Open Journal of Physical Chemistry, 2011, 1, 11-22
doi:10.4236/ojpc.2011.11003 Published Online May 2011 (
Copyright © 2011 SciRes. OJPC
Iron and Nitrogen Containing Carbon Catalysts with
Enhanced Activity for Oxygen Reduction in Proton
Exchange Membrane Fuel Cells
Chitturi Venkateswara Rao1,*, Lingam Hima Kumar1, Balasubramanian Viswanathan1,*
1National Centre for Catalysis Research, Depa r tmen t of Chemistry, Indian Institute
of Technology Madras, Chennai 600036, India
E-mail: 0Tvrao.chitturi@ymail.comH;
Received April 11th, 2011; revised April 21st, 2011; accepted May 12th, 2011.
Iron and nitrogen containing carbon catalysts were prepared by the pyrolysis of iron(III)tetramethoxy-
phenylporphyrin complex adsorbed on as-received as well as nitric acid treated carbon black and employed
them as oxygen reduction electrodes for hydrogen-oxygen PEM fuel cells. The influence of carbon surface
functional groups on the dispersion of active species and electrocatalytic performance is investigated using
electron microscopic and electrochemical techniques. The existence of quinone functional groups on the ni-
tric acid treated carbon was evident from X-ray photoelectron spectroscopy and cyclic voltammetry. Rotat-
ing disk electrode voltammetry results affirmed the good electrocatalytic activity and stability of pyrolyzed
macrocyclic complex adsorbed on nitric acid treated carbon compared to that of as-received carbon. This is
ascribed to the greater number of Fe/N active species as well as good dispersion of metal clusters over nitric
acid treated carbon support. Fuel cell tests depicted the comparable performance of pyrolyzed complex ad-
sorbed on nitric acid treated carbon with commercial Pt/C at 353 K. Durability measurements performed un-
der fuel cell operating conditions for 120 h indicate the good stability of the catalysts.
Keywords: Iron-based Clusters, Non-Precious Catalysts, Oxygen Reduction, PEM Fuel Cells
1. Introduction
Proton exchange membrane fuel cells (PEMFCs) appear
to be one of the alternate energy sources [1]. Carbon
supported platinum is the active, efficient and applicable
catalyst for hydrogen oxidation and oxygen reduction in
PEMFCs [1-5]. However, the usage of high amount of Pt
for oxygen reduction reaction (ORR) at cathode in-
creases the cost of the device and hinders commerciali-
zation. Also, Pt electrocatalysts has several drawbacks
such as high overpotential (300 mV) and sluggish ki-
netics for ORR beside the cost issue [5]. In recent years,
there have been efforts to find suitable non-Pt based
catalysts which exhibit the similar activity of Pt [6-10].
Transition metal (especially iron or cobalt), nitrogen and
carbon containing catalysts in the form of MNxCy appear
to be one of the choices for ORR [9,10].
Electrocatalysis of the ORR on transition metal macro-
cycle, cobalt(II)phthalocyanine (CoPc) adsorbed on car-
bon was reported for the first time by Jasinski [11]. There-
after, several macrocyclic complexes were investigated as
oxygen reduction electrodes for electrochemical devices
[12-14]. All experimental evidences accumulated over the
years have demonstrated that macrocyclic complexes of
Fe and Co appear to be the best. However, they suffer
from low electrochemical stability and decompose either
via hydrolysis in the electrolyte or destruction of the mac-
rocycle ring by peroxy intermediates generated during
oxygen reduction [15]. The results were not satisfactory in
terms of both the activity and stability of these Co and Fe
chelates. Later several research groups reported that the
heat-treatment of iron or cobalt macrocycles adsorbed on
carbon support improves their activity and stability
[15-22]. Moreover, a variety of methods have been em-
ployed to prepare electrocatalysts containing iron or cobalt,
nitrogen and carbon and exploited them as ORR elec-
trodes [23-25]. It was concluded that the activity depends
on the metal, the ligand and nature of support. Efforts have
been devoted to determine the composition and the struc-
ture of the active sites formed upon pyrolysis. The most
Copyright © 2011 SciRes. OJPC
widely accepted model to explain the improvement in
activity and stability is the formation of M-Nx moiety on
carbon matrix or simply MNxCy clusters (M = Fe or Co)
during the pyrolysis [10, 6-32].
