A Novel Fuel Cell Catalyst and Support Architecture Based on Edge-site Pyridinic Nitrogen-Doping on Vertically Aligned Conical Carbon Nanofibers

该项目将探索用于低温燃料电池的新型电催化剂设计的有效性和工作机理。 吡啶类氮掺杂的垂直排列碳纳米管（VACNF）结构既用作氧还原反应（ORR）电催化剂又用作贵金属催化剂组分的载体。 混合设计将潜在地提高贵金属催化剂的有效性，从而为超低铂基燃料电池催化剂打开大门，并提高燃料电池在广泛能源应用中的经济可行性。 该项目的动机是最近的一项研究，由另一个小组，在一个模型系统上的ORR，该模型系统由在石墨晶体中离子蚀刻的微槽处的定义明确的石墨边缘组成，这表明活性ORR位点是在这些边缘处形成的吡啶N旁边的碳原子。 本项目将通过专注于以定义明确的氮掺杂VACNF阵列的形式创建2-D模型系统的3-D纳米结构碳架构版本来推进当前的知识，该阵列可以在全燃料电池中实施。 该项目的具体技术目标包括：（1）理解和控制锥形堆叠VACNF侧壁上的边缘位吡啶氮作为用于ORR的无金属催化剂，ORR是燃料电池中的关键限速步骤;（2）探索吡啶边缘掺杂的VACNF作为用于阴极和阳极反应中超低Pt负载的高度稳定的分级催化剂载体;（3）研究VACNF的结构和性能。以及（3）将氮掺杂的VACNF催化剂/载体结构与Nafion离聚物接合以形成用于集成燃料电池研究的新型膜电极组件（MEA）。VACNF独特的锥形堆叠石墨结构用于在VACNF侧壁处产生精确控制的边缘位置吡啶N掺杂，同时保持内部石墨层的理想π键共轭。 在这种VACNF阵列中，垂直排列的纳米纤维之间的开放空间允许均匀的Pt沉积和有效的Nafion离聚物渗透，以形成新的互穿双连续MEA。这将改善质量传输并抑制燃料电池中常见的溢流问题。为了帮助实验设计和优化，第一性原理模型将被执行，以建立基于N掺杂剂的几何位置和配置，以及与贵金属的相互作用的N掺杂VACNF的物理和化学行为的指导方针。 这些结果将提供关键的科学认识，促进燃料电池技术可持续催化剂的开发。 除了技术目标外，该项目还将包括一些主要针对研究生，本科生和K-12学生的教育和推广组件。 这些外展计划将强调初中和高中女生的参与，并将与路易斯安那州的泽维尔大学合作，这是一所历史悠久的黑人大学。

The project will explore the effectiveness and working mechanism of a new electrocatalyst design for low-temperature fuel cells. A pyridinic, nitrogen-doped vertically aligned carbon nanofiber (VACNF) structure is used both as the oxygen reduction reaction (ORR) electrocatalyst and as the support for the noble metal catalyst component. The hybrid design will potentially increase the effectiveness of the noble metal catalyst, thereby opening the door to ultra-low platinum-based fuel cell catalysts and improving the economic viability of fuel cells for a broad range of energy applications. The project is motivated by a recent study, by another group, of the ORR on a model system consisting of well-defined graphitic edges at microgrooves ion-etched in graphite crystals, which suggested that the active ORR sites are carbon atoms next to the pyridinic N formed at these edges. The present project will advance the current knowledge by focusing on creating a 3-D nanostructured carbon architecture version of the 2-D model system in the form of well-defined nitrogen-doped VACNF arrays that can be implemented in full fuel cells. Specific technical objectives of the project include (1) understanding and controlling the edge-site pyridinic nitrogen on the sidewall of conically stacked VACNFs as a metal-free catalyst for ORR, the key rate-limiting step in fuel cells; (2) exploring the pyridinic edge-doped VACNFs as highly stable hierarchical catalyst supports for ultra-low Pt loading in both cathodic and anodic reactions; and (3) interfacing the nitrogen-doped VACNF catalyst/support architecture with Nafion ionomer to form a novel membrane electrode assembly (MEA) for integrated fuel cell studies. The unique conically stacked graphitic structure of VACNFs is employed to generate precisely controlled edge-site pyridinic N-doping at the VACNF sidewall, while maintaining the ideal pi-bond conjugation of the internal graphitic layers. In such VACNF arrays, the open space between the vertically aligned nanofibers allows uniform Pt deposition and effective Nafion ionomer infiltration to form novel interpenetrating bicontinuous MEAs. This will improve mass transport and suppress the flooding issues common in fuel cells. To assist experimental design and optimization, first-principles modeling will be performed to establish the guideline for the physical and chemical behaviors of N-doped VACNF based on the geometric location and configuration of the N dopants, and the interactions with noble metals. These results will provide critical scientific understanding that will facilitate the development of sustainable catalysts for fuel cell technologies. In addition to the technical objectives, the project will include a number of educational and outreach components directed primarily at graduate, undergraduate, and K-12 students. The outreach programs will emphasize participation by middle- and high-school girls and will also feature collaboration with Xavier University of Louisiana, a historically black university.