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

Abstract

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 α-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, α-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 H₂. 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 α-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.