Description du sujet de thèse

Certain alloys can reversibly store hydrogen at room temperature and atmospheric pressure by forming metal hydrides (MH). Their formation is exothermic, while their decomposition is endothermic. The hydrogenation process causes embrittlement, leading to pulverization of the alloy.

When MHs are used in large-scale hydrogen tanks, the alloy powders must be shaped into pellets to ensure good thermal conductivity and mechanical strength, enabling fast reaction kinetics. These facts were recently demonstrated in the European HyCARE project (2019–2023), which proved the ability of Ti(Fe,Mn) powders to store 4 kg of hydrogen.

The pellets contain the hydride-forming alloy (MH) and a polymer, typically polyvinylidene fluoride (PVDF), which acts as a binder. Thus, the pellets can be described as polymer-dispersed metal hydrides (PDMH). PVDF has a low glass transition temperature (Tg = –38°C), is easy to process, exhibits elastic mechanical behavior (30–50% elongation), and is permeable to hydrogen.

However, its use is now banned in Europe since the REACH 2025 regulation aims to prohibit the use of halogen-containing polymers in industrial applications.

Therefore, substitute polymers must have similar properties to PVDF. Moreover, as an urgent solution is needed, these materials must be readily available at an industrial scale. The most relevant short-term solution, within the timeframe imposed by REACH 2025, is to consider petrochemical-based elastomeric polymers, while simultaneously conducting research on bio-based polymers for future applications as binders.

The proposed PhD project is part of the REMEDHYS project, funded by the European Union in July 2024 under the HORIZON-JTI-CLEANH2-2024 call. REMEDHYS brings together 11 academic and industrial partners from Norway, Italy, Germany, and France. Its main goal is to develop an industrial PDMH storage unit with a capacity of 100 kg of H₂.

Project Description

Two French laboratories are involved in this project and will jointly supervise the PhD: Ingénierie des Matériaux Polymères (IMP), Lyon (UMR 5223) and Institut de Chimie et des Matériaux Paris-Est (ICMPE), Thiais (UMR 7182). The recruited PhD candidate will study the suitability of five elastomers, available on an industrial scale (ton-scale), as binders for metal hydrides. These polymers are: Crosslinked polydimethylsiloxane (PDMS), Styrene–butylene rubber (SBR), Acrylonitrile–butadiene–styrene (ABS), Hydrogenated nitrile–butylene rubber (HNBR), Ethylene–propylene rubber (EPR). These polymers have shown promising hydrogen permeability and good compatibility with metal hydride particles.

The project will begin with a study of the activation conditions and reaction kinetics of Ti(Fe,Mn)@polymer PDMH pellets for each proposed polymer. The alloy composition from HyCARE will be used: TiFe₀.₈₅Mn₀.₀₅. The composition and structure of the alloy will be characterized by EPMA and XRD.

Pellets that cannot be activated under hydrogen pressures/temperatures below 100°C / 50 bar will be excluded from the study. Furthermore, the reaction rate of the pellets should exceed 1 wt% H₂ per hour under comparable conditions.

Selected polymers will be formulated with Ti(Fe,Mn) alloy to produce PDMH composites with a polymer binder fraction of 2 wt% (~13 vol%). Pellets of 5 mm diameter and 1 cm thickness (≈0.2 cm³) will be produced to test hydrogen storage capacity and reversibility. Hydrogenation capacity and kinetics will be evaluated at a typical operating temperature of 55°C within a pressure range of 1–25 bar.

Next, the mechanical and thermal behavior of these PDMH composites will be evaluated before hydrogen storage and after 2, 5, and 20 absorption/desorption cycles. Special attention will be paid to changes in mechanical modulus (via DMA and compression tests) and variations in glass transition temperature (via DSC and DMA) during repeated hydrogen cycling.

As fatigue and mechanical failure in composites are mainly attributed to degradation of the interface between the matrix and the filler/reinforcement, these studies will be complemented by SEM analyses of these interfaces.

Contexte de travail

This PhD project will be co-supervised by Prof. Agustín Rios de Anda (IMP), Dr. Junxian Zhang (ICMPE), and Prof. Judith Monnier (ICMPE). Candidates applying for this PhD must hold an Engineering degree and/or a Master's degree (M2) in Chemistry and/or Polymer Materials Science, with a strong background in these areas. Applicants should also have good communication and writing skills in both French and English.

The PhD project will be carried out primarily at IMP (Lyon), with short research stays at ICMPE (Thiais) every 2–3 months.

Contraintes et risques

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Informations complémentaires

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