Development of Alternative and Durable High Performance Cathode Supports for PEM Fuel Cells

1. TEM image of ordered mesoporous carbon (OMC) FY07 Accomplishment Development of Alternative and Durable High Performance Cathode Supports for PEM Fuel Cells Cost-Effective Corrosion Protection to Lengthen Fuel Cell Life & Efficiency Background The poor durability of cathode supports and catalysts in proton exchange membrane fuel cells (PEMFCs) is a key technical barrier for stationary and transportation applications. The corrosion of carbon supports poses significant concerns at high electrode potentials and is accelerated during start/stop cycles and during higher temperature operation (>100°C). Graphitized supports show better but still insufficient corrosion resistance. To address the critical issues associated with the carbon support, a strong multi-disciplinary team led by Pacific Northwest National Laboratory (PNNL) with participations of Ballard Power Systems (BPS), Oak Ridge National Laboratory (ORNL), and the University of Delaware (UD) was assembled. The goal is to develop and evaluate new classes of alternative and durable high-performance cathode supports for PEM fuel cells. Graphitized mesoporous carbons will be used as the scaffolds and tungsten carbide (WC) employed to protect support surfaces, which showed promise as a stable alternative cathode support as demonstrated by our co-principal investigator’s work at UD. ORNL is collaborating with PNNL by developing synthetic methods and studying stable mesoporous carbon that will lead to materials that will achieve the performance targets for PEM fuel cells. Our research on chemical synthesis takes advantage of unique ORNL expertise in the self-assembly synthesis of mesoporous carbon. The synthetic approach that is being followed incorporates strategies such as the use of soft-templating, graphitization, pore engineering, and surface engineering that lead to the generation of highly stable mesoporous cathode supports. Technology A synthesis protocol was established for preparation of mesoporous carbon with pore size about 8 nm. No destruction of mesopore structures was observed during graphitization. The considerable reduction of micropore volumes through graphitization at 2600ºC was observed. The thermogravimetric analysis (TGA) characterization indicates that our graphitized mesoporous carbon loaded with Pt nanoparticles is considerably more stable than commercial carbon materials (e.g., VXC-72) loaded with Pt nanoparticles. Two mesoporous carbon samples before and after graphitization were sent to PNNL for further investigation.

2. Initial experiments were planned to explore the feasibility of synthesis of WC-doped mesoporous carbon via cosynthesis methodology. The initial characterization indicates that no significant structure change was observed upon doping of WC into mesostructures. Further characterization of structural integrities and electrocatalytic properties is currently underway. • Benefits • Highly stable cathodes • Less use of Pt catalysts • High electrical conductivities • Corrosion resistant • Future Work • Synthesis methods will be investigated for controlled synthesis of mesoporous carbon with tunable pore sizes (3 nm-8 nm). The space confinement effect of the resulting mesoporous carbon on the stability of Pt nanoparticles will be investigated. Optimization of the cosynthesis process for mesoporous carbon materials doped with WC will be conducted. • Points of Contact • Sheng Dai, 865-574-6228, dais@ornl.gov Comparison of TGA curves of graphitized ordered mesoporous carbons (OMC) containing two Pt loadings with that of the popular commercial support (VXC-72) containing 10wt% Pt. The scan rates used were identical for three samples. It was clear from the right figure that our graphitized mesoporous carbon is considerably more stable under oxidative conditions than the popular commercial carbon supports.