Durability startup-shutdown

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. 

Hong Kim, J. et al. 2010 Effects of Cathode Inlet Relative Humidity on PEMFC Durability during Startup-Shutdown Cycling Journal of The Electrochemical Society, vol. 157, no.l, 104-112. 

Degradation and durability of a PEM fuel cell or stack can be affected by many internal and external factors, including fuel cell design and assembly, operating conditions (e.g. humidification, temperature, cell voltage), impurities or contaminants in the feeds, environmental conditions (e.g. subffeezing or cold start), and operation modes (e.g. startup, shutdown, potential cycling). 

A long-term durability test with a optimized reP-25-based membrane showed 4,000 h of continuous operation under moderate conditions 500 mA cm" with a cell temperature of 80-85°C, H ( 100% RH)/Oj(dry) under ambient pressure (Gubler et al. 2004). The final lifetime reached 7,900h, where the membrane degradation was accelerated by several controlled/uncontrolled startup/shutdown cycles. 

Startup and shutdown can have a profound impact on fuel cell durability. Under conditions of prolonged shutdown, air will eventually cross over from the cathode to the anode, filling the anode flow channels with air. In this case. 

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