The high-quality Mg-2(Ni1-xCux) (x = 0, 0.05, 0.1 and 0.15) compounds have been successfully prepared by the method combining solid solution with sintering process in this paper. These prepared Mg-2(Ni1-xCux) compounds can exhibit a reversible hydrogen ab-/desorption process, which are strongly subject to the content of Cu, i.e., depending on x. When x0.1. For instance, the Mg-2(Ni0.85Cu0.15) compound absorbs hydrogen to form Mg-2(Ni0.9Cu0.1)H-4, Mg2Ni and MgCu2. Moreover, based on the structural analysis, the maximum solid solubility of Cu in Mg-2(Ni1-xCux) H-4 is determined for the first time to be about x = 0.1. The solid solubility of Cu thus leads to a significant decrease in Delta H-d value from 64.4 kJ mol(-1) H-2 for Mg2NiH4 to 59.8 kJ mol(-1) H-2 for Mg2Ni0.9Cu0.1H4. This result provides an efficient route for destabilizing the hydrogen desorption of Mg2Ni-based materials. (C) 2017 Elsevier B.V. All rights reserved.