Ab Initio Investigation of Water Adsorption and Hydrogen Evolution on Co9S8 and Co3S4 Low-Index Surfaces

We used density functional theory approach, with the inclusion of a semiempirical dispersion potential to take into account van der Waals interactions, to investigate the water adsorption and dissociation on cobalt sulfide Co 9 S 8 and Co 3 S 4 (100) surfaces. We first determined the nanocrystal shape and selected representative surfaces to analyze. We then calculated water adsorption and dissociation energies, as well as hydrogen and oxygen adsorption energies, and we found that sulfur vacancies on Co 9 S 8 (100) surface enhance the catalytic activity toward water dissociation by raising the energy level of unhybridized Co 3d states closer to the Fermi level. Sulfur vacancies, however, do not have a significant impact on the energetics of Co 3 S 4 (100) surface.