The development of a suitable catalyst for the oxygen reduction reaction (ORR), which is the cathode reaction of proton exchange membrane fuel cells (PEMFC), is necessary to transition from traditional energy systems to a sustainable energy future. However, the practical realization of this technology is impeded by the high cost and low durability of the cathode catalysts that perform ORR. Extensive efforts have been placed to utilize bimetallic Pt−M alloys to reduce the Pt loading and to modulate geometric, structural, and electronic effects in order to improve ORR reaction rates. To further improve catalyst stability under acidic conditions, Pt−M alloys with a chemically ordered intermetallic structure, especially the L10−PtM phase, have been considered to be one of the most promising materials. In this work, we present the synthesis and characterization of a series of monodisperse Pt-Co bimetallic NCs with well-defined sizes and a wide range of cobalt compositions. The transformation from the chemically disordered A1 to the L10 phase was achieved via thermal annealing using both a conventional oven and a rapid thermal annealing process. The resulting Pt−Co samples are studied by a variety of X-ray and electron-based techniques to identify changes in NC overall size and the structural ordering introduced by the structural transformation. The control over particle compositions achieved at the atomic scale allows us to establish a correlation between Co composition and the prominence of L10 phase and further correlate with the ORR performance and catalyst stability. This work provides fundamental insights into the intrinsic correlation between the relevant ORR activity enhancement, the chemical compositions of Pt-Co alloy catalysts and the ordering structures, which is the key to the design of bimetallic catalysts and the optimization of their catalytic performance for fuel cell applications.

Tuning the electrocatalytic oxygen reduction reaction activity of Pt−Co nanocrystals by cobalt concentration with atomic-scale understanding

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.