3D imaging by electron tomography of PFAS-free electrodes for green hydrogen
To decarbonize our society, green hydrogen produced by water electrolysis using renewable electricity is a promising pathway. However, today's electrolyzers rely on fluorinated polymers (PFAS), which face upcoming restrictions in Europe due to their environmental impact. Fluorine-free alternatives, namely hydrocarbon (HC) ionomers, are making progress in membranes, but their use in electrodes still yields limited performance, most likely due to poor dispersion of the ionomer within the electrode.
The electrode under study is a nanoporous material made of carbon aggregates supporting the catalyst (Pt nanoparticles) and bound together by the ionomer. The spatial distribution of the ionomer plays a decisive role, as it must provide ionic conduction to the catalytic sites without obstructing gas transport. Visualizing this ionomer is a significant challenge, as it forms a thin film only a few nanometers thick covering the carbon. Our group has acquired unique expertise in imaging this ionomer using electron tomography (E-TOMO). In the case of fuel cells (PEMFC), where the ionomer is fluorinated, this approach has made it possible to understand its distribution within the electrode.
The objective of this PhD project is to build upon this expertise to provide the first 3D images of HC ionomer distribution in electrodes. The methodology will be optimized to reduce analysis times by leveraging recent advances in the field. Analyses performed on various electrodes will provide key insights to optimize their fabrication process, better understand their performance, and assess their stability. E-TOMO will thus play a central role in advancing the development of fluorine-free electrodes for AEMWE electrolyzers.
Electrolyte motion in Li-ion cell: experimental and modelling approach
Li-ion batteries are an essential source of energy storage for decarbonising our energy use. The gradual introduction of silicon-based compounds into the negative electrode – traditionally made of graphite – appears to be the preferred route to increasing the technology’s energy density to between 300 and 350 Wh/kg. Silicon has a specific capacity of 3,580 mAh/g, which is almost ten times that of graphite. However, this enormous capacity is associated with a 280% volume expansion of the material, compared with just 10% for graphite during intercalation.
At the Li-ion cell level, this ‘breathing’ phenomenon occurs and must be managed. In particular, when a rigid cell is charged, the ‘breathing’ of the active materials expels the electrolyte from the electrochemical core. A lithium salt gradient may develop in the electrode plane in the electrolyte.
This thesis aims to gain a better understanding of this phenomenon by reproducing it experimentally in a specific cell, to establish measurements of lithium salt concentration, and to simulate the phenomenon in a P4D model based on an existing P2D model.
During his PhD, the candidate will develop a wide range of skills and know-how, in a unique combination.
Development of a new class of positive electrode materials for Na-ion batteries
Disordered Rock-Salts materials derived from Li2MnO2F have been extensively studied over the past decade as potential high-energy-density positive electrode materials for Li-ion batteries. At the CEA, our experience with these materials, which are highly sensitive to usage conditions, has enabled us to surpass state-of-the-art performance in full cells incorporating them. Surprisingly, very few studies have been reported on their sodium equivalents and their use in Na-ion batteries, despite their composition being low in critical and expensive materials, making them particularly suitable for this technology. This is likely due to their exacerbated instability compared to the lithiated phases. In a previous internship, we were able to develop synthesis and electrode implementation protocols that allowed us to achieve specific capacities exceeding 220 mAh·g?¹ with a material of this type, which could make it competitive with a LiFePO4-based Li-ion technology. The thesis will therefore focus on optimizing the material's composition and understanding the influence of the synthesis protocol in terms of structure (X-ray diffraction analysis) and material surface state (spectroscopy).
EFFECT OF ULTRASOUND ON THE URANIUM EXTRACTION PERFORMANCE OF MONOAMIDES
Liquid-liquid extraction of uranium using monoamides can be limited by complex phenomena, such as third-phase formation or precipitation. This third phase contains a very high concentration of uranium complexes, strongly reducing extraction efficiency and hindering extractant reuse.
The aim of the present PhD is to investigate whether ultrasound (US) can limit third-phase formation and improve uranium extraction. Sonication generates micrometric cavitation bubbles that oscillate and collapse violently, producing intense mixing and shear forces. Cavitation is known to enhance mass transfer and, in many systems, reaction kinetics. However, to the best of our knowledge, it has not yet been applied to uranium liquid-liquid extraction.
The influence of US parameters (frequency, power, irradiation time, etc.) will be investigated using a two-scale approach:
- Nanoscale: effect of US on the size and interactions of organic-phase aggregates and their relationship with extraction and third-phase formation;
- Macroscale: effect of US on mixing, viscosity, extraction kinetics, and phase separation.
Complementary characterization techniques will be used to assess the effect of US on uranium extraction. ICP-OES will quantify uranium concentrations and determine extraction yields and distribution ratios. SAXS/SANS will characterize organic-phase aggregates, while rheology will probe changes in viscosity and flow properties. NMR, IR, and UV–vis spectroscopy will provide complementary information on molecular interactions, uranium speciation, and the chemical environment of the extracting species. Together, these techniques will correlate molecular-scale organization, macroscopic properties, and uranium extraction performance.
The work will also include an instrumentation component, involving the design and development of an experimental cell suitable for in situ studies under US irradiation.
