Predicting Surface Intermixing in Alloy Nanocatalysts from First Principles Calculations

Predicting Surface Intermixing in Alloy Nanocatalysts from First Principles Calculations

Luke T. Roling and Manos Mavrikakis

Department of Chemical & Biological Engineering, University of Wisconsin-Madison, Madison, WI

Controlled catalyst design and synthesis are enhanced by a detailed fundamental understanding of phenomena occurring at the catalyst surface. One such class of phenomena that has long attracted attention is metal adatom diffusion across metal substrates, and the impact these phenomena have on catalyst growth.^1-2 We recently described the synthesis and electrochemical activity of hollow Pt-Pd nanocages with exceptional performance for the oxygen reduction reaction.³ Detailed DFT calculations predicted that the formation of these nanostructures, which occurred through etching Pd from a Pd-Pt core-shell structure, requires intermixing of Pt and Pd during the core-shell synthesis. This intermixing was accommodated by the ease of substitution of Pt into the underlying Pd substrate relative to the diffusion of Pt across the surface.

In this presentation, we extend these calculations to bimetallic combinations of ten transition metals to predict similar intermixing phenomena in the synthesis of other catalytically-relevant alloy nanocatalysts. In particular, we present results for metal adatom surface diffusion and substitution for all combinations of eight fcc and two hcp metals, considering both close-packed and open crystal facets. We also present results at two different surface coverages of metal adatoms. Our results can guide future simulation and inorganic synthesis efforts toward the atomic-scale design of nanocatalysts with controlled structures and compositions.

1. P. J. Feibelman, Physical Review Letters 1990, 65, 729.
2. T. Ala-Nissila, R. Ferrando, S. Ying, Advances in Physics 2002, 51, 949.
3. L. Zhang, L. T. Roling, X. Wang, M. Vara, M. Chi, J. Liu, S. Choi, J. Park, J. A. Herron, Z. Xie, M. Mavrikakis, Y. Xia, Science 2015, 349, 412.