Medium temperature PEMFC: impact of the drying processes of catalyst layers on their microstructure and performance

- The Proton Exchange Membrane Fuel Cell (PEMFC, using H2 and air as fuels) is a relevant solution for the production of low-carbon electrical energy. However, it is necessary to further improve its performance and durability, and reduce its cost.
- In this spirit, the national French project PEMFC95 aims at developing and characterizing PEMFC materials able to operate sustainably at 95°C (standard is 80°C) and thus more suitable and attractive for Heavy-Duty application (buses, trucks, trains…). It is supported by the French ‘Programme et Equipements Prioritaires de Recherche sur l’hydrogène décarboné’ (PEPR-H2).
- The component considered in this thesis is the catalyst layer (CL) which is a mixture of Pt/C (platinum onto carbon particles), H+ conductive ionomer, and solvents. The optimization of the CL in terms of spatial distribution of Pt/C, ionomer and pores is crucial for improving performance and durability. This is directly linked to the ink formulation and to the manufacturing process used to produce the CL. Nevertheless, the relation between the CL manufacturing process and parameters, its structure and components’ distribution, and the performance and durability of the PEMFC, is still an open question. The aim of your Ph.D. thesis is to progress on this, focusing on the drying step of the bar coater manufacturing process.
- You will contribute to the PEMFC95 project thanks to your scientific/technological developments to understand the impact of the drying process and parameters on the microstructure of CL and make the link with the performance and durability of PEMFC.
- You will have interactions and meetings with the partners of the project and with CNRS/IMFT (Toulouse), specialist of transport phenomenon in porous media.
You will be hired by CEA-Grenoble and work with permanent and non-permanent staff in the laboratory, (male and female) engineers and technicians, to discuss your ideas, perform your experiments and analyze the data. You will be managed by Joël Pauchet as your thesis director, specialist of porous media and their modeling for PEMFC, and Christine Nayoze-Coynel for her knowledge on the CL and MEA manufacturing.

More information are accessible in the attached file and/or Under request.

Discovery of new chromogenic probes for toxic using Chemistry-Trained Machine Learning

Today national and international situation justify new researches on the colorimetric detection of toxic and polluting gases (referred to as analytes in the following). For the already known and studied compounds, improvement of the detection capabilities involves increasing contrast and selectivity. For potential new analytes, it is also important to prepare for rapid identification of specific chromogenic probes. The objectives of the thesis will be to discover new chromogenic probes by using computational chemistry.
First stage of the thesis: Training of the model (ML/AI) on available database. This part of the thesis will focus on establishing a precise and robust model to classify the large experimental database available from our laboratory's previous work. This involves correlating the colorimetric results with the structures and chemical properties of the molecules described by state-of-the-art methods (e.g., https://pubs.acs.org/doi/10.1021/acs.chemrev.1c00107). At the end of this learning process, we will have a predictor (SVM, LCA, PCA…) validated on our data.
Second stage: Use of the predictor model to screen in silico several hundred thousand candidate probe molecules from commercial chemical libraries (and others), correlated with their chemical structure and property descriptions as in the first stage. After this initial screening, DFT prediction of the chromogenic response will be used to refine the selection of the best candidate molecules.
Third stage: Definition and implementation of an experimental chemical testing campaign. A fast organic synthesis platform HTE (high throughput experimentation) based on the miniaturization and parallelization of chemical reactions to optimize the implementation of synthesis reactions and tests, will save considerable time, while significantly increasing the number of possible combinations. HTE also enables the synthesis of libraries of analogous compounds. Following these massive tests, a second version of the predictor will be trained and will lead to the discovery of a new generation of chromogenic molecules.

Development of a new generation of recyclable encapsulation films for photovoltaic modules

In the context of the energy transition, photovoltaic (PV) solar energy represents a growing share of the world's electricity production, and PV itself represents a growing share of the world's energy production. The massive production and deployment of PV modules is putting increasing pressure on the environment. In particular, because of the extraction of the raw materials required for their production and their disposal at the end-of-life. Recycling tackles both of these issues.
PV modules are made of layers of different natures laminated together. In the module central layers, PV cells are embedded in an elastomer, the encapsulant. This material plays several roles: barrier properties, mechanical protection, etc. Currently, the encapsulants used are generally cross-linked EVA copolymers, which makes recycling particularly difficult.
The aim of this thesis is to develop a vitrimer encapsulant for PV applications. Such an encapsulant, with exchangeable bonds, could drastically simplify recycling without compromising the integrity of the module in its lifetime. This work will start with the formulation of the encapsulant. It will go on with the characterization of its properties (thermo-reversibility, rheology and barrier properties), its extrusion into a film and its lamination in a PV module.
This development will be iterative, thus leading to tests under application representative conditions at various stages of development. It will rely on the resources and expertise of three laboratories LCMCP (Sorbonne Université), PIMM (ENSAM) et LITEN (CEA).

