Background:
Porous carbon materials are promising candidate supports for various applications.
In a number of these applications, doping of the carbon framework with heteroatoms provides
a facile route to readily tune the carbon properties. The oxygen reduction reaction (ORR),
where the reaction can be catalyzed without precious metals is one of the common applications for
the heteroatom-doped carbons. Therefore, heteroatom doped catalysts might have a promising potential
as a cathode in Microbial fuel cells (MFCs). MFCs have a good potential to produce electricity
from biological oxidization of wastes at the anode and chemical reduction at the cathode. To the best
of our knowledge, no studies have been yet reported on utilizing Sulfur trioxide pyridine (STP) and
CMK-3 for the preparation of (N and S) doped ordered porous carbon materials. The presence of
highly ordered mesostructured and the synergistic effect of N and S atoms with specific structures
enhance the oxygen adsorption due to improving the electrocatalytic activity. So the optimal catalyst,
with significant stability and excellent tolerance of methanol crossover can be a promising candidate
for even other storage and conversion devices.
Methods:
The physico-chemical properties of the prepared samples were determined by Small Angle
X-ray Diffraction (SAXRD), N2 sorption-desorption, Transmission Electron Microscopy (TEM),
Field Emission Scanning Electron Microscopy (FESEM) and X-ray Photoelectron Spectroscopy
(XPS). The prepared samples were further applied for oxygen reduction reaction (ORR) and the optimal
cathode was tested with the Microbial Fuel Cell (MFC) system. Furthermore, according to
structural analysis, The HRTEM, and SAXRD results confirmed the formation of well-ordered hexagonal
(p6mm) arrays of mesopores in the direction of (100). The EDS and XPS approved that N and
S were successfully doped into the CMK-3 carbon framework.
Results:
Among all the studied CMK-3 based catalysts, the catalyst prepared by STP precursor and
pyrolysis at 900°C exhibited the highest ORR activity with the onset potential of 1.02 V vs. RHE and
4 electron transfer number per oxygen molecule in 0.1 M KOH. The high catalyst durability and
fuel-crossover tolerance led to stable performance of the optimal cathode after 5000 s operation,
while the Pt/C cathode-based was considerably degraded. Finally, the MFC system with the optimal
cathode displayed 43.9 mW·m-2 peak power density showing even reasonable performance in comparison
to a Pt/C 20 wt.%.cathode.
Conclusions:
The results revealed that the synergistic effect of nitrogen and sulfur co-doped on the carbon
substrate structure leads to improvement in catalytic activity. Also, it was clearly observed that the porous
structure and order level of the carbon substrate could considerably change the ORR performance.
Beyond Nitrogen in the Oxygen Reduction Reaction on Nitrogen-Doped Carbons: A NEXAFS Investigation
