Hydrogen crossover temperature dependence

The temperature dependence of this rate constant was measured by Al-Soufi et al. [1991], and is shown in Figure 6.17. It exhibits a low-temperature limit of rate constant kc = 8x 105 s 1 and a crossover temperature 7 C = 80K. In accordance with the discussion in Section 2.5, the crossover temperature is approximately the same for hydrogen and deuterium transfer, showing that the low-temperature limit appears when the low-frequency vibrations, whose masses are independent of tunneling mass, become quantal at Tisotope effect increases with decreasing temperature in the Arrhenius region by about two orders of magnitude and approaches a constant value kH/kD = 1.5 x 103 at T[Pg.174]

Temperature affects hydrogen crossover mainly by affecting the hydrogen permeability coefficient, which is temperature dependent and can be expressed in an Arrhenius form [13] ... 

As discussed above, the temperature can influence the OCV of a PEM fuel cell and thermodynamics, electrode kinetics, membrane conductivity, hydrogen crossover, and mass transfer process, and this influence will be reflected in the overall cell performance. However, the dependence of performance on temperature can be complicated by the fact that other conditions, such as RH, backpressure, gas stochiometry, flow field design, and electrode structure, also affect performance. 

---