Cell Performance at

This permits a reformulation of the cathode to include more active material and a lower internal resistance, as noted in Figure 2. The resultant lower internal resistance and higher active mass content produced a 30% increase in cell performance at high rate discharges. 

The improvement in cell performance at higher pressure and high current density can be attributed to a lower diffusion polarization at the cathode and an increase in the reversible cell potential. In addition, pressurization decreases activation polarization at the cathode because of the increased oxygen and water partial pressures. If the partial pressure of water is allowed to increase, a lower acid concentration will result. This will increase ionic conductivity and bring about a higher exchange current density. The net outcome is a reduction in ohmic losses. It was reported (33) that an increase in cell pressure (100% H3PO4, 169°C (336°F)) from 1 to 4.4 atm (14.7 to 64.7 psia) produces a reduction in acid concentration to 97%, and a decrease of about 0.001 ohm in the resistance of a small six cell stack (350 cm electrode area). 

Fuel Cell Energy presented a computer model for predicting carbonate fuel cell performance at different operating conditions. The model was described in detail at the Fourth International Symposium on Carbonate Fuel Cell Technology, Montreal, Canada, 1997 (93). The model equations are listed as follows ... 

SOFCs, like PAFCs and MCFCs, show an enhanced performance by increasing cell pressure. The following equation approximates the effect of pressure on cell performance at 1000°C (1832°F) ... 

Figure 8-8 Effect of Pressure on AES Cell Performance at 1000°C [(22) 2.2 cm diameter, 150 cm active length]... 

Figure 8-17 Cell Performance at 1000°C with Pure Oxygen (0) and Air (A) Both at 25% Utilization (Fuel (67% H2/22% C0/11%H20) Utilization is 85%) (30)...

A fixed cell area of 1 cm2, a temperature of 800°C, a total pressure of 1 bar, an oxygen partial pressure of 0.21 bar and an area specific resistance of 1 2cm2 are chosen to compare the cell performances at uniform conditions. The total current of... 

Application to water splitting or fuel cell performance at a metal surface... 

Zhang et al. [128] synthesized a self-humidifying membrane based on a sulfonated poly(ether ether ketone) (SPEEK) hybrid with a sulfated zirconia (SO / ZrO2, SZ) -supported platinum catalyst (Pt-SZ catalyst). This type of composite membrane has a higher proton conductivity than plain SPEEK, due to the effect of the Pt-SZ catalyst the membrane also provided excellent single cell performance at low humidity. 

Figure 6. SPE HCl cell performance at various temperatures (46). Conditions 5 atm Cl pressure flow rate, 8 cm3/s and 10% HCL...

F. Uribe and T. Zawodzinski, "A Study of Polymer Electrolyte Fuel Cell Performance at High Voltages. Dependence on Cathode Catalyst Layer Composition and on Voltage Conditioning". Accepted in Electrochimica Acta. (2002). 

Zone 2 corresponds to membranes with intermediate and P. Membranes in this zone should show inferior DMFC performance at low methanol feed concentration but better DMFC performance at high methanol feed concentration. Membranes in Zone 3 have relatively high and intermediate Fj, and should improve cell performance at low methanol feed concentration but should suffer high methanol crossover at high methanol concentration, like the Nafion membrane. Finally, membranes in Zone 4 exhibit better selectivity and DMFC performance should be further improved. 

Omran et al. have proposed a 3D, single phase steady-state model of a liquid feed DMFC [181]. Their model is implemented into the commercial computational fluid dynamics (CFD) software package FLUENT . The continuity, momentum, and species conservation equations are coupled with mathematical descriptions of the electrochemical kinetics in the anode and cathode channel and MEA. For electrochemical kinetics, the Tafel equation is used at both the anode and cathode sides. Results are validated against DMFC experimental data with reasonable agreement and used to explore the effects of cell temperature, channel depth, and channel width on polarization curve, power density and crossover rate. The results show that the power density peak and crossover increase as the operational temperature increases. It is also shown that the increasing of the channel width improves the cell performance at a methanol concentration below 1 M. 

The driving force for small nanoparticle catalysts is reduced cost by minimizing inactive non-surface atoms, which is the basis of most low Pt approaches. Yu and Pickup investigated the coverage dependence of Pb and Sb on commercial 40 wt% Pt supported on carbon in situ in a formic acid/02 fuel cell [29]. They found optimal coverages of 0.7 for both types of adatoms. The performance of both PtSb/C and PtPb/C far exceeded that of Pt/C. After nearly a 2 h hold at 0.6 V under fuel cell operation, the performance increase over Pt/C was 15- and 12.8-fold, respectively. Figure 4.2 is a comparison of fuel cell performance at 0.6 V as a function of adatom... 

Fig. 4.2 Plot of direct formic acid fuel cell performance at 0.6 V for Pt/C anodes as a function of Pb and Sb adatom coverages. The experimental data is compared to the two formic acid electrooxidation models proposed by Leiva (solid line) electronic enhancement and (dashed line) third-body effect [29]...

Fig. 15.7 (a) Fuel cell performance at 50 °C, anode 0.5 mg cm Pt prefabricated carbon cloth electrode cathode 0.5 mg cm transition-metal carbon paper electrode. With (filled circle) Pt/C (filled triangle) Au/C and (filled square) Ag/C. The open symbols represent the Fceu versus i plot, and the filled symbols represent the Pceu versus i plot, (b) iR-corrected Pceii and area resistance plots against log i for (filled circle) Pt/C, (filled triangle) Au/C, and (filled square) Ag/C measured using EIS during fuel cell test with H2/O2 at 50 °C. Filled symbol represents iR-corrected Fceu> and open symbols represent area resistance data [40]... 

Fig. 15.8 Fuel cell performance at 50 °C, 20 psi back pressure for both H2 and O2, anode 1.25 mg cm Pt/C cathode 2.5 mg cm catalyst loading. With (red filled circles) Pt/C (blue...

Similarly, the loss in cell performance at one level of reactant RH can be compared with the RH levels of the other reactant. The cell has passed the humidification sensitivity test when the acceptance criterion is met for example, the cell does not exceed a specified loss in performance (voltage or power) for the given range of reactant RH at the applied current densities and the other operating conditions (cell temperature, pressure, or reactant stoichiometry) [8]. 

Reduce the serum level to 5% and repeat the process—there should be veiy little difference in cell performance at this level. 

Figure 9 depicts the effect of temperature on lithium-manganese dioxide compared with zinc-silver and zinc-air cell miniature cell performance. At low temperatures the electrode reactions slow down and severely limit the ability of the cell to deliver current. Cells also lose capacity slowly when stored at room temperature, due to internal self-discharge reactions which are accelerated at higher temperatures. 

The state-of-the-art gas diffusion media are hydrophobized to such an extent that they allow transport of liquid water, an important mechanism at near-saturated conditions, as well as of water vapor and reactant gases. An important role is played by the micro porous layer (MPL). Because of the presence of small hydrophobic pores, a substantial hquid water capillary pressure can be bruit up, enabling a good gradient in the chemical potential of water to drier sections [10]. The optimization of gas diffusion media and the application of the MPL have led to significant improvement of the fuel cell performance at saturated conditions, showing their critical role. 

Uribe FA, Zawodzinski TA (2002) A study of polymer electrolyte fuel cell performance at high voltages. Dependence on cathode catalyst layer composition and on voltage conditioning. Electrochim Acta 47(22-23) 3799-3806... 

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