Polarization PEMFC

For isolating the overpotential of the working electrode, it is common practice to admit hydrogen to the counter-electrode (the anode in a PEMFC the cathode in a direct methanol fuel cell, DMFC) and create a so-called dynamic reference electrode. Furthermore, the overpotential comprises losses associated with sluggish electrochemical kinetics, as well as a concentration polarization related to hindered mass transport ... 

Polarization citrve for PEMFCs with two different cathode diffusion layers carbon fiber paper with one MPL and carbon fiber cloth with two MPLs. Operating conditions ceU temperature of 85°C, O2/H2 dewpoint temperatures of 90/100°C gas pressures of 2 atm. CFP DL was a TGP-H-090 with 20 wt% PTFE in the MPL. CCs were PWB-3 from Stackpole cathode CC had 15 wt% PTFE in the MPL near the CL and 30 wt% PTFE in the MPL near the flow field. The anode CC had 15 wt% PTFE in both MPLs carbon loading on the MPL was not specified. The catalyst Pt loading was 0.4 mg cm and the Nation loading was 1.1 mg cm for all catalyst layers the membrane was a Nation 115. (Modified from E. Antolini et al. Journal of Power Sources 163 (2006) 357-363. With permission from Elsevier.)... 

The OCV seems to be of less practical use. It is much more useful for a fuel cell to work under a load, with power being delivered to the users. With the electric energy output, the fuel cell voltage will decrease as the electric current load increases. A popular way to evaluate a fuel cell is to measure its polarization curve (abbreviated as I-V curve ), which is a plot showing the cell voltage change with current or current density. Figure 1.20 shows a typical polarization curve obtained with a PEMFC. 

Figure 3.13. Typical polarization curve for a PEMFC [14]. (Modified from Barbir F. PEM fuel cells theory and practice. New York Elsevier Academic Press, 2005, with permission from Elsevier.)...

EIS has the ability to distinguish between influences from different processes, especially when the system involves multiple-step reactions, parallel reactions, or additional processes such as adsorption. Generally speaking, the measurements and analysis of the EIS for a PEMFC are complicated compared with those of the polarization curve. However, the results from both methods are not insular, and some relationships exist between the complicated impedance spectrum and the simple polarization curve [22],... 

Wang et al. [19] developed a new method of electrode preparation with a novel silica gel additive (NSGA) instead of the traditional Nafion polymer additive (TNPA) for PEMFCs. The performance of the two types of electrodes was compared using electrochemical impedance spectroscopy coupled with a polarization curve and constant-current discharge. Figure 6.20 shows the AC... 

Figure 6.29. Polarization curves for PEMFCs with uniform and bilayer cathodes under H2/02 operation at ambient temperature and pressure. All electrodes (1 cm2) contained 0.9 mg of Nafion [25]. (Reproduced by permission of ECS—The Electrochemical Society, and the authors, from Li G, Pickup PG. Ionic conductivity of PEMFC electrodes.)...

PEMFC (Proton Exchange Membrane Fuel Cell) and SPFC (Solid Polymer Fuel Cell) are the two competing mnemonics of a low-temperature fuel cell type originated for use in space by General Electric, USA. To reflect present practice, the author will use PEFC (Proton Exchange Fuel Cell). The DMFC (Direct Methanol Fuel Cell) also uses proton exchange membranes, but is referred to by its own mnemonic. Proton exchange between polar water molecules is discussed by Koryta (1991 1993) and in the introduction to this book. 

FIGURE 27.66 Polarization curves of PEMFCs based on Nation 115 and Nation 115 23 wt% a-ZrP at 130°C and 3 atm with reactants humidified at 130°C. (Reprinted from Costamagna, P. et al., Electrochim. Acta, 47, 1023, 2002. With permission from Elsevier.)... 

Figure 2. Polarization curves for the PEMFC using electrodeposited Pt obtained via pulsating current, with various peak current densities, and DC methods. Reprinted from Kim et al. 6 with permission from Elsevier.

The performance of PEMFC is often presented by the polarization curve that shows the voltage output as a function of current density. Fig. 8 shows a typical polarization curve of PEMFC. As the PEMFC processes charge-transfer reactions and the diffusion of the reactants to and products from the electrochemical interface, the transport and kinetics within the cell determine the polarization characteristics of PEMFC. In the practical PEMFC, the terminal cell potential V... 

The first and third parentheses on the right hand side of Eq. (86) represent the electrodes and electrolyte contact resistances and the second term represent the bulk resistance of the electrolyte. Substitution of Eqs. (78-86) into (85) gives the following current-voltage relation, or polarization equation, for PEMFC... 

Fig. 11 A typical polarization curve for PEMFC along with potential losses because of the overpotentials with current densities.

Matos et al. 60] developed Nafion-titanate nanotube composites as the PEMFC electrolyte operating at elevated temperatures. The addition of 5-15 wt% nanotubes to the ionomer allowed the PEMFC performance essentially to be sustained up to 130 °C. The polarization curves of PEMFCs using composite electrolytes reflected a competing effect between an increase in water uptake due to the extremely large surface area of the nanotubes, and a decrease in the proton conductivity of the composites. 

The polarization in a PEMFC comes mainly from the slow cathodic ORR. Reducing the Pt loading (particularly in the cathode catalyst layer) without compromising... 

Figure 17. Polarization curves of ( , A) untreated and (o, A) PATBS treated Pt/Ketjen black [35]. J. Power Sources 138, Mizuhata, H. Nakao, S. Yamaguchi, T., Morphological control of PEMFC electrode by graft polymerization of polymer electrolyte onto platinum-supported carbon black, 25-30, Copyright (2004), with permission from Elsevier.

PtRu catalysts with MCMB as support [35] showed lower polarization characteristics than that with CB as support. Pt-Ru nanoparticles (1.6 nm) were supported on carbon nanotubes (200nm diameter, 8-10 um length) obtained by carbonization of PPy on an alumina membrane [36]. The amount and morphology of Pt nanoparticles depend on the types of carbon nanomaterlals, Including GNFs or CNTs [37]. Surfactant-stabilized Pt and Pt/Ru electrocatalysts for PEMFC had been prepared and investigated by X. Wang [38]. 

ICR values were taken with bare samples. If the SS is polarized in simulated PEMFC environments, a passive film forms therefore, the ICR values with passive films are normally higher than those with... 

Baumgartner, W.R., Parz, P., Fraser, S.D., Wallnfer, E., and Hacker, V. (2008) Polarization study of o PEMFC with four reference electrodes at hydrogen starvation conditions. J. Power Sources, 182, 413-421. 

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