| Proton Exchange Membrane Fuel Cell(PEMFC) is a power conversion device which translates chemical energy contained in reactant gas into electrical energy directly. Prominent advantages such as high energy conversion efficiency, high reliability, environment friendly, low noise, low working temperature, wide range of application and long life make it more and more popular and is considered a most promising power source. Water-gas management is an important issue in PEMFC and there are still much difficulties need to be solved. Water-gas management in fuel cell with dead-ended anode, bipolar dead-ended and open-ended was studied and optimized in this dissertation. Key research and conclusions are followed:Fuel cell with dead-ended anode can improve the utilization of hydrogen effectively. The running characteristics of fuel cell with dead-ended anode under different operating parameters such as anode inlet pressure, cathode stoichiometric ratio and cell temperature was focused on in the second chapter. The anode outlet solenoid valve was normally closed during each operating conditions(The longest running time of a single operating parameter was 26 hours), and so the hydrogen utilization reach 100%. The results show that, the fuel cell run steadily during its long time dead-ended anode operation by different operating parameters but with the exception of low cathode stoichiometric ratio and high current density, that leaded to water-flooding in inside the fuel cell and thus made the fuel cell running failure. The multiple locations cross-sectional SEM show that the thickness of both anode and cathode catalyst layer close to the downstream outlet was reduced while other location was almost unaffected. These observations confirm a strong correlation between the water flooding and carbon corrosion close to the cell outlet.The cathode outlet opening size of fuel cell with dead-ended anode was optimized. Three kinds of cathode outlet including single outlet, double outlet and fully opening outlet were designed. The designed cells were continuously operated for 100 hours under dead-ended anode mode and the effect of opening size in cathode outlet on cell performance had been investigated. After the experiment, the cathode cyclic voltammetry curve and the MEA multiple locations cross-sectional SEM of each fuel cell were analyzed in detail. The results showed that by increasing the cathode outlet opening size the water flooding inside the fuel cell was alleviated effectively, leading to lower performance and electrochemistry active surface area decaying, as a result the carbon corrosion of catalytic layer both anode and cathode could be significantly suppressed during continuous operation of dead-ended anode fuel cells, thus result in longer service life of the fuel cell.The purge characteristics of both dead-ended anode and dead-ended cathode fuel cell were investigated. During the purge of dead-ended anode mode, the performance was greatly reduced and the reduction slow down gradually with purge time going. The performance recovery rate was faster with the increase of current density, cathode relative humidity and working temperature but slower with the increase of anode pressure and purge duration. The dead-ended anode fuel cell ran stably after the performance recovery. While during the purge of dead-ended cathode mode the performance was sharply reduced for the first 0.2s, and then the performance reduction with a relatively low speed till the end of the cathode purge duration. After the purge the performance recovery quickly, but the cell running instability was deteriorated, especially under high current density.Fuel cell with bipolar dead-ended was assembled and run for about 60 hours, the fuel cell running characteristics with different operating conditions was investigated in detail. After the experiment, the cyclic voltammetry curve and the MEA multiple locations cross-sectional SEM were analyzed. The result showed that water flooding which lead to bad performance occured easily during the bipolar dead-ended fuel cell operation. The performance and electrochemical active surface area decay obviously. The corrosion of carbon support in both electrodes was clearly observed. Detailed investigation has revealed that variation of output voltage during a single purge period can be divided into three regions: dehydration of membrane induced ohmic loss, quasi-equilibrium state, and flooding induced concentration polarization. In order to improve this adverse situation, the cathode advance purging strategy was described with which purging was applied before flooding. The quasi-equilibrium voltage was chosen as the purging indicator and the purging process starts while the output voltage starts to decrease from the quasi-equilibrium voltage. The results show that with the introduction of the cathode advance purging strategy, the decay rates of fuel cell performance and ECSA were both greatly mitigated and the carbon corrosion had been suppressed effectively, hence the service life of the fuel cell was improved greatly. Moreover, it had also been found that cell performance and purge cycle duration increased with increasing operation pressure, whereas decreased at elevated current and cell temperature.Moisture dehumidification is introduced to help remove the excessive water inside a 3kW PEMFC stack. A radiator is set at the outlet of the stack to cool the moisture of the cathode. Thus, liquid water is condensed from the moisture due to the variation of the saturated pressure of water vapor, which can accelerate the evaporating of the liquid water inside the stack and mitigate the probability of flooding in the membrane electrode assembly. The stack with a radiator at the outlet of the cathode is fabricated to systematically investigate the effects of the stack temperature, air relative humidity, and operating pressure on the stack performance. The results show that with the help of moisture condensation, water removal ability is improved inside the stack. With the introduction of moisture dehumidification, 13% of increase in stack performance at 1000mA/cm2 is observed compared with the stack performance without moisture dehumidification. |
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