Activated carbon materials characterized by good sur-
face area, tunable porosity, and high electronic conduc-
tivity were known to influence the catalytic activity
thereby device performance. Numerous studies were
reported on the preparation of activated carbon materials
and their influence on the catalytic activity [33-35]. The
methods were mainly concentrated on the treatment of
carbon with a variety of chemical oxidants like HNO3,
H2O2, hypochlorite etc. or gaseous molecules like O2,
NH3, etc. The main purpose of the treatment was to cre-
ate surface oxygen functionalities or to generate het-
eroatom-containing carbon nanostructures which were
known to act as active sites for various processes/reac-
tions [35-37]. Of the various approaches, treatment of
carbon black with HNO3 was known to increase its hy-
drophilicity thereby increase the dispersion of metal/
metal complexes and enhances the performance of sup-
ported catalysts. In recent years, the effect of HNO3
treatment on the properties and performance of sup-
ported catalysts towards various industrially important
reactions, namely, the chemical reduction of NO with
NH3 [38], electrocatalytic oxidation of small organic
molecules such as H2 [39], CO [39,40] and CH3OH
[41,42] and electrocatalytic reduction of air [43,44] and
oxygen [45-52] were investigated. The results insisted
the enhanced activity and stability for the HNO3 treated
carbon-supported catalysts. The enhanced performance
was attributed to the increase in the surface area, high
hydrophilicity, high degree of dispersion of active spe-
cies, increase in the interaction between metal particle
and support, and synergistic effect between the metal and
oxygenated groups.
The objective of this work is to increase the number of
Fe/N active species at the surface, utilizing N4-Fe chelate
(FeTMPP) and oxidized carbon black support, and com-
pare their ORR activity and PEMFC performance with
commercial Pt/C.
2. Experimental Section
2.1. Materials
All the chemicals used were of analytical grade. Pyrrole,
p-anisaldehyde, propionic acid, N,N'-dimethylformamide,
chloroform, benzene, acetone, iron (II) acetate and con-
centrated nitric acid (70%) were obtained from Merck.
Millipore-Q water (Merck) was used throughout the
work. Commercial Pt/C was procured from E-TEK.
Carbon black (CDX975) received from Columbian
Chemicals Company, USA was used as support.
2.2. Modification of Carbon Black Support
The as-received carbon was treated with nitric acid to
increase the surface quinone/hydroquinone groups which
were known to increase the dispersion of metal com-
plexes. In a typical procedure, 0.5 g of carbon black was
treated with 20 ml of concentrated HNO3. The suspen-
sion was refluxed for 7 h and cooled. Then it was filtered,
washed with de-ionized water and methanol, and dried in
an oven at 348 K. For convenience, as-received and oxi-
dized carbon black were designated as C1 and C2 re-
spectively in the text.
2.3. Preparation of Fe-N/C Catalysts
Iron-tetramethoxyphenylporphyrin (FeTMPP) complex
was synthesized according to the method described by
Adler et al. [53]. Elemental composition (wt.%) of the
purified FeTMPP complex was found as C, 66.81; H,
4.07; N, 6.43 and Fe, 6.57. It was in good agreement
with calculated values (C, 66.95; H, 4.18; N, 6.51 and Fe,
6.49). The synthesized FeTMPP complex was adsorbed
on C1 and C2 carbon blacks by dissolving the suitable
amount of FeTMPP in chloroform followed by impreg-
nation. Then the resultant suspension was filtered,
washed with distilled water and dried at 348 K. Finally it
was ground into fine powder and heat-treated at 1073 K
for 2 h under Ar atmosphere to generate Fe-N/C catalyst.
The catalysts were prepared in such a way that it contain
approximately 2 wt.% Fe. The heat- treated FeTMPP
adsorbed on C1 and C2 were designated as C1-FeTMPP
(HT) and C2-FeTMPP (HT), respectively.
