Catalyst layer operation layers

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 ... 

B. Andreaus and M. Eikerling. Catalyst layer operation in PEM fuel cells From structural pictures to tractable models. In Device and materials modeling in PEM fuel cells, ed. K. Promislow and S. Paddison, Topics in applied physics 113, 41-90. New York Springer, 2009. 

The basic equations of catalyst layer operation, Eqs. (42-46), are valid under the assumption of isothermal, stationary conditions. Furthermore, variations of the water vapor partial pressure are neglected. The water content in the PFSI fractions and the corresponding proton conductivity are, therefore, independent of x- Upon proceeding along x, starting at x = 0 with /p(X = 0) = jo, proton current is gradually converted into C>2 flux jo2 = (j-p(x) — y o)/4. At x = 1 the transformation is complete, yp = 0, since no protons are admitted to pass the interface to the GDF. 

At high anodic overpotentials, methanol oxidation reaction exhibits strongly non-Tafel behavior owing to finite and potential-independent rate of methanol adsorption on catalyst surface [244]. The equations of Section 8.2.3 can be modified to take into account the non-Tafel kinetics of methanol oxidation. The results reveal an interesting regime of the anode catalyst layer operation featuring a variable thickness of the current-generating domain [245]. The experimental verification of this effect, however, has not yet been performed. 

Catalyst Layer Operation in PEM Fuel Cells From Structural Pictures to Tractable Models... 

How are we going to disentangle this mess The strategy of the modeling approaches reviewed in this contribution is to start from appropriate structural elements, identify relevant processes, and develop model descriptions that capture major aspects of catalyst layer operation. In the first instance, this program requires theoretical tools to relate structure and composition to relevant mass transport coefficients and effective reactivities. The theory of random... 

Kulikovsky, A.A. (2010) The regimes of catalyst layer operation in a fuel cell. Electrochim. Acta, 55, 6391—6401. Newman, ). (1991) Electrochemical Systems, Prentice Hall, Englewood Cliffs,... 

Importantly, the regime of catalyst layer operation depends on parameter e. The transition from low- to high-current mode occurs in the transition... 

A. A. Kulikovsky. Active layer of variable thickness The limiting regime of anode catalyst layer operation in a DMFC. Electrochem. Comm., 7 969-975, 2005d. 

Figure 8.1. Outline of the general framework for structure-based modeling of catalyst layer operation in polymer electrolyte fuel cells [51], (Reprinted from Elecfrochimica Acta 53.13, Liu J, Eikerling M. Model of cathode catalyst layers for polymer electrolyte fuel cells The role of porous structure and water accumulation, 4435-46, 320 08, with permission from Elsevier.)...

The modeling of structure and operation of CLs is a multiscale problem. The challenges for the theory and modeling of catalyst layer operation are, however, markedly reduced if we realize that the main structural effects occur at well-separated scales, viz. at catalyst nanoparticles (a few nm), at agglomerates of carbon/Pt ( 100 nm), and at the macroscopic device level. 

HT-PEM fuel cells operate with phosphoric acid doped polymer membrane as electrolyte. The acid is physically adsorbed to the membrane. The phosphoric acid distribution within the fuel cell components, such as membrane, catalyst layers, microporous layer, gas diffusion layers, and bipolar plates, is known to be a critical parameter for performance and life time of this type of fuel cells [10]. There are no defined specifications about phosphoric acid uptake of the bipolar plate because its impact on the fuel cell performance strongly depends on several parameters and always has to be considered in a context of the overall fuel cell design. 

There is more to catalyst layer operation than electrocatalysis, a lot more The design of fuel cell electrodes with high performance, long lifetime, and low cost is about embedding the catalyst, usually the most expensive and least stable material in the cell, into a porous composite host medium. It turns out that material selection and structural design of the host medium is as important as that of the catalyst material itself. 

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