Hydrogen PEFC

The primary advantages of the hydrogen PEFC system compared to other fuel cell systems include the following  

High relative performance H2 PEFCs can reach 1.3 kW/L fuel cell power density, 0.6 kW/L system power density, and 0.6 kW/kg mass specific power density. 

Low-temperature operation H2 PEFCs can start and operate in subfreezing temperature, although normal operating temperatures are 20-90°C. 

Facile anode kinetics for the HOR As a result, H2 PEFCs have the lowest precious metal loadings of all the PEFC types (typically 0.2-0.8 mg/cm total active area i.e. anode plus cathode). 

However, the H2 PEFC has many complex technical issues that have no simple solution. Besides issues of manufacturing, ancillary system components, control, cost, and market acceptance not treated in this text, the main technical design issues for the H2 PEFC system include the following  

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To measure the current distribution in a hydrogen PEFC, Brown et al. ° and Cleghorn et al. ° employed the printed circuit board approach using a segmented current collector, anode catalyst, and anode GDL. This approach was further refined by Bender et al. ° to improve ease of use and quality of information measured. Weiser et al. ° developed a technique utilizing a magnetic loop array embedded in the current collector plate and showed that cell compression can drastically affect the local current density. Stumper et al."° demonstrated three methods for the determination of current density distribution of a hydrogen PEFC. First, the partial membrane elec-... 

Schmidt, T.J. and Baurmeister, J., Durability and reliability in high-temperature reformed hydrogen PEFCs, ECS Trans., 3, 861, 2006. 

Here we will present several simulation results, which show how the knowledge of the functional map of the cell may help to improve the cell performance. Most of the examples presented here refer to gas-fed DMFC, although with minor modifications they can be (and were) applied to hydrogen PEFC. We end this section with a special discussion of the features of the hydrogen cell. 

Consider the cathode channel (similar arguments are applicable to the anode channel of DMFC or hydrogen PEFC). For simplicity we assume that (1) the catalyst layer is thin enough, so that there are no voltage losses associated with proton transport across the layer and (2) the diffusion losses of oxygen in the backing and catalyst layers are negligible. 

Hydrogen Cell (PEFC) To apply the Q3D model to hydrogen PEFC, one has to modify the gas composition, the diffusion coefficients and the reaction rate parameters on the anode side. The parameters used for the PEFC simulation are listed in Table 7 (those parameters which are not shown here are the same as in Table 5). Since hydrogen oxidation... 

Another well-known type of value-in-use model is the well-to-wheels analysis, in which the energy consumption, environmental impact, and sometimes cost of different transportation options are compared considering all steps from the primary resource to the vehicle. This type of model is commonly used to evaluate hydrogen PEFC vehicles. Argonne National Laboratories GREET model (11) is the most widely used of these models. 

Direct hydrogen PEFC systems require extensive thermal and water management to ensure that the PEFC stack operates under the desired design conditions (Figure 3-10). Key components are... 

This performance still requires platinum loadings that are almost ten times higher (around 3 to 5 mg/cm ) than needed in high-performance direct hydrogen PEFC. When feeding concentrated methanol directly, the cross-over can be as high as 30 to 50 percent compared with the amount oxidized electrochemically. If the concentration is reduced, the cross-over is reduced but so is the current density (due to reduced activity of the reactants). Obviously, the methanol crossed over is... 

Schmidt, T. J. and Bammeister, J. 2006. Durability and reliabihty in high-temperature reformed hydrogen PEFCs. ECS Transactions 3 861-869. 

Figure 1.8 UTC 5kW Hydrogen PEFC demonstrated in 1999 in the trunk compartment of a BMW 7 series car for use as an auxiliary power unit (APU) to control electronics and chmate control. (Image Courtesy of UTC Power Corporation.)...

For a hydrogen PEFC based on the concepts in this chapter, do you expect the open-circuit voltage to (circle one) ... 

Case 3 Hydrogen PEFC At the anode the exchange current density is very high... 

From the Nernst equation with unity reactant activity we can show the theoretical equilibrium potential, which is close to accurate for the SOFC but assumes zero crossover and only accounts for equilibrium effects. From experimental observation of a hydrogen PEFC, Parthasarathy and co-workers [30] found that... 

Sketch a typical hydrogen PEFC polarization curve with electrolyte A. Then, sketch a polarization curve with the same operating conditions, but with a thicker electrolyte B. Be sure to think about all of the effects of this change. 

Sketch the shape of the anode and cathode electrode polarizations versus current for the hydrogen PEFC on the same plot as a DMFC. 

Example 5.8 Calculation of Gas-Phase Transport Limited Current Density through Diffusion Media Calculate the oxygen and hydrogen gas-phase transport limiting current density in a hydrogen PEFC for the anode and cathode sides at 80°C, 2 atm pressure operation with fully humidified gas streams and high stoichiometry. Assume the anode... 

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