In-Depth Dynamical Structural and Optical Study of Unconventional Au Based Plasmonic Core@ Catalytic Shell Antenna-Reactor System by Electron Microscopy and Simulations

Project Information

HotElecTEM

Grant agreement ID: 101109165

DOI

10.3030/101109165

Project closed

EC signature date 28 June 2023

Start date 15 December 2023

End date 14 December 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 181 152,96

Coordinated by

UNIVERSIDAD DE ZARAGOZA
Spain

Periodic Reporting for period 1 - HotElecTEM (In-Depth Dynamical Structural and Optical Study of Unconventional Au Based Plasmonic Core@ Catalytic Shell Antenna-Reactor System by Electron Microscopy and Simulations)

Reporting period: 2023-12-15 to 2025-12-14

Summary of the context and overall objectives of the project

Global energy demand grew by 2.2% in 2024, a notably faster rate than the annual average of 1.3% seen between 2013 and 2023. Fossil fuels have 80% contribution in this production which alarmingly increases the amount of CO2 in the environment. Sunlight is a renewable energy source and an efficient use of it can lower the CO2 level significantly. Ni-based photocatalysts is showing a great efficiency with very good reproducibility, however a surge in the electric vehicle (EV) production is making Ni more valuable and it is predicted that within 2025 the global demand for Ni will exceed the supply making it a scarce material. Hence an alternate material is urgently needed and plasmonic noble metal nanoparticles (NMN) have shown a great potential in this aspect. Upon excitation with external electromagnetic wave, plasmonic NMN can produce hot electrons (e-) and holes (h+), which can drive reactions at the nanoparticle surface. This incredible phenomenon can make NMN a potential replacement of fossil fuels and Ni-based catalysts for different energy application. Besides, use of NMN for photocatalysis will also reduce the CO2 emission in the atmosphere, which is an urgent need for the globe in current scenario. However, single component NMN shows a high e--h+ recombination rate making the system less efficient. They also show a deteriorated behavior when they are subjected to high temperature, repetitive I-V cycles during the energy production reaction which prevents production of large-scale industrial devices containing these structures.
Multicomponent hybrid nanomaterials provided a paradigm shift in this aspect. In these systems, the plasmonic core acts as the energy concentrator and the shell material extracts the energy in the form of electronic excitation. Bi-metallic nanoparticles combination of Au-Pd/Pt, Ag-Pt (in face centered cubic (fcc) phase) showed great potential to be commercial photocatalyst. All these prompts make this material quite promising; however, during the catalysis process, nanomaterials containing 3H-HCP (hexagonal closed packed) or fcc Au lost the size, shape and plasmonic efficiency. So, finding a stable configuration with intense plasmon resonances at lower energies and of significant lifetime is still an open challenge and is urgent considering the global energy crisis for their applications in photocatalysis and photothermal reactions.
In HotElecTEM, our aim is to find out the best conditions to obtain an efficient, robust bi-metallic systems for photocatalytic and photothermal applications. We will use unconventional 4H(2H)-HCP Au core instead of conventional 3H-HCP Au core as fcc configuration does not provide a stable mechanical property at high temperatures (beyond 300-400K) contributed by high ductility and low stacking fault energy.
In HotElecTEM, we will synthesize composite consisting of 4H-HCP Au triangular nanoparticle (AuTNP) as the core and metal as catalytic shell to investigate the optical properties, especially hot-e- generation and transfer efficiency experimentally using low-energy electron-energy loss spectroscopy (EELS) in a state-of-the-art aberration corrected TEM (Ac-TEM) at LMA, UNIZAR, Spain and also theoretically using molecular dynamics and light-matter interaction simulation. In-situ thermal, plasmonic and structural stability of single and bi-metallic Au core and catalytic shell (metal) composite will be investigated using in-situ heating/cooling and biasing experiment in TEM.
The specific objectives defined to achieve HotElecTEM’s main goal are:
Objective (O1):
Production of Au triangular nanoparticle’s (AuTNP) and core@shell AuTNP@Pd/graphene composite with 4H-HCP (2H-HCP) configuration and optimization for enhanced optoelectronics and mechanical properties of the synthesis procedure to obtain a high-yield of the nanoparticles.
Objective (O2):
Experimentally reveal structural and (opto)electronic properties of hybrid materials by electron microscopy and spectroscopy techniques.
Objective (O3):
Unravel response and properties of the nanomaterials to external stimuli (heating/cooling and biasing) by in-situ electron microscopy.
Objective (O4):
Obtain structure and (opto)electronic properties of the identical nanomaterials by conducting computational studies (via models) congruent with the experiments

