Boosting low-temperature de/re-hydrogenation performances of MgH₂ with Pd-Ni bimetallic nanoparticles supported by mesoporous carbon

Bimetallic Pd-Ni nano-particles supported by a mesoporous carbon material CMK-3 (denoted as Pd₃₀Ni₇₀/CMK-3) were synthesized through solution impregnation and hydrogen reduction methods. Among those hierarchical Ni-Pd nano-particles, majorly large ones (>10 nm) are dispersed over the surface of CMK-3, while a litter small ones (<10 nm) are embedded into the pores. It significantly improves the de/re-hydrogenation performances of MgH₂ at low temperature. The onset desorption temperature of MgH₂-Pd₃₀Ni₇₀/CMK-3 is lowered by 150 K from that of pristine MgH₂ (above 593 K). About 6 wt% hydrogen could be released during its decomposition below 561 K. Noticeably, MgH₂-Pd₃₀Ni₇₀/CMK-3 is capable of releasing 1.3 wt% H₂ even at 373 K. 4 wt% hydrogen can be absorbed at 343 K under a hydrogen pressure of 3 MPa within 18000 s. Activation energy values of both hydrogen decomposition (65.9 kJ mol⁻¹) and absorption (78.9 kJ mol⁻¹) for MgH₂-Pd₃₀Ni₇₀/CMK-3 are greatly improved from those of as-milled MgH₂. Thermal stability of the composite system is remarkably destabilized by 4.3 kJ mol H₂⁻¹ from pristine MgH₂ according to pressure-composition isotherm curves and van't Hoff plots. The enhanced performances can be ascribed to the synergistic effects of both destabilization and catalysis from nano-dispersed Pd and Ni particles, respectively.