2.4. Characterization Techniques
The chemical compositions of the materials were deter-
mined by Hereaus CHN analyzer. Scanning electron mi-
croscope with EDX (FEI, Model: Quanta 200) was used
to observe the surface morphology and composition of
the catalysts. Surface area and pore size distribution of
carbon black were investigated by Brunauer-Emmett-
Teller (BET) analyses with nitrogen adsorption-desorp-
tion isotherms on a Carlo-Erba sorptometer (Model 1800)
instrument at 77 K. X-ray photoelectron spectroscopy
(XPS) measurements were carried out with Omicron
nanotechnology instrument using an Mg monochromatic
X-ray (hν = 1253.6 eV) at a power of 350 W operated
under the base pressure of 2 x 10-9 mbar. Particle size
was determined using transmission electron microscope
(TEM, JEOL2100). An inductively coupled plasma op-
tical emission spectroscopic (ICP-OES) technique was
employed to determine metal content in the catalysts.
Powder XRD patterns were obtained on a Siemens
Copyright © 2011 SciRes. OJPC
D5000 diffractometer operating with the Cu K radia-
tion (λ = 1.5408 Å) generated at 40 kV and 30 mA.
2.5. Electrochemical Measurements and
Single-Cell PEMFC Tests
ORR measurements were performed at room temperature
by rotating disk electrode (RDE) voltammetry using a
potentiostat (BAS 100 electrochemical analyzer) con-
nected to a three electrode cell assembled with RDE
glassy carbon disk as the working electrode, Ag/AgCl (+
0.205 V vs NHE) as the reference and Pt foil as the
counter electrodes, respectively. Oxygen saturated 0.5 M
H2SO4 was used as the electrolyte. The working elec-
trode fabricated with Fe-based catalysts was as follows
[19,20,29,30]. 16 mg of the catalyst, 0.4 ml of H2O and
0.4 ml of 5 wt.% Nafion® (Aldrich) were ultrasonically
blended for 10 min. Then 10 μl of this suspension was
pipetted onto the glassy carbon disk and dried under Ar
atmosphere. The working electrode, Pt/C (E-TEK) was
fabricated to contain 14 μgPt/cm2 according to our earlier
report [2]. Current densities were normalized to the
geometric area of the RDE disk (0.283 cm2).
Single-cell PEM tests were conducted using a home-
made fuel cell test station. Gas diffusion electrodes
(GDE) and membrane-electrode assembly (MEA) were
fabricated according to the procedure reported in litera-
ture [2,23,29]. A commercial 20 wt.% Pt/C (E-TEK) and
the prepared Fe-based catalysts were used to fabricate
anode and cathode, respectively. A homogeneous cata-
lyst suspension consisting of 12.9 mg of catalyst, 0.5 ml
of H2O and 0.3 ml of 5 wt.% Nafion solution was
blended ultrasonically for 1 h. This suspension was ap-
plied on the teflonized carbon cloth substrate by layer
wise. Both anode and cathode electrodes were then
placed in a vacuum oven at 348 K for 1 h. The anode
consists of 0.4 mgPt/cm2. The cathode fabricated with
Fe-based catalysts consists of 50 μgFe/cm2. To compare
the performance of Fe-based catalysts with Pt catalysts,
cathodes containing 50 and 100 μgPt/cm2 were fabri-
cated using 20 wt.% Pt/C (E-TEK). The single-cell
membrane- electrode assembly (MEA) was fabricated
by sandwiching the Nafion 115 membrane between the
cathode and anode by hot pressing at 413 K and 50
kg/cm2 for 1 min. All fuel cell measurements were per-
formed at 353 K. Both O2 and H2 gas back pressures
were set at 20 psi (1.38 bar). The two gases were hu-
midified prior to admission into the fuel cell by passing
them through stainless steel containers filled with H2O
kept at 373 K. Before the steady-state polarization
curves were recorded, the cell was left under open cir-
cuit conditions for 30 min (MEA conditioning). A po-
larization curve was then recorded by varying the ap-
plied potential.
3. Results and Discussion
3.1. Salient Features of Carbon Black Support
The as-received carbon black (C1) was characterized by
SEM, TEM and XRD. Specific surface area and pore
size distribution were investigated by Brunauer-Emmett-
Teller (BET) analysis. SEM and TEM images of carbon
black particles (CDX975) were shown in Figure 1. SEM
images show that the carbon black was made of spherical
aggregates about 150-200 nm in size (Figure 1a). TEM
image reveal that each aggregate being made of elemen-
tary particles of about 50-80 nm (Figure 1b). Figure 1c
represents the XRD pattern of carbon black particles.
