Facile Synthesis of Carbon Supported Nano-Ni Particles with Superior Catalytic Effect on Hydrogen Storage Kinetics of MgH₂

Metal nanocatalysis is an effective method to enhance the hydrogen storage properties of magnesium hydride (MgH₂), and the catalytic effect can be further improved by a matrix material supported nanometal. In this work, carbon supported nano-Ni (Ni@C) was synthesized by calcination of dimethylglyoxime dinickel chelate, and then it was doped into MgH₂ to improve the de/rehydrogenation kinetics. This shows that the homogeneously distributed Ni with refined particle size in carbon base leads to superior catalytic effects on hydrogen absorption/desorption of MgH₂-5 wt % Ni@C. The MgH₂-5 wt % Ni@C starts to desorb hydrogen at 187 °C, which is 113 °C lower than that of as-milled MgH₂. Moreover, it takes only 500 s to thoroughly desorb hydrogen at 300 °C, which is 3000 s faster than as-milled MgH₂ under the same dehydrogenation conditions. According to the Kissinger's method, the apparent activation energy for desorption of the MgH₂-5 wt % Ni@C is 66.5 ± 1.8 kJ mol^-1, which is about 79.9 kJ mol^-1 lower than that of as-milled MgH₂. Cycling experiments show that the capacity retentions of hydrogen absorption and desorption after 10 cycles at 275 °C are 91% and 93%, respectively. Transmission electron microscope analysis shows that part of Ni transformed to Mg₂NiH₄/Mg₂Ni during hydrogen absorption/desorption cycles.