Successful implementation of this project possesses a long-term effect on the development of low-cost sustainable photocatalyst, SERS based sensors and plasmonic-based solar cells. It has the potential to replace fossil fuel and Ni based catalysts, which are getting scarce and valuable day by day and this project has the potential to pave the way. As plasmonic catalysts has the potential to replace fossil fuels, it will lead to decrement in the CO2 and other greenhouse gas emission, which is now a global problem and is vastly compatible with “Fit for 55” EU climate policy, the objective of which is to become first climate neutral continent by 2050. Also, integration of unconventional plasmonic nanostructure in photovoltaic Solar cells can increase the efficiency significantly, making the societal impact of the project really vast.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work performed in HotElecTEM can be divided into two parts: First is the synthesis of fcc triangular Au@Pd bi-metallic system and their structural and optical study using aberration corrected transmission electron microscopy at laboratory of advanced microscopy (LMA), Universidad de Zaragoza (UNIZAR), Spain. To understand the structural stability of Au@Pd system during high temperature applications, we subjected them to in-situ heating inside a TEM up to 1000°C, and observed a unique phenomenon. Au and Pd which are considered to be miscible in all temperature and composition range was surprisingly observed to make a phase separated janus nanostructure at high temperature using in-situ TEM technique. The structures were also observed to be stable over a span of one year even after keeping in ambient atmosphere. This direct observation of their phase separation - previously only theorized - challenges conventional alloy stability concepts at the nanoscale, and could show the path to produce unique phase-separated catalytic nanoparticle system in future.
Next to understand the photocatalytic properties of the Au@Pd system, we studied how the energy generated during nanoparticle-external EM wave interaction, dissipated spatially in single particle level. We used monochromated low-loss electron energy loss spectroscopy (EELS) technique to detect the plasmon generation for Au@Pd system and spatially mapped the hot spot generation using machine learning techniques i.e. principal component analysis (PCA) and non-negative matrix factorization (NMF) process in Hyperspy software. We studied the energy dissipation pathway for different Pd shell thickness and theoretically studied the light matter interaction using boundary element method in MNPBEM toolbox in Matlab. This study will also help researchers to design bi-metallic photocatalysts based on their plasmonic responses.
The second part of the HotElecTEM project consists of fabrication of unconventional 4H-Au nanowire synthesis and deposition of catalytic material i.e. Pd to obtain a unique 4H-Au@Pd core@shell nanostructure. Like previous fcc Au@Pd core@shell structure, we also subjected bare 4H-Au nanorod and Pd deposited 4H-Au nanorod to in-situ heating up to 1000°C and observed that, unlike fcc Au@Pd system, the 4H-Au@Pd system is very much stable and remain in an alloy configuration throughout. This directly shows 4H structures have a better structural stability with respect to its fcc counterparts at high temperature. We are conducting molecular dynamics simulation in LAMMPS software to understand the thermal evolution process for both fcc and 4H structures to understand why 4H phase has superior structural stability. This study will surely help to create unique stable high temperature catalysts based on these 4H systems.
Besides this photocatalytic system, we were also able to produce a very special 4H-Au@Co, Ni system. The system as a whole appeared to be magnetic and we are currently exploring its electronic structure using core-loss EELS at LMA, UNIZAR. This system will be very interesting to both theoretical and experimental researchers as Ni, Co are widely used in both catalysis and magnetocaloric materials and generation of this unique phase for Ni and Co will pave the way for new physics and generation of devices with superior functionality.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the course of the HotElecTEM project, progress beyond the state of the art has been made in several areas. Firstly, the observation of formation of phase-separated janus fcc Au-Pd nanoparticle at high temperature is remarkable, which previously been predicted only with theory. In janus nanostructure, the individual properties of each component remain intact and hence they can be very effective for catalytic applications where materials with complementary oxidation/reduction ability are required together. We showed a very efficient and unique way to produce phase-separated catalytic systems which remains stable over a very long period of time even with the exposure of ambient atmosphere.
Also, through monochromatic low-loss EELS and associated theoretical studies show the spatial variation of energy dissipation pathway on a single particle level, when a plasmonic@ catalytic core@shell system interacts with external electromagnetic wave.
Also, we could successfully synthesize 4H-HCP Au@Pd and 4H-Au@Co, Ni core@shell system and through in-situ heating microscopy technique we showed for the first time the higher stability of 4H systems compared to conventional fcc system at high temperature. This will encourage researchers significantly to explore systems based on unconventional or metastable structure for high temperature catalytic applications. Though, a detailed theoretical study on the higher structural stability of the 4H systems is still needed and we are also currently conducting that. These observations really put the outcomes obtained from HotElecTEM project above the state of the art.
Lastly, the exploration of electronic structure of 4H-Au@Co,Ni magnetic nanomaterials using core loss EELS in HotElecTEM project will also provide pathway to produce new magnetic and catalytic materials, which was previously unexplored.

TEM structural characterization of 4H-Au nanorod

Schematic of in-situ heating study of Au Nanotriangle@Pd core@shell nanostructure inside TEM