Rubbery
polymer membranes prepared from CO2-philic PEO
and/or highly permeable PDMS are desired for efficient CO2 separation from light gases (CH4 and N2).
Poor mechanical properties and size-sieving ability, however, limit
their application in gas separation applications. Cross-linked rubbery
polymer-based gas separation membranes with a low T
g based on both PEG/PPG and PDMS units with various compositions
between these two units are prepared for the first time in this work
by ring-opening metathesis polymerization type cross-linking and in
situ membrane casting. The developed membranes display excellent CO2 separation performance with CO2 permeability ranging
from 301 to 561 Barrer with excellent CO2/N2 selectivity ranging from 50 to 59, overcoming the Robeson upper
bound (2008). The key finding underlying the excellent performance
of the newly developed cross-linked x(PEG/PPG:PDMS)
membranes is the formation of a well-connected interlocked network
structure, which endows the rubbery materials with the properties
of rigid polymers, e.g., size-sieving ability and high thermomechanical
stability. Moreover, the membrane shows long-term antiaging performance
of up to eight months and antiplasticization behavior up to 25 atm
pressure.
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.
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