Fuel cell lifetime

Figure 3.11. Estimated effect of fuel-cell lifetime on the target cost for competitive commercialisation (Staffed etal., 2007)...

To develop and introduce cost-effective, durable, safe, and environmentally desirable fuel cell systems and hydrogen storage systems. Current fuel cell lifetimes are much too short and fuel cell costs are at least an order of magnitude too high. An on-board vehicular hydrogen storage system... 

Other technical hurdles must be overcome to make fuel cells more appealing to automakers and consumers. Durability is a key issue and performance degradation is usually traceable to the proton exchange membrane component of the device. Depending on the application, 5,000 40,000 h of fuel cell lifetime is needed. Chemical attack of the membrane and electrocatalyst deactivation (due to gradual poisoning by impurities such as CO in the feed gases) are critical roadblocks that must be over come. 

As part of the early work to find alloys ofplatinum with higher reactivity for oxygen reduction than platinum alone, International Fuel Cells (now UTC Fuel Cells, LLC.) developed some platinum-refractory-metal binary-alloy electrocatalysts. The preferred alloy was a platinum-vanadium combination that had higher specific activity than platinum alone.25 The mechanism for this catalytic enhancement was not understood, and posttest analyses26 at Los Alamos National Laboratory showed that for this binary-alloy, the vanadium component was rapidly leached out, leaving behind only the platinum. The fuel- cell also manifested this catalyst degradation as a loss of performance with time. In this instance, as the vanadium was lost from the alloy, so the performance of the catalyst reverted to that of the platinum catalyst in the absence of vanadium. This process occurs fairly rapidly in terms of the fuel-cell lifetime, i.e., within 1-2000 hours. Such a performance loss means that this Pt-V alloy combination may not be important commercially but it does pose the question, why does the electrocatalytic enhancement for oxygen reduction occur ... 

Durability is a fundamental and necessary feature for PEM fuel cells to see a wide diffusion as a practical power source in any application field. The requirements for fuel cell lifetime vary with the specific application, in particular a duration of at least 5000 h is mandatory for use on cars, while even longer periods are needed for bus and stationary employments (for most applications an acceptable degradation rate is considered to be comprised in the range 2-10 pV/h [51]). However, the wide variability of operative conditions usually encountered in automotive applications, such as dynamic driving cycles, startup/shutdown phases, and freeze/thaw, makes also the target for car very difficult to be met with the current technologies. 

Understand the parameters that affect fuel processor and fuel cell lifetime and durability Approach... 

The influence of a variety of contaminants in reactants and in the fuel cells themselves on the polymer electrolyte membrane fuel cell lifetime, as well as the mechanisms of this influence, have been examined in a review by Cheng et al. (2007). 

Table 1.3. General accelerated test methods in PEM fuel cell lifetime analysis...

The effects of contaminants on fuel cell lifetime performance under conditions closer to those of practical operations, such as start/stop... 

Apparently, the effect of contaminants on catalysts is not yet thoroughly understood. To improve fuel cell lifetime and develop adequate mitigation strategies, it is important to gain a fundamental understanding of the main contamination mechanisms and their impact on fuel cell performance. More examples of contaminants contributions to catalyst poisoning can be found in Chapter 8. 

More of the current research regarding PEMFC catalyst supports focus on novel treatment processes, techniques, or different materials that allow for a more stable and active catalyst for PEMFC technologies. Based on the strict targets set upon by the DOE for fuel cell lifetimes, researchers have recognized the importance of stabilizing the support to impede corrosion mechanisms or to find novel materials ... 

FIGURE 10.1 Fuel cell bus trial results. (Reprinted from Int. J. Hydrogen Energy, 33, P. Pei, Q. Chang, T. Tang. A quick evaluating method for automotive fuel cell lifetime, 3829-3836, Copyright (2008), with permission from Elsevier.)... 

Durability, defined as the maximum lifetime of a fuel cell system with not >10% loss in efficiency at the end of life, is one of the most stringent requirements for PEM fuel cells to be accepted as practical power sources. The requirements for fuel cell lifetime vary significantly, depending on the application. The fuel cell industry has set standards that include the following (1)... 

TABLE 11.2 General Accelerated Stress Test Methods in PEM Fuel Cell Lifetime Analysis ... 

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