Interface
engineering based on the design and fabrication of micro/nanostructures
has received much attention as an effective way to improve the performance
of polymer electrolyte membrane (PEM) fuel cells while using the same
materials and quantity. Herein, we fabricated spatially hole-array
patterned PEMs with different hole depths using both the plasma etching
process and a polymeric stencil with 40 μm-sized apertures.
This novel technological approach exhibited high pattern fidelity
over a large area and controllability in the pattern depth while excluding
the problems of contact-based conventional patterning processes. All
the membrane electrode assemblies (MEAs) with the patterned PEMs with
an etch depth of 4 μm (PE4-MEA), 8 μm (PE8-MEA), and 12
μm (PE12-MEA) showed higher performance than the reference MEA
with a pristine PEM. Among the modified MEAs, the PE8-MEA showed the
highest performance enhancement because of the locally thinning effect
of the PEM, geometrically favorable features for mass transport, and
increased interfacial contact area between the PEM and the catalyst
layer.
A thin
electrolyte membrane is highly demanded for achieving high-performance
polymer electrolyte membrane fuel cells (PEMFCs) by taking advantage
of the reduced ohmic resistance-driven enhanced proton- and water-transport
property during the PEMFC operation. However, the thin membrane inherently
suffers from poor mechanical properties. In this study, we propose
a simple methodological approach that combines the plasma etching
and thermal annealing process to construct mechanically stable thinned
membrane using commercially available Nafion membranes. The morphological,
mechanical, and chemical properties of the modified Nafion membranes
were characterized through diverse measurements including field-emission
scanning electron microscopy, atomic force microscopy, stress–strain
behavior test, and Fourier transform infrared spectrometry. We observed
that the plasma etching process effectively reduced the membrane thickness;
however, it induced spike-like structures with hundreds of nanometers
in size on the membrane surface, which can cause stress-concentration-induced
mechanical degradation of the membrane. By adopting a consecutive
thermal annealing process, the roughened surface was flattened and
mechanical properties including tensile strength and elongation to
break were successfully recovered while maintaining the chemical composition
of the Nafion. Interestingly, the modified 15 μm-thick Nafion
membrane with the plasma etching and thermal process showed a much
enhanced maximum power density of 22.5 and 13.6% under the low and
high humidity condition of RH 45% @89.5 °C and RH 92% @70 °C,
respectively, compared to that of a pristine 25 μm-thick Nafion
membrane.
The instability of polymeric membranes with nano- and micro-sized apertures has been regarded as one of the main reasons behind realizing ultra-thin membranes with apertures. As is well known, when the thickness of the membrane gets thinner or the aperture size gets smaller, the possibility of geometrical deformation or structural damage by collapse or fracture increases. Herein, we suggest the design rules for the stability of polymeric membranes possessing 1D nano-line patterns monolithically constructed on micro-aperture supporting layers. The proposed theoretical model, which has been thoroughly demonstrated and analyzed based on both theoretical and experimental approaches, provides stability criteria for lateral collapse and vertical fracture of ultra-thin membranes with apertures.
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