In situ formed ultrafine metallic Ni from nickel (II) acetylacetonate precursor to realize an exceptional hydrogen storage performance of MgH2Ni-EG nanocomposite

It has been well known that doping nano-scale catalysts can significantly improve both the kinetics and reversible hydrogen storage capacity of MgH 2 . However, so far it is still a challenge to directly synthesize ultrafine catalysts (e.g., < 5 nm), mainly because of the complicated chemical reaction processes. Here, a facile one-step high-energy ball milling process is developed to in situ form ultrafine Ni nanoparticles from the nickel acetylacetonate precursor in the MgH 2 matrix. With the combined action of ultrafine metallic Ni and expanded graphite (EG), the formed MgH 2 Ni-EG nanocomposite with the optimized doping amounts of Ni and EG can still release 7.03 wt.% H 2 within 8.5 min at 300 °C after 10 cycles. At a temperature close to room temperature (50 °C), it can also absorb 2.42 wt.% H 2 within 1 h. It can be confirmed from the microstructural characterization analysis that the in situ formed ultrafine metallic Ni is transformed into Mg 2 Ni/Mg 2 NiH 4 in the subsequent hydrogen absorption and desorption cycles. It is calculated that the dehydrogenation activation energy of the MgH 2 Ni-EG nanocomposite is also reduced obviously in comparison with the pure MgH 2 . Our work provides a methodology to significantly improve the hydrogen storage performance of MgH 2 by combining the in situ formed and uniformly dispersed ultrafine metallic catalyst from the precursor and EG.