Metal nanoparticles for active and stable catalysts in renewable energy storage

The oxygen evolution reaction (OER) is crucial for the storage and conversion of H₂ fuel and requires highly active and highly stable catalysts to drive it. Our expertise in nanoparticle synthesis has allowed us to create the most active and stable nanocatalysts for OER reported to date.¹ We achieved this by synthesizing 3D branched Ru nanoparticles with structural features that both prevent dissolution and improve oxidation catalysis (Figure 1).²

In this project, Ru nanoparticles will be synthesized with low index facets which are critical for achieving stable reaction kinetics that prevent dissolution of Ru and enhance the catalytic activity. This work will combine the development of synthetic methods to control the size, shape and composition of Ru-based nanocatalysts, with advanced characterisation using high-resolution transmission electron microscope (HRTEM) and also evaluation of their electrocatalytic performance. This allows for the relationships between nanoparticle structure and catalytic performance to be fundamentally understood and tuned to create leading nanocatalyst materials.

References

1. Gloag, L. et al. Three-Dimensional Branched and Faceted Gold-Ruthenium Nanoparticles: Using Nanostructure to Improve Stability in Oxygen Evolution Electrocatalysis. Angew. Chemie Int. Ed. 57, 10241–10245 (2018).
2. Poerwoprajitno, A. R. et al. Formation of Branched Ruthenium Nanoparticles for Improved Electrocatalysis of Oxygen Evolution Reaction. Small 15, 1804577 (2019).
3. Gloag, L. et al. A cubic-core hexagonal-branch mechanism to synthesize bi-metallic branched and faceted Pd-Ru nanoparticles for oxygen evolution reaction electrocatalysis. J. Am. Chem. Soc. 140, 12760–12764 (2018).

Pt is the most catalytically active metal for fuel cell reactions, but it is also expensive. In order to convert to sustainable energy cells in a hydrogen economy, nanocatalysts need to be high-performing and use minimal amounts of scarce Pt. Strained Pt on the surface of a metal nanoparticle is a promising nanoparticle structure for highly active hydrogen evolution (HER) and oxygen reduction (ORR) electrocatalysis. As world-leaders in nanoparticle synthesis, we have been the first research group to create these via by a “bottom-up” approach involving the direct growth of Pt onto nanoparticles.^1-3 Depositing Pt directly onto Ni nanoparticles creates highly strained Pt that maximises the specific and simultaneously minimising the amount of expensive Pt that is used to provide the highest mass activities reported to date (Figure 1).

In this project, nanoparticles will be decorated with small clusters of Pt atoms for use as high performance HER and ORR catalysts. The state-of-the-art electron microscopes provided by Electron Microscopy Unit, UNSW, will allow characterisation of complex nanocatalyst materials made of multiple metals with atomic-level precision. By controlling the position of Pt atoms on different metal nanoparticle structures, both electrocatalytic activity and stability will be optimised to create the most advanced and effective nanoparticle catalysts.

References

1. Alinezhad, A. et al. Controlling Pt Crystal Defects on the Surface of Ni-Pt Core-Shell Nanoparticles for Electrocatalysts for Oxygen Reduction. ACS Appl. Nano Mater.  3, 5995-6000 (2020).

2. Alinezhad, A. et al. Direct Growth of Highly Strained Pt Islands on Branched Ni Nanoparticles for Improved Hydrogen Evolution Reaction Activity. J. Am. Chem. Soc. 141, 16202–16207 (2019)

3. Alinezhad, A. et al. Controlling hydrogen evolution reaction activity on Ni core–Pt island nanoparticles by tuning the size of the Pt islands. Chem. Commun. 57, 2788-2791 (2021)

The state-of-the-art electron microscopes managed by Professor Richard Tilley allow analysis of 3D structure, atomic arrangement and elemental composition of nanoparticles with unprecedented resolution at the nanoscale (Figure 1).^1,2 As the first group in Australia to have in situ Transmission Electron Microscopy (TEM) facilities, we are paving the way for research into nanocatalyst design at the atomic level.

The structure of nanoparticles during catalysis is one of the hottest topics in fuel cell research at the moment. By understanding where and how gas molecules interact with nanocatalysts, the most active and stable catalyst materials can be designed from a fundamental basis. In this project, you will image real time changes to nanoparticle structure in the presence of different gases, to visually track interactions of molecules with catalytically active sites. The tomography capabilities of our microscopes allows for 3D visualisation of complex and intricate nanocatalyst structures that are leading particles for electrocatalytic reactions (Movie).

[video] Figure 2: Tomographic reconstruction of a Au-Ni branched nanoparticle used for biomass oxidation.2

References

1. Chen, H.-S. et al. Preserving the Exposed Facets of Pt3Sn Intermetallic Nanocubes During an Order to Disorder Transition Allows the Elucidation of the Effect of the Degree of Alloy Ordering on Electrocatalysis. J. Am. Chem. Soc. 142, 3231–3239 (2020).

2. Chen, H.-S. et al. Role of the Secondary Metal in Ordered and Disordered Pt–M Intermetallic Nanoparticles: An Example of Pt3Sn Nanocubes for the Electrocatalytic Methanol Oxidation. ACS Catal. 11, 2235-2243 (2021).

3. Poerwoprajitno, A. R. et al. Faceted Branched Nickel Nanoparticles with Tunable Branch Length for High Activity Biomass Oxidation Electrocatalysis. Angew. Chem. Int. Ed. 123, 15615-15620(2020).