Optimizing the Size of Platinum Nanoparticles for High Oxygen Reduction Reaction Activity

The reactivity of ultra-small nanoparticles and atom precise clusters consisting of less than 50 atoms depends not only on the nanoparticle size and on the surface to volume ratio but also on the exact atomicity of the metal cluster. This has been attributed to unique cluster structures, isomers, and structural fluctuations leading to distinct electronic properties, special surface sites, and defects with altered, and even enhanced, reactivity.

High oxygen reduction reaction (ORR) activity has been for many years considered as the key to many energy applications. By combining theory and experiment were prepared Pt nanoparticles with optimal size for the efficient ORR in proton-exchange-membrane fuel cells. Optimal nanoparticle sizes are predicted near 1, 2, and 3 nm by computational screening. To corroborate the computational results, it has been addressed the challenge of approximately 1 nm sized Pt nanoparticle synthesis with a metal–organic framework (MOF) template approach.

Thanks to the capability of the aberration corrected HR-TEM TITAN offered by the Core Facility the international team was capable to confirm the presence of atomically precise nanoclusters of an atomicity near 12 and of size 1.14 ± 0.35 nm.

The authors published the results in two prestigious scientific journals, Angewandte Chemie (https://doi.org/10.1002/anie.201904492) and Journal of the American Chemical Society (https://pubs.acs.org/doi/10.1021/jacs.9b07083), where the highest to date mass activity among pure Pt catalysts for the ORR within similar size range was reported and details of synthesis and characterization of the novel MOF template containing Pt nanoclusters were described, respectively.

B. Garlyyev, K. Kratzl, M. Rück, J. Michalička, J. Fichtner, J.M. Macak, T. Kratky, S. Günther, M. Cokoja, A.S. Bandarenka, A. Gagliardi, R.A. Fischer R.A: Optimizing the Size of Platinum Nanoparticles for Enhanced Mass Activity in the Electrochemical Oxygen Reduction Reaction, Angewandte Chemie - International Edition, 58 (2019), p. 9596.

K. Kratzl, T. Kratky, S. Günther, O. Tomanec, R. Zbořil, J. Michalička, J. M. Macák, M. Cokoja, R. A. Fischer: Generation and Stabilization of Small Platinum Clusters Pt12±x Inside a Metal–Organic FrameworkJ. Am. Chem.Soc. 141 (2019), p. 13962.

Figure 1: A) Predicted mass activities plotted versus nanoparticle diameters. Optimal nanoparticles (blue triangles) are identified at diameters of 1.1 nm, 2.07 nm, and 2.87 nm. B) Low-index surfaces (111) (blue) and (100) (red) depicted on the 2.87 and 3 nm nanoparticle.
Figure 2: A) Overview HR-TEM image of Pt nanoparticles and size distribution histogram (inset). B) Detailed HR-TEM image shows the magnified image of six single Pt nanoparticles and the table shows their size.