Improved Hydrogen Storage Kinetic Properties of MgH2 with NiO/NiCo(Fe)2O4/(Ni)

Abstract

Developing catalysts with exceptional catalytic activity is crucial in solid hydrogen storage. Two catalysts, NiO/NiCo₂O₄ and NiO/NiFe₂O₄/Ni, are successfully prepared and incorporated into MgH₂ for the first time to investigate the hydrogen storage properties of MgH₂. The experimental results indicate that the hydrogen desorption temperatures for the composites of MgH₂ + 5 wt % NiO/NiCo₂O₄ (MgH₂ + NC) and MgH₂ + 5 wt % NiO/NiFe₂O₄/Ni (MgH₂ + NF) occur at 241 and 175 °C, respectively. Hydrogen desorption of ball-milled MgH₂ begins at 272 °C. Both MgH₂ + NF and MgH₂ + NC exhibit excellent hydrogen absorption kinetics. At 150 °C and 3 MPa, MgH₂ + NF and MgH₂ + NC can absorb 5.93 and 5.95 wt % of H₂ in as little as 1 min, respectively. The desorption activation energies of MgH₂ + NF and MgH₂ + NC are 88.38 and 81.56 kJ/mol, respectively, compared to pure MgH₂, which has an E_a of 181.4 kJ/mol. Furthermore, cycle experiments demonstrate that both MgH₂ + NC and MgH₂ + NF display excellent cycle stability, maintaining hydrogen storage capacities of approximately 99.8 and 98%, respectively, after 10 cycles. In situ formed Fe extends the defect structure and interfaces with MgH₂, thus providing additional hydrogen diffusion channels. Moreover, the embedded clusters of Mg₂NiH₄/Mg₂CoH₅ function as “multistage hydrogen pumps”, providing surface pathways for efficient hydrogen absorption. This study offers experimental evidence and novel insights aimed at enhancing the kinetic performance of MgH₂ for hydrogen storage.