The effect of temperature on the hydrogenation of sintered Ni by the hydrogen evolution reaction (her) in 0.6 M K2CO3 + H2O electrolyte was investigated in the range 25-95 degrees C. At 25 degrees C, hydrogenation leads to the formation of three different species, provisionally identified as beta-NI-, hexagonal-Ni- and alpha-Ni-hydride phases, based on their respective redox potentials and thermostability. Their penetration into the metal ranged from a few tens to a few hundred monolayers. Above room temperature, the overall efficiency and penetration of Ni hydrogenation increased significantly. Furthermore, there is definite evidence that, at T greater than or equal to 65 degrees C, the beta-Ni-hydride phase evolves into new Ni-hydrogen species of higher thermal stability, regarding which there is no previous knowledge. The results of electrolytic Ni deuteration by electrolysis of K2CO3 + D2O conformed to those obtained in light water.