Cell cold start operation

For the CRYO-SEM tests, the cell before operation and after the cell shutdown at —20°C was used. Cross-sections of the cathode catalyst layer were observed. Figure 1.40 shows micrographs of the dry pre-operation MEA catalyst layer and the MEA catalyst layer after the cold start operation. Compared with the dry catalyst layer, ice formation is clearly observed at the upper... 

Experiments with operation at three relative humidities of the nitrogen in the wet purge process, i.e. 22, 35 and 76%, were conducted to investigate the relationships between the cell resistances just before the cold start operation and the operation periods (expressed by the amount of water produced) under these three wet conditions of the polymer membrane. The experimental results of the 0.04 A cm cold start at —20°C and —10°C are plotted in Figure 1.42. The durations of the operation and current density are used here to estimate the amount of water produced by... 

To examine the characteristics from the completion of the membrane rehydration to the shutdown, Figure 1.43 shows the estimated amounts of produced water following the membrane rehydration in the experiments. The amounts after the membrane rehydration at —20°C are very similar for the various cell resistances before the cold start operation, but there is great variability among the amounts with the — 10°C operation. These results indicate that after the end of the membrane rehydration, the produced water that is not absorbed on the membrane immediately freezes at —20°C while this water may remain as super-cooled water at — 10°C, and this is then reflected in the larger amounts of produced water and the larger variations at — 10°C in Figure 1.43. 

The major requirement for a reliable hydrogen sensor operation in the fuel cell environment is in 100% condensing humidity Most of the fuel cells have abundant humidity and the sensor needs to operate continuously in humid environments. In some cases, the hydrogen sensor can also be operated at very low temperatures (as low as —40°C). The fuel cells regularly have a cold start, when operated from a very low ambient temperature the sensor needs to attain ambient temperature quickly (<30 s) and continue operation well below ambient temperature before the fuel cell itself reaches the ambient temperature. 

Most solid-state sensors are heated to well above 100°C and can operate in the "cold start" condition in a fuel cell. Another important performance parameter for a hydrogen sensor in a fuel cell is its resistance to water entry. Most fuel cells have excess of liquids including water during operation. It is highly possible that water will splash or penetrate into the hydrogen sensor mounted in the ventilation or outlet of a fuel cell. Hydrophobic... 

In Albany, NY, the state government started leasing Honda FCX hydrogen fuel cell cars on a cold November morning. Previous fuel cell vehicle demonstration programs have occurred in warmer areas to ensure that the fuel cell stacks would not freeze up. Subzero temperatures can change any liquid water present into expanding ice crystals that can puncture thin membranes or crack water lines. Honda has demonstrated that their fuel cell units can operate under winter conditions, this was an important achievement for practical fuel cell cars. 

The freeze-resistant 2005 FCX models can operate at -20°C. Other companies, including DaimlerChrysler and GM have also had success with cold-starting cells. The technique used is to keep all water present as a vapor and not allow water droplets to occur. 

Cold-start tests are also important in order to observe how freezing temperatures affect the material properties of the diffusion layers. Oszcipok et al. [262] dried a fuel cell through purging with N2 prior to cooling it down to -10°C. At this point, the cell was started and operated at different voltages. After more than 10 tests, the cell was disassembled and it was observed that the FF channel pattern was visible on the cathode DL. 

M. Oszcipok, D. Riematm, U. Kronenwett, M. Kreideweis, and M. Zedda. Statistic analysis of operational influences on the cold start behavior of PEM fuel cells. Journal of Power Sources 145 (2005) 407--415. 

As mentioned earlier, cold start of the fuel cell system is considered successful when the cell temperature increases above 0°C before the cell shuts down due to oxygen starvation. Next, how long must the cell be able to run under such a condition A simple, back-of-envelope calculation can be made. Fuel cell operation generates both heat and water. Heat generation from the fuel cell operation is calculated with the relation... 

Combining Eqs. (3) and (4), we can conclude that product water of approximately 1 mg/cm2 is a criterion for successful self-startup. As shown with Eqs. (3) and (4), the temperature increase is proportional to the product water, and therefore, the product water from the fuel cell operation, Am o, is considered a quantitative index to measure the cold-start performance. 

Measure the emissions from a partial oxidation/autothermal fuel processor for a proton exchange membrane (PEM) fuel cell system under both cold-start and normal operating conditions. 

Measured emissions from a fuel processor (without fuel cell) over several operating conditions including cold-start. 

In addition to the individual polymer electrolyte membrane fuel cells and their bipolar plates, special heat-exchanger plates must also be included in the battery stack. Cooling fluid is circulated through these plates in order to eliminate the heat produced during battery operation. At least one such plate must be provided for any two cells when the battery is to be operated with high current densities. These plates could also be used to warm up the battery for a cold start-up. 

Cold start Initial water in membrane, operating voltage, cell temperature, current Results ice formation in cathode layer pores and in active reaction sites increases electrical resistance and decreases performance performance reduces less than 1% per cold start-up Pinton et a ., 2009... 

Jiao K and Li X (2009), Effects of various operating and initial conditions on cold start performance of polymer electrolyte membrane fuel cells, International Journal of Hydrogen Energy, 34,8171-8184. 

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