Catalyst coated membranes (CCMs) in polymer electrolyte fuel cells are subjected to mechanical stresses in the form of fatigue and creep that deteriorate the durability and lifetime of the cells. The present article aims to determine the effect of in-situ hygrothermal fatigue on the microstructure and mechanical properties of the CCM. The fatigue process is systematically explored by the application of two custom-developed accelerated mechanical stress test (AMST) experiments with periodic extraction of partially degraded CCMs. Cross sectional and top surface scanning electron microscope (SEM) images of the end-of-test CCMs reveal the formation of mechanically induced cracks and delamination due to cyclic tensile and compressive fatigue stress. Tensile and expansion tests are conducted at different stages of degradation to evaluate the evolution in the mechanical and hygrothermal properties of the CCM. The tensile test results indicate gradual reductions in final strain, ultimate tensile strength, and fracture toughness with increasing number of fatigue cycles. The decay in tensile properties is attributed to the microstructural damage and micro-cracks formed during the AMST. Moreover, it is shown that the hygrothermal expansion of the CCM is more sensitive to conditioning than mechanical degradation. Polymer electrolyte fuel cells (PEFCs) are a prime candidate to replace gasoline and diesel internal combustion engines for transportation applications due to their environmental benefits combined with rapid start-up, high efficiency, and high power density at relatively low operating temperature.1 The commercialization of PEFCs is dependent on the development of membrane electrode assemblies (MEA) capable of meeting the automotive industry durability targets.2 However, the current PEFC technology is facing insufficient longevity, mainly because of the deterioration of the proton exchange membrane (PEM) component.1 Hence, an essential step to accomplish the commercialization requirements for PEFCs is to enhance the membrane durability and lifetime. Among various types of membranes utilized in PEFCs, perfluorosulfonic acid (PFSA) ionomer membranes (e.g., Nafion from DuPont) are the most widely used materials due to the superior chemical stability attributed to the chemically inert C-F bonds of the polytetrafluoroethylene (PTFE) base structure. 3Chemical and mechanical degradation mechanisms are recognized as the principal root causes for lifetime limiting failures of PFSA ionomer membranes in fuel cells. Understanding of the degradation mechanisms, their interactions, and the corresponding failure modes could provide valuable insight toward decelerating the rate of the membrane degradation and thereby extend the lifetime.2 Chemical degradation is caused by the attack of radical species in the form of hydroxyl (•OH) and hydroperoxyl (•OOH) radicals generated through decomposition of hydrogen peroxide (H 2 O 2 ) by metal contaminants.2,4,5 Hydroxyl radicals also form as a by-product of the electrochemical reaction bet...
At AFCC continuous effort has been made to improve the power density of fuel cell stack for automotive application in the past decade*. The unique challenges in durability posed by the need for much higher power generation per catalyst loading, kW/mg-Pt is still a major driver and a minimum viable stack functionality for mass production. This presentation will focus on one of the ways to meet the above criterion using mature Pt/C technology (10 to 50 wt% Pt on a high surface area carbon) for oxygen reduction in the cathode. The catalysts were custom made by Tanaka Kikinzoku Kogyo K.K to maximize and stabilize the Pt nanoparticles activity during their life cycle. The graph shows the linear dependency of a mix of the above catalysts characteristics such as Pt surface area (CO Chemisorption), Pt crystallite size (XRD), and catalyst surface area (N2 BET) as a function of Pt wt% on Carbon. With more in-depth analyses, preliminary optimization of catalyst layer for each of the above catalysts will be performed and the results will be discussed. These activities would facilitate the understanding of the effect of catalyst characteristics, catalyst structure (ionomer, catalyst layer thickness, EPSA, etc.), and electrode Pt loading (0.25 and 0.15 mg-Pt/cm2) on the high current density performance up to 3 A/cm2. Identifying the above parameters would leverage further development in maximizing the fuel cell functionalities and improving the stack durability. *Reference:AFCC accomplishments, http://www.afcc-auto.com/company/about-us/ Figure 1
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