ClimatSunPV: Study of BIPV components with photonic functionalities, self-cooling capacity and urban heat island mitigation effects.

The integration of PV modules into building envelope or other applications in particular presents different constraints reducing their electrical performance compared to ground installations due to the change in their operating conditions. The objective of this PhD thesis would be the research of a global design method of a BIPV facade or roof in order to optimize its production and its impact on the integration system (building, etc.) by overcoming its constraints: static and mobile shading, temperature gradients due to low albedo, favorable solar radiation especially in cold periods, localized overheating… Different approaches will be considered:
1- Optimize the temperature management of the PV field or the uniformity of the temperature field by forced convection (with air or water as heat transfer fluid): case of a double skin facade (or roof) (extraction or recovery of heat from the rear face of the PV modules through numerical and experimental analysis of natural or forced ventilation paths (air flow) and case of a single wall facade (or roof) (with other cooling methods);
2- Passive cooling of BIPV and PV systems: research from numerical models and experimental studies and validation of simple passive technological solutions (fins, heat sinks, graduated materials, materials with photonic effect, among others).

Ultrasensitive static/dynamic flexible force transducer

In this thesis, the principles and challenges in the development by printing and characterisation of conformable organic piezoelectric matrices for medical use under stress will be examined. A stretchable/conformable piezoelectric sensor, produced on a stretchable substrate, will be developed with materials (PVDF-TrFE type polymer or composite). These developments will make it possible to study the feasibility of using such piezoelectric components in various fields.
The aim of the study carried out to date has been to produce a flexible piezoelectric device based on the principle of a double-sided sensor so as to eliminate the contribution of bending. This sensor must also be stiff enough to be deployed through a 3mm diameter catheter. In this context, the work carried out in this thesis will focus on the development of a flexible piezoelectric sensor capable of converting the mechanical energy of low stresses, coupled with a piezoresistive sensor capable of measuring static stresses. The use of polymers offers greater flexibility, and they are implemented in the form of thin films, making them lightweight and space-saving. In order to achieve these objectives, a dedicated sensor structure guaranteeing redundant measurement (piezoelectric and piezoresistive sensor) will be studied, produced and characterised. The sensor manufacturing process will have to be optimised to increase their efficiency. Optimisation of the architecture of the electrodes and the geometry of the active layers will be tested on a test bench in order to assess their ability to measure static and dynamic stresses simultaneously over the widest possible range of forces. At the same time, fundamental characterisations of the material will be carried out in order to establish correlations between the structure and electrical properties of the sensors.

Modeling of corrosion by the cellular automata method: taking into account diffusion in solution and heat transfer.

The materials’ degradations caused by corrosion is a major issue in industry. Their experimental study in the laboratory, necessary in most cases, often proves difficult to perform. It also has its limits, because the processes involved generally take place over long periods of time and in complex environments, which are therefore difficult to reproduce. In this context, modeling is a powerful and complementary approach to the experimental approach, insofar as it is likely to lead to the development of predictive numerical tools and/or interpretation aids.
Modeling by the cellular automata (CA) method, proposed in this thesis, is used in fields as varied as physics, biology, chemistry and social sciences.
It consists of paving a space with a network of identical cells, each being characterized at time t by a state (which is part of a predefined set of possible states) whose temporal evolution is calculated by means of rules of transition which take into account the states of neighboring cells. Its main asset is to explore the spatio-temporal dynamics of simplified representations of systems likely to be very complex in reality.
Significant advances in corrosion modeling using the CA method have been made over the past ten years at CEA/DPC/SCCME/LECA. 3D extension of existing 2D models has in particular been successfully achieved, as well as the coupling of spatially separated anodic and cathodic reactions. This made it possible to study with the same model the competition between generalized corrosion and different types of localized corrosion. 3D models of intergranular corrosion have also been developed.
In the thesis proposed here, it will be a question of developing a CA model allowing the study of corrosion processes in which the diffusion of corrosive species in solution and/or a temperature that is both variable in time and inhomogeneous in space may prove to be dimensioning (pitting and crevice corrosion, evolution of macroscopic defects). We will take advantage of two main features: firstly the equations governing diffusive transport and heat transfers are similar (they will be simulated using 3D random walks), secondly the AC method is particularly suitable for the study of phenomena involving time-dependent interfaces/boundaries.
The model developed will be implemented in C language and CUDA, in order to perform simulations on mixed CPU/GPU computers (parallel programming on graphics cards). Code development will therefore be the main activity, with simulations being performed on dedicated CEA and ENSCP machines. In order to validate the results provided by the model, reference will be made to experimental results selected from the literature and from SCCME/LECA data.

