Influence of MoO₃ (110) Crystalline Plane on Its Self-Charging Photoelectrochemical Properties

Nanocrystalline molybdenum oxide (α-MoO₃) thin films with iso-oriented crystalline layers were synthesised by the anodisation of Mo foils. Upon band-gap excitation using light illumination, α-MoO₃ generates excited electrons for reductive reactions and stores some of the excited electrons in its layered crystalline structure via alkali cation intercalation. These stored electrons can be subsequently discharged from α-MoO₃ to allow reductive reactions to continue to occur under non-illuminated conditions. The modulation of water concentrations in the organic/aqueous anodisation electrolytes readily produces α-MoO₃ crystals with high degree of (kk0) crystallographic orientation. Moreover, these (kk0)-oriented MoO₃ crystals exhibit well-developed {hk0} and {0k0} crystal facets. In this paper, we show the benefits of producing α-MoO₃ thin films with defined crystal facets and an iso-oriented layered structure for in situ storing of excited charges. α-MoO₃ crystals with dominant (kk0) planes can achieve fast charging and a strong balance between charge release for immediate exploitation under illuminated conditions and charge storage for subsequent utilisation in dark. In comparison, α-MoO₃ crystals with dominant (0k0) planes show a preference for excited charge storage.