We
report semi-interpenetrating polymer network (semi-IPN) membranes
prepared easily from a cross-linked network using poly(acrylic acid)
(PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for
both proton-exchange membrane fuel cell (PEMFC) and proton-exchange
membrane water electrolyzer (PEMWE) applications. Thermal esterification
between PAA and PVA induced three-dimensional cross-linking to improve
mechanical toughness and reduce hydrogen crossover, while the hydrophilic
nature of the PAA–PVA-based cross-linked matrix still enhanced
the water uptake (WU) and hence conductivity of the Nafion penetrant.
The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with
a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and
improved thermal, mechanical, and dimensional stability compared to
a recast Nafion membrane (re-Nafion). The membrane was also highly
effective at managing water due to its low WU and high conductivity.
Furthermore, its hydrogen permeability was 49.6% lower than that of
re-Nafion under the actual fuel cell operating conditions (at 100%
RH and 80 °C). NPP-95 exhibited significantly improved conductivity
and PEMFC performance compared to re-Nafion with a current density
of 1561 mA/cm2 at a potential of 0.6 V and a peak power
density of 1179 mW/cm2. Furthermore, in the PEMWE performances,
NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm2 at 2.0 V and much lower ohmic resistance than re-Nafion between
60 and 80 °C.
We prepared Nafion
composite membranes by impregnating Nafion-212
with polydopamine, poly(sulfonated dopamine), and poly(dopamine-
co
-sulfonated dopamine) using the swelling–filling
method to generate nanopores in the Nafion framework that were filled
with these polymers. Compared to the pristine Nafion-212 membrane,
these composite membranes showed improved thermal and mechanical stabilities
due to the strong interactions between the catecholamine of the polydopamine
derivatives and the Nafion matrix. For the composite membrane filled
with poly(sulfonated dopamine) (N-PSDA), further interactions were
induced between the Nafion and the sulfonic acid side chain, resulting
in enhanced water uptake and ion conductivity. In addition, filling
the nanopores in the Nafion matrix with polymer fillers containing
aromatic hydrocarbon-based dopamine units led to an increase in the
degree of crystallinity and resulted in a significant decrease in
the hydrogen permeability of the composite membranes compared to Nafion-212.
Hydrogen crossovers 26.8% lower than Nafion-212 at 95% relative humidity
(RH) (fuel cell operating conditions) and 27.3% lower at 100% RH (water
electrolysis operating conditions) were obtained. When applied to
proton exchange membrane-based fuel cells, N-PSDA exhibited a peak
power density of 966 mW cm
–2
, whereas N-PSDA showed
a current density of 4785 mA cm
–2
, which is 12.4%
higher than Nafion-212 at 2.0 V and 80 °C.
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