Dehydrogenation Reaction for NaOH System: A First‐Principles Study

Abstract

The crystal structures, electronic, dielectric, and vibrational properties of NaH, Na(2)O and NaOH are systematically investigated by first-principles calculations and the quasiharmonic approximation. The phonon dispersion relations and the phonon density of states of the phases and their thermodynamic functions including the heat capacity, the vibrational enthalpy, and the vibrational entropy are calculated using a direct force-constant method. Based on these results, the dehydrogenation reaction, NaH+NaOH-->H(2)+Na(2)O, is predicted to take place at 528 K, which is in agreement with the experimental observed value.

Manganese Borohydride As a Hydrogen-Storage Candidate: First-Principles Crystal Structure and Thermodynamic Properties

“…The vibrations cannot be treated directly from the phonon calculations for H 2 gas molecule because the phonon approach always considers the system as a crystal solid and thus neglects the translational and rotational modes. The Gibbs energy was calculated by combining both computational and experimental results using eq : G T ( H 2 ) = E e l ( H 2 ) + E Z P E ( H 2 ) + p V + Δ G T ( H 2 ) where, E el (H 2 ) is the electronic binding energy of a H 2 molecule obtained from constant velocity MD simulation using VASP Δ G T (H 2 ) can be calculated using eq .…”

“…The vibrations cannot be treated directly from the phonon calculations for H 2 gas molecule because the phonon approach always considers the system as a crystal solid and thus neglects the translational and rotational modes. The Gibbs energy was calculated by combining both computational and experimental results using eq 7: 44 where, E el (H 2 ) is the electronic binding energy of a H 2 molecule obtained from constant velocity MD simulation using VASP. 10 E ZPE (H 2 ) is the zero-point energy of a H 2 molecule, p and V are the pressure (1 atm) and the molar volume (of the H 2 ideal gas), respectively, and the last term ∆G T (H 2 ) is the temperature-dependent Gibbs energy with respect to the temperature of 0 K. As a common procedure, 45 ∆G T (H 2 ) can be calculated using eq 8.…”