3 research outputs found
Nitrogen-Doped Graphene with Pyridinic Dominance as a Highly Active and Stable Electrocatalyst for Oxygen Reduction
The nitrogen-doped graphene (NG)
with dominance of the pyridinic-N
configuration is synthesized via a straightforward process including
chemical vapor deposition (CVD) growth of graphene and postdoping
with a solid nitrogen precursor of graphitic C<sub>3</sub>N<sub>4</sub> at elevated temperature. The NG fabricated from CVD-grown graphene
contains a high N content up to 6.5 at. % when postdoped at 800 °C
but maintains high crystalline quality of graphene. The obtained NG
exhibits high activity, long-standing stability, and outstanding crossover
resistance for electrocatalysis of oxygen reduction reaction (ORR)
in alkaline medium. The NG treated at 800 °C shows the best ORR
performance. Further study of the dependence of ORR activity on different
N functional groups in these metal-free NG electrodes provides deeper
insights into the origin of ORR activity. Our results reveal that
the pyridinic-N tends to be the most active N functional group to
facilitate ORR at low overpotential via a four-electron pathway
Carbon Nitrogen Nanotubes as Efficient Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions
Oxygen reduction and evolution reactions
are essential for broad range of renewable energy technologies such
as fuel cells, metal-air batteries and hydrogen production through
water splitting, therefore, tremendous effort has been taken to develop
excellent catalysts for these reactions. However, the development
of cost-effective and efficient bifunctional catalysts for both reactions
still remained a grand challenge. Herein, we report the electrocatalytic
investigations of bamboo-shaped carbon nitrogen nanotubes (CNNTs)
having different diameter distribution synthesized by liquid chemical
vapor deposition technique using different nitrogen containing precursors.
These CNNTs are found to be efficient bifunctional electrocatalyst
for oxygen reduction and evolution reactions. The electrocatalytic
activity strongly depends on the nanotube diameter as well as nitrogen
functionality type. The higher diameter CNNTs are more favorable for
these reactions. The increase in nanotube diameter itself enhances
the catalytic activity by lowering the oxygen adsorption energy, better
conductivity, and further facilitates the reaction by increasing the
percentage of catalytically active nitrogen moieties in CNNTs
Achieving Highly Efficient, Selective, and Stable CO<sub>2</sub> Reduction on Nitrogen-Doped Carbon Nanotubes
The challenge in the electrosynthesis of fuels from CO<sub>2</sub> is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO<sub>2</sub> to CO. The unprecedented overpotential (−0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO<sub>2</sub> activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed COOH and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode