Layered materials such as BP and TMDCs are reported to be highly sensitive to environmental gases (O2 and H2O in particular), and degradation becomes more rapid for thinner samples. However, the mechanism of their degradation remains an active subject of study, and numbers of distinct mechanisms have been proposed. For instance, some have attributed the degradation of BP to its hydrophilic surface; others have identified a low barrier to oxygen dissociation and dangling edge O atoms as the primary drivers of degradation. Furthermore, evidence for a photo-assisted oxidation mechanism has been reported. While layered TMDCs such as MoS2 have been suggested to be air-stable in their pristine form, in practice, degradation upon exposure to H2O and O2 is welldocumented. It has been suggested this reactivity can be attributed to edge defects, grain boundaries and surface vacancies. Rapid degradation has also been observed in Secontaining TMDCs such as TiSe2, TaSe2, and NbSe2. We have shown herein that, akin to BP and TMDCs, ZnSe-based II-VI LHs exhibit chemical sensitivity toward humid air. We showed previously that the degradation of these materials leads to the formation of Se and ZnO. Limiting the presence of water mitigates this degradation (vide supra). Hence, water plays an important role in the degradation process. However, the role of water remains unclear, as the source of oxygen in the ZnO degradation product could either come from atmospheric O2, similar to the reported degradation route of BP, both H2O and O2, a route potentially similar to that of the corrosion of metals such as Fe, or from the oxygen in H2O alone. Exposure of ZnSe(ba) to a O2-free, 50% RH environment led to the minor changes in both white light reflectance and CA comparable to those observed for ZnSe(ba) incubated in a dry environment (Figure However, little mechanistic insight is provided by these experiments alone.