Revisiting the Chemical Stability of Germanium Selenide (GeSe) and the Origin of its Photocatalytic Efficiency

Recently, germanium selenide (GeSe) has emerged as a promising van der Waals semiconductor for photovoltaics, solar light harvesting, and water photoelectrolysis cells. Contrary to previous reports claiming perfect ambient stability based on experiments with techniques without surface sensitivity, here, by means of surface-science investigations density functional theory, it is demonstrated that actually both: i) the bulk crystals; ii) atomically thin flakes GeSe are prone oxidation, formation self-assembled germanium-oxide skin sub-nanometric thickness. Surface oxidation leads decrease bandgap stoichiometric GeSe1?x, while energy increases upon Ge1?xSe. Remarkably, oxide crystals plays key role in physicochemical mechanisms ruling photoelectrocatalysis: underlying provides electron–hole pairs, formed affords active sites catalytic reactions. The germanium-oxide/germanium-selenide heterostructure different bandgaps enables activation photocatalytic processes absorption wavelengths, inherently superior activity. Finally, discovered that, depending specific solvent-GeSe interaction, liquid phase exfoliation can induce Se nanowires.