低氢气计量比下车载工况燃料电池电堆耐久性研究

Durability of a Fuel Cell Stack with Low Hydrogen Stoichiometry under Driving Cycle Conditions

考察了1.9 k W质子交换膜燃料电池电堆在低氢气化学计量比,电流快速连续变载条件下的耐久性。在244 h工况运行后,在电流密度为800 m A×cm-2的条件下,电堆单电池平均电压从0.616 V下降到0.464 V,衰退率为0.623m V×h^(-1),由此可见电堆出现快速性能衰退。在实验过程中,车载工况使得电堆阴阳极进气压力以及进气温度出现明显波动,从而导致膜电极组件(MEA)遭受周期性的机械应力与热应力冲击。此外,在氢气化学计量比为1.05条件下,电流快速连续加载会导致供气系统响应迟缓,气体供应不及时,甚至导致燃料局部供应不足,这可加剧载体碳腐蚀。极化曲线、循环伏安法(CV)测试、电化学交流阻抗谱(EIS)表征发现,电化学活性面积的下降引起了电堆的快速、不可逆的衰退。扫描电子显微镜(SEM)、透射电子显微镜(TEM)表征显示阳极催化层厚度变薄,阴阳极催化剂颗粒出现不同程度的长大。可见,在车载工况下,由于低氢气计量比引起的局部缺氢,加速了碳载体腐蚀,并使Pt颗粒的团聚以及流失,影响燃料电池性能。

The durability of a 1.9 k W fuel cell stack was studied under low hydrogen stoichiometric ratio and continuous rapid current changing driving cycle conditions. The average cell voltage of the stack at 800 m A×cm^-2 declined from 0.616 V to 0.464 V with a decay rate of 0.623 m V×h^-1 after 244 h driving cycle tests, which means the stack has rapid degradation. The pressure and temperature differences between the anode and cathode of the fuel cell fluctuate significantly during the test. Therefore, MEA of the fuel cell is suffered from periodic mechanical and heat impact. In addition, the fuel supply lagges behind the rapidly change of current when the hydrogen stoichiometry is 1.05, which leads to local hydrogen starvation and carbon corrosion. Polarization curve, cyclic voltammetry（CV） and electrochemical impedance spectrum（EIS） results show that the stack suffers from an irreversible degradation as a consequence of the reduction in electrochemical active areas. Scanning electron microscope（SEM） and transmission electron microscope（TEM） micrographs show that the anode catalytic layer becomes thinner and the catalyst particle size increases in both anode and cathode areas. Therefore, hydrogen starvation caused by low hydrogen stoichiometric ratio can reduce the stack performance which is caused by carbon corrosion, catalyst aggregation and dissolution.