Iron oxide (Fe 3 O 4 ) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe 3 O 4 -SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe 3 O 4 nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe 3 O 4 -SGO composite membranes. Nafion/Fe 3 O 4 -SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe 3 O 4 -SGO (3 wt%) composite membrane at 120 C under 20% relative humidity (RH) was 11.62 mS cm
À1, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe 3 O 4 -SGO composite membrane delivered a peak power density of 258.82 mW cm À2 at a load current density of 640.73 mA cm À2 while operating at 120 C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm À2 was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm
À2. Thus, Nafion/Fe 3 O 4 -SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.
Cerium
oxide–anchored amine-functionalized carbon nanotubes
(CeO2–ACNTs) are applied as radical scavengers as
well as solid proton conductors to realize hybrids with Nafion (Nafion/CeO2–ACNTs) for a proton-exchange membrane fuel cell (PEMFC)
operating at low relative humidity (RH). Reinforcement due to the
existence of ACNTs offers good mechanical strength and proton conductivity
to hybrid, and addition of CeO2 mitigates the chemical
degradation of hybrid. The proton conductivity of Nafion/CeO2–ACNTs at 20% RH is 12.2 mS cm–1, which
is 4 and 5 times better than that of recast Nafion and Nafion-212,
respectively. PEMFC integrated with Nafion/CeO2–ACNTs
delivers a maximum power density of 174.25 mW cm–2 at a load current density of 334.66 mA cm–2 while
operating at 60 °C under 20% RH. In contrast, under identical
condition, the maximum power densities of 83.14 and 72.55 mW cm–2 are achieved by recast Nafion and Nafion-212, respectively.
Additionally, PEMFC integrated with Nafion/CeO2–ACNTs
exhibits a decay of only 0.21 mV h–1 over 200 h
while keeping at 60 °C under 20% RH. Compared to Nafion/CeO2–ACNTs, the recast Nafion and Nafion-212 are experienced
the accelerated decay (recast Nafion, 0.65 mV h–1; Nafion-212, 0.59 mV h–1). PEMFC performance,
hydrogen crossover as well as morphology of specimens are probed before
and after durability test; the Nafion/CeO2–ACNTs
exhibits high stability than other specimens. Thus, Nafion/CeO2–ACNTs can be exploited to address various critical
issues associated with commercial Nafion in PEMFC applications.
Cerium
oxide-anchored titanium carbide (CeO2-TiC) is
realized as a potential inorganic filler when modifying the Nafion
matrix of a proton-exchange membrane fuel cell (PEMFC). A hydrothermal
strategy was employed to synthesize CeO2-TiC of high crystallinity
as a filler to mitigate the problematic properties of a proton-exchange
membrane (PEM). CeO2-TiC with a weight ratio of 0.5, 1,
1.5, or 2% was incorporated into a Nafion matrix to form a hybrid
by adopting a solution-casting procedure. Reinforcement owing to the
presence of TiC provides increased tensile strength to PEM, and the
addition of CeO2 improves the durability of PEM by scavenging
free radicals. The microstructural, thermomechanical, physiochemical,
and electrochemical properties of PEM, including contact angle, water
sorption, water uptake, and proton conductivity, were extensively
studied. Random dispersion of CeO2-TiC in the Nafion matrix
improves the thermal stability, tensile strength, and water uptake
while retaining proton conductivity, as compared with those of pristine
Nafion. As a result, optimized Nafion/CeO2-TiC (1 wt %)
achieved undiminished PEMFC performance compared to that of pristine
Nafion while operating the device at 60 °C and 100% relative
humidity. In addition, Nafion/CeO2-TiC (1 wt %) experienced
the degradation of merely 0.6 mV h–1 during 200
h operation under identical conditions. Compared to that of Nafion/CeO2-TiC (1 wt %), pristine Nafion and Nafion-212 displayed accelerated
and comparable degradation (for pristine Nafion, 1.3 mV h–1; for Nafion-212, 0.4 mV h–1). PEMFC power output,
hydrogen permeability, and morphology of samples were examined after
the durability test; the results indicate that Nafion/CeO2-TiC (1 wt %) is extremely stable. Since various Nafion hybrids have
been reported as highly durable PEMs, this study is expected to open
up new perspectives to expanding their applications, especially in
sustainable PEMFC technology.
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