Fuel cell power density

One of the main reasons is the low power density of fuel cells. Power density, defined as power produced per unit weight or unit volume of the power source, is one of the most important factors for a power source for transportation as well as energy density, defined as energy produced per unit weight or volume. As for fuel cells, unlike batteries, energy density would not be such a serious problem as power density because energy density can be increased when more fuel is loaded. 

Designed and tested advanced membrane technology that separates pure hydrogen from reformate, thereby enabling higher fuel cell power densities and eliminating potential for electrode poisoning. 

Analysis of a series of scenarios involving catalyst loadings, pressures, and temperatures led to the conclusion that the stack would have to operate at high temperature (e.g., 160 C) and elevated pressure (e.g., 3 atmospheres) to satisfy DOE fuel cell power density (kW/cm ) goals. 

Overall, this structure-based approach has proven its assets in electrode diagnostics and in providing guidelines for the optimized structural design of catalyst layers [11-15]. Vital performance aspects that can be rationalized are catalyst utilization, distributions of reactants, reaction rates, and electrode potential, as well as effects on the overall fuel cell power density and water balance. 

The theoretical tools discussed in this contribution address various optimization tasks in PEMFC research (i) highest system efficiencies and fuel cell power densities and, thus, minimum overvoltage losses in CCLs (ii) optimum catalyst utilization and, thus, minimal Pt loading (and minimal cost), and (iii) waterhandling capabilities of CCLs and their impact on the water balance of the complete fuel cell. Structural parameters, as well as operating and boundary conditions that control the complex interplay of processes enter at three major levels of the theory. 

Figure 19.19 Fuel cell power density as a function of the current density at 70°C, 1-3 atm. Reprinted with permission from Ernst et al. (1999).

However, efficiency is not the only important performance measure. As the current is lowered at constant voltage operation, the fuel cell power density is decreasing. Below a certain level of power or power density, given by... 

If all the losses that we have looked at, activation, ohmic and concentration, are combined then the actual operational graph of a fuel cell, the J-V curve, is produced. The current is usually expressed as current density J, i.e. the quotient of the current divided by the geometrical surface of the electrodes. Thus from the j-V curve, we can get the short-circuit current density Jsc, the open-circuit voltage Vqc, and the fuel cell power density, i.e., the J x V product All of these parameters are very important in the evaluation of the photocatal)dic fuel cell performance. 

FUEL CELL PERFORMANCE 1.7.1. Fuel Cell Power Density... 

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. 

Tsai, T. and Barnett, S.A. (1997), Increased solid-oxide fuel cell power density using interfacial ceria layers. Solid State Ionics, 98, 191-196. 

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