Tuning the Electrocatalytic Oxygen Reduction Reaction Activity of PtCo Nanocrystals by Cobalt Concentration and Phase Transformation Methods

2018 Spring Symposium

Jennifer D. Lee, Ph.D. Candidate, Christopher B. Murray Group, Department of Chemistry, University of Pennsylvania

Abstract – The proton exchange membrane fuel cell (PEMFC) is a critical technology to enhance the clean, sustainable production and usage of energy, but practical application remains challenging because of the high cost and low durability of the cathode catalysts that perform oxygen reduction reaction (ORR). Efforts have been placed on the study of introducing first-row transition metals in Pt-M alloys to reduce the Pt loading and modulate geometric, structural and electronic effects. To further improve the ORR reaction rate and catalysts stability, alloys that adopt an intermetallic structure, especially the tetragonal L10-PtM phase, has been one of the most promising materials. In this contribution, monodisperse PtCo nanocrystals (NCs) with well-defined size and Co composition are synthesized via solvothermal methods. The transformation from face-centered cubic (fcc) to ordered face-centered tetragonal (fct) structure was achieved via thermal annealing. Depending on the selection of transformation methods, different degrees of ordering were introduced and further correlated with their ORR performance. A detailed study of the annealing temperature and composition dependent degree of ordering is also highlighted. This work provides the insight of discovering the optimal spatial distributions of the elements at the atomic level to achieve enhanced ORR activity and stability.