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

Kansas State University, Manhattan KS

Investigators

Abstract

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.