IR-corrected cell voltage

Xu et al. [4,28] investigated the effect of RH on electrode kinetics at 120 °C with Nafion - 12-membrane-based PEM fuel cells. Figure 8.5 shows the influences of RH on the IR-corrected cell voltage in a low current density range (<100 mA cm ). 

FIGURE 8.5 IR-corrected cell voltage at 120 °C in a low current density range (<100 mA cm" ) at different RHs. Both H2 and O2 partial pressures were kept at 1.0 atm. The flow rate was kept constant at 100 ml min" for both the gases [4,28]. 

Fig. 7 CeU G2 cathode catalyst-layer and GDL mass-transport overpotentials, oxygen reduction reaction (ORR) overpotential, and iR-corrected cell voltage as a function of current density at different durability testing times (1,054 total hours at constant 0.90 A cm Gore PRIMEA series 5620 MEA (50.0-cm active area, 0.40/0.60mg Pt cm, 35- am Gore SELECT membrane) SGL SIGRACET GDL 24BC (5wt%/23wt% PTFE substrate/MPL) at both sides. See the Appendix for durability testing conditions. RH Relative humidity, A Anode, C Cathode...

Figure 1.5 The slope of E ath versus log /orr through the fuel-cell-relevant potential range has an apparently constant value near RT/F (measured current density, here designated i, is corrected for hydrogen crossover current, designated i and the measured cell voltage is ir-corrected to provide the cathode potential E) [Neyerlin et al., 2006].

Figure 12.7 Comparison of mass-specific, IR-corrected activities for Pt cathode catalysts prepared on the basis of various carbon materials at different cell voltages for air (a) and oxygen (b) fed PEMFC. Tceu = 333 K, anode H2 feed, Pt/C, 0.4mgpt/cm, dew point 333 K cathode Pt/C, 0.6mgc/cm, dew point 328 K, ambient pressure on both sides. Abbreviated Sibunit sample designations contain the experimental batch numbers. BET surface areas of carbon supports amount to 415, 292, 72.3, 21.9, and 210 for Sib619, Sib20P, SibI9P, Sib2677, and Vulcan, respectively. (From ref. 18, with permission from Springer.)...

The performance of H2/O2 AEMFCs on commercial Pt/C, Au/C, and Ag/C cathodes was first reported by Varcoe and his coworkers [39, 40]. Figure 15.7a shows the steady-state cell voltage (Eceii) versus current density (i) plots for the AEM-MEAs containing three different metal/C (Pt/C, Au/C, and Ag/C) cathodes. Pt/C was found to outperform the Ag/C and Au/C catalysts, with a peak power density of 62 mW cm at a current density of 140 mA cm [40]. The performance of the catalysts decreased in order of Pt/C > Au/C > Ag/C. The iR-corrected Eceii in Fig. 15.7b shows that the three MEAs had similar overpotential trends within the... 

Figure 2.5 shows the actual results from a single cell test with a cathode Ft loading of 0.40 mg cm". The OCV was 0.98 V. The resistance of the cell was found to be around 80 mQ cm, measured by the impedance technique at current densities of 0.1 and 0.4 A cm , as shown in Figure 2.6. It is clear from Figure 2.5 that even after the iR correction, the V-1 curve still shows significant voltage decline with increase in the current density, implying that in this iR-dominated region there are still voltage losses due to activation and mass transport.

The measured cell voltage of 0.8 V, which serves as a performance benchmark, can be resolved into the various contributions of anode and cathode overpotential, Nemst corrections for gaseous reactants under non-standard conditions, and IR losses in the separator, anode and bipolar plate (Table 2). The open circuit potential (Fig. 2) is calculated to be 1.12 V at the reduced CO2 partial pressure resulting from Boudouard corrosion at 750°C. From this we subtract first the 100 mV polarization required to bring the anode into the potential regime of the C/ CO2 electrode. 

The power supply is an Electro Products model D-612T. For automatic interrupted operation, it is connected to the electrolysis cell through a mercury relay operated by a Flexopulse timer (Eagle Signal Corp.). Voltages are read at the power supply and corrected for IR drop in the leads to th6 cell. 

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