Numerical modeling of hydrogen/deuterium absorption in transition-metal alloys Olga Dmitriyeva, Rick Cantwell, Matt McConnell Coolescence LLC Boulder, Colorado, U.S.A. 1
QuantumEspresso Electronic structure calculations and material modeling based on density functional theory (DFT): http://quantum-espresso.org APPLICATIONS: condensed matter physics, chemistry / pharmatheutical 2
Nuclear active environment (NAE) 1. igh : loading ratio 2. Presence of dopants or impurities 3. Structural morphology: (voids, cracks, dislocations, surface morphology) 3
Figures of merit Figures of merit to explore the variations in physical properties: ydrogen adsorption energy ydrogen-ydrogen separation 4
Nuclear active environment (NAE) 1. igh : loading ratio Figure of merit: adsorption energy 2. Presence of dopants or impurities 3. Structural morphology: (voids, cracks, dislocations, surface morphology) Figure of merit: - separation Figure of merit: adsorption energy 5
Adsorption energy (100) surface modeled as slab: 6
Adsorption energy (100) surface modeled as slab: 7
Adsorption energy (100) surface modeled as slab: 8
Results: loading ratio Loading of palladium with hydrogen reduces adsorption energy* * Similar results reported by M. Johansson et al ydrogen adsorption on palladium and palladium hydride at 1 bar, Surf. Science 604 (2010) 718-729 As a result: mobile atomic hydrogen weakly binded to the surface and available for reaction 9
Results: loading ratio Loading of palladium with hydrogen reduces adsorption energy* * Similar results reported by M. Johansson et al ydrogen adsorption on palladium and palladium hydride at 1 bar, Surf. Science 604 (2010) 718-729 As a result: mobile atomic hydrogen weakly binded to the surface and available for reaction there is another way to lower adsorption energy 10
Nuclear active environment (NAE) 1. igh : loading ratio Figure of merit: adsorption energy 2. Presence of dopants or impurities 3. Structural morphology: (voids, cracks, dislocations, surface morphology) Figure of merit: - separation Figure of merit: adsorption energy 11
Presence of dopants (near-surface alloys - NSA) side view top view X/Y: X-solute, Y-host (Rh/) Near surface solute concentration is different from bulk 2 dissociation energy remains low Adsorption energy is reduced ost () Result: mobile atomic Solute (Rh) hydrogen weakly binded to the surface and available for reaction. J.Greeley M.Mavrikakis, Alloy catalyst designed from first principles, Nature Mat. Vol3,(2004) pp.810-812 12
Near-surface alloys V Mo Fe (111) J.Greeley M.Mavrikakis, Alloy catalyst designed from first principles, Nature Mat. Vol3,(2004) pp.810-812 13
Near-surface alloys V Mo Fe (111) Fe/ Mo/ V/ J.Greeley M.Mavrikakis, Alloy catalyst designed from first principles, Nature Mat. Vol3,(2004) pp.810-812 14
Near-surface alloys V Mo Fe (111) Fe/ Mo/ V/ / Li/ B/ O/ F/ C/ Se/ As/ Cl/ 15
Results: presence of dopants Substitutional or interstitial sublayer doping reduces hydrogen adsorption energy. If reaching high hydrogen loading ratios is impossible, sublayer doping can be used to reduce adsorption energy to allow hydrogen to move more freely along the surface 16
Nuclear active environment (NAE) 1. igh : loading ratio Figure of merit: adsorption energy 2. Presence of dopants or impurities 3. Structural morphology: (voids, cracks, dislocations, surface morphology) Figure of merit: - separation Figure of merit: adsorption energy 17
Structural morphology: monovacancy in bulk (P. agelstein, 2012) fcc is replaced with comes from octahedral site to form 2 molecule Change 2 position and - separation within the cell to find minimum of total energy - separation close to 1 Angstrom monovacancy 18
Monovacancy in subsurface layer fcc (100) plane is missing in sublayer 2 molecule comes into octahedral site from above and progresses towards the monovacancy 2 separation is 0.72 A Case I monovacancy 19
Monovacancy in subsurface layer surface surface surface mono vacancy mono vacancy F mono vacancy F Case I Case I Case II Case I Case III Case I 20
Monovacancy in subsurface layer case I pure 2 separation (angstrom) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 Octahedral site on the surface - in vacuum -unloaded Monovacancy 0 0.5 1 1.5 2 2.5 Distance from the surface (Angstrom) 21
Monovacancy in subsurface layer case II 2 1.8 -unloaded 2 separation (angstrom) 1.6 1.4 1.2 1 0.8 0.6 Octahedral site on the surface - in vacuum Monovacancy 0 0.5 1 1.5 2 2.5 Distance from the surface (Angstrom) 22
Monovacancy in subsurface layer case III F/ 2 separation (angstrom) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 Octahedral site on the surface - in vacuum 2F sublayer -unloaded Monovacancy 0 0.5 1 1.5 2 2.5 Distance from the surface (Angstrom) 23
Effect of electronegativity 1.1 4.5 1.05 4 - separation (angstrom) 1 0.95 0.9 0.85 0.8 0.75 - in vacuum 3.5 3 2.5 2 1.5 1 0.5 Electronegativity 0.7 F O Cl C Se Rh As Li B 0 - separation (bulk) - separation (near surface) Electronegativity 24
Results: surface morphology - separation can be decreased by high : loading or by doping the sublayer - separation at monovacancy depends on electronegativity of doping elements and can reach 0.72 Angstrom 25
Conclusions QantumEspresso allows quick scan of potential NAE in transition-metal alloys ydrogen loading is confirmed to reduce adsorption energy in the same way as near-surface alloys. igh : ratio or NSA Low adsorption energy is mobile igh probability of reaction - separation can be decreased by introducing: defects chemical dopants (electronegativity effect) 26