H2 Desorption from MgH2 Surfaces with Steps and Catalyst-Dopants

Date
2014-03-20
Authors
Reich, J.
Wang, Lin-Lin
Johnson, Duane
Johnson, Duane
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Authors
Research Projects
Organizational Units
Ames Laboratory
Organizational Unit
Journal Issue
Series
Department
Ames Laboratory
Abstract

Light-metal hydrides, like MgH2, remain under scrutiny as prototypes for reversible H-storage materials. For MgH2, we assess hydrogen desorption/adsorption properties (enthalpy and kinetic barriers) for stepped, catalyst-doped surfaces occurring, e.g., from ball-milling in real samples. Employing density functional theory and simulated annealing in a slab model, we studied initial H2 desorption from stepped surfaces with(out) titanium (Ti) catalytic dopant. Extensive simulated annealing studies were performed to find the dopant’s site preferences. For the most stable initial and final (possibly magnetic) states, nudged elastic band (NEB) calculations were performed to determine the H2-desorption activation energy. We used a moment-transition NEB method to account for the dopant’s transition to the lowest-energy magnetic state at each image along the band. We identify a dopant-related surface-desorption mechanism that reloads via bulk H diffusion. While reproducing the observed bulk enthalpy of desorption, we find a decrease of 0.24 eV (a 14% reduction) in the activation energy on doped stepped surface; together with a 22% reduction on a doped flat surface, this brackets the assessed 18% reduction in kinetic barrier for ball-milled MgH2 samples with low concentration of Ti from experiment.

Comments

Reprinted with permission from J. Phys. Chem. C. 2014. 118(13), pp. 6641–6649, doi:10.1021/jp412826u. Copyright 2014 American Chemical Society.

Description
Keywords
Citation
DOI
Collections