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 degrees C, which is 113 degrees C lower than that of as-milled MgH2. Moreover, it takes only 500 s to thoroughly desorb hydrogen at 300 degrees 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 degrees C are 91% and 93%, respectively. Transmission electron microscope analysis shows that part of Ni transformed to Mg2NiH4/Mg2Ni during hydrogen absorption/desorption cycles.