At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components o...At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.展开更多
At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell PEMFC deteriorates markedly. The object of this work is to study the degradation mechanism of key compo- nents o...At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell PEMFC deteriorates markedly. The object of this work is to study the degradation mechanism of key compo- nents of PEMFC—membrane-electrode assembly MEA and seek feasible measures to avoid degradation. The ef- fect of freezethaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freezethaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable per- formance under subzero temperature and gas purging is proved to be the effective operation.展开更多
The frost resistance and compressive strength degradation of concrete under the simultaneous action of compressive load and freeze-thaw cycles were experimentally investigated. Air-entrained and non-air-entrained spec...The frost resistance and compressive strength degradation of concrete under the simultaneous action of compressive load and freeze-thaw cycles were experimentally investigated. Air-entrained and non-air-entrained specimens with different water/cement(w/c) ratios were subjected to different compressive stress by specially designed apparatus, while the specimens suffered freeze-thaw cycles. In order to track the strength degradation process, the nondestructive tests were carried out after each freeze-thaw cycle got the residual strength for each specimen. Based on the experimental data, a variable Kss was proposed to describe the damage velocity. Experimental results indicate that the deterioration processes are accelerated by the compressive loads, and the damage velocity increases with the increases of the preloading levels and w/c ratios. The air entrainment decreases the damage velocity and improves the frost resistance of non-air-entrained concrete, although it would reduce the compressive strength of concrete.展开更多
基金Supported by the National Natural Science Foundation of China (No.20206030) and Ministry of Science and Technology 863 Hi-Technology Research and Development Program of China (2005AA501660).
文摘At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.
基金the National Natural Science Foundation of China (No.20206030) Ministry of Science and Technology 863Hi-Technology Research and Development Program of China (2005AA501660)
文摘At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell PEMFC deteriorates markedly. The object of this work is to study the degradation mechanism of key compo- nents of PEMFC—membrane-electrode assembly MEA and seek feasible measures to avoid degradation. The ef- fect of freezethaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freezethaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable per- formance under subzero temperature and gas purging is proved to be the effective operation.
基金National Natural Science Foundation of China ( No. 50678101)
文摘The frost resistance and compressive strength degradation of concrete under the simultaneous action of compressive load and freeze-thaw cycles were experimentally investigated. Air-entrained and non-air-entrained specimens with different water/cement(w/c) ratios were subjected to different compressive stress by specially designed apparatus, while the specimens suffered freeze-thaw cycles. In order to track the strength degradation process, the nondestructive tests were carried out after each freeze-thaw cycle got the residual strength for each specimen. Based on the experimental data, a variable Kss was proposed to describe the damage velocity. Experimental results indicate that the deterioration processes are accelerated by the compressive loads, and the damage velocity increases with the increases of the preloading levels and w/c ratios. The air entrainment decreases the damage velocity and improves the frost resistance of non-air-entrained concrete, although it would reduce the compressive strength of concrete.
