Ionomers impregnation

The factors 4 and 4 accormt for the heterogeneity of the interface. The interfacial flux conditions. Equations (6.56) and (6.57), can be straightforwardly applied at plain interfaces of the PEM with adjacent homogeneous phases of water (either vapor or liquid). However, in PEFCs with ionomer-impregnated catalyst layers, the ionomer interfaces with vapor and liquid water are randomly dispersed inside the porous composite media. This leads to a highly distributed heterogeneous interface. An attempt to incorporate vaporization exchange into models of catalyst layer operation has been made and will be described in Section 6.9.4. 

Impregnating these layers with PFSA ionomer for enhanced proton conduction or hydrophobizing agents like Teflon for sufficient gas porosity is optional. However, ionomer impregnation is indispensable in CLs with thicknesses of > 1 ftm. Ultrathin CLs with - 100-200 nm, on the other hand, can operate well without these additional components, based on sufficiently high rates of transport of dissolved reactant molecules and protons in liquid water, which could ensure uniform reaction rate distributions over the entire thickness of the layer. 

Improving Catalyst Utilization by Ionomer Impregnation of Gas Diffusion Electrodes... 

Fig. 13. Effects of CO level (ppm) in the hydrogen feed stream on the performance of a PEFC at 80 °C. Both electrodes were based on an ionomer-impregnated Pt/C catalyst and thin sputtered platinum film, of total loading 0.45 mg Pt/cm [17].

Al Hot-pressed Pt black/PTFE layers B1 Ionomer - impregnated Pt/C//PTFE... 

Fig. 25. Air cathode catalyst utilization for different types of catalyst layers in contact with ionomeric membranes. , Platinum black/PTFE (4 mg/cm ) ionomer-impregnated gas-diffusion electrodes (0.45 mg Pt/cm ) A, thin film of Pt/C//ionomer composite (0.13 mg Pt/cm ). The advantage of thin-film catalyst layers increases particularly at high current density (lower cell voltage) because transport limitations within the catalyst layer are minimized.

A1) Applied and hot-pressed Pt /PTFE (A2) Electroless deposition of Pt on membrane (A3) Applied and hot-pressed Pt/C(or Pt)//ionomer within ionomer-impregnated carbon paper (A4) Alloy catalyst sputtered onto array of nanowhiskers and the catalyzed array embedded into the membrane surface (Bl) Pt/C//PTFE applied to substrate and impregnated with recast ionomer (B2) (Bl) + sputtered Pt layer (B3) Pt catalyst electrodeposited... 

Fig. 23 Air cathode catalyst mass utilization (A mg-1 Pt) for different types of catalyst layers as developed chronologically for hydrogen/air PEFC. Squares PTFE-bonded Pt black at 4 mg Pt/cm2 circles ionomer-impregnated, PA- type electrodes (0.45 mg Pt/cm2) triangles thin-film Pt/C//ionomer composite (0.13 mg Pt/cm2). The relative advantage of thin-film catalyst layers is seen to increase with cell current density, as expected from the lower transport limitations involved (see Sect. 8.3.7.2.3) [10,11].

Prepare Nation ionomer-impregnated Pt/C catalyst ink by dispersing Pt/C catalyst and Nafion solution in isopropanol, followed by a thorough ultrasonic treatment the weight ratio of Nafion to the carbon support of Pt/C is controlled at 4 5. 

FIGURE 3.31 A comparison of the calculated proton concentration in Pt-NSTF layers, displayed as pH versus Ef, with that encountered in ionomer impregnated CLs. (Reprinted from Chan, K. and Eikerling, M. 2011. /. Electrochem. Soc., 158(1), B18-B28, Figures 1,2,3,4,5,6. Copyright (2011), the Electrochemical Society. With permission.)... 

Pt dissolution mainly occurs in the high potential region where proton concentrations in UTCLs are significantly smaller than those in ionomer-impregnated CLs, as can be seen in Figure 3.31. Since Pt dissolution exhibits a strong dependence on proton concentration kdiss (Rinaldo et al., 2010), Pt dissolution rates... 

J. Shim, H. Y. Ha, S. A. Hong and I. H. Oh, Chtuacteristics of the Ntifion ionomer-impregnated composite membrane for polymer electrolyte fuel cells, J. Power Sources 109, 412-417 (2002). 

Polyolefins like polyethylene (PE) and PE terephthalate (PET) are the most widely used polymers in many commercial applications. Owing to its excellent chemical and electrochemical stability, low cost, and easy preparation, in the recent decade, some of the researchers have shifted attention to these polymers. Sulfonated poly(arylene ether sulfone), poly(vinylbenzyl chloride) (PVBC), and polystyrene (PS) have been grafted onto PE [41-43], which were designed for DMFC, proton-exchange man-brane fuel cell (PEMFC), or AFC. In addition, PET has also been utilized for DMEC through Nafion ionomer impregnating by Lee and cowoikers [44]. 

Ionomer impregnation In the ionomer impregnation method described by Gottesfeld and Zawodzinski (1997) the catalytically active side of GDL is painted with solubilized PFSA in a mixture of lower aliphatic alcohols and water. To improve reproducibility of the GDL/catalyst assembly, the catalyst and ionomer are premixed before the catalyst layer is deposited, rather then ionomer impregnation of Pt/C//PTFE layer. 

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