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.

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).

Modeling of Particles Capture by Aqueous Foams

Role of cement paste and fine aggregates in the triaxial behavior of concrete

Multiscale analysis of plastic strain localization under laser driven shock loading

The localization of plastic deformation in expanding metal shells has been studied for several years in CEA/DAM. In addition to explosively driven shells, the laser driven expansion of thin metal sheets yields biaxial tension conditions representative of shell pieces. This kind of set-up is being developed in CEA/DAM and generates strain rates around 10000/s on sheet parts of centimetric width. The evolution of the experimental set-up to millimetric geometries will allow to reach higher stretching rates, unexplored up to now. For all these geometries, for which the sheet thickness is low with respects to the grain size, the influence of the material microstructure is probably significant and the deformation process shall be analyzed at this scale.
The aim of this PhD work is to study plastic strain localization in a sheet of a body centered cubic (BCC) metal under laser shock loading. The phenomenon will be investigated with finite element simulations incorporating the physics at the mesoscale: plastic slip and twinning. An homogenized polycrystalline approach, using an isotropic constitutive model with mean dislocation density as an internal state variable, and a full field approach including grains, their crystal orientations and slip systems, will be compared.

Enhancing micro-mobility battery pack lifetime by using proper and cost effective thermal management

Urban mobility options are diversifying, notably with the deployment of micro-mobility vehicles (electric bikes, cargo bikes, scooters, electric carts). Their usage poses increasing challenges for powertrains, especially for batteries. Li-Ion batteries are temperature-sensitive and require effective thermal regulation to maximize their lifespan. This constraint is well-considered in the automotive sector, which often employs onboard cooling systems to cool or warm batteries.

Micro-mobility vehicles often incorporate battery packs with a simple and cost-effective design, featuring minimal components and lacking a thermal management system. If these batteries are used in severe weather conditions or under high electrical loads, their lifespan can be significantly affected, directly impacting their overall environmental footprint. The development of new thermal management solutions tailored to usage patterns and industrial viability will be the central theme of this thesis.

We aim to achieve the following objectives:

- Investigation of typical usage profiles for these mobility devices (current profiles, external thermal constraints, charging and discharging conditions, integration constraints within the vehicle).
- Design and development of innovative thermal management systems.
- Prototyping and characterization of one or more solutions.
- Integration of thermal results into an aging model to analyze the effects on lifespan.

This thesis proposes an approach combining design, simulation/modeling, and prototyping/characterization. The laboratory is equipped with a dedicated platform for battery pack assembly, featuring rapid prototyping tools (3D printing, laser cutting and welding, mechanical workshop), as well as a testing platform enabling advanced characterizations of battery systems.

Assessment of a new model for the investigation of an hypothetical Steam Generator Tube Rupture (SGTR) accident in Lead-cooled Fast Reactors (LFR).

The purpose of this PhD thesis is to implement and assess a new vapor explosion model in the
CEA code Europlexus, to investigate an hypothetical steam generator tube ruptures (SGTR) inside
the primary coolant pool of a lead-cooled fast reactors (LFR).

Assimilation of transient data and calibration of simulation codes using time series

In the context of scientific simulation, some computational tools (codes) are built as an assembly of (physical) models coupled in a numerical framework. These models and their coupling use data sets fitted on results given by experiments or fine computations of “Direct Numerical Simulation” (DNS) type in an up-scaling approach. The observables of these codes, as well as the results of the experiments or the fine computations are mostly time dependent (time series). The objective of this thesis is then to set up a methodology to improve the reliability of these codes by adjusting their parameters through data assimilation from these time series.
Work on parameter fitting has already been performed in our laboratory in a previous thesis, but using scalars derived from the temporal results of the codes. The methodology developed during this thesis has integrated screening, surrogate models and sensitivity analysis that can be extended and adapted to the new data format. A preliminary step of transformation of the time series will be developed, in order to reduce the data while limiting the loss of information. Machine learning /deep learning tools could be considered.
The application of this method will be performed within the framework of the nuclear reactor severe accident simulation. During these accidents, the core loses its integrity and corium (fuel and structure elements resulting from the reactor core fusion) is formed and can relocate and interact with its environment (liquid coolant, vessel’s steel, concrete from the basemat…). Some severe accident simulation codes describe each step / interaction individually while others describe the whole accident sequence. They have in common that they are multiphysic and have a large number of models and parameters. They describe transient physical phenomena in which the temporal aspect is important.
The thesis will be hosted by the Severe Accident Modeling Laboratory (LMAG) of the IRESNE institute at CEA Cadarache, in a team that is at the top of the national and international level for the numerical study of corium-related phenomena, from its generation to its propagation and interaction with the environment. The techniques implemented for data assimilation also have an important generic potential which ensures important opportunities for the proposed work, in the nuclear world and elsewhere.

