Study on hydrogen storage properties of Mg-X (X = Fe, Co, V) nano-composites co-precipitated from solution

A systematic investigation has been performed on the hydrogen sorption properties of the Mg-X (X = Fe, Co, V) nano-composites co-precipitated from solution through an adapted Rieke method. It is found that the co-precipitated Fe, V or Co has high catalytic efficiency in enhancing the hydrogen sorption kinetics of nano-sized Mg. The Mg-V nano-composite shows faster hydrogen absorption kinetics than the Mg-Fe and Mg-Co nano-composites at lower temperatures. For instance, the hydrogen capacity within 2 h at 50 degrees C is 4.4 wt% for the Mg-V nano-composite, while for the Mg-Fe nano-composite it is 2.6 wt% and for the Mg-Co nano-composite it is 3.9 wt%. However, the hydrogenated Mg-Fe and Mg-Co nanocomposites display significantly lower hydrogen desorption temperatures compared with the hydrogenated Mg-V nano-composite. The hydrogen desorption activation energies of the hydrogenated Mg-Fe and Mg-Co nano-composites are 118.1 and 110.1 kJ mol(-1) H-2, much lower than that of the Mg-V nano-composite (147.7 kJ mol(-1) H-2). High catalytic effectiveness of the co-precipitated Fe, Co or V depends not only on its intrinsic activity, but also on its distribution state, which may be entirely different from previous composites prepared through physical routes.