Non-stoichiometric Ni₃ZnC_0.7 carbide loading on melamine sponge-derived carbon for hydrogen storage performance improvement of MgH₂

The high operating temperatures and slow kinetics limit the application of MgH₂-based hydrogen storage materials. Here, a composite of Ni₃ZnC_0.7/carbon nanotubes loaded onto a melamine sponge-derived carbon (MS) skeleton is prepared and loaded onto MgH₂. During dehydrogenation, Ni₃ZnC_0.7 reacts with MgH₂ and in situ changes to Mg₂Ni/Zn. The transformation of Mg₂Ni/Mg₂NiH₄ serves as a “hydrogen pump”, providing diffusion channels for hydrogen atoms and molecules to promote the de-/hydrogenation processes. Moreover, Zn/MgZn₂ provides the catalytic sites for the transformation of Mg/MgH₂. The length of the Mg–H bond is elongated from 1.72 to 1.995 Å, and the dissociation energy barrier of MgH₂ is reduced from 1.55 to 0.49 eV. As a result, MgH₂ with 2.5 wt% MS@Ni₃ZnC_0.7 can absorb 5.18 wt% H₂ at 423 K within 200 s, and its initial dehydrogenation temperature is reduced to 585 K. After 20 cycles, the dehydrogenation capacity retention is determined to be 94.6%. This work demonstrates an efficient non-stoichiometric metal carbide catalyst for MgH₂.