Optimization of the catalytic layer for CO2 electroreduction integrated into a PEM electrolyzer
This thesis focuses on optimizing the catalytic layer for CO2 electroreduction in an acidic medium, integrated into a proton-exchange membrane (PEM) electrolyzer. The aim is to upgrade CO2 by converting it into valuable chemicals, such as carbon monoxide. The acidic environment inherent to PEM electrolyzers helps limit carbonate formation, improving CO2 conversion efficiency. However, CO2 reduction in acidic media competes with the hydrogen evolution reaction, which reduces the selectivity of electroreduction products. This work seeks to develop noble-metal-free catalysts inspired by those used for oxygen reduction in fuel cells, improve the properties of carbon supports, and optimize the design of the catalytic layer, in particular thickness, porosity and hydrophobicity, to maximize CO2 conversion into target molecules. Finally, the active layer will be integrated into a 16 cm² PEM electrolyzer to assess overall performance and gain insights into the mechanisms involved through electrochemical characterization.
Functionalized aluminosilicate nanotubes for photocatalysis
Rising energy demand and the need to reduce the use of fossil fuels to limit global warming have created an urgent need for clean energy collection technologies. One interesting solution is to use solar energy to produce fuels. Low-cost materials such as semiconductors have been the focus of numerous studies for photocatalytic reactions. Among them, 1D nanostructures are promising because of their interesting properties (high and accessible specific surface areas, confined environments, long-distance electron transport and facilitated charge separation). Imogolite, a natural hollow nanotubes clay, belongs to this category. Its particularity does not lies in its chemical composition (Al, O and Si) but in its intrinsic curvature, which induces a permanent polarization of the wall, effectively separating photo-induced charges. Several modifications of these materials are possible (coupling with metal nanoparticles, functionalization of the internal cavity), enabling their properties to be modulated.We have demonstrated that this clay is a nanoreactor for photocatalytic reactions (H2 production and CO2 reduction) under UV illumination. In order to obtain a useful photocatalyst, it is necessary to extend photon collection into the visible range. One strategy considered is to encapsulate and covalently graft dyes acting as antennae in the cavity. The aim of this thesis is to synthesize imogolites with different internal functionalizations, to study the encapsulation and grafting of dyes into the cavity of these functionalized imogolites, and finally to study the photocatalytic properties.
Thermally conductive yet electrically insulating polymer nanocomposite based on core-shell (nano)fillers oriented by magnetic field
Advances in power electronics, electric motors and batteries, for example, are leading to a significant increase in heat production during operation. This increase in power density combined with reduced heat exchange surfaces amplifies the challenges associated with heat dissipation. The absence of adequate dissipation leads to overheating of electronic components, impacting on their performance, durability and reliability. It is therefore essential to develop a new generation of heat dissipating materials incorporating a structure dedicated to this structure.
The objective and innovation of the PhD student's work will lie in the use of highly thermally conductive (nano)fillers that can be oriented in an epoxy resin in a magnetic field. The first area of work will therefore be to electrically isolate the thermally conductive (nano)charges with a high form factor (1D and 2D). The electrical insulation of these charges of interest will be achieved by a sol-gel process. The synthesis will be controlled and optimised with a view to correlating the homogeneity and thickness of the coating with the dielectric and thermal performance of the (nano)composite. The second part will focus on the grafting of magnetic nanoparticles (NPM) onto thermally conductive (nano)fillers. Commercial NPMs will be evaluated as well as grades synthesised in the laboratory. The (nano)composites must have a rheology compatible with the resin infusion process.
Quantum computing with nuclear spins
Nuclear spins in solids are amongst the quantum systems with the longest coherence times, up to minutes or even hours, and as such are attractive qubit candidates; however, controlling and reading out individual nuclear spins is highly challenging. In our laboratory, we have developed a new way to do so. The nuclear spin qubits are interfaced by an electron spin ancilla to which they are coupled by the hyperfine interaction. The electron spin is then measured by microwave photon counting at millikelvin temperatures [1,2]. Nuclear-spin single-shot readout is performed via the electron spin [3], and coherent control is achieved through the use of microwave Raman transitions [4]. The electron spins are Er3+ ions in a CaWO4 crystal, and the nuclear spins are 183W atoms in the matrix, which have a spin 1/2.
