To understand the role of produced by-product on the reaction kinetics of GdTe in water, Thermodynamics calculations were performed at 25℃ by varying the mole fraction of reacting reagents (Figure ). Both the production of H2 and Gd2O3 increase with increase in mole fraction of GdTe that reacts with 1 mole of H2O. However, their production saturates at around 0.66 mole fraction of GdTe where the amount of Gd2Te3 starts increasing. Further, for all increasing mole fraction of H2O that reacts with 1 mole of GdTe, production of both H2 and Gd2O3 increases. However, the GdTe is fully consumed at around 0.5 mole fraction H2O and the amount of Te starts increasing. This indicates that the formation of Gd2O3 helps in formation of . This causes Gd to atoms to react with water and form Gd2O3. However, 3-coordinated Te atom in (111) surface is more reactive than 6-coordinated Gd atom and hence, forms respective oxide. Further, the reaction of Gd in water shows less activity (0.0011 μmol min -1 gm -1 ) for HER in comparison with GdTe (Figure ). As, d-band centre of Gd atom is at -0.35 eV for Gd (100) surface, which is less appropriate than the Gd atom on (100) surface of GdTe for the adsorption of hydrogen.