The carbon particles exhibited characteristic (002) and
(101) diffraction peaks at 2θ values around 25 and 43˚,
respectively. The broad diffraction peak (002) with low
intensity indicates the amorphous nature of carbon black.
The BET specific surface area of the carbon sample is ~
260 m2/g. The pore diameter distribution is shown in
Figure 1d confirms the dominant pore diameter of the
carbon particles is in the range of 2 - 50 nm, which was
in the mesopore range. In fact, mesopores with pore di-
ameters of 2 - 50 nm were accessible to nitric acid oxida-
tion since they possess a combination of high surface
area and large pore diameter [54]. Also, mesoporous
structure was a key factor contributing to the feasibility
of carbon supports in electrocatalysis [55].
3.2. XPS Analysis of C1 and C2 Carbon Blacks
To gain more insight into the surface functionalities cre-
ated by nitric acid treatment, XPS measurements were
performed. XPS survey-scan spectra show C1s and O1s
peaks at 284 and 532 eV in the both as-received (C1) and
nitric acid treated carbon (C2) samples. The observed
C1s peak mainly represents amorphous carbon. The in-
crease in the intensity of O1s peak from C1 to C2 indi-
cates the presence of greater oxygen functionalities in the
C2 sample. This is due to the nitric acid treatment. The
assignment of peaks in the C1s spectra is in good agree-
ment with literature reports [56,57]. The deconvoluted
XP C1s and O1s spectra of the C1 and C2 samples are
shown in Figure 2. The predominant C1s peak appears
at 284.7 ± 0.1 eV for both C1 and C2 samples represent
the amorphous nature of carbon. The peaks appeared at
binding energies 284.3 ± 0.1 and 285.0 ± 0.1 eV are at-
tributed to the sp2 C and sp3 C, respectively. In the case
of functionalized carbons, the additional peaks appeared
at binding energies 286.1, 287.5, and 288.7 eV are at-
tributed to the -C-O-, -C=O, and –O-C-O-, respectively.
The absence of shake-up peak of carbon in C1 and C2
samples at 290.5 eV (π-π* transition) indicates the amor-
Copyright © 2011 SciRes. OJPC
phous nature of carbon samples. The separation of 0.7 ±
0.1 eV between sp2 and sp3 peaks found for the amor-
phous C1 and C2 samples are in good agreement with
the literature report [58]. It can be seen that the func-
tional groups with either C-O bonds or C=O bonds are
almost negligible on the as-received carbon (C1) whereas
the functional groups with both C-O and C=O bonds are
found to be present on the oxidized carbon (C2).
The deconvoluted XP O1s spectra give two peaks for
the C1 and C2 samples. The peaks at binding energies
531.6 ± 0.1 and 533.2 ± 0.1 eV are attributed to the oxy-
gen doubly bonded to carbon in quinones, ketones, and
aldehydes and oxygen singly bonded to carbon in ethers
and phenols respectively. The intensities of both the C-O
and C=O peaks increase after HNO3 treatment. The in-
crease in surface concentration of oxygen from 1.3 to 7.8
at.% is observed.
3.3. XPS Analysis of C1-FeTMPP(HT) and
C2- FeTMPP(HT) Catalysts
The studies performed on Fe-based non-precious ORR
catalysts impart that the presence of Fe/N species at the
surface plays an important role in the adsorption and
reduction of molecular oxygen [10,26,32,50-52]. To
probe the nature of the species existed on the surface,
XPS measurements were performed and the correspond-
ing X-ray photoelectron (XP) narrow scan spectra are
provided in Figure 3. Fe2p and N1s spectra are the av-
erage of 256 and 128 scans over the region of interest.