[1] E. Albertinale et al., Nature 600, 434 (2021)
[2] Z. Wang et al., Nature 619, 276 (2023)
[3] J. Travesedo et al., arxiv (2024)
[4] J. O'Sullivan et al., arxiv (2024)
Magnetic DIsks as Transducer of Angular Momentum
The proposed topic is a collaborative project to exploit suspended magnetic disks as novel microwave transducers of orbital angular momentum. Our goal is to develop ultra-high fidelity opto-mechanical modulators operating at GHz frequencies by integrating magnetic materials into optical components. This innovative concept arises from recent progress in the study of angular momentum conservation laws by magnon modes in axi-symmetric cavities, leading to new opportunities to develop a more frugal, agile, and sustainable communications technology. Our proposed design has the potential to achieve coherent interconversion between the microwave frequency range in which wireless networks or quantum computers operate and optical network frequencies, which is the optimal frequency range for long-distance communications. In this regard, our proposal not only proposes new applications of magnonics to the field of optics not previously envisioned, but also builds a bridge between the spintronics and the electronic and quantum communities.
In this proposal, the elastic deformations are generated by the magnetization dynamics through the magneto-elastic tensor and its contactless coupling to a microwave circuit. We have shown that coherent coupling between magnons and phonons can be achieved by precisely tuning the magnetic resonance degenerate with a selected elastic mode via the application of an external magnetic field. We expect to achieve ultra-high fidelity conversion by focusing our study on micron-sized single crystal magnetic garnet structures integrated with GaAs photonic waveguides or cavities. In addition, we propose the fabrication of suspended cavities as a means to minimize further energy leakage (elastic or optical) through the substrate.
The first challenge is to produce hybrid materials that integrate high quality garnet films with semiconductors. We propose a radically new approach based on micron-thick magnetic garnet films grown by liquid phase epitaxy (LPE) on a gadolinium-gallium-garnet (GGG) substrate. The originality is to bond the flipped film to a semiconductor wafer and then remove most of the the GGG substrate by mechanical polishing. The resulting multi-layer is then processed using standard lithography techniques, taking advantage of the relative robustness of garnet materials to chemical, thermal or milling processes.
The second challenge is to go beyond the excitation of uniform modes and target modes with orbital angular momentum as encoders of arbitrarily large quanta of nJ? for mode multiplexed communication channels or multi-level quantum state registers. The project will take advantage of recent advances in spin-orbit coupling between azimuthal spin waves as well as elastic scattering of magnons on anisotropic magneto-crystalline tensors. In this project, we also want to go beyond uniformly magnetized state and exploit the ability to continuously morph the equilibrium magnetic texture in the azimuthal direction as a means of engineering the selection rules and thus coherently access otherwise hidden mode symmetries.
Modeling and experimental validation of a catalytic reactor and optimization of the process for the production of e-Biofuels
During the past 20 years, « Biomass-to-liquid » processes have considerably grown. They aim at producing a large range of fuels (gasoline, kerozene, diesel, marine diesel oil) by coupling a biomass gazéification into syngaz unit (CO+CO2+H2 mixture) and a Fischer-Tropsch (FT) synthesis unit. Many demonstration pilots have been operated within Europe. Nevertheless, the low H/C ratio of bio-based syngaz from gasification requires the recycling of a huge quantity of CO2 at the inlet of gaseification process, which implies complex separation and has a negative impact on the overall valorization of biobased carbon. Moreover, the possibility to realize, in the same reactor, the Reverse Water Gas Shift (RWGS) and Fischer-Tropsch (FT) reaction in the same reactor with promoted iron supported catalysts has been proved (Riedel et al. 1999) and validated in the frame of a CEA project (Panzone, 2019).
Therefore, this concept coupled with the production of hydrogen from renewable electricity opens new opportunities to better valorize the carbon content of biomass.
The PhD is based on the coupled RWGS+FT synthesis in the same catalytic reactor. On the one hand a kinetic model will be developed and implemented in a multi-scale reactor model together with hydrodynamic and thermal phenomena. The model will be validated against experimental data and innovative design will be proposed and simulated. On the other hand, the overall PBtL process will be optimized in order to assess the potential of such a process.
Exploration of Diamond-Based Nanomaterials for (Sono)photocatalysis: Applications in Hydrogen Production and CO2 Reduction
Nanodiamonds (NDs) are increasingly being studied as semiconductors for photocatalysis, thanks in particular to the very specific positions of their valence and conduction bands, which can be modulated. For example, it has recently been shown that NDs can produce hydrogen under sunlight with an efficiency similar to that of TiO2 nanoparticles. Other studies also show the possibility of photogenerating solvated electrons from certain NDs for CO2 reduction or the degradation of stubborn pollutants.
