基于微型燃料电池阴极氧气传输的研究

Research on oxygen transport based on mini-PEM fuel cell cathode

燃料电池中阴极的氧气传输涉及不同的机理,包括气体在流场中的对流、在气体扩散层(GDL)中的分子扩散、在催化层(CL)中的努森扩散及在水膜和离子膜中的渗透作用。氧气传输阻力可用单电池的极限电流来评价。通过调控氮氧混合气中氧气的百分含量测得一系列的极限电流(I),计算出不同氧分数下的总传输阻力(R_(total))。从R_(total)-I曲线可知,氧气在燃料电池中的传输分为两个区域:一是干态区域(电流密度小于1500 mA/cm^2),R_(total)趋近于常数;二是湿态区域(电流密度大于1 500 mA/cm^2),R_(total)急剧上升。R_(total)-I曲线能清晰反映燃料电池在各电流密度下工作时的氧气传输情况。

The oxygen transport in PEMFC involves various transport mechanisms,including convection in the flow channel,molecular diffusion and Knudsen diffusion in the pores of gas diffusion layer(GDL)and catalyst layers(CL),and permeation through the layers of ionomer or water in catalyst active sites.The limiting current of mini-fuel cell is used to evaluate gas transport resistance at the cathode.This work measures a series of limiting current by using high excess H2 and diluted O2 in N2to calculate Rtotal.From the Rtotal-curve,more than about 1 500 mA/cm2,transport resistance is nearly constant,corresponding to relatively dry condition and less about than 1 500 mA/cm2;transport resistance increases rapidly,corresponding to relatively wet condition.Rtotal-curve can be used to evaluate the oxygen transport condition under each current density,and can also directly reflect the Rtotal transport resistance.