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SL-DRT-24-0016 - Advanced modeling of Gas Diffusion Layers for Fuel Cells: ink impregnation and drying, 3D phase distribu

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
In the frame of advanced H2 solutions for the energy transition, the Proton Exchange Membrane Fuel Cell (PEMFC) is a relevant solution for the production of low-carbon electrical energy. The European Project DECODE proposes to develop a fully digital chain of design tools, including raw material properties, manufacturing and assembly of the different components, to predict the performance of such ‘virtual’ stack. This will help reducing the development cost and time of improved materials/components suitable for different applications in the future. The component considered in this thesis is the Gas Diffusion Layer (GDL), which is a combination of a fibrous microporous substrate and of a micro/nano porous layer (MPL for microporous layer). The work will be split into different steps: a) based on (real or virtual) 3D images of the substrate, simulation of the hydrophobic and MPL coating and drying to derive the 3D distribution of the components (fibers, hydrophobicity and MPL); b) simulation of single and two-phase transport properties of the GDL to supply inputs to upper scale performance models; c) sensitivity analysis of the main manufacturing processes (ink properties, drying parameters…)

Advanced modeling of Gas Diffusion Layers for Fuel Cells: ink impregnation and drying, 3D phase distribution, and effective properties

SL-DRT-24-0055 - New sustainable electrode materials for High Temperature Electrolysis

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
High temperature electrolysis is considered as the high efficiency technology for hydrogen production with low carbon emissions. The electrolysis reaction occurs in a solid oxide cell (SOC) composed of a dense electrolyte of yttria stabilized zirconia (YSZ), sandwiched between two porous electrodes. The most common hydrogen electrode material is a cermet of Ni and YSZ, and the oxygen electrode is a perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). To make the high temperature electrolysis more sustainable to better support the European eco-system towards the achievement of the Sustainable Development Goals and the objectives of the Paris Agreement, there is a critical need to reduce reliance on critical raw materials (CRM). The objective of the thesis is therefore to limit the use of CRM in the oxygen electrode material. Critical elements such as cobalt will be substituted by new cations on the A and/or B site of the crystal lattice, while maintaining equivalent performance and long-term stability. At the same time, in order to limit losses during synthesis, a part of the work will be carried out on the synthesis process efficiency and on the increase in capacity of the synthesis method. After a bibliographic study on oxygen electrode materials for high temperature electrolysers, the proposed work will initially be focused on the synthesis by chemical routes as well as on fine characterization of the perovskites. The thermal and chemical compatibility with the other materials constituting the cell will be studied, then this work will lead to the shaping of the materials with the most interesting properties in order to test them electrically and electrochemically. The electrochemical behaviour of the electrodes will be analysed in order to understand the influence of substitutions and to determine the electrochemical performance of the different compositions studied.

New sustainable electrode materials for High Temperature Electrolysis

SL-DRT-24-0017 - Exploring the Future of Satellite Communications: Dual-Band Electronically Reconfigurable Flat Lens Ante

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
CEA Leti offers a PhD topic to develop new electronically scanning antennas for efficient data transmission in satellite communications (Satcom). Novel efficient electronically scanning antennas are essential for future satellite communications (Satcom). Electronically reconfigurable flat lens antennas, also known as transmitarrays, are a promising architecture to achieve high scanning performance. Each element of the flat lens introduces an optimized phase shift on the impinging wave emitted by a primary source, to steer and shape the radiation pattern. The phase profile over the lens can be dynamically modified by adding reconfigurable devices in the cells, such as switches (e.g. pin diodes) or varactors. Compared to phased arrays, these antennas attain high-gain beam-steering with a significantly lower power consumption and architectural complexity. The Ph.D. work aims to propose and experimentally demonstrate novel concepts and design methods for wideband/multi-band electronically beam-steering flat lens antennas. The main research goals are: . Study of new approaches for designing unit cells with broad radiation patterns, stable performance under oblique incidence and wideband/multiband operation. . Electrically thin subwavelength cells and Huygens’ radiating elements will be investigated to tailor the angular and frequency response of the cell. . Novel design solutions to enable a fine electronic control of the phase shift introduced by the cells. Multilayer cells comprising either pin diodes or varactors, or a combination of both, will be analyzed. The trade-offs between phase resolution, bandwidth, power consumption, number of reconfigurable devices and bias lines, will be studied. . Development of dedicated synthesis procedures to enable the independent control and shaping of the radiation pattern at two or multiple frequencies. . Experimental demonstration of high-gain dual-band fixed-beam and electronically 2-D beam-steering prototypes achieving extremely wide scan ranges (±60° or greater). The demonstratators will be optimized to work in typical Satcom bands (e.g. around 20 GHz and 30 GHz).

Exploring the Future of Satellite Communications: Dual-Band Electronically Reconfigurable Flat Lens Antennas with Ultra-Wide Scan Range

SL-DRF-24-0157 - Development of III-V semiconductor core/shell quantum dots for use in photodetectors and photocatalysis

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
Colloidal semiconductor nanocrystals, also termed quantum dots (QDs), have been discovered around 40 years ago, which has given rise to the 2023 Nobel prize in Chemistry. They have attracted considerable interest due to their unique size-dependent optical and electronic properties. In particular, their band gap can be simply changed by adjusting their size via the so-called quantum confinement effect. It occurs for many semiconductors when at least one of their dimensions is reduced to a few nanometers. Most research has been conducted on binary cadmium- and lead-based QDs (CdSe, PbS, etc.), which cover the visible and near infrared spectral range and can be easily synthesized. However, due to the toxicity of these compounds, their use in real-life applications is strongly limited. Our team is focusing on the development of toxic heavy metal-free and environmentally benign QDs such as III-V semiconductor materials (InP, InSb), which have a high potential for use in biomedical applications, energy conversion, photocatalysis, and optoelectronics. In this project, we want to develop synthesis methods for size- and shape-controlled III-V QDs, first in batch and then in continuous flow. Continuous flow synthesis has many advantages compared to conventional batch synthesis due to the enhanced mass and heat transfer in small-sized tubular reactors and the higher reproducibility in fully automated processes. The surface chemistry of the obtained QDs is a key parameter, which governs their chemical stability and processibility, photoluminescence quantum yield (PLQY), photostability, and electrical transport properties. Therefore, appropriate surface functionalization is required for essentially all types of applications of QDs encompassing photocatalysis, photodetectors, LEDs, and biological imaging/detection. Here, we will develop methods for the precisely controlled growth of various types of inorganic shells to passivate and stabilize the QDs, focusing on metal chalcogenides (ZnS, ZnSe) and ceramic-type materials (e.g., Al2O3, TiO2, and ZrO2) as well as combinations thereof. Characterization of the optical and structural properties will be performed using UV-vis and photoluminescence (PL) spectroscopy, time-resolved PL and PLQY measurements, Raman spectroscopy, NMR and FTIR spectroscopy, X-ray diffraction, elemental analysis, and electron microscopy. In the second part of the project, the potential of the obtained QDs for use in NIR photodiodes as well as for the photocatalytic CO2 reduction will be evaluated.

Development of III-V semiconductor core/shell quantum dots for use in photodetectors and photocatalysis