As seen in the figure, both the catalysts have a compo-
nent corresponding to iron and nitrogen species at the
surface. The increase in the intensity of Fe2p and N1s
peaks from C1-FeTMPP(HT) to C2-FeTMPP(HT) de-
note the presence of greater Fe/N content at the surface
of C2-FeTMPP(HT) catalyst. The Fe2p3/2 narrow scan
spectra shown in Figure 3(a) are characterized by a
broad peak in the range of 705 and 711 eV suggests the
existence of iron in different oxidative states [59]. The
vertical lines on the figure pinpoint the average binding
energies of Fe2+ (707.1 - 708.7 eV), Fe0 (metallic iron/iron
carbides, 706.7 - 707.2/706.7 - 706.9 eV), and Fe3+ (710.1
- 711.2 eV). The XP N1s spectra of the catalysts shown in
Figure 3(b) are characterized by two peaks and a tail at
high energy. The vertical lines on the figure pinpoint the
average binding energies of pyridinic (398.1-398.5 eV),
Figure 1. (a) SEM image; (b) TEM image; (c) XRD pattern; (d) pore size distribution of the as-received carbon black (C1).
Copyright © 2011 SciRes. OJPC
(a) (b)
(c) (d)
Figure 2. Deconvoluted XP C1s and O1s spectra of as-received carbon, C1 (a and b) and oxidized carbon, C2 (c and d).
(a) (b)
Figure 3. X-ray photoelectron spectra in (a) Fe2p and (b) N1s regions of the catalysts C1-FeTMPP (HT) and C2-FeTMPP (HT).
pyrrolic (399.8 - 401.3 eV), and quaternary (401.5 -
403.1 eV) type nitrogen. Integration of the relative Fe
and N elemental abundances indicates that the C1-
FeTMPP(HT) catalyst contain ~0.7 at.% Fe and ~2.2
at.% N while C2-FeTMPP(HT) catalyst contain ~1.3
at.% Fe and ~3.4 at.% N at the surface.
Copyright © 2011 SciRes. OJPC
3.4. Electro-catalytic Performance of the
The as-received (C1) and oxidized (C2) carbon black
supports were electrochemically analyzed to check the
nature of the surface functional groups present. Cyclic
voltammograms obtained for carbons C1 and C2 in de-
aerated 0.5M H2SO4 was shown in Figure 4. A well-
defined redox peaks at ~0.55 V vs NHE was observed
for C2. The observed redox peaks are corresponding to
the presence of quinone/hydroquinone groups on the
carbon surface [48,60]. These results are in good agree-
ment with XPS results obtained for C1 and C2.
Linear sweep voltammograms (LSVs) recorded for the
catalysts in O2-saturated 0.5M H2SO4 at a scan rate of 5
mV/s and rotation rate of 2500 rpm are shown in Figure
5(a). For comparison, LSV recorded for Pt/C is also
shown. A single steep reduction wave with a well-de-
veloped limiting plateau similar to that of Pt/C was ob-
served for Fe-based catalysts. Voltammograms also de-
pict the higher ORR activity and positive shift of ORR
onset potential for C2-FeTMPP(HT) compared to C1-
FeTMPP(HT). The onset potential for ORR on C1-
FeTMPP(HT), C2-FeTMPP(HT) and Pt/C catalysts are
+840, +880 and +910 mV vs NHE, respectively. It de-
notes that the over potential for ORR on C2- FeTMPP
(HT) decreased by 40 mV compared to C1-FeTMPP
(HT). These results confirmed that the presence of oxy-
gen functionalities (quinone groups) on carbon surface
played an important role in formation and dispersion of
Fe/N active sites thereby enhanced ORR performance.
Electrocatalytic ORR activity observed for the heat-
treated FeTMPP/C was due to the creation of Fe/N moi-
ety on carbon matrix during the pyrolysis [29,30]. Re-
cently, we have demonstrated the necessity of Fe-N4
clusters for the facile reduction of dioxygen molecule
from density functional theory calculations [61]. In
comparison with Pt/C, C2-FeTMPP(HT) catalysts exhib-
ited high overpotential (ca. 30 mV) and also low ORR
activity. Even though the ORR performance was inferior
to that of Pt/C, still there is a possibility to improve the
performance of carbon supported Fe/N clusters by suit-
able electrode fabrication or by the modification of its
electronic structure or by increasing the number of active
sites through modified synthesis. Current density-time
plots recorded for the electrodes in O2-saturated 0.5M
H2SO4 at 0.7 V were shown in Figure 5(b). The per-
formance of C2-FeTMPP(HT) was found to be better
compared to C1-FeTMPP(HT). This may be due to the
strong bonding interactions between the active species
and oxidized carbon. Also, the performance was compa-
rable with Pt/C.
