多孔层的孔隙特性和各向异性对燃料电池瞬态性能的影响

燃料电池(Fuelcell,FC)与外部环境之间的传热和多孔层的传质均会影响FC内的水热气电状态,进而影响到催化层的电化学反应速率,从而显著影响其瞬态性能(Transient performance,TSP)。多孔层的孔隙特性和各向异性是影响其传热传质能力的关键因素,充分认识其对FC-TSP的影响规律,对于优化车载FC动力源的负载响应有重要意义。为此,综合考虑FC与外部环境动态热交换,内部水热气电等各物理性质的空间动态分布以及气、液和溶解相等多相时变转化关系,建立FC多相三维瞬态传质传热数值模型,以分析多孔层非均质性质对动态过程的影响。进一步,以电流密度的阶跃变化模拟动态负载,分析FC的电压,膜的水含量和温度,微孔层|催化层界面的氧浓度。结果表明,多孔层的孔径大小和分布及各向异性对FC的TSP有明显影响。另外,不同热条件对FC的内部物理量分布的影响较对TSP的影响更为显著。

Effect of Pore Characteristics and Anisotropy of Porous Layer on the Transient Performance of Fuel Cell

The heat transport between a fuel cell(FC) and the external thermal environment and the mass transport of the porous layer will affect the hydrothermal, gas-electric state in the FC, which in turn affects the electrochemical reaction rate of the catalyst layer,thereby significantly affecting its transient performance(TSP). The pore characteristics and anisotropy of the porous layer are the key factors affecting its heat and mass transport capacity. Fully understanding its influence on the FC-TSP is of great significance for optimizing the load response of the vehicle-mounted FC power source. To this end, comprehensively considering the dynamic heat exchange between FC and the external environment, the spatial dynamic distribution of physical properties such as water, heat and electricity, as well as the multi-phase time-varying transformation relationship of gas, liquid and dissolved phase, the multi-phase 3D transient mass and heat transfer numerical model of FC was established to analyse the influence of heterogeneous properties of porous layer on the dynamic process. Further, the dynamic load was simulated with a step change of the current density, and the voltage of the FC, the water content and temperature of the membrane, and the oxygen concentration at the microporous layer | catalyst layer interface were analysed. The results show that the pore size and distribution and anisotropy of the porous layer have obvious effects on the TSP of the FC. In addition, the influence of different thermal conditions on the distribution of internal physical quantities of FC is more significant than that of TSP.