Chemical Engineering of Active Surfaces in II–V Material Technologies for Cooled Infrared Detection
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Écriture
This PhD thesis builds on previous research aimed at improving the passivation of HgCdTe photodiodes, particularly those based on P-i-N architectures. It seeks to understand the physicochemical mechanisms responsible for the degradation of interfaces between the semiconductor material and the passivation layer. Previous studies have highlighted the influence of residual contaminants, surface oxidation, and excess tellurium on the electrical properties of devices.
The main objective is to develop surface engineering processes that enable better control of the chemical composition and defects at these interfaces. Various chemical and electrochemical treatments will be investigated to limit oxidation, reduce contamination, and improve surface stability. Characterization will rely on advanced techniques such as X-ray Photoelectron Spectroscopy (XPS), Hard X-ray Photoelectron Spectroscopy (HAXPES), and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), complemented by electrical and electrochemical measurements. Particular attention will be paid to establishing quantitative correlations between the chemical composition of interfaces, their electrochemical properties, and their electrical behavior. These results will help identify the key parameters governing photodiode performance and optimize passivation treatments. The developed processes will then be evaluated on structures representative of P-i-N photodiodes, particularly with a view to operation at elevated temperatures. Finally, this thesis incorporates an eco-innovation component aimed at making manufacturing processes more environmentally friendly. The development of in-situ electrochemical treatments and new, so-called “green” chemistries could make it possible to replace certain conventional bromine-based solutions. Ultimately, this research will contribute to the development of higher-performance, more stable infrared detectors that require less demanding cooling systems, while potentially reducing the environmental impact of manufacturing processes.
Molecular dynamics simulation of interfaces for U/Pu separation processes
The recycling of uranium and plutonium is a key challenge for closing the nuclear fuel cycle. It involves a stage based on a liquid-liquid extraction separation process, which consists of selectively transferring certain chemical elements from an aqueous phase to an organic phase. How do molecules organise themselves at the interface between these two phases to enable the separation of uranium and plutonium? This question is crucial for developing more efficient processes. This PhD thesis aims to understand, at the molecular level, how the structure of liquid–liquid interfaces controls the transfer of species between the two phases. The PhD student will develop molecular dynamics simulations and advanced computational methods to study various extraction systems, notably those based on monoamides and TBP. The objective will be to link the molecular organisation of the interfaces to the extraction mechanisms and to the thermodynamic and kinetic properties of the transfer, by comparing the simulations with available experimental data. Conducted at the CEA ISEC’s Laboratory of Actinide-Ligand Interactions, in collaboration with the Laboratory of Multi-Scale Theories and Methodologies at the Marcoule Institute of Separative Chemistry, this PhD research lies at the heart of the challenges facing the fuel cycle and the recycling of strategic metals. It will offer in-depth training in molecular modelling, physical chemistry, programming and scientific computing, within a multidisciplinary research environment and in collaboration with experimental scientists involved in process development. The PhD student, who will have a background in physical chemistry, theoretical chemistry or physics, and an interest in modelling, programming and scientific computing, will be encouraged to disseminate their scientific findings through publications and presentations at national and international conferences. The PhD will enable the candidate to acquire expertise in molecular modelling, physical chemistry, programming and numerical computation, with career prospects in academic research, research organisations and industrial R&D, particularly in the fields of nuclear science, materials and processes.
Tuning the Electronic Structure of Tungsten Oxide Thin Films by Combinatorial Deposition: Impact of Intrinsic and Extrinsic Defects on Electrochemical Properties (DETOX Project)
We are offering a fully funded PhD position within the DETOX project, a collaborative research project involving CEA-TECH, CEA-INSTN, the Bordeaux Institute of Condensed Matter Chemistry (ICMCB), and FCSEL-LaRFIS at Polytechnique Montréal.
The DETOX project is dedicated to accelerated materials discovery, with a particular emphasis on electrochemical materials for electrochromic and photoelectrocatalytic applications. These two functionalities share a common redox origin: electrochromic materials reversibly modulate their optical properties under an applied voltage, while photoelectrocatalytic materials promote hydrogen production through solar-driven water splitting. Hence, understanding and controlling the relationship between defects, electronic structure, and electrochemical performance is a key scientific challenge.
The PhD project will focus on the synthesis of tungsten oxide (WO3)-based thin films using combinatorial magnetron sputtering. Tuning deposition parameters—including target composition, working pressure, and reactive atmosphere—the candidate will investigate how intrinsic and extrinsic defects influence the structural, morphological, electronic, and electrochemical properties of the deposited materials.
Combinatorial thin-film deposition provides a powerful high-throughput approach for rapid exploration of complex materials parameter spaces. Coupled with artificial intelligence and machine learning tools for data analysis and materials prediction, this strategy offers a significant acceleration in the discovery and optimization of functional materials.
The successful candidate will join a multidisciplinary consortium having complementary expertise in thin-film deposition, electrochemistry, materials characterization, and data-driven materials science. Throughout the project, the student will work closely with researchers from the four partner institutions, benefiting from their active supervision and scientific support.
The PhD will be carried out within the DIADEM Priority Research Programme and Equipment (PEPR), a national initiative coordinated by CNRS and CEA which aims to accelerate the discovery of innovative materials through artificial intelligence.
The research will be held primarily in Bordeaux, France at two partners laboratories:
- CEA Tech Materials Screening Platform (PRTT Nouvelle-Aquitaine)
- Bordeaux Institute of Condensed Matter Chemistry (ICMCB)
The project will also include regular research visits to CEA-INSTN in Saclay and an international research stay of 9 to 12 months at Polytechnique Montréal (Canada), providing the candidate a valuable international research experience.