Homogenously dispersed, ultrafine Ni nanoparticles (Ni NPs) have been grown in a mesoporous carbon (MC) matrix (MC-Ni-insitu) and efficiently catalyze low-temperature, hydrogen desorption from Mg(BH4)(2). The onset desorption temperature (T-onset) of this MC-Ni-insitu-Mg(BH4)(2) system is 44 degrees C compared to 275 degrees C (T-onset) for pure Mg(BH4)(2). This is the lowest value reported for hydrogen desorption from this metal hydride. The activation energy (En) of MC-Ni-insitu-Mg(BH4)(2) was determined to be 21.3 kJ/mol which is less than half the value of 45.9 kJ/mol for pure Mg(BH4)(2). We ascribe this reduction to the synergistic effects of nanoconfinement and the homogeneously dispersed, ultrafine Ni NPs active sites in the mesoporous carbon. Crown Copyright (C) 2016 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved.