MOF-derived Ni nanoparticles dispersed on monolayer MXene as catalyst for improved hydrogen storage kinetics of MgH2

A novel catalyst-MOFs derived Ni nanoparticles dispersed on exfoliated monolayered MXene functional carrier was prepared and introduced into MgH2 in this work. Striking improvements in hydrogen storage properties were achieved for MgH2 when the catalyst was added. Concisely, the hydrogen releasing peak temperature of the MgH2 + 10 wt% Ni@C-MXene is 241.1 degrees C, about 120.2 degrees C lower than that of the additive-free MgH2. According to Kissinger method, the dehydrogenation activation energy of the MgH2 + 10 wt% Ni@C-MXene composite is calculated to be 54.79 kJ mol 1, over 60% lower when compared with the pristine MgH2 (145.08 kJ mol(-1)). At 300 degrees C, the MgH2 + 10 wt% Ni@C-MXene composite releases about 5.6 wt% hydrogen within 2 min, while only 2 wt% hydrogen is desorbed even the dehydriding time prolongs to 60 min for the pure MgH2. In addition, the completely dehydrogenated MgH2 + 10 wt% Ni@C-MXene exhibits eminent hydrogen absorption performance, with approximate 5 wt% hydrogen uptaken within 2 min under 3.2 MPa hydrogen pressure at 150 degrees C. Moreover, an excellent hydrogen cycling stability is achieved in the MgH2 + 10 wt% Ni@C-MXene without decay for both capacity and kinetics after 10 cycles. Beside the regular XRD, XPS and TEM techniques to clarify the evolution of Ni and Ti during hydrogen de/absorption cycling, more importantly we performed the first principle based calculations to reveal how the in-situ formed Ti-0 would affect the Mg2Ni/Mg2NiH4 mutual transformation. Apart from the nano confinement effect of MXene for Ni/Mg2Ni/Mg2NiH4, the in-situ formed Ti-0 from MXene also favors the "hydrogen pump" effect of Mg2NiH4 due to the decreased formation energy Ef under the assistance of Ti0. Through such a synergistic "nano-confinement and facilitated hydrogen pump" effect, the hydrogen de-/ absorption kinetics of MgH2 is significantly accelerated.