Catalyst layer fundamentals

Zhang, H., Wang, X., Zhang, J., and Zhang, J. Conventional catalyst ink, catalyst layer, and MEA preparation. In PEM fuel cell electrocatalysts and catalyst layers Fundamentals and applications, ed. J. Zhang. London Springer, 2008. 

Yuan, X. Z., Wang, H. (2008). PEM fuel cell fundamentals. PEM Fuel Cell Electrocatalysts and Catalyst Layers Fundamentals and Annlications. Springer London pp. 1-87. 

Shen, P.K. In Zhang, J. (ed.) PEM Fuel Cell Electrocatalysts and Catalyst Layers, Fundamentals and Applications, pp. 355-380. Springer, London (2008)... 

Sun X, Saha MS (2008) Nanotubes, nanolibers and nanowires as supports for catalysts. In Zhang J (ed) PEM fuel cell electrocatalysts and catalyst layers fundamentals and applications. Springer, New York... 

Eikerling M, Malek K, Wang Q (2008) Catalyst layer modeling structtue, properties, and performance. In Zhang JJ (ed) PEM fuel cells catalysts and catalyst layers—fundamentals... 

H Zhang, X Wang, J Zhang, Chapter 19, in PEM Fuel Cell Electrocatalysts and Catalyst Layers Fundamentals and Applications, ] Zhang (Ed.), 2008, Springer-Verlag, London. 

Zhang J (2008) PEM fuel cell electrocatalysts and catalyst layers fundamentals and applications. Springer, London... 

In order to make catalyst layers with high platinum utilization and better performance, we need to determine how various factors affect Pt utilization. Although this objective has been receiving more attention, we have not achieved a fundamental understanding of the relationships of composition, structure, effective properties, and fuel cell performance—a fact that may limit the optimal design and fabrication of CLs. 

The materials of greatest interest in view of fundamental understanding and design are the polymer electrolyte membrane and the catalyst layers. They fulfill key functions in the cell and at the same time offer the most compelling opportunities for innovation through design and integration of advanced materials. 

At macroscopic level, the overall relations between structure and performance are strongly affected by the formation of liquid water. Solution of such a model that accounts for these effects provides full relations among structure, properties, and performance, which in turn allow predicting architectures of materials and operating conditions that optimize fuel cell operation. For stationary operation at the macroscopic device level, one can establish material balance equations on the basis of fundamental conservation laws. The general ingredients of a so-called "macrohomogeneous model" of catalyst layer operation include ... 

Recently Meng17 developed a transient, multiphase, multidimensional PEFC model to elucidate the fundamental physics of cold start. The results showed the importance of water vapor concentration in the gas channels, which implies that large gas flow rates benefit cold-start performance. They also found that ice growth in the cathode catalyst layer during cold start was faster under the land than under the gas channels, and accumulated more at the interface between the cathode catalyst layer and GDL. 

To increase fundamental knowledge about ionic resistance, it is important to develop a methodology to experimentally isolate the contributions of the various cell components. Electrochemical impedance spectroscopy has been widely used by Pickup s research group to study the capacitance and ion conductivity of fuel cell catalyst layers [24-27] they performed impedance experiments under a nitrogen atmosphere, which simplified the impedance response of the electrode. Saab et al. [28] also presented a method to extract ohmic resistance, CL electrolyte resistance, and double-layer capacitance from impedance spectra using both the H2/02 and H2/N2 feed gases. In this section, we will focus on the work by Pickup et al. on using EIS to obtain ionic conductivity information from operational catalyst layers. 

This chapter has examined a variety of EIS applications in PEMFCs, including optimization of MEA structure, ionic conductivity studies of the catalyst layer, fuel cell contamination, fuel cell stacks, localized impedance, and EIS at high temperatures, and in DMFCs, including ex situ methanol oxidation, and in situ anode and cathode reactions. These materials therefore cover most aspects of PEMFCs and DMFCs. It is hoped that this chapter will provide a fundamental understanding of EIS applications in PEMFC and DMFC research, and will help fuel cell researchers to further understand PEMFC and DMFC processes. 

The membrane and ionomer humidification reqnire-ments are of paramount importance for PEMFC operation since the proton conductivity is a fundamental necessity in the membrane as well as in the electrode for the fnel cell to function. The operating conditions of cnrrent PEMFCs are dictated by the properties of the membranes/ionomers. At present, the most important membrane type (e.g., Naflon membranes from DuPont) is based on PFSA ionomers that are used in the membrane and the catalyst layers. Figure 21.3 shows the proton conductivity versus RH for three different... 

Once one chooses to create a catalyst layer with finite thickness, however, one must then consider the transport of reactants through the thickness of that layer. At the most fundamental level, an examination of the two defining reactions of a fuel cell reveals the engineering challenge that must be confronted in designing a catalyst layer. These reactions are, of course... 

The exchange current density is the key property of catalyst layers. It determines the value of the overpotential needed to attain the targeted fuel cell current density. This property, thus, links fundamental electrode theory with practical aspects of fuel cell performance. The following parameterization distinguishes explicitly the effects of different structural characteristics,... 

In spite of the complexity of catalyst layers, the presented theoretical tools contribute to the fundamental understanding of structure-funetion relations, and they provide guidelines for upgraded diagnostics and design. Parasitic voltage losses that are eaused by reduced activity of the catalyst, impaired mass transport, and insuffieient water management could be minimized. 

Use of a high methanol concentration but maintaining an adequate concentration in the anode catalyst layer at a given current density to maximize the system specific energy and cell performance. For achieving this aim it is fundamental an optimum design of the fuel supply system (that allows the orientation-independent operation of the fuel cell), the anode current-collector, and the anode diffusion layer. 

RDE is a commonly used technique for investigating the ORR in terms of both the electron transfer process on electrode surface and diffusion—convection kinetics near the electrode. To make appropriate usage in the ORR study, fundamental understanding of both the electron transfer process on electrode surface and diffusion—convection kinetics near the electrode is necessary. In this chapter, two kinds of RDE are presented, one is the smooth electrode surface, and the other is the catalyst layer-coated electrode. Based on the electrochemical reaction 0 + ne R), the RDE theory, particularly those of the diffusion—convection kinetics, and its coupling with the electron-transfer process are presented. The famous Koutecky—Levich equation and its... 

---