Abstract
MgH2 is one of the most promising hydrogen storage materials due to its high hydrogen storage capacity and favorable reversibility, but it suffers from stable thermodynamics and poor dynamics. In the present work, an intersected Y2O3/NiO hybrid with spherical hollow structure is synthesized. When introduced to MgH2 via ball-milling, the Y2O3/NiO hollow spheres are crushed into ultrafine particles, which are homogenously dispersed in MgH2, showing a highly effective catalysis. With an optimized addition of 10 wt% of the hybrid, the initial dehydrogenation peak temperature of MgH2 is reduced to 277 °C, lowered by 109 °C compared with that of the bare MgH2, which is further reduced to 261 °C in the second cycle. There is ca. 6.6 wt% H2 released at 275 °C within 60 min. For the fully dehydrogenation product, hydrogenation initiates at almost room temperature, and a hydrogenation capacity of 5.9 wt% is achieved at 150 °C within 150 min. There is still 5.2 wt% H2 desorbed after 50 cycles at a moderate cyclic condition, corresponding to the capacity retention of 79.2%. The crystal structure and morphology of the Y2O3/NiO hybrid is well preserved during cycling, showing long-term catalysis to the hydrogen storage of MgH2. The Y2O3/NiO hybrid also inhibits the agglomeration of MgH2 particles during cycling, favoring the cyclic stability.
Highlights
Hydrogen is considered to be one of the most promising clean energy carriers, while safe, efficient and low-cost storage of hydrogen is the key bottleneck technology for largescale application of hydrogen energy to date [1,2,3]
For the as-prepared Y2O3/NiO hybrid, only sharp peaks from Y2O3 (PDF-# 43-0661) and NiO (PDF-# 44-1159) are detected, indicating that the synthesized product is composed of Y2O3 and NiO with high crystallinity
The dehydrogenation temperature is significantly reduced by the introduction of the hybrid, where an increasing reduction is obtained with the increasing addition of the hybrid from 2 to 10 wt%, but the reduction becomes limited when the addition is further increased to 12 wt%
Summary
Hydrogen is considered to be one of the most promising clean energy carriers, while safe, efficient and low-cost storage of hydrogen is the key bottleneck technology for largescale application of hydrogen energy to date [1,2,3]. The introduction of the second metal element commonly leads to large capacity decrease of Mg-based hydrides. The reduced particle size results in a shortened diffusion distance, improving the hydrogen de-/absorption kinetics of MgH2 leading to a 50% decrease in activation energy [21]. Direct synthesis of MgH2 nanoparticles smaller than 20 nm is so far difficult to achieve due to its high reactivity in nanoscale. In this case, thermodynamic modification by reducing particle size is practically difficult. By confining Mg particles in polymethyl methacrylate, a hydrogen absorption capacity of only 4.8 wt% H2 is obtained at 200 ◦C and 3 MPa H2 [20]
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