# The Formation of Metal Hydrides on the Surface of Spherical Structures and the Numerical Evaluation of the Hydrogenation Process

## TL;DR

This study examines how hydrogenation affects titanium and zirconium coatings on aluminum hydroxide granules, revealing structural and chemical changes that could improve hydrogen storage.

## Contribution

The study provides new insights into hydride formation and hydrogen penetration in Ti- and Zr-coated AlO3 granules through experimental and mathematical analysis.

## Key findings

- Hydrogenation caused surface roughening, grain boundary separation, and microcrack formation in Ti- and Zr-coated AlO3 granules.
- Hydride conversion rates were 3.5% for Ti and 1.6% for Zr, with hydrogen penetration depths of 1200 nm and 850 nm, respectively.
- FTIR analysis confirmed the formation of metal–hydride bonds and dihydroxylation after hydrogenation.

## Abstract

Hydrogen possesses distinctive characteristics that position it as a potential energy carrier to substitute fossil fuels. Nonetheless, there is still an essential need to create secure and effective storage solutions prior to its broad application. The use of hydride-forming metals (HFMs) for hydrogen storage is a method that has been researched thoroughly over the past several decades. This study investigates the structural and chemical modifications in titanium (Ti) and zirconium (Zr) thin coatings over aluminum hydroxide (AlO3) granules before and after hydrogenation. The materials were subjected to hydrogenation at 400 °C and 5 atm of hydrogen pressure for 2 h, with a hydrogen flow rate of 0.8 L/min. The SEM analysis revealed significant morphological changes, including surface roughening, a grain boundary separation, and microcrack formations, indicating the formation of metal hydrides. The EDS analysis showed a reduction in Ti and Zr contents post-hydrogenation, likely due to the formation of hydrides. The presence of hydride phases, with shifts in diffraction peaks indicating structural modifications due to hydrogen absorption, is confirmed by the XRD analysis. The FTIR analysis revealed dihydroxylation, with the removal of surface hydroxyl groups and the formation of new metal–hydride bonds, further corroborating the structural changes. The formation of metal hydrides was confirmed by the emergence of new peaks within the 1100–1200 cm−1 range, suggesting the incorporation of hydrogen. Mathematical modeling based on the experimental parameters was conducted to assess the hydride formation and the rate of hydrogen penetration. The hydride conversion rate for Ti- and Zr-coated AlO3 granules was determined to be 3.5% and 1.6%, respectively. While, the hydrogen penetration depth for Ti- and Zr-coated AlO3 granules over a time of 2 h was found to be 1200 nm and 850 nm approximately. The findings had a good agreement with the experimental results. These results highlight the impact of hydrogenation on the microstructure and chemical composition of Ti- and Zr-coated AlO3, shedding light on potential applications in hydrogen storage and related fields.