Durability Evaluation

Good durability is a key requirement for the eommereialization of fuel cells. After many years of intensive researeh and development, eonventional power generation teehnologies have achieved excellent durability. These technologies set up a benehmark for fuel cells to meet or, better, to exeeed. At the time this artiele is being written, the reliabihty of a PEM fuel eell is much lower than that of an internal combustion engine, while the eost of the former is much higher than that of the latter. 

A fuel cell decays with time, and the rate of decay determines its durability. The decay is related to the aging of the fuel cell components, especially the membrane electrolyte, the catalysts, and the catalyst support. The decay of the membrane will cause its thinning and mechanical property deterioration. The loss of its mechanical properties often causes a fuel cell to fail prematurely and catastrophically. The decay of the catalyst is normally due to the particle size increase and the particle dissolution and redistribution. Catalyst decay rarely causes a sudden failure of a cell. The decay of the catalyst-support is often related to its corrosion. Corrosion makes the electrode more prone to flooding and accelerates the growth and redistribution of the catalyst particles. 

The following methods can help determine the root causes of the decay and gauge its extent. 

For example, if the H2 crossover current density is 1 mA cm , and assuming the number of electrons (n) involved in the rate determining step, the exchange current density (io), and the charge transfer coefficient (a) of the ORR are 1, 0.01 mA cm, and 0.5, respectively, then the potential loss due to the hydrogen crossover is 0.12 V at T = 25 °C, calculated according to the following  

Please note that n, io, and a used in the calculation are for the ORR instead of the HOR. The reason is that H2 splits into and e when it reaches the cathode, H2 2H -l-2e , and then the ORR forms water O.5O2 + 2H +2e H2O. Since the overpotential due to the HOR is much smaller than that due to the ORR, the latter determines the cathode potential drop. 

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Most of the laboratory development work for this technology on mix design, formulations, processing conditions, property determination and durability evaluation has been completed. In addition, conceptual design and optimization of process conditions for a semi-commercial hydraulic block machine have been worked out. 

In the following subsections, each component of the PEM fuel cell will be described, and modelling and empirical experience of the overall system will be presented, as well as stability and durability evaluations. 

Xiao, J. and Gitis, N., Novel Testing Method and Apparatus for Characterizing Terminological Properties of Lubricant and Durability Evaluation of thin Film Coating, The 7 China National Tribology Conference, pp. 306-307. 

Various evaluations, ranging from the basic components to the entire system, are needed in the development of a fuel cell system. The evaluation may include physical, mechanical, chemical, electrochemical, electrical, and software systems. Performance evaluation is short while durability evaluation may take hours to years. Accelerated evaluation can be utilized once a baseline is established, but establishing the baseline itself may take years. 

Chu W, Karbhari V M and Wu L (2004), Durability evaluation of moderate temperature cured E-glass/vinylester systems . Compos Struct, 66, 367-376.doi 10.1016/j. compstruct. 2004.04.058... 

M.C. Lee, C.H. Wang, W.X. Kao, Y.C. Chang, T.N. Lin, and Y.H. Shiu, Fabrication and Performance Test for Durability Evaluation of lNER-SOFC-MEA(W-l2) via Spin Coating Process, INER-5353R, INER, Taiwan, July 2008. 

Lee, T.N. Lin, W.X. Kao, R.J. Yang, and L.S. Lee, Performance and Durability Evaluation of the Anode-supported Solid Oxide Fuel Cell after Long-term operation. Paper number XOO-002, Proceedings of 2012 Taiwan Symposium on Carbon Dioxide Capture, Storage and Utilization, November 25-27, Taipei. 

For a more complete system-based durability evaluation, it is common to include the DOC and DPF in the aging protocol, and to rely on HC oxidation over... 

J. D. Minford, Durability evaluation of adhesive bonded structures, in Adhesive Bonding (L. H. Lee, ed.). Chapter 9, Plenum Press, New York (1991). 

Brewis, Comyn, and Phanopoulos i) have very recently made joint durability evaluations of nonextracted, water-extracted, and solvent-extracted wood adherends their results indicate that the level of surface extractions have a major influence on both strength and durability of the joints. 

Finally, reference should be made to the extensive and recent durability evaluations of rubber-to-steel bonded joints in seawater. These kinds of bonds have been of especial interest to the fabricators of the deep ocean oil rigs. Stevenson ) has shown that the rate of adhesive bond failure between two metals of different electrochemical potential have special qualities that need to be understood by the designer. First, however, he demonstrated that mechanical strain in the elastomer layer did not seem to have any effect on bond durability. Furthermore, if the two adherends were electrochemically inert then the bonds were completely stable after periods as long as three years in saltwater. There was, however, an expected result when one adherend was more noble. While that adherend would be less corroded because of the electrochemical protection by the more anodic adherend, there was also a distinct increase in the rate of adhesive bond failure at that interface. 

Chatterjee, S., Conway, R., Lanni, T., et al. (2002). Performance and Durability Evaluation of Continuously Regenerating Particnlate Eilters on Diesel Powered Urban Buses at NY City Transit - Part It, SAE Technical Paper, 2002-01-0430. 

Fig. 3 Testing apparatus for start-stop durability evaluation. Mass Flow Controller (MFC)...

Some durability evaluations use a combination of these elements of accelerated ageing. For example, an indication of the durability of adhesives used for bonding thermoplastic pressure pipe systems is given in EN 14814 2007, Adhesives for thermoplastic piping systems for fluids underpressure. Specifications, which references the test method given in ISO 9311-3, where test... 

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