Durability degradation rates

One of the stacks was operated at a fixed current over more than 400 hours and its durability was evaluated. The three cells did not lead to the same degradation rates. The lowest degradation rate was obtained on the central cell (10%/1000 h) whereas it was much higher on the upper and lower extreme cells (35 and 49%/l 000 h respectively). Such degradation values are of the same order of magnitude as some of those reported in literature. 

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. 

Plastics usually exhibit high corrosion resistance and low degradation rates and are highly durable materials. 

In recycling of polymeric materials, right balance between durability in use and biodegradability are of essence. Formation of right combination of polymorphic crystals of poly(butylene adipate) may be a good answer for tailoring its properties to achieve expected balance. The a-form crystals showed the fastest degradation rate, while the... 

Initially, improvement in electrochemical performance was the main objective however, long-term stability or durability is probably even more important for marked success. An acceptable performance degradation rate would be a loss of <1% per 1000 h. Figure 9.12 shows the results of a long-term endurance test performed with this state-of-the-art cell, operated over a period of about 2000 h... 

During S-cell stack performance test, the reformed gas with 6,820 seem flow rate and air with 13,000 seem rate were respectively used as fuel and oxidizer gas to complete l-V-P and durability tests. The reformed gas generated from methane and water vapor through the home-made reformer installed in the SOFC measurement system. According to our experiences about measuring the degradation rate of SOFC MSC cell stack, the most suitable applied current density is located around 400 mA/cm at 700 C. So, the constant current density is kept at 400 mA/cm in long term durability test. 

In order to obtain the compostable polymer materials with the best compromise between mechanical and processing properties and cost, as well as compostability, various blends of biodegradable polymers have been studied. For example, blends such as PLA/PHA, PLA/ starch have improved performance with respect to degradation rate, permeability characteristics, and thermal and mechanical properties. Overall processability is thus improved and the range of possible applications for PLA is broadened. Blends of PLA and natural fibres have increased durability and heat resistance and resulted in a lower cost to weight ratio compared to unblended PLA [6]. 

The presence of phosphoric acid makes the chemistry in the Fenton test far more complex [69]. Firstly, the presence of phosphoric acid was shown to suppress the formation of radicals due to the lowered pH. Secondly, it was suggested that the presence of phosphoric acid further suppressed the degradation rate, possibly due to the formation of iron phosphates or by the ionization of the polymer. It was concluded that the presence of ferrous ion in the membrane-electrode interface had a negative impact on the fuel cell durability. However, this effect was mainly connected to the deterioration of the catalyst activity [69]. 

The required durability target of HT-PEMFC systems differs for APU and CHP applications. For the APU application, the systems need to satisfy the durability target of 20,000 h with the degradation rate of 1 %/1000 h by 2015 [4]. The APU systems need to operate in the mode of daily cycles to stand-by condition and weekly cycles to off condition [4]. For the micro-CHP in the power range of 1-10 kW, the lifetime of... 

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