Development of a predictive power model for a photovoltaic device under spatial constraints

CEA is developing new cell and module architectures and simulation tools to assess the electrical performance of photovoltaic (PV) systems in their operating environment. One of these models, called CTMod (Cell To Module), takes into account not only the different materials making up the module, but also the different cell architectures. For space applications, the community wants to use terrestrial silicon-based technologies that can be integrated on flexible PVAs (Photovoltaic Assembly). The space environment imposes severe constraints. A relevant evaluation of performance at the start and end of a mission is therefore essential for their dimensioning.
The aim of this thesis is to correlate physical models of radiation-matter degradation in space with electrical models of photovoltaic cells. Performance degradations linked to the various electron, proton and ultraviolet (UV) irradiations of the space environment will be evaluated and validated experimentally. Linked to the CTMod Model, this new approach, never seen in the literature, will able to get a more accurate understanding of interactions between radiations and PVAs. These degradations result from non-ionizing energy deposition phenomena, quantified by the defect dose per displacement, and ionizing ones quantified by the total ionizing dose for protons and electrons. In the case of UV, the excitation of electrons in matter generates chain breaks in organic materials and colored centers in inorganic materials. Initially, the solar cell used in the model will be a Silicon cell, but the model can be extended to include other types of solar cell under development, such as perovskite-based cells.

Develoment of lithium mediated ammonia electrolyzer

Recent developments in electrochemical ammonia (NH3) synthesis using lithium (Li) metal deposition in THF-based electrolytes in the presence of protic species, reinvigorated the research interest in direct NH3 electrolyzes technology thanks to its surprisingly high performance in terms of synthesis rate and faradaic efficiency. However, the main drawback is poor energy efficiency due to minimum voltage requirements associated to Li metal deposition and H2 oxidation reactions on the opposite electrodes. In this project, we propose to study the nitridation reaction of Li-alloy forming metals that can enable the decrease in electolyzer voltage. This study will be performed using a 3-electrode electrochemical pressure cell and differential scanning calorimetry – thermogravimetric analysis under N2, H2 pressures. The goal here is to couple existing knowledge in chemical looping synthesis of ammonia with electrochemical synthesis. Porous (carbon or steel tissue) electrodes will be developed with nanoparticles of Li-alloy forming metals and their performance will be studied in an electrolyzer. The assumed 3-step reaction mechanism to form NH3 is as follows: Li deposition > nitridation > protonation. This mechanism is already a subject of discussion for pure Li metal which will be further complicated with the use of alloy forming metals. Therefore, we propose an in-depth study using x-ray photoemission spectroscopy. The ultimate objective of the project is to accelerate the direct NH3 electrolysis technology and address the Power-to-X needs of renewable electricity sources.

Experimental study and thermo-hydraulical modelling of a heat and cold storage prototype coupling thermocline and latent heat technologies

Heating and cooling in residential buildings hold a 28% share in the total energy consumption of Europe, out of which 75% of the energy is still generated from fossil fuels, while only 19% comes from renewable energy sources. To increase the share of renewable energy in the near future, the French energy commission has identified 4th generation district heating networks as a plausible option. Key hardware components for next generation smart urban heating networks are heat and cold storages, which allows a shift between production and consumption as necessary.
The prototype that will be studied in this thesis couples in a same component heat and cold storage, in order to obtain significant gains in terms of compactness and cost. Cold storage is based on ice-water phase change transition around finned tubes in charging mode (-6°C), and on direct contact between water and ice in discharging mode (direct contact = water flow through the ice and directly exchange heat without any wall between water and ice). Heat storage is based on thermocline technology with water (60-70°C) as coolant.
The prototype is currently under manufacturing in the framework of a European Project and will be operational at the beginning of the thesis. The objective of the thesis is on the one hand to experimentally characterize the performances of the storage, on the other hand to work on a numerical modelling of the storage. The thermos-hydraulical modeling of the discharge in cold mode, with direct contact between ice and water, is particularly challenging. The study of the addition of Phase Change Material capsules for heat storage (50-60°C), in order to boost energy and power, will also be studied with potential implementation in prototype during the thesis.

