Enhanced hydrogen absorption and desorption properties of MgH2 with NiS2: The catalytic effect of in-situ formed MgS and Mg2NiH4 phases

In the present study, the NiS2 was synthesized by a one-step hydrothermal method. Then the MgH2-x wt % NiS2 (x = 0, 0.5, 1, 3, 5, 10) composites were prepared by mechanical ball-milling and their hydrogen storage properties were studied. Results indicate that the doped NiS2 changes into MgS and Mg2NiH4 during the heating process. Increasing NiS2 content significantly improves the hydrogenation and dehydrogenation kinetics of the composites. The onset dehydrogenation temperature is observed to shift downward from 330 degrees C for the ball-milled MgH2 to 210 degrees C for the MgH2-10 wt% NiS2 composite. Also, the MgH2-5 wt% NiS2 sample can absorb more than 5.1 wt% H-2 within 1 h at 100 degrees C, while the ball-milled MgH2 can hardly absorb H-2 at the same temperature. The enhanced hydrogen sorption kinetics is mainly attributed to the catalytic effect of in-situ formed MgS and Mg2NiH4 phases. In addition, the composites exhibit good cyclic performance, and the phase composition, microstructure, and reversible hydrogen storage capacity have almost no change during hydrogenation cycles. (C) 2020 Elsevier Ltd. All rights reserved.