The steep increase of ORR peak current observed for
C2-FeTMPP(HT) compared to C1-FeTMPP(HT) may be
due to the high surface area and distribution of active
sites. BET surface area determined for the C1-FeTMPP
(HT) and C2-FeTMPP(HT) catalysts was 57 and 103
m2/g respectively. In order to check the effect of surface
Figure 4. Typical cyclic voltammograms of as-received carbon (C1) and oxidized carbon (C2) in Ar-saturated 0.5M H2SO4;
Scan rate–10 mV/s.
Copyright © 2011 SciRes. OJPC
(a) (b)
Figure 5. (a) Linear sweep voltammograms (LSVs) for ORR on C1-FeTMPP(HT), C2-FeTMPP(HT) and Pt/C catalysts in
O2- saturated 0.5M H2SO4; Scan rate–5 mV/s and rotation rate–2500 rpm and (b) Current density–time plots of C1-
FeTMPP(HT), C2-FeTMPP(HT) and Pt/C catalysts at 0.7 V vs NHE.
quinone groups on the dispersion of active species, TEM
images were recorded for heat-treated FeTMPP adsorbed
on C1 and C2. The corresponding images were shown in
Figure 6(a) and 6(b). Good dispersion of metal cluster
species were observed in the case of oxidized carbon com-
pared to as-received carbon. The average size of cluster
species in C2-FeTMPP(HT) was 11 nm compared to 25
nm for C1-FeTMPP(HT). The small cluster size was due to
the increased number of surface functionalities (quinones)
on carbon. Good dispersion of metallic clusters in the oxi-
dized carbon might have originated from interfacial bonds
with the surface oxygen functionalities. Thus the migration
and the coalescence of the active species were considerably
lowered by the presence of oxygenated groups which act as
anchors for the supported clusters. Therefore by increasing
the number of oxygen functionalities on the carbon support
by nitric acid treatment, the dispersion of the active species
as well as their performance is increased. EDX spectra
confirmed the presence of Fe, N, C and a small amount of
oxygen in both the catalysts. Since the preparation method
involves the pyrolysis of macrocyclic complex at 1073 K,
there will be a possibility for the existence of iron oxides
and iron carbide. But it has been reported that the ORR
activity of iron oxides/hydroxides in acid media is negligi-
ble [51]. Also, metallic iron and iron carbide were inactive
and not stable in acid media. So the ORR activity is attrib-
uted to the Fe/N clusters created in the carbon matrix.
3.5. Single-cell PEMFC Performance with Pt and
Fe-based ORR Catalysts
Single-cell PEMFC performance with C1-FeTMPP(HT),
C2-FeTMPP(HT), and Pt/C as ORR electrodes was
tested at 353 K and the corresponding polarization
Figure 6. TEM images of (a) C1-FeTMPP(HT) and (b) C2-
curves are shown in Figure 7. The performance observed
with high Pt loading (100 μg/cm2) at cathode is in good
Copyright © 2011 SciRes. OJPC
agreement with earlier report [51]. In the similar way,
fuel cell measurements are performed with Fe-based
catalysts and compared with commercial Pt/C. The open
circuit voltage (OCV) values observed with C1-
FeTMPP(HT), C2-FeTMPP(HT), and Pt/C cathodes un-
der identical conditions are ~0.85, ~0.89, and 0.93 V
respectively. The cell potential values measured at dif-
ferent current densities for all the catalysts are provided
in Table 1. The cell potential values found with C2-
FeTMPP(HT) cathode are higher than that of C1-
FeTMPP(HT) at all the current densities. The high per-
formance is due to the good dispersion and high concen-
tration of Fe/N active species at the surface. Jia et al. [37]
also observed the enhanced oxygen reduction perform-
ance for Pt catalysts supported on HNO3 modified car-
bon using gas diffusion electrode approach. Sawai and
Suzuki [44] also reported the remarkable enhancement in
the performance of the air cathodes fabricated with py-
rolyzed cobalt hexacyanoferrate dispersed on HNO3-
treated carbon support. They proposed that the hydro-
philic carboxylic acid groups produced by surface oxida-
tion enhance wetting of the catalyst layer and enhanced
proton conductivity in the catalyst layer. At low current
density of 50 mA/cm2, C2-FeTMPP(HT) exhibited a cell
potential of 0.779 V which is close to be found with Pt/C
(0.813 V) with same metal loading. However, the per-
formance of C2-FeTMPP(HT) is inferior to that of Pt/C
at medium and high current densities. This is due to the
low conductivity of C2-FeTMPP(HT). The performance
could be improved further by utilizing highly conductive
carbon support and optimization in the MEA manufac-
ture and operating conditions. To determine the Tafel
slope values, iR-corrected polarization curves are plotted
and shown in the inset of Figure 7. Tafel slopes are ob-
Table 1. Estimated metal loading, particle size, and single-cell PEMFC performance of Pt and Fe-based catalysts.
