Positive Activation Effect: V Promotes the Formation of the Ti ₄ Fe ₂ O Phase and Cracks on the Surface of TiFe-Based Alloys

This research investigates the hydrogen storage properties and microstructural characteristics of Ti–Fe–Mn–V alloys for industrial applications, with a focus on understanding their activation mechanisms. The incorporation of V enhances the activation potential of the alloys, lowering the minimum activation temperature from 673 to 523 K. This modification also reduces the plateau pressure in the PCT curves, which improves the hydrogen absorption and desorption kinetics. However, this benefit comes with a decrease in hydrogen storage capacity, representing a trade-off. A specific oxide, Ti 4 Fe 2 O, is identified on the surface of V-containing alloys. Although this oxide phase is relatively unstable, it adsorbs hydrogen, facilitating exposure of the underlying TiFe matrix and enabling activation at lower temperatures. The addition of V also increases the alloys’ susceptibility to cracking and promotes more significant particle refinement. These cracks provide additional pathways for hydrogen absorption, while the reduced particle size shortens the diffusion length, both contributing to enhanced kinetics. The combined effects of altered surface chemistry and microstructural changes due to V incorporation result in improved activation and kinetic properties.