Degradation phenomena in anion exchange membrane electrolysers
The production of hydrogen using anion exchange membrane water electrolysis (AEMWE) is a promising technology for the storage of large quantities of electricity. Some AEMWE systems are already commercially available, but their deployment is hindered by the lack of understanding of the factors which limit their durability. The proposed work aims therefore to study, at single-cell level, degradation phenomena given rise to by, among other factors, the intermittant nature of electrolyser operation when powered using renewable energy sources. This study will focus on the mechanisms (thermal, fluidic, (electro)chemical) responsible for degradation of the various cell components. It will utilise test facilities available at CEA, and be enriched by the modelisation of physical degradation mechanisms for integration into a digital code. Real electrolysers need to be able to function for several years, so an early task in this work will be the definition of accelerated stress test (AST) protocols which will precipitate degradation in a targeted fashion, and in a relatively short space of time. Electrochemical data produced during these ASTs will be followed by post-test physical characterisation (XPS, XRD, SEM) of component microstructure, in order to elucidate degradation mechanisms.
Analyzis and modelling of ions-catalyst-ionomer interactions in an AEM electrolyzer cell
CEA/Liten is a research organization on new energies. It offers a PhD on the production of green hydrogen by electrolysis of water using a new technology. The 3 types of water electrolysis to produce hydrogen from electricity are: high temperature electrolysis, low temperature alkaline electrolysis, low temperature PEM electrolysis (proton exchange membrane). All these types of electrolysis have their advantages and disadvantages. Very recently, a new type of electrolysis was born: low temperature electrolysis with AEM membrane (OH- anion exchange). It is a compromise between PEM and alkaline electrolysis to benefit from the advantages of these 2 technologies. First prototypes of such a device exist at the CEA and are studied at the cell or stack scale but the mechanisms involved in the electrochemical and chemical reactions at smaller scales within the electrodes are still poorly understood. In particular, the interactions (ion exchanges, ionic potentials) between the ionomer of the active layer, the membrane and the solution of water and diluted KOH are poorly understood. The objective of the thesis is 1/ to study these mechanisms and to quantify them by developing elementary experiments then, 2/ to model them and implement these models in an existing in-house electrolyzer code and finally 3/ to simulate polarization curves to validate all the models of the code including those developed by the doctoral student.
This thesis will span 2 laboratories: an experimental laboratory and a simulation laboratory in which the student will find all the skills necessary to achieve these objectives. This thesis is linked to several projects involving people from the CEA and other French university laboratories. The student will therefore be in a working environment where this theme is booming.
The candidate is required to have good knowledge of electrochemistry and polymer chemistry and to have notions of modeling and use of software such as Comsol.
Understanding the fundamental properties of PrOx based oxygen electrodes through ab-initio and electrochemical modelling for solid oxide cells application
Solid Oxide Cells (SOCs) are reversible and efficient energy-conversion systems for the production of electricity and green hydrogen. Nowadays, they are considered as one of the key technological solutions for the transition to a renewable energy market. A SOC consists of a dense electrolyte sandwiched between two porous electrodes. To date, the large-scale commercialization of SOCs still requires the improvement of both their performances and lifetime. In this context, the main limitations in terms of efficiency and degradation of SOCs have been attributed to the conventional oxygen electrode in La0.6Sr0.4Co0.2Fe0.8O3. To overcome this issue, it has recently been proposed to replace this material with an alternative electrode based on PrOx. Indeed, this material has a high electro-catalytic activity for the oxygen reduction and good transport properties. The performance of cells incorporating this new electrode is promising and might enable to reach the targets required for large-scale industrialization (i.e. -1.5A/cm2 at 1.3V at 750°C and a degradation rate of 0.5%/kh). However, it has been shown that PrOx undergoes phase transitions depending on the cell operating conditions. The impact of these phase transitions on the electrode properties and on its performance and durability are still unknown. Thus, the purpose of the PhD is to gain an in-depth understanding of the physical properties for the different PrOx phases in order to investigate their role in the electrode reaction mechanisms. The study will contribute to validate whether PrOx based electrodes are good candidates for a new generation of SOCs and help to identify an optimized electrode using a methodology combining ab-initio calculation with electrochemical modelling.
Hydrogen and ammonia combustion within porous media: experiments and modelling
- Context
Current energy prospects suggest the use of hydrogen (H2) and ammonia (NH3) as carbon-free energy carriers to achieve neutrality by 2050. NH3 offers advantages like high energy density and safe storage but faces combustion challenges such as narrow flammability and high NOx emissions. Interestingly, some H2 can be obtained by partial cracking of NH3 to create blends of more favourable combustion properties, with open questions regarding pollutant emissions and unburnt NH3 content.
- Challenges
Porous burners show promise for safe and low-pollutant combustion of NH3/H2 blends. However, material durability issues and the complexity of flame stabilization pose significant hurdles. Fortunately, recent advances in additive manufacturing enable the precise tailoring of porous matrices, but the experimental characterization remains difficult due to the opacity of the solid matrix.
- Research objectives
The PhD candidate will operate an experimental bench at CEA Saclay to conduct combustion experiments with NH3/H2/N2+air mixtures in various porous burners. Key tasks will include designing new burner geometries, comparing experimental results with numerical simulations, and advancing the modelling of porous burners using 1D Volume-Averaged Models and asymptotic theory. Experimental measurements will include hotwire anemometry, infrared thermometry, output gas composition analysis, chemiluminescence, and laser diagnostics. The porous burners will be manufactured using 3D printing techniques with materials such as stainless steel, inconel, alumina, zirconia, and silicon carbide.
The research aims to develop more robust and efficient porous burners for NH3/H2 combustion, enhancing their practical application in achieving carbon neutrality. The candidate will contribute to advancing the field through experimental data, innovative designs, and improved modelling techniques.
Modeling condensation and solidification of air gases on a cold wall: application to the simulation of the Loss of Vacuum of a liquid hydrogen tank
The increasingly widespread use of liquid hydrogen (LH2), particularly for low-carbon mobility, raises safety issues given its highly flammable nature. One of the major accidents involving cryogenic systems is the air ingress following a rupture of the outer shell of a vacuum-insulated tank. In such an event, the gases in the air liquefy and solidify on the cold walls, resulting in a high heat deposit and sudden system overpressure. The discharge line and the safety devices must be sized to evacuate the cryogenic fluid safely and avoid any risk of explosion. The aim of this thesis is to develop a model to simulate this type of scenario using the CATHARE code. A particular effort will be made to model heat exchange by liquefaction and solidification through the tank wall. This work will benefit from the loss of vacuum experimental campaign to be carried out in LH2 by CEA as part of the ESKHYMO ANR project. In addition, the use of a CFD local-scale simulation tool such as neptune_cfd could help in the construction of models in CATHARE by up-scaling. Finally, the methodology developed will be applied to simulate a system representative of an industrial facility.