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

该项目将探索一种新的低温燃料电池电催化剂设计的有效性和工作机理。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)的电催化剂，也用作贵金属催化剂组件的载体。这种混合设计可能会提高贵金属催化剂的效率，从而为超低铂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。该项目是由另一个小组最近对ORR进行的一项研究推动的，该模型系统由离子刻蚀在石墨晶体中的微槽处的石墨化边缘组成，该模型系统表明，活性ORR位置是靠近在这些边缘形成的吡啶氮的碳原子。本项目将促进现有知识的发展，重点是以可在全燃料电池中实施的明确定义的掺氮VACNF阵列的形式创建2-D模型系统的3-D纳米结构碳结构版本。该项目的具体技术目标包括(1)了解和控制锥形堆叠VACNF侧壁上的边缘位置吡啶氮作为燃料电池中关键的限速步骤ORR的无金属催化剂；(2)探索在阴极和阳极反应中作为高度稳定的分级催化剂载体的吡啶类边缘掺杂VACNF；以及(3)将掺氮VACNF催化剂/载体体系与Nafion离聚体连接，形成用于集成燃料电池研究的新型膜电极组件(MEA)。利用VACNF独特的锥形堆积石墨化结构在VACNF侧壁产生精确可控的边缘位吡啶氮掺杂，同时保持内部石墨化层的理想的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铂沉积和有效的Nafion离聚体渗透，形成新型的互穿双连续MEA。这将改善质量传输，并抑制燃料电池中常见的泛滥问题。为了辅助实验设计和优化，将根据氮掺杂的几何位置和构型以及与贵金属的相互作用，通过第一性原理模拟来建立氮掺杂VACNF的物理化学行为的指导方针。这些结果将提供关键的科学理解，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学生的教育和推广部分。外展项目将强调初中和高中女生的参与，还将与历史上的黑人大学路易斯安那州泽维尔大学合作。

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.