Mechanical Properties of PEMFC Electrodes According to Fabrication Methods

Abstract

Electrodes in a polymer electrolyte membrane fuel cell (PEMFC) are the crucial element performing electrochemical reactions and are the most vulnerable mechanically. Various operating conditions (freeze-thaw, start-up, shut down) generate buckling, cracks, and delamination in electrodes. These mechanical failures not only directly affect the performance of the PEMFC cell but also act as a fatal factor in shortening the lifespan. Therefore, understanding and improving the mechanical properties of electrodes is essential for designing high-durability PEMFCs. Furthermore, the fabrication method of electrodes is a factor that causes not only performance but also distinct mechanical property differences since it determines their internal structure and surface characteristics. However, evaluating the mechanical properties of electrodes has been challenging because they are fragile and hard to separate from substrates. Therefore, this study evaluated the intrinsic mechanical behaviors of the electrodes according to fabrication methods via a free-standing tensile test. The effect of fabrication methods was analyzed for blade coating and spray coating methods used universally from industry to laboratory. The difference in mechanical properties between the two methods was identified by analyzing the internal structure and distribution of ionomer agglomerate. For blade-coated electrodes, modulus (372.5 MPa) and elongation (2.44%) were 2-2.7 times higher than spray-coated electrodes (172.9 MPa,0.9%). The difference in mechanical properties originated from the electrodes’ surface and internal structures. Blade-coated electrodes were composed of smaller pores and volume than the spray coating using FIB-SEM. The modulus ratio according to the internal structure through finite element analysis (using ABAQUS software) was consistent with the actual experimental value. In addition, blade-coated electrodes have high elongation and strength because they enable uniform stress transmission with a smooth surface and uniform ionomer binder distribution (analyzed by HAADF-STEM and EDS). This study contributes to a better understanding of the mechanical properties of electrodes according to the fabrication methods and provides guidelines for mechanical improvement. Figure 1