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

该项目将探索低温燃料电池新型电催化剂设计的有效性和工作机制。一种吡啶、氮掺杂的垂直排列碳纳米纤维（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。这种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。该项目的动机是由另一个小组最近的一项研究，在一个模型系统上，由石墨晶体中离子蚀刻的微槽中定义良好的石墨边缘组成的ORR，这表明活性ORR位点是在这些边缘形成的吡啶N旁边的碳原子。目前的项目将通过专注于以明确的氮掺杂VACNF阵列的形式创建二维模型系统的三维纳米结构碳结构版本来推进现有的知识，该系统可以在全燃料电池中实现。该项目的具体技术目标包括：(1)了解并控制锥形堆VACNFs侧壁边缘位置的吡啶氮作为燃料电池关键限速步骤ORR的无金属催化剂；(2)探索吡啶边掺杂VACNFs作为阴极和阳极反应中超低铂负载的高稳定性分级催化剂载体；(3)将氮掺杂的VACNF催化剂/载体结构与Nafion离子单体连接，形成一种用于集成燃料电池研究的新型膜电极组件（MEA）。利用VACNF独特的锥形堆叠石墨结构，在VACNF侧壁产生精确控制的边位吡啶n掺杂，同时保持内部石墨层理想的pi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离子浸润，形成新的互穿双连续mea。这将改善质量运输，并抑制燃料电池中常见的水浸问题。为了帮助实验设计和优化，将基于N掺杂剂的几何位置和构型以及与贵金属的相互作用进行第一性原理建模，以建立N掺杂VACNF的物理和化学行为准则。这些结果将提供关键的科学理解，将促进燃料电池技术可持续催化剂的发展。除了技术目标之外，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成部分。拓展项目将强调初中和高中女生的参与，并将与路易斯安那州泽维尔大学（Xavier University of Louisiana）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.