Polymer electrolyte membrane fuel cells operating under ultra-low stoichiometric anode flow conditions

Official URL: http://risc01.sabanciuniv.edu/record=b1818129 (Table of Contents)

The polymer electrolyte membrane fuel cell is a system that converts chemical energy of hydrogen directly into electrical energy. 2020 targets set by the U.S. Department of Energy for light duty vehicles are already accomplished except for the cost, durability and efficiency. The efficiency can be improved by turning off the anode exit of the fuel cell (dead-ended anode mode) and forcing all the hydrogen to move to the cathode. Even though this maximizes the hydrogen utilization and the efficiency, the accumulated water and nitrogen causes local fuel starvation which leads to irreversible carbon support degradation and performance loss. One way to overcome this issue is to allow a very small amount of continuous purging in the anode (ultralow flow mode) which helps evacuation of the accumulated water and nitrogen. In this thesis, the effect of dead-ended anode and ultra-low flow modes on the performance loss was evaluated for two different types of samples. It was shown that the ultra-low flow mode damaged two times less than the dead-ended anode mode while yielding a 99.93 % hydrogen utilization. However, the amount of carbon corrosion is still more than the normal operation mode for a commercial sample. To improve the durability, research on new materials is necessary. An accelerated stress test designed specially to promote carbon corrosion was proposed so that novel materials can be evaluated for their performance against carbon corrosion under real operation conditions quickly and easily. To be able to realize such kind of a procedure, a high precision flow control set up that can maintain ultra-low flows was designed.