Helmholtz-Zentrum Geesthacht, 2017-10-19
http://www.hzg.de/056204/index_0056204.html.en

"Theoretical and experimental investigation of diffusion processes in materials for hydrogen and electrochemical energy storage"

Efi Hadjixenophontos / Early Stage Researcher at the University of Stuttgart, Germany

Efi receives the H&E Poster award at the 10th International Symposium Hydrogen & Energy in Zao, Japan, in February 2016. Efi is seen here with Prof. Shin-ichi Orimo, who congratulates Efi on this success and presents the award to her.

Working title of thesis

Novel complex metal hydrides for efficient and compact storage of renewable energy as hydrogen and electricity.

Objectives

Hydrogen storage for transportation applications continues to be one of the most challenging barriers to the widespread commercialization of hydrogen-fueled vehicles. Magnesium Hydride is one of the materials of large interest since along with its abundance, it is a low density material that can store an important weight percentage of hydrogen. The objective of this project is to study the physical properties of metal hydride thin films for hydrogen or Lithium (Li) storage and ion conductivity. Final goal of the project is to combine two materials, MgH2 and LiBH4 and test the compound as a hydrogen storage material.  

Tasks and methodology

The focus will be given to thin films of Magnesium Hydride (MgH2) and Lithium Boron Hydride (LiBH4). We will use ion beam sputtering to create thin films. Structural and microscopic characterization of the thin films as well as electrochemical testing will be carried out in order to see if this method delivers suitable model material to study conversion reactions and ionic transport in volume and across interfaces. To a major part, the project will deal with the conversion reaction of MgH2 with Li. Another will be the ion conductivity of LiBH4. The effect of doping LibH4 with Iodine or other halogens in improving conductivity will also be part of the experimental tasks. Experimental methods such as X-Ray Diffraction measurements are an important part of this project in order to confirm the structure of the thin film materials. The project will also try to apply Atom Probe Tomography to study the microstructural details of the conversion reaction by 3D atomic mapping.

 

University of Stuttgart


Nanoanalysis by atom probe tomography

Atom probe tomography is a most advanced microscopic analysis technique based on the principle of field ion microscopy. Atoms are individually desorbed from the specimen, identified, and localised. From the measured data, the three-dimensional atomic structure of nanometer-sized specimens is reconstructed numerically. Significant improvements in the total volume of analysis, in the range of materials that can be investigated, and in specimen preparation have recently broadened the range of possible applications of this method decisively. In this review, the physical basis of this exciting nano-analytical tool is presented to some detail, to allow the reader an individual understanding of advantages and limitations of the method. The design of actual instruments is described, the physics of field desorption and volume reconstruction algorithms are discussed. Furthermore, the application of the method to relevant problems of material physics in nanotechnology is illustrated by a few case studies.

 

Exchange chamber of samples

Exchange chamber of samples

Measurement chamber

Measurement chamber

Field ionisation and evaporation

All FIM techniques make use of the fact that electrical fields are concentrated at tips of sharp curvature. Supplying moderate voltages, enormous field strengths in the range of some 10 V/nm are easily obtained at the apex of nanometer sized tips, whereas fields of such a magnitude would be never obtained in macroscopic geometries. So, a typical field ion microscope consists of an ultra-high vacuum chamber with a specimen stage holding the sample tip, a high voltage supply and a viewing screen with the capability to image the ion impacts. A positive potential is supplied to the metallic specimen while the entrance face of the screen is kept at ground. In order to reduce thermal energies, a cryostat is required to cool the tip down to 20 to 50 K.

UHV Ion Beam Sputtering device for thin film deposition:

Ion beam sputtering is a physical vapor process that we use in our group to deposit thin film materials. The apparatus consists of an ion source (Ar or O2 gas), a target revolver which can hold up to four different materials and a sample holder with the substrates that can be heated up to 700°C. Ionization of the gas is employed by a cathodic source. The ions are then accelerated, deflected and focused using a high voltage. Finally they are neutralized in a plasma before they hit the target. As a major advantage, this techniques warrants a completely field-free space around targets and substrates. It is possible to deposit layers from a monolayer to few μm in thickness, and it’s suitable for a broad range of materials. Also reactive sputtering under oxygen, nitrogen or hydrogen atmosphere is easily performed.

Ultra-thin LiPON films – Fundamental properties and application in solid state thin film model batteries


Targets

Targets

Short CV

I grew up in Cyprus and took the national exam for entry into Greek and Cypriot Universities. In spite of earning a coveted spot at the University of Cyprus, and after much deliberation, I decided to turn the offer down and pursue my ambition to experience different cultures and learn different languages, while I studied.
I moved to France instead, to start my studies in physical chemistry in Montpellier and to study French. Next, I added English to my science skills through MESC, an international master’s, offering a unique experience to explore electrochemistry and materials science, while working at various European universities. During my master’s degree I was elected class president for my teamwork skills and ability to manage and coordinate the multi-lingual/multi-cultural group.
My academic work stood out enough that a position for my master’s thesis project was created for me in Montreal, Canada, working on modified carbons and ionic liquids for electrochemical capacitors. After my thesis, I collaborated with CIRIMAT in Toulouse, France, giving me the opportunity to spend 10 additional months doing research on nanocarbon materials and ionic liquids for solid state electrochemical capacitors.
Today, I am combining my degrees, lab experience, and languages with the ECOSTORE Marie Curie Initial Training Network, as I work toward a PhD in Stuttgart.