Fuel cell membranes characteristics

Transport properties of hydrated PFSA membranes strongly depend on nanophase-segregated morphology, water content, and state of water. In an operational fuel cell, these characteristics are indirectly determined by the humidity level of the reactant streams and Faradaic current densities generated in electrodes, as well as the transport properhes of catalyst layers, gas diffusion layers, and flow... 

The PA-doped /m-PBI fuel cell membrane maintains thermal and physical stability while operating at high temperature. To illuminate the fundamental differences in polymer film architecture, polymers with similar physical characteristics were prepared by the conventional PPA Process (Table 13.1). Even though the ratio of phosphoric acid-to-polymer repeat unit (PA/PRU) achieved by both processes were nearly identical, the PPA Process produces membranes with much higher proton diffusion coefficients and conductivities. The higher protmi diffusion coefficients of membranes produced by the PPA... 

Another promising approach is to develop a new generation of radiation-grafted membranes having snlfonic add groups directly attached to the fluorinated polymer backbone without grafting an aromatic ring (polystyrene) host. Some attempts have been reported [95,129,130,143], but more research is needed to estabUsh preparation procedures, the properties of the membranes, and fuel cell performance characteristics. 

Li, Q., R. He, J. O. Jensen and N. J. Bjerrum. PBI-based polymer membranes for high temperature fuel cells - preparation, characteristics and fuel cell demonstration. Fuel Cells 4(3) 147-159, 2004. 

Gubler, L., Ben youcef, H., Alkan Giirsel, S., Wokaun, A. and Scherer, G.G. (2007a) Crosslinker effect on fuel cell performance characteristics of ETFE based radiation grafted membranes. Electrochem. Soc. Trans. 11, 27-34. 

Shim, J., Ha, H. Y., Hong, S. and Oh, I. 2002. Characteristics of the Nation ion-omer-impregnated composite membrane for polymer electrolyte fuel cells. Journal of Power Sources 109 412-417. 

Ramya, K., Velayutham, G., Subramaniam, C. K., Rajalakshmi, N. and Dhathathreyan, K. S. 2006. Effect of solvents on the characteristics of Nation/ PTFE composite membranes for fuel cell applications. Journal of Power Sources 160 10-17. 

It is important to note that Vie and Kjelstrup [250] designed a method of measuring fhe fhermal conductivities of different components of a fuel cell while fhe cell was rurming (i.e., in situ tests). They added four thermocouples inside an MEA (i.e., an invasive method) one on each side of the membrane and one on each diffusion layer (on the surface facing the FF channels). The temperature values from the thermocouples near the membrane and in the DL were used to calculate the average thermal conductivity of the DL and CL using Fourier s law. Unfortunately, the thermal conductivity values presented in their work were given for both the DL and CL combined. Therefore, these values are useful for mathematical models but not to determine the exact thermal characteristics of different DLs. 

X. Liu, H. Guo, F. Ye, and C. F. Ma. Water flooding and pressure drop characteristics in flow channels of proton exchange membrane fuel cells. Electrochimica Acta 52 (2007) 3607-3614. 

Dynamic characteristics of a fuel cell engine are of paramount importance for automotive application. Three primary processes govern the time response of a PEFC. They are (1) electrochemical double-layer discharging, (2) gas transport through channel and GDL, and (3) membrane hydration or dehydration (i.e., between a dry and a hydrated state). The time constant of double-layer discharging is between micro- and milliseconds, sufficiently short to be safely ignored for automotive fuel cells. The time constant for a reactant gas to transport through GDL can be estimated simply by its diffusion time, i.e.,... 

Figure 1.14 Fuel cell characteristics of a 25 cm DEFC recorded with a 30% Pt-Sn (90 10) catalyst. Influence of the working temperature. Anode catalyst, 1.5 mgcrn [30% Pt-Sn (90 10)/XC72] cathode catalyst, 2 mgcm (40% Pt/XC72 from E-TEK) membrane, Nafion 117 ethanol concentration, 1 M. ( ) 50°C ( ) 70°C (A) 90°C (T) 100°C ( ) 110°C.

Figure 1.16 Fuel cell characteristics of a DEFC recorded at 90°C with a 60% Pt-Sn (90 10)/XC72 catalyst for different Nafion membranes. (A) Nafion 117 ( ) Nafion 115 ( ) Nafion 112.

Fig. 13.26. The effect of reformate and reformate with 2% air anode feed on the voltage-current characteristics of a Dow membrane in the reference cell. (Reprinted with permission from Research and Development of Proton-Exchange-Membrane (PEM) Fuel Cell System for Transportation Applications, Phase I. Final Report, prepared for the U.S. Dept, of Energy by General Motors, 1996, Fig. 3.4.5.5.)...

Professor S. Srinivasan and his team have studied the effect of pressure and characteristics of the current-potential relations in a hydrogen-oxygen fuel cell with a proton exchange membrane (Y. W. Rho, O. A. Velev, S. Srinivasan, and Y. T. Kho,./. Electrochem. Soc. 141 2084, 2089, 1994). In this problem, it is proposed to study the applicability of the theoretical dependence of the cell potential as a function of pressure. The temperature is 25 °C and it may be assumed that the pressure of the gas in each of the compartments, i.e., the anodic compartment (hydrogen) and the cathodic compartment (oxygen), are the same, Pn =Po P- For the formation of water in its standard state, the relevant thermodynamic quantities are ... 

Another characteristic of the proton-conducting membrane is that it has low permeability to oxygen and hydrogen in the gas phase so that a high coulombic efficiency exists [7], In addition, in this fuel cell type, the electrodes are normally formed on a thin layer on each side of a protonconducting polymer membrane used as an electrolyte, and platinum catalysts are required for both the anode and the cathode for the proper operation of this fuel cell [9],... 

Cho E.A., Jeon U.-S., Fla H.Y., Hong S.-A., Oh I.-H. Characteristics of composite bipolar plates for polymer electrolyte membrane fuel cells. Journal of Power Sourses 125 (2004) 178-182. 

It is expected that the intermacromolecular complexes display entirely new physical and chemical characteristics different from those of the individual polymer components. So the following applications are, for example, considered membranes for dialysis, ultrafiltration, fuel cells and battery separators, wearing apparel, electrically conductive and antistatic coatings for textiles, medical and surgical prosthetic materials, environmental sensors or chemical detectors, and electrodes modified with specific polymers. 

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