**6.1 Kinetic models**

The uptake of hydrogen and release of hydrogen in hydrogen storage systems is made of adsorption, penetration through the surface, internal diffusion and chemical reaction [56]. **Figure 5** below show the detailed steps of these processes:

The two possible reaction modes for hydrogenation and dehydrogenation reactions are geometrical contraction and nucleation growth. These reaction routes are supported by theoretical and experimental research [57]. Hydrogen storage

**Figure 5.** *Hydrogenation and dehydrogenation steps (Adapted from [58]).*

kinetic models are thereby segregated according to these reaction routes. These models are founded on isothermal fitting and non-isothermal calculation analysis methods [58]. These methods help determine kinetic parameters and reaction modes this subsequently leads to a better understanding of the kinetic mechanism.
