Two different synthesis techniques will be followed in parallel, one using vacuum arc melting and the other ball milling. The resulting materials will be characterized and compared.

With the vacuum arc melting technique, the melting points of the individual elements are reached, producing small metallic ingots (100-200 g) based on TiFe and HEA. This process will take place under inert atmosphere conditions using water-cooled copper crucibles. This process will be repeated several times to increase homogeneity. The resulting ingots will finally be crushed to obtain a powder. 

The ball milling synthesis technique, on the other hand, involves mixing the Ti and Fe metal powders and the multi-metal HEA powders, placed in a special jar with a high-energy planetary mill. Ball milling can be performed both in an inert atmosphere and in a hydrogen atmosphere (reactive ball milling). Special attention will be paid to the ball milling parameters that influence the chemical and physical characteristics of the final material, such as rotation speed,time, and ball/powder ratio.

A preliminary study will also be conducted on the possibility of developing a small-scale prototype reactor.

The developed materials will be characterized using different techniques.

1.  XRD will define the lattice parameters of the cruistalline structures as a function of the stoichiometric ratios for optimizing the H2 absorption/release efficiency. 

Furthermore, the changes in the crystallographic structures as a function of temperature can be verified using a climate cell capable of operating in a temperature range between -100°C and 400°C; 

2. Morphological analyses will be performed on the synthesized samples though SEM-EDS, at high magnifications (up to 300,000X) and with high beam potential (up to 30kV). 

Furthermore, a semi-quantitative analysis will be performed through mapping on different areas of the samples and the homogeneity of the metals in the alloy will also be assessed; 

3. The employment of TEM will offfer high resolution of transmission images that will allow to verify the lattice structures and defects present at the atomic level of post-synthesis metal alloys and metal hydrides after H2 absorption testing.

4. Surface area meausirements (BET technique) use N2 as the gas and will allow to verify any differences in surface area, formation, size, and distribution of pores, due to the different preparation methods of the metal alloys.

5. Finally thermal-calorimetric techniques (TG-DSC) will allow to study, over a wide temperature range (from -90°C to 1000°C), any variations in phase transition temperatures as the composition and preparation vary.

The characterisation of the hydrogen absorption and desorption propertiesof different types of materials will be investigated, in order to optimise the synthesis parameters based on the measured performance, both from a thermodynamic point of view (hydrogenation enthalpy and entropy, solid/gas equilibrium pressure as a function of temperature) and from a kinetic point of view (charging and discharging times) using Sievert volumetric equipment. 

This technique will allow kinetics and PCT (Pressure-Composition-Temperature) measurements to be performed over a wide range of T (from ambient to 500 °C) and P (from 10-4 to 200 bar).

Using the same Sievert volumetric equipment, the resistance of the materials produced to exposure to gases containing impurities such as CO2, H2O, O2 or CH4 will be verified, as well as any thermal processes or exposure to pure hydrogen necessary to regenerate the metal alloys. This activity will also allow the materials to be evaluated as purification systems for hydrogen contaminated by impurities. 

In addition, to verify the presence of any impurities and/or contaminants in the metal hydride, the following will be used: 

1. Mass spectrometry, with this technique it is possible to verify the purity of the gases during the desorption processes, especially after the “forced pollution” tests with CO2, H2O, O2 and CH4 on the metal hydride matrix;

2. XPS, through X-ray photoelectron spectroscopy measurements, it will be possible todetect the presence of contaminants at the surface level (from a few tens of nanometres to fractions of a micron, depending on the composition of the material).