Description du sujet de thèse

The goal of this thesis is to apply advanced transmission electron microscopy (TEM) methodologies to the study of high-entropy alloys. High Entropy Alloys (HEA) are multi-metallic alloys composed of at least five different elements, each with atomic concentrations ranging from 5% to 35%. It has been shown that the presence of many metals can lead to the formation of single-phase solid solutions, in some cases bridging the solubility gap between metals that are immiscible in bi- and tri-metallic compounds (Y. Yao et al., Science 2018, 359, 1489). Beyond the fundamental interest in understanding their structure and chemical composition, these alloys are used as platforms for the discovery of new materials for electrocatalysis and hydrogen storage, based on predictions from artificial intelligence approaches applied to simulated data (T. A.A. Batchelor et al. Joule 2019, 3, 834-845).
Transmission electron microscopy provides information on the atomic structure and chemical composition of alloys with atomic-scale resolution. Within the framework of this thesis, electron microscopy will be used not only for the study of HEAs structure at the nano- and atomic scale, but also to monitor in real time their evolution during electrochemistry reactions. More specifically, the objectives are as follows:

1. Develop a “high throughput” TEM analysis protocol to accelerate structural characterisation and enable the efficient analysis of a large number of HEAs. Subsequently, a neural network will be trained using the structural and chemical data obtained by TEM coupled with the electrocatalytic properties of the same set of HEAs, with the objective to discover new efficient electrocatalysts for ethanol electro-oxydation. This first task is part of the PEPR Diadème M2P2_HEA project, which aims to discover new multi-metallic electrocatalysts using artificial intelligence approaches.
2. Study the formation mechanism of HEAs by in situ electrochemical electron microscopy (EC-TEM) in the liquid phase, using a dedicated electrochemical sample holder.
3. Study, again using in situ EC-TEM, the evolution of HEAs at the nanoscale during electrocatalysis reactions for applications in the energy field, such as the ethanol electro-oxidation or oxygen electroreduction of in fuel cells.

Contexte de travail

The candidate will join the doctoral school in Physics and Chemical Physics (ED 182) of the Strasbourg University. The project will be carried out within the 3D TEM group of the Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS). Our expertise lies in the study of nanomaterials by in situ TEM in controlled gas or liquid environments, as well as the 3D reconstruction of nanostructured materials by electron tomography. Within the group, we have dedicated sample holders for the in situ analysis of nanomaterials during electrochemical or gas-phase reactions. We are also equipped with three electron microscopes, including one equipped with a probe corrector that is particularly well suited to scanning transmission electron microscopy (STEM) studies, and a second operating at 300 kV equipped with an image corrector that enables high spatial (up to ~100 pm) and temporal (up to 1 µs) resolutions to be achieved. The candidate will also benefit from the team's collaborative network and will have the opportunity to participate in a consortium working on the AI-driven discovery of new HEAs for electrocatalysis, involving the ICPMS and two other laboratories (LCMCP and ITODYS, Paris), as well as the SOLEIL synchrotron (ROCK light line) and IFP Energies Nouvelles.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

The PhD project will last three years. There are not specific risks associated to this PhD thesis.