham, NC 27708 United States [2] Center for the Environmental Implication of NanoTechnology (CEINT), Duke University, Durham, NC 27708 United States.

ABSTRACT
Developing electrocatalysts with both high selectivity and efficiency for the oxygen reduction reaction (ORR) is critical for several applications including fuel cells and metal-air batteries. In this work we developed high performance electrocatalysts based on unique winged carbon nanotubes. We found that the outer-walls of a special type of carbon nanotubes/nanofibers, when selectively oxidized, unzipped and exfoliated, form graphene wings strongly attached to the inner tubes. After doping with nitrogen, the winged nanotubes exhibited outstanding activity toward catalyzing the ORR through the four-electron pathway with excellent stability and methanol/carbon monoxide tolerance. While the doped graphene wings with high active site density bring remarkable catalytic activity, the inner tubes remain intact and conductive to facilitate electron transport during electrocatalysis.

No MeSH data available.


Related in: MedlinePlus

Electrocatalytic activity of the N-wNT catalyst: (a) CV curves acquired at 100 mV/s in O2 or Ar saturated 0.1 M KOH. (b) Rotating-disk voltammograms in O2-saturated 0.1 M KOH acquired at 10 mV/s and different rotating speeds. (c) Koutecky-Levich plots of J−1 versus ω−1/2 at different electrode potentials, the inserted image shows estimated number of electrons transferred at different potentials. (d) Comparison of the RDE voltammograms for catalysts with different structure and composition as specified (all acquired at 1600 rpm and 10 mV/s).
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f3: Electrocatalytic activity of the N-wNT catalyst: (a) CV curves acquired at 100 mV/s in O2 or Ar saturated 0.1 M KOH. (b) Rotating-disk voltammograms in O2-saturated 0.1 M KOH acquired at 10 mV/s and different rotating speeds. (c) Koutecky-Levich plots of J−1 versus ω−1/2 at different electrode potentials, the inserted image shows estimated number of electrons transferred at different potentials. (d) Comparison of the RDE voltammograms for catalysts with different structure and composition as specified (all acquired at 1600 rpm and 10 mV/s).

Mentions: We performed cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements in 0.1 M KOH to assess the catalytic activity of N-wNT material that had been deposited onto a glassy carbon electrode. The N-wNT catalyst exhibited a symmetrical and rectangular CV curve when the electrolyte was saturated with Ar (Figure 3a). In strong contrast, a pronounced catholic ORR peak with an onset potential of ~ 0.91 V versus reversible hydrogen electrode (RHE) was observed in O2 saturated electrolyte. Noticeably, the ORR peak is much stronger with more positive onset voltage than most of the metal-free catalyst developed152628, suggesting large surface area of winged nanotubes. The high ORR activity is also evident from its onset potential (~0.93 V) and half-wave potential (~0.79 V) in the RDE polarization curve (Figure 3b). The corresponding Koutecky-Levich plot (J−1 vs ω−1/2) obtained on the basis of analyzing the RDE curves of different electrode rotating speeds (in rpm, Figure 3b) at various potentials exhibited excellent linearity (Figure 3c). The average number of electrons transferred per oxygen molecule involved in the ORR can be analyzed on the basis of the Koutecky-Levich equations (Supporting Information)8. The number of electrons transferred were determined to be all around 4 at different potentials examined (Figure 3c, inserted), demonstrating N-wNT was highly efficient and catalyzing the ORR though the four-electron pathway with oxygen being directly reduced to water. The kinetic currents (Jk) were 12.5 mA cm−2 at 0.4 V and 14.2 mA cm−2 at 1.0 V, indicating highly active catalytic activity. The N-wNT was free from metal species as discussed above, and this enables a solid correlation between the winged structure and electrochemical performance.


Highly efficient oxygen reduction electrocatalysts based on winged carbon nanotubes.

