Membrane electrode assembly degradation

Modeling of Membrane-Electrode-Assembly Degradation in Proton-Exchange-Membrane Fuel Cells - Local H2 Starvation and Start-Stop Induced Carbon-Support Corrosion... 

Abstract In recent years, the importance of fuel cell vehicles has been increasing in the North American, European, and Japanese markets amid desires to reduce COj emissions and resolve energy problems. Therefore, improving stack durability has become an increasingly important issue. However, many membrane electrode assembly degradation phenomena occur in the stack under various vehicle operating conditions. This chapter presents an analysis of membrane electrode assembly degradation phenomena and the results obtained with several durability improvement measures. 

S. Kim, B. K. Ahn, and M. M. Mench. Physical degradation of membrane electrode assemblies rmdergoing freeze/thaw cycling Diffusion media effects. Journal of Power Sources 179 (2008) 140-146. 

The properties of Nafion at freezing temperatures can be quite relevant, for example, within the context of fuel cells in vehicles with regard to cold-starting, as well as the degradation of membrane/electrode assemblies due to the freezing of in situ water. 

Bae, S.J., Kim, S.-J., Park, J.I., Lee, J.-H., Cho, H., and Park, J.-Y. (2010) Lifetime prediction through accelerated degradation testing of membrane electrode assemblies in direct methanol fuel cells. Int.J. Hydrogen Energy, 35, 9166-9176. Shao, M. (2011) Palladium-based electrocatalysts for hydrogen oxidation and oxygen reduction reactions. J. Power Sources, 196, 2433-2444. 

The reasons for the deterioration of ceU performance can be distinguished in reversible and irreversible power loss. Inevitable irreversible performance loss is caused by carbon oxidation, platinum dissolution, and chemical attack of the membrane by radicals [7]. Reversible power loss can be caused by flooding of the cell, dehydration of the membrane electrode assembly (MEA), or change of the catalyst surface oxidation state [8]. If corrective actions are not started immediately, reversible effects lead to irreversible power loss that we define as degradation. In this chapter, we focus on the degradation of the catalyst layer due to undesired side reactions. 

While most modeling efforts have focused on steady-state operation, the dynamic behavior is of paramount importance for fuel-cell transportation appHcations due to the inherent load variation involved. Transient phenomena in automotive fuel cells are not yet fully understood. In addition to the complex dynamic response involving various time scales, severe degradation of membrane electrode assemblies... 

MSC-MEA (Membrane Electrode Assembly) in cell test are 650. 568 and 443 mW/cm at 750, 700 and 650°C, respectively. For single cell MSC stack with 80% hydrogen, the maximum power densities are 391, 306 and 194 mW/cm at 750, 700 and 650 C, respectively, and the estimated degradation rate of --0.3%/kh is obtained after 1,100 hrs operation. For 5-cell MSC stack with reformed gas, the stack delivers 115.4 Watts at 700°C and 0.77 V of average cell voltage and shows no degradation after 110 hrs operation. 

Carter RN, Gu W, Brady B, Yu PT, Subramanian K, Gasteiger HA (2009) Membrane electrode assembly (MEA) degradation mechanism studies by current distribution measurements. 

The performanee and durability of a membrane electrode assembly (MEA) is affected signifieantly by the eathode eleetrode eomposition and structure, due to the poor kineties of oxygen reduetion and reaetant transport limitations. Utilization and stability of platinum or its alloys in the PEMFC play important roles in fuel cell efficiency, durability, and the drive for eost reduction through reduced Pt loadings. Cathode catalyst layer degradation is a critical issue for fuel cell durability to meet the requirement of > 5000 hours for automotive applications and > 40,000 for stationary applications. 

Galibiati et al. [147] observed gradually increased hydrogen crossover and short circuit current during continuous operation at 400 mA cm for 6000 h at 180 °C, which is an indication of membrane-related degradation. Post mortem analysis of membrane-electrode assemblies that had been operated at constant load of 200 mA cm at 150 °C, revealed considerable membrane thinning starting after about... 

Jao TC, Ke ST, Chi PH et al (2010) Degradation on a PTFE/Nafion membrane electrode assembly with accelerating degradation technique. Int J Hydrogen Energy 35 6941-6949... 

Membrane electrode assemblies (MEAs) durability with cycling (10 % degradation) h - - 5000... 

Fig. 2. Typical membrane-electrode assembly in a proton exchange membrane fuel cell (PEMFC). The enlarged part shows that on a microscopic scale the gas diffusion layers, the electrodes and the membrane are inhomogeneous, leading to restrictions for the transport of gases, electrons, and protons. Under heavy loads these conditions cause large inhomogeneities in temperature, pH, and electrochemical potential, which are highly significant for membrane degradation processes.

Kim S and Mench M M (2007), Physical degradation of membrane electrode assemblies undeigoing freeze/thaw cycling Micro-structure effects . Journal of Power Sources, 174,206-220. 

Furthermore, most degradation experiments are performed using membrane electrode assemblies (MEAs). Although certainly needed for applications, studies using MEAs are not only rather time-consuming, difficult to analyze and expensive, but also prone to a large number of experimental variables in MEA... 

Corrosion and degradation phenomena at various parts of the membrane electrode assembly (MEA) are strongly accelerated by temperature temperature uncertainty can affect the performance predictions of PEMFC models accounting for degradation phenomena, as shown by Placca et al. (2009). 

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