Abstract:

The oxygen mass transfer resistance in the cathode catalyst layer of proton exchange membrane fuel cell (PEMFC) is the main bottleneck limiting the polarization performance of membrane electrode with low Pt at high current densities. To reduce the oxygen mass transfer resistance of the cathode catalyst layers is of highly significance for the improvement of PEMFC performance and accelerating its commercial applications. In the paper, the sources and contributions of oxygen mass transfer resistance in catalyst layers have been analyzed. It is pointed out that the local oxygen mass transfer resistance is primarily caused by the resistance across the three-phase contact interface among the gas phase, ionomer, and Pt nanoparticles. The influences on the oxygen mass transfer resistance, especially the local one have been expounded from four aspects of Pt nanoparticle, ionomer, carbon support and the water formed, respectively. The methods of reducing oxygen mass transfer resistance have also been summarized. Finally, the design of cathode catalyst layers with low Pt for PEMFC is prospected. It is proposed that constructing suitable support pore structure, rationalizing the Pt particle distributions both inside and outside of the pores, controlling ionomer thickness and its distribution, as well as strengthening water transfer, could help to reduce the oxygen mass transfer resistance and thus to promote the cell power outputs at high current densities.

Key words: mass transfer, porous media, fuel cells, cathode catalyst layer, low Pt loading, local oxygen mass transfer resistance

摘要：

质子交换膜燃料电池（proton exchange membrane fuel cell，PEMFC）阴极催化层的氧传质阻力是限制高电流密度下低Pt载量膜电极极化性能的主要瓶颈。研究如何降低阴极催化层氧传质阻力对于提高PEMFC的性能、加快其商业化应用至关重要。本文首先分析了催化层氧传质阻力产生的根源及构成，指出氧气穿越气相、离聚物、Pt纳米粒子三相接触界面时产生的局部氧传质阻力是其重要部分；接着从Pt纳米粒子、离聚物、碳载体和水这四方面阐述了各因素对氧传质阻力特别是局部氧传质阻力的影响，归纳总结了降低氧传质阻力的方法；最后对低Pt载量PEMFC阴极催化层设计进行了展望，提出从构建适宜的载体孔结构、合理分布孔道内外Pt粒子数量、控制离聚物厚度及分布，以及强化水转移等方面着手，以降低氧传质阻力，提高电池在高电流密度下的功率输出。

关键词: 传质, 多孔介质, 燃料电池, 阴极催化层, 低Pt载量, 局部氧传质阻力