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Study on the Performance Improvement of Polymer Electrolyte Membrane Fuel Cell with Non-humidified Conditions : 고분자 전해질막 연료전지의 무가습 운전 조건에서 성능 향상에 관한 연구

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공과대학 기계항공공학부
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서울대학교 대학원
Polymer electrolyte membrane fuel cellGas diffusion layerWater managementNon-humidified conditionSelf-humidified systemPressurized system
학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2014. 2. 김민수.
As depleting fossil fuels and environmental problems like global warming have been arisen, needs for eco-friendly and renewable energy have been increased. Fuel cell is one of the most famous renewable energy. And it is considered as an alternative energy to fossil fuels. Fuel cell generates electricity by chemical reaction of fuel and oxidant. There are different types of fuel cells such as Polymer electrolyte membrane fuel cell (PEMFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and Solid oxide fuel cell (SOFC). Above all, polymer electrolyte membrane fuel cell (PEMFC) is considered as an alternative to internal combustion engine because its advantages like relatively low operation temperature, short start-up time, and quick response etc.
However, there are some problems to replace internal combustion engine with PEMFC. Too many auxiliary components (Balance of plant) are one of the crucial problems of fuel cell systems, because it takes a large volume of the system. Balance of plants (BOP) is composed of hydrogen provide system, air provide system, cooling system and water management system. Removing the external humidifier is one of the solutions to simplify the BOP system. In PEM fuel cell reaction, pure water is generated. To remove the external humidifier, fuel cell has to use this generated water to humidify membrane of fuel cell because the hydration level of membrane is crucial to the performance of fuel cell. Water inside the membrane transmit proton from anode to cathode. So, hydration level of membrane is directly related to the proton conductivity of membrane. Therefore, the ohmic loss of fuel cell increases when the hydration level of membrane decreases.
Generally, when dry air and fuel is fed to the fuel cell, performance of fuel cell deteriorates because the ohmic loss of fuel cell increases. So, generated water management is very important to enhance the performance of fuel cell when dry air and fuel is fed to the fuel cell.
So far, lots of studies about fuel cell with non-humidified are conducted by many researcher. Because the deterioration of performance which is caused by low hydration level of membrane is the main issue, many researches are conducted to enhance the performance of fuel cell when it performs under non-humidified conditions. To improve the performance of fuel cell without external humidifier, many researchers conduct experimental studies about hydrophilic micro porous layer (MPL). However, improving the hydrophilicity can cause serious problem, flooding, because MPL is very tiny and thin porous material.
In this study, by stacking two gas diffusion layers (GDL), we suggest new type of GDL assembly. Because this double layer GDL has tiny water trap between two GDL, it can retain more generated water than typical GDL. And also, we set relatively low porous GDL to channel side. This method makes generated water hard to penetrate from MPL to channel. By using this double layer GDL, water retention of GDL increases, then hydration level of membrane also increases. Such results improve the performance of fuel cell by enhancing proton conductivity of membrane.
As mentioned above, the performance of fuel cell when we supply dry inlet gas is improved by applying double layer GDL. However, the performance of non-humidified fuel cell is lower than fully humidified fuel cell despite double layer GDL is applied to non-humidified fuel cell. So, pressurized fuel cell system is applied to non-humidified conditions. By using back pressure regulator, increases the pressure of inlet gas which is fed to fuel cell. When we applied pressurized system to non-humidified conditions, the results show that the performance of fuel cell increases. As the pressure of the inlet gas of fuel cell increases 1 atm to 2 atm, the performance improve to fully humidified system.
As a result, as we applied double layer GDL and pressurized system, we could get a satisfactory performance of fuel cell. From this result, fuel cell could operate without external humidifier by applying double layer GDL and pressurized system.
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