Nano Fe and Mg2Ni derived from TMA-TM (TM = Fe, Ni) MOFs as synergetic catalysts for hydrogen storage in MgH2

TMA-TM (TM = Fe, Ni) MOFs were synthesized successfully by a facile method. A MgH2-TM MOF (TM = Fe, Ni) composite was obtained via ball milling and the corresponding hydrogen storage performance was investigated. Particularly, high-resolution transmission electron microscopy was performed to in situ characterize the dehydrogenation behavior of the MgH2-TM MOF composite. The results reveal that nano alpha-Fe and Mg2NiH4/Mg2Ni derived from the TMA-TM MOFs display a synergetic improving effect on the de/hydrogenation of MgH2. During the hydrogen desorption process, Mg2NiH4/Mg2Ni works as a hydrogen pump to quickly deliver hydrogen and facilitates hydrogen diffusion. Meanwhile, alpha-Fe accelerates the nucleation and growth of Mg by reducing the nucleation energy of Mg from MgH2. The hydriding activation energy of the MgH2-TM MOF declines to 45.3 kJ mol(-1) H-2. Meanwhile, the peak dehydriding temperature of the MgH2-TM MOF is 530.9 K, which is much lower compared with the MgH2-Fe MOF composite (541.7 K) and as-milled MgH2 (685.2 K). Therefore, nano Mg2Ni and alpha-Fe derived from the TMA-TM MOFs can remarkably improve the hydrogen storage properties of the MgH2/Mg system due to their synergetic catalytic effects.