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.

The Nafion® electrolyte membrane, which provides a proton pathway, is an essential element in fuel cell systems. Thermal treatment without additional additives is widely used to modify the mechanical properties of the membrane, to construct reliable and durable electrolyte membranes in the fuel cell. We measured the microscopic mechanical properties of thermally annealed membranes using atomic force microscopy with the two-point method. Furthermore, the macroscopic property was investigated through tensile tests. The microscopic modulus exceeded the macroscopic modulus over all annealing temperature ranges. Additionally, the measured microscopic modulus increased rapidly near 150 °C and was saturated over that temperature, whereas the macroscopic modulus continuously increased until 250 °C. This mismatched micro/macroscopic reinforcement trend indicates that the internal reinforcement of the clusters is induced first until 150 °C. In contrast, the reinforcement among the clusters, which requires more thermal energy, probably progresses even at a temperature of 250 °C. The results showed that the annealing process is effective for the surface smoothing and leveling of the Nafion® membrane until 200 °C.

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.

No abstract