Integration of climate change in the decarbonization pathways of energy systems
The decarbonization of energy systems relies on technico-economic and environmental studies spanning 20 to 25 years. A major scientific challenge lies in coupling climate and energy modeling in these studies. The objective of this thesis will be to develop a groundbreaking methodology that integrates climate science model projections and their variability into the design of energy systems at various scales (local and national).
This research will be divided into three main parts. First, it will assess the impact of climate change on energy production, conversion, transport, and storage technologies. Second, it will develop a methodological framework to select and integrate the diversity of climate scenarios into energy models, enabling the evaluation of their impacts. Finally, it will evaluate the severity of extreme climate events by analyzing their magnitude and frequency of occurrence in the models. This work will contribute to improving the robust design of energy systems under climate constraints and applying it to case studies.
Modelling of an infiltrated electrode for high-temperature co-electrolysis coupling ab initio calculations and electrochemical kinetics
Due to their flexibility, high-temperature electrochemical converters based on solid oxide cells (SOCs) can co-electrolyse water vapour and CO2 to produce a synthetic gas, an essential precursor for the production of synthetic fuels (e-fuels). However, to reach industrial production levels, the performance and durability of SOCs must be improved. Indeed, during co-electrolysis, the standard Ni/YSZ electrode undergoes microstructural changes and suffers from carbon deposition. To limit these degradations, it has recently been proposed to infiltrate the electrode with a ceria-based catalyst (GDC). However, the exact role of the GDC remains unclear to date. This thesis therefore aims to improve our understanding of how the electrode functions and degrades by using an ab initio modelling approach coupled with electrochemical kinetics simulations. Firstly, the atomic-scale mechanisms will be studied using the electronic density functional theory (DFT). These reaction mechanisms will then be used as input data for an electrochemical model capable of simulating performance and degradation in relation to a given microstructure. Moreover, the CEA/Liten has developed a numerical tool that can generate synthetic microstructures representative of infiltrated electrodes. This tool, when applied to the GDC-Ni/YSZ electrode, will be coupled with electrochemical models to optimise the microstructure. The results obtained during this PhD will allow recommendations to be made for the manufacturing of optimised electrodes for co-electrolysis at the CEA.
New High-Temperature Heat Pump (> 250°C) upgrading industrial waste heat < 90°C by hybridizing thermodynamic cycles
Decarbonizing industry is crucial to mitigate the impacts of human activities on the environment. Particularly, high-temperature heat (> 250°C) needs are substantial and difficult to decarbonize because of the high amount of energy required. Thermodynamic cycles of Heat Pump (HP), such as Reversed Brayton (RB) cycle, allow for upgrading industrial waste heat to higher temperature usable by processes. However, the energy efficiency of HP to produce heat > 250°C from 100°C from 80°C waste heat with low energy consumption was developed in our laboratory.
This doctoral thesis offers to study an innovative high-temperature HP combining an AHT with a RB cycle. The concept consists of using the AHT to elevate the temperature level of waste heat to temperature > 100°C and provide it to the RB cycle to generate high-temperature heat > 250°C at a low energy cost. Thus, this hybrid system offers a solution to meet industrial needs in decarbonized high-temperature heat. The main challenges laying ahead are the selection of relevant coupling architectures, as well as the study and development of efficient thermal transfer interfaces.
This research work will require mastering modelling tools of thermodynamic cycles and heat exchangers. The thesis will also involve an experimental aspect, since validation of the numerical results on a laboratory test bench are expected.
Fe–Zeolite coupling in a fixed-bed catalytic reactor for the direct hydrogenation of CO2 into sustainable aviation fuel (SAF)
The thesis aims to maximize CO2 conversion yields towards Sustainable Aviation Fuels (SAF, C8–C16). Currently, direct CO2 hydrogenation over an iron-based catalyst predominantly produces short-chain olefins (C2–C4), which do not meet SAF specifications. The proposed approach is to combine an iron-based catalyst with a zeolite catalyst within a single reactor, thereby integrating olefin production via CO2 hydrogenation with their subsequent conversion into longer-chain hydrocarbons in the SAF range (C8–C16). The zeolites investigated will exhibit properties tailored to this objective while retaining conventional formulations compatible with process scale-up.
The objective of the thesis is to understand how the formation of long-chain hydrocarbons suitable for the SAF fraction can be promoted by combining iron-based and zeolite catalysts within a single reactor. Two research areas will be investigated to achieve this objective. The first will focus on short olefin oligomerization (ethylene, propylene, butylene), assessing the influence of operating conditions and the presence of by-products from CO2 hydrogenation on the distribution of the resulting hydrocarbons. The second will investigate the integrated CO2 hydrogenation and olefin oligomerization process, aiming to understand the interactions between the two reactions and identify operating conditions that maximize selectivity and yield towards SAF-range hydrocarbons. Particular attention will be paid to the effects of thermal gradients and heat transfer phenomena on catalytic performance, product distribution, and catalyst stability.
