Performance losses

A further complication arises from the fact that the point of maximum damage to the pump by cavitational pitting happens somewhere between the incipient cavitation and the point of complete performance loss (56). Whereas it is difficult to predict incipient cavitation, it is even more difficult to determine the point of maximum damage. Many attempts have been made, but no method has been accepted. It has been reported that the damage is... 

Oil and Grease—Over 10 ppm will cause noticeable thermal performance loss. 

A considerable decrease in platinum consumption without performance loss was attained when a certain amount (30 to 40% by mass) of the proton-conducting polymer was introduced into the catalytically active layer of the electrode. To this end a mixture of platinized carbon black and a solution of (low-equivalent-weight ionomeric ) Nafion is homogenized by ultrasonic treatment, applied to the diffusion layer, and freed of its solvent by exposure to a temperature of about 100°C. The part of the catalyst s surface area that is in contact with the electrolyte (which in the case of solid electrolytes is always quite small) increases considerably, due to the ionomer present in the active layer. 

Eickes C, Piela P, Davey J, Zelenay P. 2006. Recoverable cathode performance loss in direct methanol fuel cells. J Electrochem Soc 153 A171-A178. 

Column/injector maintenance. The use of a guard column, in addition to scheduled injector maintenance, provides significantly improved GC performance. Loss of performance manifests itself in poor peak shape and reduced sensitivity. This is particularly noticeable with atrazine but also with the other analytes. Maintenance should include removal of a 30-60 cm section of the guard column and replacement of the... 

Reliability/longevity Consistent performance over life of vehicle Durability, cycle life, and minimal performance loss due to contaminants and a range of operating conditions over time... 

Carbon Monoxide. Carbon monoxide, a fuel in high-temperature cells (MCFC and SOFC), is preferentially absorbed on noble metal catalysts that are used in low-temperature cells (PAFC and PEFC) in proportion to the hydrogen-to-CO partial pressure ratio. A particular level of carbon monoxide yields a stable performance loss. The coverage percentage is a function of temperature, and that is the sole difference between PEFC and PAFC. PEFC cell limits are < 50 ppm into the anode major U.S. PAFC manufacturers set tolerant limits as < 1.0% into the anode MCFC cell limits for CO and H20 shift to H2 and C02 in the cell as the H2 is consumed by the cell reaction due to a favorable temperature level and catalyst. 

Low redox cycling tolerance. Redox cycling occurs when the fuel flow to the stack is interrupted. Air leaking in from the environment will oxidize the nickel. Upon recovery of the fuel flow the nickel oxide will reduce again. Such a cycle will cause considerable performance loss due to coarsening of the nickel particles in the anode. 

Aluminum is produced according to the Hall-Heroult process [42-44]. At the cathode, AlxFy species are reduced and lead to liquid aluminum. As the electrolysis proceeds, the metal from the aluminum oxide precipitates at the bottom of the cell. At the anode, oxygen evolution takes place producing carbon dioxide/monoxide and hence resulting in current and performance losses [42-44]. 

Stable performance was demonstrated to 4,000 hours with Nafion membrane cells having 0.13 mg Pt/cm and cell conditions of 2.4/5.1 atmospheres, H2/air, and 80°C (4000 hour performance was 0.5 V at 600 mA/cm ). These results mean that the previous problem of water management is not severe, particularly after thinner membranes of somewhat lower equivalent weight have become available. Some losses may be caused by slow anode catalyst deactivation, but it has been concluded that the platinum catalyst "ripening" phenomenon does not contribute significantly to the long-term performance losses observed in PEFCs (5). 

AFCs suffer a drastic performance loss with fuels containing CO2 from reformed fuels, and from the presence of CO2 in air (approximately 350 ppm CO2 in ambient air). The negative impact of CO2 arises from its reaction with OH ... 

DMFC performance losses causedby average (left) and extreme (right) contamination of Pt cathodes by crossover Ru. (P. Zelenay, Electrochemical Society Transactions, 1,483 (2006). Reproduced by permission of The Electrochemical Society.)... 

It is important to note that most of fhese sfudies concenfrated on the cathode side of the PEMFC because it has been shown that the difference between materials on the anode side does not represent a major performance loss due to flooding at high- or low-humidity conditions [97]. Therefore, the type of DL used on the anode side does not result in major differences over a wide range of operating conditions. 

For any battery applications, the separator should have uniform pore distribution to avoid performance losses arising from nonuniform current densities. The submicrometer pore dimensions are critical for preventing internal shorts between the anode and the cathode of the lithium-ion cell, particularly since these separators tend to be as thin as 25 /[Pg.192]

As shown in this review, test equipment integrated with several diagnostic techniques is preferred for a deeper insight into the mechanisms that cause performance losses and spatial non-uniform distribution. As a consequence, more information, which is simultaneously obtained with these diagnostic tools, will strongly support development of empirical models or validate theoretical models predicting performance as a function of operating conditions and fuel cell characteristic properties. 

Analysis of performance loss due to non-ideal geometries caused by fabrication needs... 

The relative contribution to performance loss (TMP rise at constant flux) of resistance PF or CEOP depends on the particle size. For particles >0.5 pm the resistance is relatively small (see effect of particle size in Equation 6.4) and CEOP due to cake height, 8C, is the major effect [48], It is also observed that biofilms can contribute substantial CEOP effects as well as resistance, and in a recent biofouling study more than 50% of the required TMP rise was due to CEOP effects [32]. 

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