Study of the thermoconversion and de-polymerization mechanisms of plastic wastes in supercritical water conditions

The waste valorization is a hot topic that has attracted great interest in the Circular Carbon Economy. Substantial efforts have been devoted to strengthening sustainable processes in recent years. These are based on the development of systems to improve carbon circularity (material and energy recycling).Global production of plastics doubled from 230 million tons in 2000 to 460 million tons in 2019. This exponential production/consumption has significant consequences on the environment. Despite the existence of recycling methods, only 9% of global plastic production is currently recycled, and the remaining quantity (not valorized) represents a real source of pollution [1].
Mixtures of different types of plastics make sorting stages difficult, which represents the main disadvantage for material recycling systems. An interesting application recently reported in the literature is the use of the hydrothermal gasification process to treat waste (and mixtures of difficult-to-sort) plastics to produce a gas rich in CH4 and H2 [2]. Hydrothermal gasification (HTG) is a thermochemical process which employs the supercritical conditions of water (T > 374 ° C, P > 221 bar), in order to convert the organic carbon contained in the wet feedstock into a gaseous phase (which contains CH4, H2, CO and CO2, mainly). In addition, the flexibility of the process also allows the study of de-polymerization of these wastes in conditions close to the critical point of water, which facilitates the production of chemical intermediates (and their reuse) in the chemical industry.
Thus, the understanding of the conversion mechanisms of different types of plastics (and their mixtures) seems essential to valorize these wastes. However, the identification of reaction pathways is still a major scientific obstacle. The objective of the thesis is the study of the reaction mechanisms of transformation of model plastics (and their mixtures) in supercritical water conditions. Understanding the phenomena will lead to the optimization of the HTG process (with and without catalysts) to facilitate the production of a gas rich in CH4/H2 and the production of intermediates for the chemical industry. The focus of this PhD work will involve: i) the study of thermo-conversion and de-polymerization of plastics; ii) the study of the behavior of catalysts in the supercritical water environment (activation/deactivation); iii) the study of selectivity towards the production of a gas containing CH4/H2 and the production of chemical intermediates.

Study of fracture toughness - microstructure relationships of new high performance oxide dispersion strengthened steels

ODS steels are considered for the development of components for fourth generation reactors. They offer high tensile and creep strength and good resistance to irradiation [1-3]. This high level of reinforcement is accompanied by a reduction in ductility and toughness. Tube shaping changes the microstructure, so the properties of the material in its final form should be evaluated. The work of B. Rais [4] made it possible to compare the different tests and to develop a test and an analysis method for measuring toughness on thin tubes.

This present PhD will use this new test to evaluate the toughness of various ODS grades. Varied microstructures from historical and recent productions will assessed to identify the mechanisms, the key parameters driving toughness and to identify the microstructural parameters which drive the response of the material. In this work we will be interested in ferritic / martensitic grades, some of which come from a manufacturing process which is the subject of a patent application [5-6] and for which we observe for the first time remarkable properties in resilience, associated with good hot mechanical properties.

The study will be based on a comparison of experience and finite element modeling. This applied research work will allow the student to acquire solid skills in fracture mechanics and fine characterization of materials (SEM, EBSD, etc.). A good understanding of the mechanical properties/microstructure relationships will make it possible to understand the origin of the observed properties and to propose new optimizations on the microstructures to improve the mechanical behavior and/or the shaping of the material.

Student profile: Engineer or M2 Mechanics/Materials

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