Due to the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline electrolytes, the development of more efficient HOR catalysts is essential for the next generation of anion‐exchange membrane fuel cells (AEMFCs). In this work, CeOx is selectively deposited onto carbon‐supported Pd nanoparticles by controlled surface reactions, aiming to enhance the homogenous distribution of CeOx and its preferential attachment to Pd nanoparticles, to achieve highly active CeOx‐Pd/C catalysts. The catalysts are characterized by inductively coupled plasma–atomic emission spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy to confirm the bulk composition, phases present, morphology, elemental mapping, local oxidation, and surface chemical states, respectively. The intimate contact between Pd and CeOx is shown through high‐resolution STEM maps. The oxophilic nature of CeOx and its effect on Pd are probed by CO stripping. The interfacial contact area between CeOx and Pd nanoparticles is calculated for the first time and correlated to the electrochemical performance of the CeOx‐Pd/C catalysts. Highest recorded HOR specific exchange current (51.5 mA mg−1Pd) and H2–O2 AEMFC performance (peak power density of 1,169 mW cm−2 mgPd−1) are obtained with a CeOx‐Pd/C catalyst with Ce0.38/Pd bulk atomic ratio.
Transition-metal-
and nitrogen-codoped carbide-derived carbon/carbon
nanotube composites (M-N-CDC/CNT) have been prepared, characterized,
and used as cathode catalysts in anion-exchange membrane fuel cells
(AEMFCs). As transition metals, cobalt, iron, and a combination of
both have been investigated. Metal and nitrogen are doped through
a simple high-temperature pyrolysis technique with 1,10-phenanthroline
as the N precursor. The physicochemical characterization shows the
success of metal and nitrogen doping as well as very similar morphologies
and textural properties of all three composite materials. The initial
assessment of the oxygen reduction reaction (ORR) activity, employing
the rotating ring–disk electrode method, indicates that the
M-N-CDC/CNT catalysts exhibit a very good electrocatalytic performance
in alkaline media. We find that the formation of HO
2
–
species in the ORR catalysts depends on the specific
metal composition (Co, Fe, or CoFe). All three materials show excellent
stability with a negligible decline in their performance after 10000
consecutive potential cycles. The very good performance of the M-N-CDC/CNT
catalyst materials is attributed to the presence of M-N
x
and pyridinic-N moieties as well as both micro-
and mesoporous structures. Finally, the catalysts exhibit excellent
performance in in situ tests in H
2
/O
2
AEMFCs,
with the CoFe-N-CDC/CNT reaching a current density close to 500 mA
cm
–2
at 0.75 V and a peak power density (
P
max
) exceeding 1 W cm
–2
. Additional
tests show that
P
max
reaches 0.8 W cm
–2
in an H
2
/CO
2
-free air system
and that the CoFe-N-CDC/CNT material exhibits good stability under
both AEMFC operating conditions.
In
this paper we present a study on stable radicals and short-lived
species generated in anion-exchange membrane (AEM) fuel cells (AEMFCs)
during operation. The
in situ
measurements are performed
with a micro-AEMFC inserted into a resonator of an electron paramagnetic
resonance (EPR) spectrometer, which enables separate monitoring of
radicals formed on the anode and cathode sides. The creation of radicals
is monitored by the EPR spin trapping technique. For the first time,
we clearly show the formation and presence of stable radicals in AEMs
during and after long-term AEMFC operation. The main detected adducts
during the operation of the micro-AEMFC are DMPO-OOH and DMPO-OH on
the cathode side, and DMPO-H on the anode side. These results indicate
that oxidative degradation involving radical reactions has to be taken
into account when stability of AEMFCs is investigated.
Platinum group metal (PGM)‐free catalysts for oxygen reduction reaction have shown high oxygen reduction reaction activity in alkaline media. In order to further increase the power density of anion‐exchange membrane fuel cells (AEMFCs), PGM‐free catalysts need to have a high site density to reach high current densities. Herein, synthesis, characterization, and utilization of heat‐treated iron porphyrin aerogels are reported as cathode catalysts in AEMFCs. The heat treatment effect is thoroughly studied and characterized using several techniques, and the best performing aerogel is studied in AEMFC, showing excellent performance, reaching a peak power density of 580 mW cm−2 and a limiting current density of as high as 2.0 A cm−2, which can be considered the state‐of‐the‐art for PGM‐free based AEMFCs.
Owing
to the sluggish kinetics of the hydrogen oxidation reaction
(HOR) in alkaline electrolyte, it is considered a limiting reaction
for the development of anion-exchange membrane fuel cell (AEMFC) technology.
Studies of alkaline HOR catalysis mainly focus on carbon-supported
nanoparticles, which have weak metal–support interactions.
In this contribution, we present a unique support based on transition
metal carbides (TMCs = Mo2C, Mo2C–TaC,
and Mo2C–W2C) for the HOR. PtRu nanoparticles
are deposited onto the TMC supports and are characterized by a variety
of analytical techniques. The major findings are (i) experimental
and theoretical evidence for strong-metal support interaction by both
X-ray absorption near-edge structure and density functional theory,
(ii) the kinetic current density (j
k,s) @25 mV of PtRu/Mo2C–TaC catalyst are 1.65 and
1.50 times higher than that of PtRu/Mo2C and PtRu/Mo2C–W2C, respectively, and (iii) enhanced
“tethering” of PtRu nanoparticles on TMC supports. Furthermore,
the AEMFC based on the PtRu/Mo2C–TaC anode exhibited
a peak power density of 1.2 W cm–2 @70 °C,
opening the doors for the development of advanced catalysts based
on engineering support materials.
Non-precious-metal catalysts are
promising alternatives for Pt-based
cathode materials in low-temperature fuel cells, which is of great
environmental importance. Here, we have investigated the bifunctional
electrocatalytic activity toward the oxygen reduction reaction (ORR)
and the oxygen evolution reaction (OER) of mixed metal (FeNi; FeMn;
FeCo) phthalocyanine-modified multiwalled carbon nanotubes (MWCNTs)
prepared by a simple pyrolysis method. Among the bimetallic catalysts
containing nitrogen derived from corresponding metal phthalocyanines,
we report the excellent ORR activity of FeCoN-MWCNT and FeMnN-MWCNT
catalysts with the ORR onset potential of 0.93 V and FeNiN-MWCNT catalyst
for the OER having
E
OER
= 1.58 V at 10
mA cm
–2
. The surface morphology, structure, and
elemental composition of the prepared catalysts were examined with
scanning electron microscopy, X-ray diffraction, and X-ray photoelectron
spectroscopy. The FeCoN-MWCNT and FeMnN-MWCNT catalysts were prepared
as cathodes and tested in anion-exchange membrane fuel cells (AEMFCs).
Both catalysts displayed remarkable AEMFC performance with a peak
power density as high as 692 mW cm
–2
for FeCoN-MWCNT.
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