Band alignments of the Y 2 Ti 2 O 5 S 2 surfaces that appeared on the Wulff shape were calculated using the core level alignment approach. The O eq with two Ti and two Y atoms as nearest neighbours was chosen as the reference 'core level' atom to relate and compare the bulk and slab energies. Surfaxe was used to ensure the core level energy came from the O eq closest to the mid-point of the slab. A more detailed description of calculation of the method used can be found in our previous work. The surface band alignments are shown in Figure Plotted with bapt. Similar variation in band offsets between different facts was observed in many other systems. The calculated ionisation potentials between different facets of SnS varied by as much as 0.9 eV from the lowest-energy (100) facet. In In 2 O 3 , a valence band offset of 0.7 eV was observed both experimentally from x-ray photoelectron spectroscopy (XPS) and computationally from hybrid-DFT for the non-polar (111) and polar (100) surfaces. The same computational study also showed a 0.5 eV offset between the non-polar ( ) and ( ) facets. The fluctuations were also seen in quinary La 5 Ti 2 MS 5 O 7 (M = Ag, Cu) where the conduction bands of the (100), ( ) and (1 12) facets were offset from the other facets' conduction band edges by almost 2 eV. Combining the band edge positions with Wulff construction, it can be seen that the facets that favour each of the half-reactions are almost equally split. The spatial separation of the hydrogen and oxygen evolution facets has been observed experimentally. The efficiency of water splitting could be potentially improved if the deposition of reduction and oxidation co-catalysts was separated between the basal (001) facets and the side (101) and ( ) facets. Of course, as with the surface energies, the ionisation potentials and electron affinities are calculated under the assumption that the surfaces form an interface with vacuum. The presence of a surface/water interface in a real aqueous solution will alter the position of band edges, reflecting the intrinsic nature of the semiconductor. An upward shift of the bands due to the electron transfer between water and the material is expected for natively n-type semiconductors. Based on experimental data and the bulk band alignment favouring n-type behaviour based on doping rules, Y 2 Ti 2 O 5 S 2 is expected to be intrinsically n-type, so an upward shift of band edges may be expected.