Effect of Stress and Composition on Electrochemical Degradation of Proton Exchange Membrane Fuel Cell (PEMFC) Cathode Catalysts

应力和成分对质子交换膜燃料电池 (PEMFC) 阴极催化剂电化学降解的影响

• 批准号: 0931080
• 负责人: Anil Virkar
• 金额: $ 29.19万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0931080&HistoricalAwards=false
• 关键词: Effect; Stress; Composition; Electrochemical; Degradation

0931080VirkarThis project investigates the role of surface stress and composition on cathode catalyst degradation in Proton Exchange Membrane (PEM) fuel cells. Loss of cathode catalyst activity occurs by four main mechanisms: (a) Particle detachment from carbon support, (b) Agglomeration and sintering, (c) Ostwald ripening, and (d) Pt dissolution at cathode and precipitation in the membrane. Ostwald ripening and Pt precipitation in the membrane depend on Pt ion concentration (Pt2+ and/or Pt4+) in aqueous electrolyte and/or ionomer. Ostwald ripening involves coupled transport of Pt2+/Pt4+ ions through aqueous/ionomer medium and electrons through carbon support. Agglomeration and sintering involve coupled transport of Pt2+/Pt4+ through aqueous electrolyte/ionomer medium and electron transport through direct particle contact. In mechanism (d), Pt precipitation occurs by a reaction of Pt2+/Pt4+ and H2. Thus, three mechanisms - agglomeration/sintering, Ostwald ripening and precipitation of Pt in the membrane depend upon Pt2+/Pt4+ ion concentration. All factors which increase Pt2+/Pt4+ concentration will increase degradation kinetics. Intellectual Merits: Many factors determine Pt2+/Pt4+ concentration, some materials related and some related to operating conditions. This proposed work addresses fundamental materials-related properties which determine Pt2+/Pt4+ concentration such as the thermodynamics of alloy systems and surface stress. Fundamental thermodynamic parameter of interest is the partial molar enthalpy of Pt alloy formation. The role of stress is also of profound significance. First, it is known that greater tendency for growth of smaller particles is the surface energy effect, which essentially is the effect of pressure on chemical potential. The greater the magnitude of surface compression, the greater is the chemical potential and degradation kinetics. In pure Pt catalysts, only particle size determines this stress. However, in core-shell catalysts comprising Pt shell and an alloy or non-noble metal core, additional coherency stresses exist. By suitable choices of lattice parameters and interfacial structure, the chemical potential can be reduced thereby reducing Pt2+ concentration and thus reducing degradation kinetics. This proposes to investigate a) the effect of Pt2+ /Pt4+ concentration and temperature on the kinetics of pure Pt, Pt alloy, and core-shell catalysts; and b) the role of stress and alloy composition on the chemical potential of Pt using electrochemical techniques. Broader Impacts: The results of this research should provide a scientific basis for the synthesis of degradation-resistant cathodes. The proposed methodology is general and applicable to essentially all electrochemical devices which require the use of nanosize materials in electrodes and the presence of aqueous/ionic medium. The University of Utah has a strong commitment to undergraduate and graduate education and in enhancing the involvement of socially under-represented groups. One undergraduate student and one graduate student will participate in this research.

本项目研究了质子交换膜(PEM)燃料电池中表面应力和成分对阴极催化剂降解的影响。阴极催化剂活性的丧失主要有四种机制：(A)颗粒从碳载体上脱落，(B)团聚和烧结，(C)Ostwald熟化，(D)铂在阴极上的溶解和膜中的沉淀。膜的Ostwald熟化和铂沉淀依赖于水中电解质和离聚体中的铂离子浓度(Pt2+和/或Pt4+)。Ostwald熟化包括Pt2+/Pt4+离子通过水/离聚体介质的耦合传输和电子通过碳载体的耦合传输。团聚和烧结涉及Pt2+/Pt4+通过水溶液/离聚体介质的耦合传输和通过粒子直接接触的电子传输。在机理(D)中，铂的析出是通过Pt2+/Pt4+和H2的反应进行的。因此，Pt~(2+)/Pt~(4+)离子在膜中的聚集/烧结、奥斯瓦尔德熟化和铂沉淀三种机制取决于Pt2+/Pt4+离子浓度。所有增加Pt2+/Pt4+浓度的因素都会增加降解动力学。智力优势：决定Pt2+/Pt4+浓度的因素很多，有些与物质有关，有些与操作条件有关。这项拟议的工作涉及决定Pt2+/Pt4+浓度的基本材料相关性质，如合金体系的热力学和表面应力。最基本的热力学参数是铂合金形成的偏摩尔热。压力的作用也具有深远的意义。首先，众所周知，表面能效应是较小颗粒生长的更大趋势，本质上是压力对化学势的影响。表面压缩的幅度越大，化学势和降解动力学越大。在纯铂催化剂中，只有颗粒大小决定了这个应力。然而，在由铂壳和合金或非贵金属核组成的核壳催化剂中，存在额外的共格应力。通过选择合适的晶格参数和界面结构，可以降低化学势，从而降低Pt2+的浓度，从而降低降解动力学。用电化学方法研究了Pt2+/Pt4+浓度和温度对纯铂、铂合金和核壳催化剂动力学的影响，以及应力和合金组成对铂化学势的影响。更广泛的影响：这项研究的结果应该为合成耐降解阴极提供科学依据。所提出的方法是通用的，基本上适用于所有需要在电极中使用纳米材料和存在水/离子介质的电化学装置。犹他大学坚定地致力于本科生和研究生教育，并加强社会代表性不足群体的参与。一名本科生和一名研究生将参与这项研究。