Fuel cell performance Tafel equation

The j-E curve can be used not only to quantitatively describe the overall fuel cell performance but also to identify and quantify the activation loss, ohmic loss, and the mass transfer limited current density. At low current density, the ohmic loss is negligible and hence the activation loss can be directly obtained from the j-E curve at low current density. The semi-log plot of the/-E curve is linear for low current density and it can be fit to a Tafel equation (Equation 5.83) as shown in Figure 8.1 at low current density. Using the line fit to the Tafel equation. 

In this chapter the scope of our discussion was restricted by the macrohomogeneous model of CL performance and its derivatives. The first numerical macrohomogeneous models of CCL for a PEM fuel cell were developed by Springer and Gottesfeld (1991) and by Bernard and Verbrugge (1991). These models included the diffusion equation for oxygen transport, the Tafel law for the rate of ORR and Ohm s law for the proton transport in the electrolyte phase. A similar approach was then used by Perry, Newman and Cairns (Perry et al., 1998) and by Eikerling and Kornyshev (1998) for combined numerical and analytical studies. 

It is generally thought that as temperature increases so do reaction kinetics. However, the situation in a fuel cell, an electrochemical device, is far more compU-cated. The reaction mechanism will depend on the surface environment of the catalyst particle and the potential at which the reactimi is taking place. The electrode overpotential associated with the ORR represents the largest voltage loss in fully humidified fuel cells and so it is important that the situation not be exacerbated in running fuel cell under hot and dry conditions. In the kinetically controlled region of the fuel cell operation, the performance can be described by the Tafel equation ... 

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