Cheng Y, Zhang H, Varanasi CV, Liu J - Sci Rep (2013)

Electrocatalytic activity of the N-wNT catalyst: (a) CV curves acquired at 100 mV/s in O2 or Ar saturated 0.1 M KOH. (b) Rotating-disk voltammograms in O2-saturated 0.1 M KOH acquired at 10 mV/s and different rotating speeds. (c) Koutecky-Levich plots of J−1 versus ω−1/2 at different electrode potentials, the inserted image shows estimated number of electrons transferred at different potentials. (d) Comparison of the RDE voltammograms for catalysts with different structure and composition as specified (all acquired at 1600 rpm and 10 mV/s).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3824170&req=5

f3: Electrocatalytic activity of the N-wNT catalyst: (a) CV curves acquired at 100 mV/s in O2 or Ar saturated 0.1 M KOH. (b) Rotating-disk voltammograms in O2-saturated 0.1 M KOH acquired at 10 mV/s and different rotating speeds. (c) Koutecky-Levich plots of J−1 versus ω−1/2 at different electrode potentials, the inserted image shows estimated number of electrons transferred at different potentials. (d) Comparison of the RDE voltammograms for catalysts with different structure and composition as specified (all acquired at 1600 rpm and 10 mV/s).
Mentions: We performed cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements in 0.1 M KOH to assess the catalytic activity of N-wNT material that had been deposited onto a glassy carbon electrode. The N-wNT catalyst exhibited a symmetrical and rectangular CV curve when the electrolyte was saturated with Ar (Figure 3a). In strong contrast, a pronounced catholic ORR peak with an onset potential of ~ 0.91 V versus reversible hydrogen electrode (RHE) was observed in O2 saturated electrolyte. Noticeably, the ORR peak is much stronger with more positive onset voltage than most of the metal-free catalyst developed152628, suggesting large surface area of winged nanotubes. The high ORR activity is also evident from its onset potential (~0.93 V) and half-wave potential (~0.79 V) in the RDE polarization curve (Figure 3b). The corresponding Koutecky-Levich plot (J−1 vs ω−1/2) obtained on the basis of analyzing the RDE curves of different electrode rotating speeds (in rpm, Figure 3b) at various potentials exhibited excellent linearity (Figure 3c). The average number of electrons transferred per oxygen molecule involved in the ORR can be analyzed on the basis of the Koutecky-Levich equations (Supporting Information)8. The number of electrons transferred were determined to be all around 4 at different potentials examined (Figure 3c, inserted), demonstrating N-wNT was highly efficient and catalyzing the ORR though the four-electron pathway with oxygen being directly reduced to water. The kinetic currents (Jk) were 12.5 mA cm−2 at 0.4 V and 14.2 mA cm−2 at 1.0 V, indicating highly active catalytic activity. The N-wNT was free from metal species as discussed above, and this enables a solid correlation between the winged structure and electrochemical performance.

Bottom Line: We found that the outer-walls of a special type of carbon nanotubes/nanofibers, when selectively oxidized, unzipped and exfoliated, form graphene wings strongly attached to the inner tubes.After doping with nitrogen, the winged nanotubes exhibited outstanding activity toward catalyzing the ORR through the four-electron pathway with excellent stability and methanol/carbon monoxide tolerance.While the doped graphene wings with high active site density bring remarkable catalytic activity, the inner tubes remain intact and conductive to facilitate electron transport during electrocatalysis.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemistry, Duke University, Durham, NC 27708 United States [2] Center for the Environmental Implication of NanoTechnology (CEINT), Duke University, Durham, NC 27708 United States.

ABSTRACT
Developing electrocatalysts with both high selectivity and efficiency for the oxygen reduction reaction (ORR) is critical for several applications including fuel cells and metal-air batteries. In this work we developed high performance electrocatalysts based on unique winged carbon nanotubes. We found that the outer-walls of a special type of carbon nanotubes/nanofibers, when selectively oxidized, unzipped and exfoliated, form graphene wings strongly attached to the inner tubes. After doping with nitrogen, the winged nanotubes exhibited outstanding activity toward catalyzing the ORR through the four-electron pathway with excellent stability and methanol/carbon monoxide tolerance. While the doped graphene wings with high active site density bring remarkable catalytic activity, the inner tubes remain intact and conductive to facilitate electron transport during electrocatalysis.

No MeSH data available.


Related in: MedlinePlus