Influencing mechanism of carbon monoxide on the hydrogen absorption performance of Zr2Fe

Unraveling CO adsorption behaviors and its poisoning effects on ZrCo surface

“…4(b), where the pressure of CO gas is fixed under ultrahigh vacuum conditions (5 × 10 −11 mbar). 44,63 It can be seen that the Gibbs free energy Δ G increases as the temperature increases, and there are cross points among those lines shown in Fig. 4(b), indicating that the equilibrium of CO coverage changes and the corresponding temperatures present the CO desorption temperatures.…”

“…E DFT CO is the DFT calculated energy and CO ( T ,p 0 ) is the chemical potential of the CO molecule at different temperatures T as in thermodynamic tables. 62 Since there are vast mass differences between solid atoms and adsorbed molecules, the effect of vibrational energy to the surface has been found to be negligible, 44,63,64 where the Gibbs free energies of the solid surfaces can be approximately replaced by DFT calculated energies. Therefore, the Gibbs free energy Δ G ZrCo ( T , p , n CO ) can be rewritten as follows:Δ G ZrCo ( T , p , n CO ) = E n CO /ZrCo − E ZrCo − n CO E DFT CO − n CO CO ( T ,p 0 ) − n CO k B T ln( p CO /p 0 ).In this formula, the n CO adsorbates on the surface with a lower Δ G ZrCo ( T , p , n CO ) value are more stable under the given conditions, providing information about the CO equilibrium coverage on the ZrCo surface under different conditions.…”

“…E DFT CO is the DFT calculated energy and mCO (T,p 0 ) is the chemical potential of the CO molecule at different temperatures T as in thermodynamic tables. 62 Since there are vast mass differences between solid atoms and adsorbed molecules, the effect of vibrational energy to the surface has been found to be negligible, 44,63,64 where the Gibbs free energies of the solid surfaces can be approximately replaced by DFT calculated energies. Therefore, the Gibbs free energy DG ZrCo (T, p, n CO ) can be rewritten as follows:…”

“…12 For designing high functional metal hydrides with impurity tolerance, the poisoning factors, such as the constituent elements, the intrinsic properties of material surface, and nature of bonding interaction, should be elucidated. [42][43][44] Among the gaseous impurities, CO is one of the most drastic deactivators of hydrogen storage alloys and its concentration in the hydrogen isotopes needs to be strictly controlled in SDS. 23,45,46 However, to the best of our knowledge, few theoretical studies have focused on the interaction of CO with the ZrCo surface, in sharp contrast to those of transition-metal surfaces in the heterogeneous catalysis context.…”