MoS2 crystals exhibit excellent catalytic properties and great potential for photocatalytic production of solar fuels such as hydrogen gas. In this regard, the photocatalytic stability of exfoliated single- and few-layer MoS2 immersed in water is investigated by μ-Raman spectroscopy. We find that while the basal plane of MoS2 can be treated as stable under photocatalytic conditions, the edge sites and presumably also defect sites are highly affected by a photoinduced corrosion process. The edge sites of MoS2 monolayers are significantly more resistant to photocatalytic degradation compared to MoS2 multilayer edge sites. The photostability of MoS2 edge sites depends on the photon energy with respect to the band gap in MoS2 and also on the presence of oxygen in the electrolyte. These findings are interpreted in the framework of an oxidation process converting MoS2 into MoOx in the presence of oxygen and photoinduced charge carriers. The high stability of the MoS2 basal plane under photocatalytic treatment under visible light irradiation of extreme light intensities on the order of P ≈ 10 mW/μm(2) substantiates MoS2's potential as photocatalyst for solar hydrogen production.
Keywords: MoS2; Raman spectroscopy; photocatalytic selectivity; photocatalytic stability; solar water splitting; two-dimensional materials.