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European Microscopy Congress 2020 Abstract Database

Identical location and in situ heating (S)TEM for the study of catalysts nanomaterials and single atoms

Identical location and in situ heating (S)TEM for the study of catalysts nanomaterials and single atoms

Session

PSA.5 - Nanoparticles & Catalysts

Authors

Dr. Francisco Ruiz-Zepeda (1, 3), Dr. Matija Gatalo (1), Dr. Nejc Hodnik (1), Dr. Primož Jovanović (1), Leonard Moriau (1), Dr. Andraž Pavlišič (1), Dr. Marjan Bele (1), Prof. Goran Dražić (1), Davide Menga (2), Burak Koyutürk (2), Dr. Tim-Patrick Fellinger (2), Prof. Miran Gaberšček (1, 4)

Affiliations

1. National Institute of Chemistry
2. Technical University Munich
3. Institute of Metals and Technology
4. University of Ljubljana

Keywords

Identical location TEM, In situ TEM, Catalysts, Nanostructure, Nanoparticles, Single atoms

Abstract text

Research on catalyst nanomaterials has gain high attention especially for finding novel approaches of renewable energy sources. Current fossil fuel sources of energy are finite, but more importantly they are causing environmental harm to the planet [1]. In addition to solar and wind energies, the hydrogen based energies are of great interest among the developing sustainable energies, however the energy conversion electrocatalyst used in fuel cells and electrolyzers still need to be optimized to fulfill the demands of the modern life. In this work, we employ two transmission electron microscopy (TEM) techniques [2, 3] to study catalysts as in the form of nanomaterials and single atoms. By using aberration corrected STEM, we performed an identical location approach [3] to study how catalysts degrade after being activated or electrochemically cycled. This technique consists in studying the same location of the material before and after submitting it (ex situ) to a physical or chemical process, hence allowing to track changes in morphology and composition occurring on the same spot. Particularly since the catalytic properties of nanomaterials depend on exposed surfaces, size, crystal structure and shape, this approach gives direct feedback on how the material can be improved in terms of activity and stability. As one of the case studies, a PtCu₃ catalyst was chosen to observe the same location of the metal nanoparticles before and after being submitted to an activation protocol. Several distinct phenomenon were identified and analyzed: re-shaping, porosity formation, nanoparticle size-decreasing, surface platinum-skin-layer thickening, but most importantly facet dependent dealloying, which was also compared to the Kinetic Monte Carlo dealloying modelling [4]. By adapting the method in a similar way, an identical location study of atomically dispersed Zn-N-Cs was performed for the observation of active‐site imprinting atomically dispersed Fe-N-C by a pyrolytic template ion reaction [5]. As a second part, an in situ heating [2] STEM study of the growth mechanism of PtCu₃ nanoparticles supported on high surface area carbons (HSAC) was performed, providing insight into the annealing part of the synthesis [6]. The composite was obtained from a partial galvanic displacement of copper on carbon support with a platinum precursor salt, and subsequent annealed in order to obtain PtCu₃ catalyst nanoparticles. In situ heating was also performed on electrospun polyacrylonitrile (PAN) polymer nanofibers with Pt precursor, which was first stabilized at 250 °C in air and then carbonized at 750 °C and 1100 °C in a vacuum. This experiment allowed us to observe how the formation of 5 nm Pt particles occurred at the surface of the carbon fibers. As in all cases, the study aims to show how in situ heating and IL-(S)TEM are a powerful approach to obtain valuable information regarding physical or chemical processes ocurring in the catalyst (nanomaterials and single atoms) by providing a better understanding of the growth mechanism, activity and stability.

References

[1] S. Chu, Y. Cui, N. Liu. The path towards sustainable energy. Nature Materials 16 (2017) 16–22. 

[2] H. Saka, T. Kamino, S. Ara, K. Sasaki. In Situ Heating Transmission Electron Microscopy MRS Bulletin 33 (2008) 93-100.

[3] K. J. J. Mayrhofer, J. C. Meier, S. J. Ashton, G. K. H. Wiberg, F. Kraus, M. Hanzlik, M. Arenz. Fuel cell catalyst degradation on the nanoscale. Electrochem. Commun. 10 (2008) 1144-1147.

[4] F. Ruiz-Zepeda, M. Gatalo, A. Pavlišič, G. Dražić, P. Jovanovič, M. Bele, M. Gaberšček, N. Hodnik. Atomically resolved anisotropic electrochemical shaping of nano-electrocatalyst. Nano Lett. 19 (2019) 4919-4927.

[5] D. Menga, F. Ruiz‐Zepeda, L. Moriau, M. Šala, F. Wagner, B. Koyutürk, M. Bele, U. Petek, N. Hodnik, M. Gaberšček, T.‐P. Fellinger. Active‐Site Imprinting: Preparation of Fe–N–C Catalysts from Zinc Ion–Templated Ionothermal Nitrogen‐Doped Carbons. Advanced Energy Materials 9 (2019) 1902412.

[6] M. Gatalo, F. Ruiz-Zepeda, N. Hodnik, G. Dražić, M. Bele, M. Gaberšček. Insights into thermal annealing of highly-active PtCu3/C Oxygen Reduction Reaction electrocatalyst: An in-situ heating transmission Electron microscopy study. Nano Energy 63 (2019) 103892.