Abstract
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.
Highlights
IntroductionAs global environmental issues—including global warming and air pollution—get severe, renewable, and sustainable power sources have attracted significant attention
The extra electricity can be employed to generate hydrogen, and it can be used for providing sustainable electricity by using fuel cells
Were conducted at the same conditions as polarization tests with impedance spectroscopy measurements were conducted at the same conditions as polarization tests with impedance (HCP 803, Biologic, France)
Summary
As global environmental issues—including global warming and air pollution—get severe, renewable, and sustainable power sources have attracted significant attention. Even with significant technological advances in fuel cell components, including the catalyst, electrolyte membrane, gas diffusion layer, and bipolar plates, it is still challenging to create high-performance, reliable, and durable fuel cells [6–11]. When it comes to the stability issue of the electrolyte membrane, though the widely used Nafion® electrolyte membrane—. Concerning the chemical stability, radicals such as H2 O2 , HO, and HOO, generated during the oxygen reduction reaction, deteriorate the membrane’s surface, leading to the formation of a pinhole [12–15] This issue has been addressed and partially solved through a remarkable achievement: introducing radical scavengers, such as organic chemical species, inorganic nanoparticles, and metal ions, into the electrolyte membranes [16–18]. This study deduced the morphological rearrangement of microscopic structures in the Nafion® membrane based on a comparison of the changed microscopic and macroscopic mechanical properties of thermally annealed Nafion® membranes
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