In the search for alternative sources
to replace fossil fuels,
carbon nitride materials can be used in a variety of ways. In the
present work, porosity is introduced to the carbon nitride material
using mesoporous silica material, MCM-41, as a hard template, and
a mesoporous carbon nitride (MCN) material is synthesized. Further,
the MCN is modified by immobilizing metal phthalocyanine (MPc, where
M = Mn, Fe, Co, Ni, Cu, and Zn). The resulting MPc-incorporated MCN
materials (MPc@MCN) were tested for the electrocatalytic oxygen reduction
reaction (ORR) in acidic and basic media. Detailed studies reveal
that the FePc@MCN and CoPc@MCN materials exhibit higher ORR activity
than the other composites in 0.1 M KOH. FePc@MCN follows a direct
four-electron oxygen reduction mechanism and shows ORR onset potential
(vs RHE) at 0.93 V (in 0.1 M KOH), which is very close to the onset
potential exhibited by the state-of-the-art material, Pt-C (1.0 V),
and higher than several similar composites of MPc with carbon supports
tested in similar environments. Besides, due to the inherent property
of coordination through nitrogen present on the MCN, FePc@MCN shows
excellent stability even after 3000 cyclic voltammetry (CV) cycles.
FePc@MCN was found to have a better methanol tolerance in comparison
to Pt-C in basic medium. CoPc@MCN shows a highly selective two-electron
reduction reaction in both acidic and basic media at lower overpotential
than many of the reported catalysts for the two-electron oxygen reduction.
Therefore, these materials (FePc@MCN and CoPc@MCN) can be used as
suitable alternatives to replace Pt and other expensive materials
in ORR and related applications.
The synthesis of defect-rich materials is of significant interest for electrochemical energy conversion, including water splitting. Herein, we report a novel strategy for the synthesis of sulfur-doped mesoporous conducting carbon nitride supported defect-rich cobalt sulfide (O-Co 3 S 4 @S-MCN). Mesoporous silica material (MCM-41) is used as a template for the synthesis, and it performs dual functions: introducing porosity and providing in situ oxygen to fill the defects. O-Co 3 S 4 @S-MCN is highly crystalline and shows characteristic diffractions indicating the formation of defect-rich Co 3 S 4 . X-ray photoelectron spectroscopy proves the presence of Co−S (777.9 eV) and Co−O (782.4 eV) bonds in O-Co 3 S
Mesoporous carbon nitride (MCN) is synthesized using mesoporous silica material (MCM-41) as a sacrificial template. 5,10,15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(II) (cobalt tetramethoxyphenylporphyrin, CoTMPP), which consists of methoxy groups as the electron-rich center is...
Hydroperoxyl intermediate is a vital component in the mechanism of electrochemical oxygen reduction reaction (ORR) and several other important chemical reactions. The selectivity and kinetics of ORR are controlled by the energetics of *OOH intermediate (* represents the active site). The present work integrates iron phthalocyanine (FePc) with sulfonic acid-functionalized multiwalled carbon nanotubes (MWCNTs-SO 3 H). The resulting composite (FePc@MWCNTs-SO 3 H) demonstrates significantly improved kinetics and higher four-electron selectivity for the electrochemical reduction of oxygen compared to its counterpart without functionalization (FePc@MWCNTs) in alkaline, neutral, and acidic media. Based on the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) results and DFT calculations, it is proposed that sulfonate groups are involved in the water-assisted hydrogen-bonding interaction with the FeOOH intermediate. This interaction causes a substantial increase in selectivity and kinetics of ORR. Apart from the ORR, the findings of the current work strongly recommend that the functional groups on carbon support can be manipulated to get improved kinetics and selectivity of several important chemical transformations.
Water
oxidation is a crucial half-cell reaction in water splitting,
metal–air batteries, and CO2 reduction. In this
work, cobalt- and vanadium-containing mixed oxides [Co
x
(VO)
y
O
z
] are synthesized, and further, a unique composite of mixed
oxide nanocrystals with a covalent organic polymer [Co
x
(VO)
y
O
z
@COP] is prepared. A high increase in activity and stability
is exhibited by the Co
x
(VO)
y
O
z
@COP in comparison
to its independent oxide counterparts. Higher activity is attributed
to the presence of the VO2+/VO2
+ couple,
which helps in the facile oxidation of CoOOH to CoO2 and
enhances the oxygen evolution reaction activity. The optimized composite
material Co
x
(VO)
y
O
z
@COP(1:1) shows a low overpotential
of 265 and 298 mV for the current densities of 10 and 30 mA cm–2, respectively. The composite shows a low Tafel slope
(43 mV/dec), high turnover frequency (3.6 s–1 at
1.58 V), and high durability (tested for 14 h continuous oxygen evolution
at 1.53 and 1.60 V). The durability is further supported by (i) chronopotentiometry
(10,000 s at 25 mA cm–2), (ii) negligible variation
in the linear sweep voltammetry responses and electrochemically active
surface area values before and after 1000 cyclic voltammetry cycles,
(iii) negligible dissolution of cobalt during catalysis observed from
inductively coupled plasma mass spectroscopy of the electrolyte, and
(iv) insignificant change in the catalyst surface composition observed
from post-catalysis X-ray photoelectron spectroscopy. To the best
of our knowledge, this Co
x
(VO)
y
O
z
@COP(1:1) material
shows a higher activity in comparison to previously reported crystalline/amorphous
cobalt–vanadium oxides. In addition, the increase in activity
and stability from bare oxides to composite suggests that the COP
shall work as a reliable catalytic support for future applications.
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