SOFC中低浓度干甲烷在Ni/YSZ阳极上的反应

固体氧化物燃料电池(SOFC)趋向于直接使用甲烷天然气为燃料,确定甲烷在固体氧化物燃料电池阳极发生的化学与电化学反应非常重要.以Ni/YSZ为阳极、YSZ板做电解质、LSM为阴极,用涂浆法制作电解质支撑的电池,研究低浓度干甲烷在固体氧化物燃料电池中的反应.改变甲烷浓度、电池工作温度、电解质厚度,用在线色谱测量不同电流密度下,阳极出口气体产生速率.根据阳极出口气体产生速率变化,分析干甲烷在阳极的反应变化.通过氧消耗计算和转移电子数的分析,说明甲烷在电池阳极发生不同类型的反应.电流密度小时,甲烷发生部分氧化反应.电流密度大时,发生氢氧化和CO氧化,部分甲烷发生总反应为完全氧化的反应.部分甲烷发生完全氧化反应的同时,部分甲烷仍发生部分氧化反应,但其反应速率随电流密度增加逐渐降低.甲烷浓度和试验温度增加,甲烷开始发生完全氧化的电流密度增加.

Reactions of Low Concentration Dry Methane on Ni/YSZ Anode of SOFC

The recent trend in solid oxide fuel cell (SOFC) concerns the direct use of methane or natural gas. It is very important to know the chemical and electrochemical reactions of methane over the anode of SOFC. The reactions of low concentration dry methane on SOFC with Ni/YSZ anode, YSZ electrolyte and LSM cathode were studied. Using 8% (mol) YSZ plates as electrolyte, the fuel cells with different anode thickness were made by slurry coating process. The gas composition at the anode outlet was measured by on-line chromatogram at different current density for SOFCs with different methane concentration, operating temperature and electrolyte thickness. Based on the production rate of CO, H2 and CO2, the varieties of methane reaction at anode were analyzed. Consumption of oxygen and shifted electrons were calculated to certify the different reactions occured. At low current density, methane decomposition reaction and deposited carbon oxidation reaction occur; the overall reaction is partial oxidation of methane (POM). With the increasing of current density, hydrogen oxidation and carbon monoxide oxidizing to carbon dioxide take place at the same time, and the overall reaction is direct oxidation of methane (DOM). When the reaction of DOM occurring, a portion of methane still takes part in POM reaction, but the rate of POM decreases with the increasing of current density. The threshold current density at which DOM begins to occur increases with the increase of methane concentration and operation temperature.