Cell potential at different current densities
Catalyst Metal
loading (wt.%)
Particle size
Cell OCV
(V) 50 mA/cm2 250 mA/cm2 500 mA/cm2
C1-FeTMPP(HT) Fe - 1.96 25 - 37 0.85 0.742 0.616 0.495
C2-FeTMPP(HT) Fe - 1.97 8 - 15 0.89 0.779 0.655 0.545
Pt/C (E-TEK)
(cathode with 50
Pt - 19.8 3.5 - 3.9 0.93 0.813 0.711 0.634
Pt/C (E-TEK)
(cathode with 100
,, ,, 0.94 0.835 0.746 0.671
Figure 7. Single-cell PEMFC performance of C1-FeTMPP(HT), C2-FeTMPP(HT), and Pt/C oxygen reduction electrodes at
353 K Anode: 0.4 mgPt/cm2 and cathode: 50 μgFe/cm2. For comparison, performance of Pt/C as cathode with 50 or 100
μgPt/cm2 also shown. Inset shows the Tafel plots for the catalysts.
Copyright © 2011 SciRes. OJPC
Figure 8. Cell potential-time response of C1-FeTMPP(HT), C2-FeTMPP(HT), and Pt/C oxygen reduction elec-
trodes in single-cell PEMFC at 50 mA/cm2 for 120 h.
tained from the linear region at low current density. The
Tafel slope for C1-FeTMPP(HT), C2-FeTMPP(HT), and
Pt/C catalysts is –73, –71, and –67 mV/decade respec-
tively. The Tafel slope obtained for Pt/C is close to the
theoretical Tafel slope at 353 K (-70 mV/decade) [52].
The cell potential-time response of the catalysts recorded
at 50 mA/cm2 for 120 h is shown in Figure 8. Under
identical PEMFC conditions, the cell with C2-FeTMPP
(HT) and Pt/C as cathodes exhibited stable voltage with
low polarization losses, whereas the C1-FeTMPP(HT) as
cathode exhibited significantly high polarization losses
within the period of 120 h. The good stability of C2-
FeTMPP(HT) compared to C1-FeTMPP(HT) is due to
the strong bonding interactions between the active spe-
cies and oxidized carbon.
4. Conclusions
The role exerted by the oxygenated surface groups in the
dispersion of Fe/N active species responsible for oxygen
reduction was studied. The results showed that the in-
troduction of surface oxygen complexes (quinones) on
carbon support enhanced the electrocatalytic ORR activ-
ity thereby fuel cell performance. The good ORR activity,
single-cell PEMFC, and stability performance of carbon
supported Fe/N clusters advance them as potential ORR
electrodes for PEMFC applications.
5. Acknowledgements
The authors thank the authorities of Ms. Columbian
Chemicals Company, USA for financial and material
support. The authors also wish to acknowledge Depart-
ment of Science and Technology (DST), India for creat-
ing the National Centre for Catalysis Research at IIT
6. References
[1] B. Viswanathan and M. Aulice Scibioh, “Fuel Cells-Prin-
ciples and Applications,” Universities Press (India) Private
Limited, New Delhi, 2006.
[2] Ch. Venkateswara Rao and B. Viswanathan, “Monodis-
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