Page 87 - Introduction to Transfer Phenomena in PEM Fuel Cells

76 Introduction to Transfer Phenomena in PEM Fuel Cells
where (c) is a empirically obtained constant. We find in the literature
[LAU 01], another formula, totally empirical but giving better results,
expressing losses as concentration, shown by the following equation:
⋅
nj
⋅
η conc = mexp ( ) [2.78]
where (m) expressed in (V) and (n) expressed in (cm²/mA) are empirical
coefficients.
Another empirical equation suggested by Kim et al. [KIM 95] is as
follows:


j

d
⋅
η conc = cexp  [2.79]
5
where (c) and (d) being empirical coefficients, with values c = 3.10 V and
d = 0.125 A.cm² being suggested [LAR 03].
The curve in Figure 2.6 shows the evolution of voltage loss as a
concentration that a fuel cell can have. The grouping of the different
polarizations is presented in Figure 2.7.

Figure 2.6. Evolution of polarizations as concentration