Study of oxide formation at the interface of Grade 91/Grade 91 steels during a hot isostatic pressing (HIP)-assisted diffusion bonding cycle
This PhD project aims to understand and mitigate oxide formation at the interface of Grade 91 steels joined by hot isostatic pressing (HIP)-assisted diffusion bonding.
This process offers significant potential for manufacturing complex components for the future DEMO nuclear fusion reactor.
However, the formation of oxides, particularly silica (SiO2), at the bonding interface can weaken the joints and significantly reduce their impact toughness.
The main objective is to identify the physicochemical parameters governing oxide formation at high temperatures.
The study will focus on the effects of silicon and manganese contents, temperature, and oxygen partial pressure.
Model alloys and Grade 91 steel will be investigated experimentally under controlled atmospheres.
Experimental findings will be compared with thermodynamic simulations based on the CALPHAD method.
HIP-bonded joints will then undergo multiscale microstructural characterization and mechanical testing.
Optimization strategies, including surface preparation and degassing conditions, will be assessed to minimize interfacial oxidation.
The expected outcomes include a reliable bonding procedure that can be transferred to EUROFER 97 steel and potentially applied to other industrial sectors.
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.
Experimental and theoretical approach to select deep eutectic solvents for the delamination of photovoltaic panels
Multimaterial assemblies recycling such as photovoltaic (PV) panels is necessary to guarantee the circularity of materials. Today, PV panels recycling is mostly managed through pyrometallurgy which is limited in terms of materials recovery (polymers are incinerated and recovered silicium and silver yields are low) and emits noxious and greenhouse gases, such as HF generated by fluorinated polymer incineration.
Chemical delamination processes consist in the immersion of panels into a hot solvent to swell the polymeric tie-layers and separate the materials. These processes have the potential to largely improve recovery yields of all materials, but they are environmentally impacting due to the operating conditions and solvent use.
The solvent choice defines the impact of the process. In the current literature, this choice is mostly based on trial and error approaches that are tedious. Moreover, efficient solvents for PV delamination are generally toxic and flammable, which limits the environmental relevance of the processes.
Deep eutectic solvents (DES), which are the association of a hydrogen bond donor and acceptor (HBD and HBA), present interesting solvent properties for such processes. The use of organic hydrophobic molecules as HBA or HBD can impart the solvents with a dual hydrophobic and hydrophilic character that brings a capacity to interact with various molecules to the solvent, including polymers. As HBA/HBD combinations are numerous, it is important to develop a systematic methodology for their choice.
The present topic proposes a methodology based on a combination of theoretical modelling and experimental validation measurements to better understand the contributions of HBD/HBA structures on DES properties. The study will focus on the identification of the interactions between DES and EVA (ethylene vinyl acetate), a widely used polymer in PV panels, through the study of phenomenon of solubilization and solvolysis (covalent bond breakage) to identify the contributions to the delamination phenomenon. At the end of the thesis, the DES selection will be validated through the demonstration of the delamination of a PV panel and the analysis of the separated layers.
Design and implementation of innovative alloys for high-performance NdFeB magnets via the grain-boundary diffusion process
Permanent magnets based on rare earth elements (RE), particularly neodymium-iron-boron (Nd-Fe-B) magnets, are essential for high-performance motors and generators for use in electric vehicles and wind turbines. To increase their resistance to demagnetization, heavy rare earth elements (HRE) such as dysprosium (Dy) or terbium (Tb) are partially substituted for neodymium. However, these HREs, although crucial for magnetic properties, are critical materials with supply risks. Hence, the challenge is to reduce their content while maintaining performance, in order to meet the growing demand for high-performance magnets. In this context, the grain boundary diffusion (GBD) process of HREs emerges as the most effective solution. It enables the diffusion of HREs from the surface of sintered magnets toward grain boundaries and then into the magnetic phase grains. This localization of HREs at the grain peripheries improves resistance to demagnetization while preserving high remanence, thereby reducing the required amount of HREs.
The objective of this Ph.D is to provide a comprehensive understanding of the diffusion and localization mechanisms of HREs while limiting parasitic reactions that unnecessarily consume them. The doctoral work will combine a comprehensive experimental approach, including the development of HRE-RE-M (where M is a transition metal) alloys for GBD, the study of diffusion, the characterization of equilibrium phases, and detailed magnetic and thermodynamic analyses, particularly through an in-depth study of phase diagrams. This approach aims to define the optimal compositions and diffusion conditions to achieve the targeted magnetic performances.
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).