Fuel permeability

There is also a significant drawback the inherently higher fuel permeability of polymers. The strengthening of environmental regulations (PZEV Partial Zero Emission Vehicle) leads to severe requirements concerning fuel impermeability, needing modification of the techniques now in use. Moreover, some carmakers such as Ford and GM require higher mechanical and thermal resistance, and conductive materials. 

Direct fuel permeability data were scarce in the literature for these inorganic/PBl hybrid... 

The fuel used for testing fuel permeability according to ECE-R 34 (ECE Regulation 34 Certification of Vehicles with respect to Fire Prevention) is either a test fuel or a commercial high-octane fuel. Before the actual test begins, the fuel tank is filled to 50% of its nominal content and pre-stored with full pressure compensation to ambient pressure at 40°C until it reaches a constant weight loss, but no longer than four weeks. This time is the minimum required for the plastic wall to swell with fuel [515]. 

A higher current density of 0.52 amp cm was obtained for the SPTES-50 polymer membrane-based MEA as compared with a current density of 0.24 amps cm for Nafion-117 membrane-based MEA at 0.6 V potential. Similarly, a higher peak power density of 0.34 W cm was obtained using SPTES-50 polymer membrane compared with 0.16 W cm using Nation-117 membrane in MEAs, measured under the same conditions. Estimates of hydrogen fuel permeability based upon measured open circuit voltage (OCV) indicate that SPTES-50 MEA and Nafion-117 exhibit similar rates of fuel crossover. 

From these shortcomings, the tasks for the designation of improved fuel cell membranes, compared with the state of the art, can be defined. The property profile of improved ionomer fuel cell membranes includes high -conductivity, low water/ methanol uptake, low methanol (and other liquid fuel) permeability, and fuel cell-applicability also at T > 100°C, because the higher the fuel cell operation temperature, the higher the fuel utilization, and applicability also in other (electro)membrane processes. Last but not least, the membranes should have a low price. 

Low methanol (and other liquid fuel) permeability Fuel cell-applicability also at T > 100°C... 

Many new polymers have been synthesized and tested for their proton conductivity, methanol permeability, thermal as well as mechanical stability, electrode-manbrane interface connectivity, etc., aiming at improvanent in m brane performance for fuel cell applications. These efforts seem to continue with insightfirl vision and strong commitment in the fnture. However, only a handful of polymers are currently being used as the materials for commercial apphcations, and they are not necessarily the polymers of the best performance properties. This is mainly due to the cost factor that governs the present membrane rrrarket. The fuel cell performance of membranes is, on the other hand, known primarily ruled by the various factors, mainly, membrane fuel permeability, electrode-membrane adhesion (or compatibility), thermal and mechanical stabilities. The knowledge of the effects of these factors on... 

DN4265 42 58-72 1.00 C NS High ACN for balance of low temperature, fuel resistance, and low fuel permeability... 

DN003 50 70-85 1.02 C SS Very high ACN level for excellent resistance to oils and fuels. Low fuel permeability... 

Two main methods were used for fuel permeability determination ex situ and in situ methods. The former method, also named diffusion cell method, was mostly used for methanol permeability measurements [22,84,85]. In this measurement, a diffusion cell was used, consisting of two reservoirs of distinct composition, with a sample membrane between them. The membrane acts as a parting plane to prevent liquid passing through directly and only permit permeation of the molecules in solution. The two reservoirs were injected with aqueous methanol solution with a certain... 

MEA should be fabricated from the sample PEMs and then assembled into the single-cell system, which is the same as fuel cell. Potential step experiments were performed to evaluate fuel permeability using an electrochemical interface with a certain flow rate of humidified H2 at the anode and humidified N2 at the cathode. The anode served as both the counter and reference electrodes. The cathode potential was increased gradually, and the steady-state current density corresponds to the H2 crossover current density. Although more complicated than ex situ method, the in situ method is much more accurate and closer to the real situation of fuel cell operation. 

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