Catalyst layer performance modeling approaches

Since then, other groups have adopted similar models. Assets of this approach are versatile (i) it relates global performance of CCLs to immeasurable local distributions of reactants, electrode potential and reaction rates (ii) it defines a penetration depth of the active zone and (iii) it suggests an optimum range of current density and catalyst layer thickness with minimal performance losses and highest utilization of the catalyst. 

We begin with the discussion of cell thermodynamics and electrochemistry basics (Chapter 1). This chapter may serve as an introduction to the field and we hope it would be useful for the general reader interested in the problem. Chapter 2 is devoted to basic principles of structure and operation of the polymer electrolyte membrane. Chapter 3 discusses micro- and mesoscale phenomena in catalyst layers. Chapter 4 presents recent results in performance modeling of catalyst layers, and in Chapter 5 the reader will find several applications of the modeling approaches developed in the preceding chapters. 

At each level (ID, 2D, or 3D), there is a great variety of approaches to modeling of the cell components performance. For example, ID models typically resolve catalyst layers, while 3D models usually treat CLs as thin interfaces. 

COMMENTS We could also have added the catalyst layer diffusion resistance. This model, while serving as a useful qualitative tool, is not precise, simply because we have no idea of the thickness of any layer of liquid water of ionomer locally in the electrode structures. Also, some local flooding simply turns off the current in this location by these effects, but this only means areas which are flooding have reduced performance. Other areas in the fuel ceU may not be flooded, so that the net effect of the flooding is actually to reduce the electrochemicaUy active surface area, which is an approach taken by modely including flooding, discussed later in this chapter. 

The main preparation methods for H2 technical electrodes for low temperature fuel cells have been examined. It has been demonstrated that the electrochemical behavior of the electrodes depends on their fabrication, thus affecting the fuel cell operation. The preparation of the catalyst of the active layer also influences its physical properties and electrochemical performance. Different electrochemical approaches to study HOR on model, as a first approximation, and technical electrodes, are exhaustively analyzed and their kinetic parameters are discussed to evaluate their performance and system modelling. The existence of a gap between the knowledge obtained from studies on model electrodes and technical electrodes is emphasized. To optimize the performance of practical fuel cell electrodes, the preparation of high surface area catalysts with the same characteristics as those shown at the atomic level then seems necessary. In this sense, mechanistic studies are fimdamental to... 

---