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The theoretical contributions to overall cell voltage in a proton exchange membrane fuel cell (PEMFC) were calculated, accounted for, and compared to measured IR free cell voltage as relative humidity was varied from 30-110%. The intrinsic oxygen reduction reaction (ORR) kinetics in a PEMFC, with regards to water and proton activity, were shown to be independent of above 50-60%, but significant losses in ORR kinetics were observed at lower values. The losses amounted to ca. 20 mV at , corresponding to an approximate two-fold decrease in the ORR exchange current density. The dependence of ORR kinetics on water and proton activity is consistent with reduced activity at low .
Neyerlin et al. (Sat,) studied this question.