Development of a numerical model of the POSEIDON irradiator for qualification in Co-60 radiosterilisation

CEA/Saclay research centre has several 60Co irradiation facilities dedicated to gamma irradiation for both CEA and industrials R&D needs in various fields such as electronuclear, defence, electronics, space as well as health applications.

In the more specific field of health, an irradiator is used to radiosterilise, i.e. to neutralise microbiological contaminants (such as bacteria, viruses, microbes, spores) using ionising radiation, for medical devices such as hip prostheses, orthopaedic screws or plates, on behalf of their suppliers. The great advantage of gamma radiation sterilization, compared with other sterilization alternatives (gas or cold immersion in liquid chemicals), is that medical devices do not have to be removed from their sealed pouches; they are processed directly through their packaging.

Radiosterilization of medical devices is a highly demanding process, in line with the requirements of ISO 13485 and ISO 11137. Firstly, the doses delivered must be neither too low, to ensure product sterility, nor too high, to avoid altering their integrity. Secondly, three qualification stages are required to guarantee validation of irradiation sterilization processes. The first two, known as installation and operational qualification, are respectively designed to demonstrate that the sterilization equipment has been installed in accordance with its specifications and is operating correctly, delivering appropriate doses within the limits of defined acceptance criteria. In particular, operational qualification consists in characterizing the irradiator in terms of dose distribution and reproducibility, by considering the volumes to be irradiated filled with a homogeneous material, with envelope densities representative of the products to be treated. Finally, the third qualification stage, known as performance qualification, must demonstrate, specifically for the medical products to be treated, that the equipment operates consistently, in accordance with predetermined criteria, and delivers doses within the specified dose range, thus producing a product that meets the specified requirement for sterility.

Depending on the supplier, irradiation packaging cartons are generally filled with a variety of different medical products, corresponding to a wide range of sizes and weights. The effects on spatial dose distribution of all possible product loading configurations should therefore be examined, including for different fill rates of the cartons on the irradiator's dynamic conveyor. Finally, it should be noted that the qualification processes must be repeated following any modification likely to affect dose or dose distribution, and therefore each time the sources are restocked. These processes are currently carried out exclusively by measurement, using a multitude of dosimeters appropriately distributed within and on the surface of the packages.

The Laboratoire des Rayonnements Appliqués (DRMP/SPC/LABRA), in charge of the POSEIDON gamma irradiator dedicated to the radiosterilization of medical equipment at CEA/Saclay would like to have a digital tool enabling these validation processes to be carried out by simulation. One of the major benefits expected from the use of this tool is to considerably reduce the downtime of the POSEIDON irradiator, imposed by the experimental validation phases.

The aim of the present thesis is to implement a numerical model of the POSEIDON irradiator, enabling the validation phases to be reproduced by simulation, as quickly as possible, while ensuring the accuracy of the results, to the desired precision. This work will be carried out at the DM2S/SERMA/CP2C laboratory (CEA/Saclay) with regular exchanges with the LABRA laboratory. CP2C is specialized, among other things, in radiation protection studies using numerical simulations.

Thus, the subject of the thesis, divided into three stages, will explore an alternative validation approach to that, carried out experimentally:

• The first stage will involve the development of a numerical model of the POSEIDON irradiator, integrating the dynamic nature of radiosterilization treatments. This numerical model will be based on a calculation methodology to be decided during the thesis (Monte-Carlo or deterministic method), with a compromise between the quality of the results obtained and the speed of calculation execution. For this stage, the radiation transport Monte Carlo code TRIPOLI-4® will be used as a reference, with comparisons made using other numerical tools such as MCNP®, PENELOPE, GEANT4, NARMER-1, etc.;

• The second stage will successively involve validation of the selected numerical model by comparison with experimental measurements, to be defined and carried out during the thesis, and its application to the calculation of operational qualification processes and performances for different families of supplier cartons. As regards validation of the calculations, the instrumentation used for gamma dose measurements will be numerically modelled and analysed, taking into account all the physical phenomena involved in absorbed dose (photon and electron doses). The aim is to consolidate calculation/measurement comparisons for experiments carried out during the thésis;

• The final step will be to analyze the contribution of the numerical model in relation to the experimental approach. This computational approach will nevertheless need to be optimized in terms of calculation time, in order to facilitate the sensitivity analyses to be carried out.

During the thesis, various directions of research will be investigated, such as improving the modelling of reflections during photon transport in a closed environment (PAGURE irradiator casemate; use of deep learning techniques for deterministic codes), implementing stochastic geometries to model the contents of the packaging to be irradiated, and improving algorithms to reduce computation times.

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