With a view to accelerating the development of nanodiamond-based ‘solar-to-X’ technologies, we propose in this thesis to integrate nanodiamonds as photocatalysts in a sonophotocatalytic approach. Acoustic cavitation, generated by ultrasound, can improve mass transfer by dispersing catalytic particles and can produce additional reactive species (hydroxyl radicals, superoxides). It also emits sonoluminescence, which can promote the photogeneration of charges and should limit the recombination of charge carriers.
The first phase of the work will focus on the synthesis of nanodiamond-based photocatalysts, exploring various surface chemistries and their association with co-catalysts. Both classical and sonochemical synthesis methods will be used, as preliminary studies have shown that sonochemistry can effectively modify the surface chemistry of NDs. The photocatalytic properties of these materials will first be evaluated, leading to the design of a sonophotocatalytic cell. Further studies will explore the synergies between sonochemistry and photocatalysis for hydrogen production or CO2 reduction. This thesis will be carried out as part of a collaboration between the NIMBE at the Saclay CEA centre and the ICSM at the Marcoule CEA centre.
Brines for metal recycling
Critical metals are essential for a range of technologies that are vital to reduce our carbon dioxide emissions. However, the global recycling rate for metals contained in electronic waste is below 20%, indicating that electronic waste is a relatively untapped source of metals. Additionally, it is increasingly urgent to develop effective processes for recycling waste from products like solar panels, as the volume of waste solar pannels generated is set to rise significantly in the coming years. Currently, conventional hydrometallurgical methods often rely on toxic aqueous solutions to dissolve metals, which presents substantial environmental challenges.
This project proposes an innovative alternative by using concentrated brines (aqueous salt solutions) to oxidize and dissolve metals. This thesis will investigate the fundamental properties of brines and their ability to dissolve metals through various techniques, particularly electrochemical methods. Artificial intelligence methods developed within the lab will be employed to screen a wide range of brines that would allow metal dissolution. Subsequently, brine-based recycling processes will be developed to recover metals from printed circuit boards and solar panels. Finally, metal separation and the treatment of used brines will be explored using membrane and electrochemical processes.
Understanding the mechanisms of direct CO2 hydrogenation using (Na,K)FeOx catalysts via theoretical-experimental coupling
In the context of climate change, we need to reduce our CO2 emissions by using less energy. Another approach is to capture, store and use CO2, with the aim of moving towards a circular carbon economy and, ultimately, defossilization. With this in mind, the direct hydrogenation of CO2 enables it to be transformed into molecules of interest such as hydrocarbons, via the coupling of the reverse water gas shift (RWGS) reaction and Fischer-Tropsch synthesis (FTS).
Computational operando catalysis has recently emerged as a reasoned alternative to the development of new catalysts, thanks to a multi-scale approach from the atom down to the active particle, to model catalyst selectivity and activity. New tools combining ab initio simulations (DFT) and molecular dynamics (MD) via machine learning algorithms bridge the gap between the precision of DFT calculations and the power of atomistic simulations. Current bifunctional catalysts (active for RWGS, and FTS) for direct CO2 hydrogenation are based on doped iron oxides (metal promoters).
The aim of this project is the theoretical study of Na-FeOx and K-FeOx catalysts doped with Cu, Mn, Zn and Co, in 4 stages: DFT simulations (adsorption energies, density of states, energy barriers, transition states), microkinetic modeling (reaction constants, TOF), construction of interatomic potentials by DFT/machine learning coupling, simulation of whole particles (selectivity, activity, microscopic quantities).
This theoretical study will go hand in hand with the synthesis and experimental measurements of the studied catalysts, and optimized catalysts emerging from the computational results. All the accumulated data (DFT, MD, catalytic properties) will be fed into a database, which can eventually be exploited to identify descriptors of interest for CO2 hydrogenation.
Magneto-ionic gating of magnetic tunnel junctions for neuromorphic applications
Magneto-ionics is an emerging field that offers great potential for reducing power consumption in spintronics memory applications through non-volatile control of magnetic properties through gating. By combining the concept of voltage-controlled ionic motion from memristor technologies, typically used in neuromorphic applications, with spintronics, this field also provides a unique opportunity to create a new generation of neuromorphic functionalities based on spintronics devices.
The PhD will be an experimental research project focused on the implementation of magneto-ionic gating schemes in magnetic tunnel junction’s spintronics devices. The ultimate goal of the project is to obtain reliable and non-volatile gate-control over magnetisation switching in three-terminal magnetic tunnel junctions.
One major challenge remains ahead for the use of magneto-ionics in practical applications, its integration into magnetic tunnel junctions (MTJ), the building blocks of magnetic memory architectures. This will not only unlock the dynamic control of switching fields/currents in magnetic tunnel junctions to reduce power consumption, but also allow for the control of stochasticity, which has important implications in probabilistic computing.