Description

Title of the thesis project: Influence of grain boundaries in high-pressure HYdrogen COASTal storage materials for green hydrogen

Scientific description of the research project

Hydrogen is seen as a clean, mobile energy carrier and source of fuel, as it has the great advantage of being present on the planet in an abundant amount. A genuine ‘hydrogen economy’ is henceforth envisioned. Much of the technology is established from the chemical industry using high-value materials, but cost pressure from investment and maintenance is becoming significant now that these technologies are rolled out at the gigawatt scale. One of the main challenges consists of the development of suitable, cost-effective, and durable materials for the transportation of hydrogen. Indeed, a major concern with hydrogen is that it is very detrimental to the durability of materials. This problem affects the structural materials in various industries, from subsea pipelines to aircraft and nuclear reactors. This severe degradation can manifest itself in several ways, such as a decrease in tensile elongation to cause fracture, or a decrease in the static load that can be supported by the metallic structure, for example. The effects of hydrogen on the ductility, toughness, and tensile strength are known to be significant, as the performance and lifetime of materials are drastically reduced in the presence of hydrogen. This outcome, known as Hydrogen Embrittlement (HE), was first described in 1875 by Johnson. This phenomenon results from a combination of different parameters related to the material’s characteristics, the source of hydrogen (internal or external), and the mechanical solicitations.

Nowadays, coastal areas are quickly becoming one of the main sources of green hydrogen due to their favorable potential for wind, tidal/wave, and solar power to drive water electrolysis. While complementary, these green power sources do show some intermittence, making buffering of the produced gaseous hydrogen in e.g. high-pressure tanks, necessary. These tanks and auxiliary equipment already exist; however, they are currently made from non-optimized materials, due to a lack of understanding in detail of the underlying failure mechanisms. Especially, the most important role of crystal interfaces, such as grain and grain boundaries, is not fundamentally understood.

In this project, the applicants will leverage their complementary expertise in model material synthesis, characterization, and simulation (LaSIE), as well as high-pressure materials testing and atomic-scale analysis (FAU), to gain fundamental insights into the role of grain boundaries (GBs) as critical failure points in hydrogen-facing materials under pressure. Nickel (Ni) is selected as the model material due to its well-characterized behavior and suitability for fundamental studies. The applicants will synthesize Ni single crystals (SX) and bicrystals (BX) at the macroscale, enabling the isolation and analysis of individual grain boundaries and the comparison to boundary-free systems. The central objective of the proposal is to assess and predict grain boundary networks and microstructures that exhibit reduced sensitivity to hydrogen embrittlement through grain boundary engineering. 

Programme

SO1: Fabricate the samples with zero or one grain boundaries. 

To fill an important gap concerning the effect of GB, it is necessary to have access to experimental knowledge on samples of different, well-defined single GBs. 

SO2: Develop a database of material characterization testing on representative grain boundaries in nickel. 

There is a strong need to document the effect of GB on the diffusion of hydrogen in metals, using a harmonized building protocol which will be established in the framework of this project. These will be exposed to electrochemical (LaSIE) and high-pressure (FAU) hydrogen in the form of protium and deuterium. 

SO3: Develop an atomistic numerical modelling approach for simulating and predicting hydrogen diffusion and trapping at the GB.

In this Sub-objective, the atomistic level investigation will be done to understand the fundamentals of hydrogen embrittlement of GBs and TJs. 

SO4: To facilitate the uptake and exploitation of the project results by the academic community, technology developers, and end-users. 

Communication is a key lever to ensure that the project effectively reaches specific audiences, promoting the project and its results, generating awareness and interest, and encouraging engagement with the project activities and results. The main strategic objective of the communication plan is to ensure that the project results are widely communicated to the target communities via appropriate means and translated into meaningful and tangible action. 

Description of the Doctoral Candidate’s tasks:

Technical program

In La Rochelle : 

Crystal growth of a bi-crystal and a tri-crystal

Characterization (XRD, EBSD, TEM) of each grain and grain boundary (a minimum of 4 GBs) and a triple junction

Hydrogen charging (electrochemical), TDS 

Mechanical testing with and without H

Modelling application in FEM

In FAU Erlangen :

Gaseous hydrogen charging (cylindrical samples), TDS

Atom Probe

HRTEM at least one bi-crystal and one tri-crystal

Mechanical testing on cylindrical samples with and without H

Secondment in HEREON:

Synchrotron nano-tomography and diffraction imaging to capture 3D defect distributions.

Communication program

Participation in one domestic conference/year and one international conference

Writing of at least 2 journal papers as first author

3 outreach activities (ma these en 180s, et fête de la science, Long night of science at FAU)

Training Program

In agreement with both doctoral schools, La Rochelle and FAU Erlangen