Water in Catalyst Layers The Watershed

Until about 10 years ago, CCL models had neglected effects related to formation and transport of water. Up to that point, large drops in fuel cell voltage as the current density was ramped up to 1 A cm 2 or above had been frequently observed 

The effects of porous structure and liquid water accumulation on steady-state performance of conventional CCLs were explored in Eikerling (2006) and Liu and Eikerling (2008). In these modeling works, uniform wetting angle was assumed in secondary pores, with a value 0 90°. The full set of equations presented in the section Macrohomogeneous Model with Constant Properties are solved with the following boundary conditions  

Q-cl) = this defines the working point of the PEFC, that is, the proton flux at the PEM-CCL boundary (x = 0)Jo = j(0) as well as the oxygen flux at the CCL-PTL boundary. 

was assumed to be fixed. Instead, in Liu and Eikerling (2008), the oxygen partial pressure at the flow field (EE) was assumed to be controlled, and diffusive gas transport PTL was accounted for as given by Equation 4.20. This modification allowed distinct signatures in Eceiiijo) due to limited oxygen transport in either CCL or PTL to be compared. 

The proton flux is converted completely into electron flux in the CCL and, 

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The MHM and the water balance model decouple when the liquid saturation is constant with this assumption, effective parameters of transport and reaction will be constant as well. This is the situation normally evaluated in CCL modeling. It will be considered next. Specific effects due to the complex coupling between porous morphology, liquid water formation, oxygen transport, and reaction rate distributions will be discussed in the section Water in Catalyst Layers The Watershed. ... 

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