TY - JOUR
T1 - Equilibrium hydrogen pressures in the V–H system from first principles
AU - Otani, Noriko
AU - Kuwabara, Akihide
AU - Ogawa, Takafumi
AU - Fisher, Craig A.J.
AU - Tanaka, Isao
AU - Akiba, Etsuo
N1 - Funding Information:
This work was partially supported by the Research and Development of Technology for Hydrogen Utilization project of the New Energy and Industrial Technology Development Organization (NEDO), Japan, and partially by the Materials Research by Information Integration Initiative (MI2I) project of the Japan Science and Technology Agency (JST).
Funding Information:
This work was partially supported by the Research and Development of Technology for Hydrogen Utilization project of the New Energy and Industrial Technology Development Organization (NEDO) , Japan, and partially by the Materials Research by Information Integration Initiative (MI 2 I) project of the Japan Science and Technology Agency (JST) .
Publisher Copyright:
© 2019 Hydrogen Energy Publications LLC
PY - 2019/11/5
Y1 - 2019/11/5
N2 - Equilibrium hydrogen pressures over hydrogenated vanadium, i.e., crystalline VHx with 0≤x≤2, are estimated based on first-principles calculations to assess the suitability of V-based alloys for use as hydrogen storage materials. For intermediate H contents (x = 0.5 and 1) corresponding to partial site occupancies, a multistep process was used to determine the ground-state structures. First, a large number of configurations with H on tetrahedral (T) or octahedral (O) sites in bcc–type lattices were ranked in terms of energetical stability sans vibrational contributions. Next, phonon calculations were carried out for the lowest-energy structures identified in the first step and zero-point energies added to the electronic energies. Hydrogen pressures for V-VH0.5 and VH-VH2 equilibria were then calculated using these ground-state free energies and thermodynamic equations. Calculation of vibrational energies was simplified by identifying the linear relationship between H content and zero-point energy, which depends only on the type of sites occupied by H atoms. Whereas H atoms preferentially occupy T sites when vibrational terms are ignored, their inclusion leads to H atoms preferentially occupying O sites in both VH0.5 and VH at 0 K. Inclusion of vibrational energy also leads to a better match with reported experimental hydrogen pressures highlighting its importance when assessing the stabilities of different H distributions in metal lattices. The method outlined consists of a more exhaustive configurational search than has been considered previously, and should be useful for systematic investigation of a wide variety of V-based alloys.
AB - Equilibrium hydrogen pressures over hydrogenated vanadium, i.e., crystalline VHx with 0≤x≤2, are estimated based on first-principles calculations to assess the suitability of V-based alloys for use as hydrogen storage materials. For intermediate H contents (x = 0.5 and 1) corresponding to partial site occupancies, a multistep process was used to determine the ground-state structures. First, a large number of configurations with H on tetrahedral (T) or octahedral (O) sites in bcc–type lattices were ranked in terms of energetical stability sans vibrational contributions. Next, phonon calculations were carried out for the lowest-energy structures identified in the first step and zero-point energies added to the electronic energies. Hydrogen pressures for V-VH0.5 and VH-VH2 equilibria were then calculated using these ground-state free energies and thermodynamic equations. Calculation of vibrational energies was simplified by identifying the linear relationship between H content and zero-point energy, which depends only on the type of sites occupied by H atoms. Whereas H atoms preferentially occupy T sites when vibrational terms are ignored, their inclusion leads to H atoms preferentially occupying O sites in both VH0.5 and VH at 0 K. Inclusion of vibrational energy also leads to a better match with reported experimental hydrogen pressures highlighting its importance when assessing the stabilities of different H distributions in metal lattices. The method outlined consists of a more exhaustive configurational search than has been considered previously, and should be useful for systematic investigation of a wide variety of V-based alloys.
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U2 - 10.1016/j.ijhydene.2019.09.010
DO - 10.1016/j.ijhydene.2019.09.010
M3 - Article
AN - SCOPUS:85073014621
VL - 44
SP - 28909
EP - 28918
JO - International Journal of Hydrogen Energy
JF - International Journal of Hydrogen Energy
SN - 0360-3199
IS - 54
ER -