一氧化碳及二氧化碳毒化對質子交換膜燃料電池性能影響之暫態分析

Abstract

二氧化碳毒化相對於一氧化碳毒化對質子交換膜燃料電池所造成的影響較弱，然而在一些較好的重組器，由於一氧化碳含量較低(<10 ppm)，二氧化碳毒化變的明顯重要。本論文利用數值模擬計算，探討質子交換膜燃料電池在陽極觸媒層受到一氧化碳及二氧化碳毒化後，其內部氫氣、一氧化碳之濃度、白金表面覆蓋率、電流密度分佈的暫態行為。在陽極觸媒層內，由於一氧化碳會與白金形成穩定的鍵結，造成氫氣的使用率下降，因此主要考慮氫氣與一氧化碳因吸附、脫附以及電化學氧化行為造成在白金表面覆蓋率的改變。而二氧化碳毒化主要是藉由逆向水氣轉移反應，進而影響燃料電池的性能。研究中主要是改變不同的氫氣、一氧化碳及二氧化碳濃度，來探討不同氣體成分條件下對於燃料電池內部所產生之現象。 研究結果顯示，在PH=0.8 atm，PCO2=0.2 atm，通入一氧化碳濃度為10 ppm，電流密度由1.262 A/cm2降到0.908 A/cm2，約下降28%。當一氧化碳濃度為50 ppm，電流密度由0.49 A/cm2降到0.4A/cm2，約下降18% ，因此隨著一氧化碳濃度的上升，二氧化碳毒化現象會減弱。亦即，二氧化碳毒化只在一氧化碳濃度較低時，才會較明顯。

The effects of variable CO and CO2 concentrations on the performance of PEMFC were investigated. The CO2 poisoning is a minor source of performance losses compared to CO poisoning in general conditions. The significance of CO2 poisoning，however, emerges in presence of low CO concentration (<10 ppm), e.g., with good fuel reforming systems. It is well accepted that the reverse water gas shift reaction (RWGS) is the main effect of the CO2 poisoning effects, through which a large part of the catalytic surface area becomes inactive due to hydrogen dissociation. The mechanism of CO poisoning lies in the preferential adsorbing of CO to the platinum surface and the blocking of active sites of hydrogen. These phenomena were described with adsorption, desorption, and electro-oxidation processes of CO and hydrogen in present work. The results showed that, by contaminating the fuel with CO of 10 ppm at the condition of PH=0.8 atm and PCO2=0.2 atm, the current densities was lowered 28% of non-poisoned performance. With 50 ppm CO, the performance drop was 18%. For reformed gas, CO2 poisoning had the largest effect when the CO content was small.