IR correction

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].

Table 5. Lamb shift contribution for the ground state of 208Pb81+ i0n (in eV). The notations are the same as in Table 4. The finite nuclear size correction is calculated for a Fermi distribution with (r2 1,/2 = 5.505 0.001 fm. The SESE (a) (irred) correction is obtained by an interpolation from the known values for Z = 70, 80,92. The inaccuracy of the Uehling approximation for VPVP (f) and S(VP)E corrections is neglected. The zero value presented for the nuclear polarization is due to the cancellation of the usual nuclear polarization [35] with the mixed nuclear polarization (NP)-vacuum polarization correction [36]. The latter effect arises when the nucleus interacts with a virtual electron-positron pair. For lead, due to the collective monopole vibrations, specific for this nucleus, mixed NP-VP effect becomes rather large. Therefore, the nuclear polarization effects which otherwise limit very precise Lamb shift predictions are almost completely negligible for 208Pb, making this ion especially suitable for the most precise theoretical predictions...

The ohmic loss in this system was found to be approximately 50 ohms using an 1-R compensator when galvanostatic electrolysis was conducted. The open circles in Fig. 1 show the photocurrent vs. the IR-free potential, assuming that the solution resistance does not change with potential. Thus, for current densities exceeding 100 mA cm-2, the IR correction exceeds 1 V with the present geometry. 

Figure 7 Steady-state iR corrected Tafel plots of cathodic ORR performance of several binary Pt alloy electrocatalysts at 90 °C and 5-atm pressure. Performance for a Pt/C electrocatalyst is shown for comparison. The electrodes had 0.3mg/cm metal loading and the loading of the metal on carbon support was 20%. The humidifaction temperature for the anode and cathode gas streams were kept at 10 and 5°C above the cell temperature. 

Fig. 32 Measured, iR-corrected, hydrogen/air PEFC voltage versus current density in operation at 80 °C on high stoichiometric flow of hydrogen with a range of concentrations of carbon monoxide. Pt catalyst was at 0.2 mg cm-2 on each...

Some ORR kinetic measurements reported most recently (2005) were performed directly on the dispersed catalyst of an operating PEFC cathode at an elevated temperature of 80 °C and a somewhat elevated air pressure of 1.5 atm [81], The surface area of Pt available in such cathodes was evaluated by voltammetry, as shown in Fig. 42. The latter report adheres to ORR rate evaluation based on currents measured at 0.9 V versus RHE, and these results are given in Table 7. The iR-corrected, versus log 7cen... 

Therefore, for an anodic polarization curve, the true potential, E, is less than the experimentally measured potential, Eexp, by an amount equal to the IR correction, Iex aR s, as indicated in Fig. 6.8. This correction becomes smaller as Iex a becomes smaller and as R s becomes smaller (i.e., lower solution resistivity and/or shorter distance between the WE and RE). 

On comparison of Eq 6.16 and 6.18, it is seen that a single IR correction equation may be written for both anodic and cathodic polarization ... 

This equation is used directly to determine icorr, providing that the experimentally measured potential, Eexp, is the actual potential at the WE/electrolyte interface, E (i.e., no IR correction is needed). Under these conditions, the analysis procedure involves evaluating the slope of the E versus iex curve at Ecorr, as shown in Fig. 6.12, to determine Rp. From Rp, and known or experimentally determined Tafel constants (P values), icorr is calculated. If an IR correction is necessary, then, because E = Eexp - iexRs (Eq 6.20) ... 

For a given electrolyte resistivity, and relative to positioning the reference-electrode or salt-bridge tip, how can the magnitude of the IR correction be reduced ... 

Briefly describe how the current-interrupt IR-correction is performed. 

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.)...

Fig. 1.78 IR corrected performance of a 1 x 1 size direct methanol fuel cell with a PSSA-PVDF membrane (USC-MEA 7) at 90 C and 20 psig Og. 

In electroanalysis, diffusion currents are quite small (< 100 /rA), which means that the aqueous solution IR drop between the reference electrode and the DME can be neglected in all but the most accurate work. Electrolytes prepared with organic solvents, however, may have fairly large resistances, and in some instances IR corrections must be made. 

Small cylinders (wires) or spheres if practically feasible may be used advantageously as test electrodes in polarization studies, since the IR correction decreases as the electrode is made smaller. 

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