Driving force of metal hydrogenation(H2 storage alloy)

[nakamura25]

Hi there~
I have some questions about hydrogen storage alloys. (TiFe, ZrV2, LaNi5, Mg2Ni, etc.)

As far as I know, the hydrogen sorption precesses are as following:
Hydrogen molecules "physically" absorbed on the surface of alloy which is called alpha-phase.
Hydrogen molecules become hydrogen atoms.
Hydrogen atoms diffuse into crystal lattice of alloy which is called beta-phase.

And the desorption processes are just the opposite.

My questions are:
What is the driving force for the hydrogen molecules to split into hydrogen atoms?
Also, what is the driving force that makes hydrogen atoms diffuse into crystal lattice of alloy.
For thedesorption processes:
What makes hydrogen atoms diffuse to the surface of alloy?
And what makes the hydrogen atoms become hydrogen molecules?

These questions have troubled me for a long time.
Thank you in advance for your kindly responses!

 

[Navin A S]

The driving force for the hydrogen molecules to split into hydrogen atoms is the chemical potential of hydrogen which is determined by the binding energy of the alloy. The hydrogen molecules must overcome this energy barrier to become hydrogen atoms. The driving force that makes hydrogen atoms diffuse into crystal lattice of alloy is the energetic difference between the lattice and the surface of the alloy. The hydrogen atoms prefer to be in the lower energy state of the lattice, so they will move there. For the desorption processes, what makes hydrogen atoms diffuse to the surface of alloy is the same energetic difference, but this time the surface has a lower energy state than the lattice. This causes the hydrogen atoms to move to the surface. The hydrogen atoms then become hydrogen molecules due to the kinetic energy of the atoms combined with the attractive force of the hydrogen molecules.

 

[oswaler]

Hello there,

The driving force for the hydrogen molecules to split into hydrogen atoms is the energy released during the reaction. This energy is typically provided by heat or a catalyst. Once the hydrogen atoms are formed, they are able to diffuse into the crystal lattice of the alloy due to the attractive forces between the hydrogen atoms and the metal atoms in the alloy. This can also be influenced by factors such as temperature, pressure, and the alloy's structure and composition.

For the desorption processes, the driving force for the hydrogen atoms to diffuse to the surface of the alloy is the concentration gradient between the inside and outside of the alloy. This means that the hydrogen atoms will naturally move from areas of higher concentration (inside the alloy) to areas of lower concentration (outside the alloy). As for the hydrogen atoms becoming hydrogen molecules, this is due to the recombination of the atoms, which releases energy in the form of heat or light.

I hope this helps to clarify your questions. Hydrogen storage alloys are complex systems and there is still ongoing research to fully understand their mechanisms. Thank you for your interest in this topic.