The family of cation-deficient Ruddlesden-Popper Ln 2 Ti 2 O 5 S 2 (Ln = Y, Nd, Sm, Gd, Tb, Dy, Ho and Er) compounds exhibit this behaviour with measured optical band gaps in the 1.8-2.2 eV. Sm 2 Ti 2 O 5 S 2 , Gd 2 Ti 2 O 5 S 2 and Tb 2 Ti 2 O 5 S 2 have been identified as promising photocatalysts for water splitting. All three compounds exhibit rates of H 2 and O 2 evolution of about 20 µmol h -1 in the absence of hydrogen or oxygen evolution co-catalysts. Y 2 Ti 2 O 5 S 2 demonstrated simultaneous stoichiometric production of H 2 and O 2 when loaded with Rh/Cr 2 O 3 and IrO 2 as hydrogen and oxygen evolution co-catalysts, respectively, achieving rates of about 2.5 µmol h -1 and 1.25 µmol h -1 , resulting in an apparent quantum yield (AQY) of 2.3% under UV light. Higher evolution rates of were 80 µmol h -1 (H 2 ) and 40 µmol h -1 (O 2 ) achieved when the co-catalysts were loaded and tested as separate half-reactions, so Y 2 Ti 2 O 5 S 2 performs better compared to its lanthanide counterparts. More recently an improved AQY for oxygen evolution of 6.3% for 420 nm light was reported with Co 3 O 4 co-catalyst loading. With an experimental band gap of 1.9 eV, predicted suitable band alignment for water redox and calculated low hole and electron effective masses of 0.5 m e in the in-plane direction, Y 2 Ti 2 O 5 S 2 indeed has all the indicators of a promising earth-abundant photocatalyst. While several computational studies have focused on the properties of the bulk Y 2 Ti 2 O 5 S 2 , this study aims to unveil the surface properties using state-of-the-art computational methodology. In particular, this study explores surface behaviour and energetics during relaxations, and how that relates to the band edge positions of the surfaces. Additionally many-body perturbation theory calculations are performed to calculate bulk optoelectronic properties, including the exciton binding energy, to support our hybrid DFT calculations and explore the optical behaviour of the system.