Fan Linhao, Wang Yun, Jiao Kui
State Key Laboratory of Engines, Tianjin University, 135 Yaguan Road, Tianjin 300350, China.
Renewable Energy Resources Laboratory, Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697-4075, United States.
ACS Nano. 2020 Dec 22;14(12):17487-17495. doi: 10.1021/acsnano.0c07856. Epub 2020 Dec 11.
Understanding the O permeation phenomenon in the ionomer thin film on platinum (Pt) nanoparticles is vital to improve the electrocatalyst performance of proton exchange membrane fuel cells at a low Pt loading. In this study, the ionomer film structure, O density distribution, transport fluxes, and permeation routes are investigated for carbon-supported polyhedral Pt nanoparticles (cube and tetrahedron) in the facet, edge, and corner regions. The molecular dynamic simulation takes into account the molecular interactions among the ionomer, Pt nanoparticles, carbon support, and O molecules. The results show that a dense ionomer ultrathin layer with a tight arrangement of perfluorosulfonic acid is present on the Pt facets (namely region A). In the ionomer near the Pt edges and corners (namely region B), the structure is less dense due to the weaker Pt attraction, resulting in a higher O density than that in region A. O fluxes in the different regions show that approximately 90% of O molecules reach the Pt cube and tetrahedron nanoparticles their upper corner and edge regions. In the vicinity of Pt nanoparticles, O permeation routes are inferred to penetrating region B to the Pt upper corners or edges instead of region A to the Pt facets.
了解离聚物薄膜在铂（Pt）纳米颗粒上的氧渗透现象对于提高质子交换膜燃料电池在低Pt负载量下的电催化剂性能至关重要。在本研究中，研究了碳负载的多面体Pt纳米颗粒（立方体和四面体）在晶面、棱边和角区域的离聚物膜结构、氧密度分布、传输通量和渗透路径。分子动力学模拟考虑了离聚物、Pt纳米颗粒、碳载体和氧分子之间的分子相互作用。结果表明，在Pt晶面上（即区域A）存在一层排列紧密的全氟磺酸离聚物超薄致密层。在靠近Pt棱边和角的离聚物中（即区域B），由于Pt的吸引力较弱，结构较疏松，导致氧密度高于区域A。不同区域的氧通量表明，约90%的氧分子通过其上角和棱边区域到达Pt立方体和四面体纳米颗粒。在Pt纳米颗粒附近，推断氧的渗透路径是穿过区域B到达Pt上角或棱边，而不是从区域A到达Pt晶面。
