Structure, thermodynamic stability, and elec-tronic properties of CaH2 surfaces in (001),(110), and (111) crystallographic orientations are investigated using ab initio modeling. We show that stoichiometric surfaces terminated with a hydrogen atomic plane are the most en-ergetically favorable and discuss properties of hydrogen vacancies (VH) at these surfaces. The average calculated work function of the most stable pristine surfaces (~5.2 eV) is in agree-ment with experimental data for powder sam-ples. Neutral hydrogen vacancies host localized electrons and induce defect states in the band gap, thereby shifting the e?ective work func-tion to much lower values of ~2.7 eV. Surface VH are predicted to aggregate into dimers and form electron-rich centers (e-)Ca2+(e-) sta-ble to over 800 K. These results suggest that hydrogen-deficient surfaces of CaH2 can host a large concentration of localized electrons and, thus, give rise to new catalytic functionalities involving electron transfer between the surface, catalysts supported on it, and reacting species.
Revised: October 8, 2020 |
Published: February 27, 2017
Citation
Ong P., L. Johnson, H. Hosono, and P.V. Sushko. 2017.Structure and stability of CaH2 surfaces: on the possibility of electron-rich surfaces in metal hydrides for catalysis.Journal of Materials Chemistry A 5, no. 11:5550-5558.PNNL-SA-121592.doi:10.1039/C6TA09561E