Energy and diffusion of hydrogen atoms in titanium substituted vanadium hydrides from ab initio calculations

• Ti substitution expands any crystal structure of vanadium metal or hydride.
• H atoms are repulsed by Ti atoms despite their high electrochemical affinity.
• Strong electrochemical bonding between Ti and H lowers the formation energy.
• Ti substitution reduces hydrogen diffusion by over 90% at room temperature.

The equilibrium lattice parameters, formation energy, and diffusion behavior of hydrogen atoms in vanadium hydrides with and without Ti substitution were calculated by ab initio calculations and quantum correction by zero point energy was achieved using phonon vibration calculations. The calculated formation energies indicated that Ti substitution induces instability in the vanadium hydrides and electron density calculations showed that hydrogen has strong electrochemical affinity with Ti. The diffusion behavior was examined by the nudged elastic band (NEB) method to investigate the transition states of the hydrides. It revealed that Ti substitution is shown to reduce the diffusion coefficient and this effect was decreased with increasing temperature. The results of this study are expected to provide useful guidelines for understanding hydrogen absorption and desorption properties of hydrogen storage materials.