Various properties of Pd3Ag/TiAl membranes from density functional theory

Understanding of transition metal (Ru, W) doping into Nb for improved thermodynamic stability and hydrogen permeability: density functional theory calculations

Hydrogen solubility and diffusivity are the key features of hydrogen permeable membrane materials. To characterize the hydrogen permeation performance of NbTM (TM = W, Ru) phases, their hydrogen diffusion coefficient and solution coefficient, thermodynamic stability and chemical bonding are studied by a series of first principles calculations. The phonon spectra and elastic constants show that NbTM is dynamically stable. The TM-H chemical bonds have an ionic/covalent mixed character and are stronger than the Nb-H bond. The preferential diffusion paths of H in both Nb₁₆H and Nb₁₅TMH are from a tetrahedral interstitial site (TIS) to another TIS. The TM doping in Nb₁₆H lowers the solubility and energy barrier of H diffusion and enhances the H diffusion coefficient (D), with Nb₁₆RuH exhibiting the highest D value for TIS to TIS diffusion (2.14 × 10^-8 m² s^-1) at 600 K. This study shows that alloying and temperature could significantly affect the solubility and diffusivity of hydrogen in Nb. Moreover, TM doping could greatly improve the hydrogen diffusion performance with good control of hydrogen embrittlement.

Effects of Mo alloying on stability and diffusion of hydrogen in the Nb16H phase: a first-principles investigation

First-principles calculations and climbing-image nudged elastic band method were used to investigate the effects of Mo alloying on the structural stability, mechanical properties, and hydrogen-diffusion behavior of Nb.

First-Principles Investigation of Atomic Hydrogen Adsorption and Diffusion on/into Mo-doped Nb (100) Surface

To investigate Mo doping effects on the hydrogen permeation performance of Nb membranes, we study the most likely process of atomic hydrogen adsorption and diffusion on/into Mo-doped Nb (100) surface/subsurface (in the Nb12Mo4 case) via first-principles calculations. Our results reveal that the (100) surface is the most stable Mo-doped Nb surface with the smallest surface energy (2.75 J/m2). Hollow sites (HSs) in the Mo-doped Nb (100) surface are H-adsorption-favorable mainly due to their large adsorption energy (−4.27 eV), and the H-diffusion path should preferentially be HS→TIS (tetrahedral interstitial site) over HS→OIS (octahedral interstitial site) because of the correspondingly lower H-diffusion energy barrier. With respect to a pure Nb (100) surface, the Mo-doped Nb (100) surface has a smaller energy barrier along the HS→TIS pathway (0.31 eV).

Effects of Ni doping on various properties of NbH phases: A first-principles investigation

Changes in the stability, hydrogen diffusion, and mechanical properties of the NbH phases from Ni-doping was studied by using first-principles methods. The calculation results reveal that the single H atom adsorption is energetically favorable at the tetrahedral interstitial site (TIS) and octahedral interstitial site (OIS). The preferred path of H diffusion is TIS-to-TIS, followed by TIS-to-OIS in both Nb₁₆H and Nb₁₅NiH. Ni-doping in the Nb₁₅NiH alloy lowers the energy barrier of H diffusion, enhances the H-diffusion coefficient (D) and mechanical properties of the Nb₁₆H phase. The value of D increases with increasing temperature, and this trend due to Ni doping clearly becomes weaker at higher temperatures. At the typical operating temperature of 400 K, the D value of Nb₁₅NiH (TIS) is about 1.90 × 10⁻⁸ m²/s, which is about 80 times higher than that of Nb₁₆H (TIS) (2.15 × 10⁻¹⁰ m²/s). Our calculations indicated that Ni-doping can greatly improve the diffusion of H in Nb.