Hydrangea-like NiO@KNbO3 as catalyst doping for MgH2: Boosting hydrogen storage performance

Abstract

MgH2 is regarded as one of the most favorable materials for hydrogen storage caused by its safety, high efficiency, considerable capacity for storing hydrogen, and low cost. However, the application of this material is limited owing to subpar thermodynamics and kinetics, which can be improved via combination with other materials. A hydrangea-like NiO@KNbO3 was prepared by solvent thermal, hydrothermal, and calcination methods. Then, different amounts of NiO@KNbO3 (3, 5, 7, and 10 wt %) were added to MgH2 using ball-milling. MgH2 composite material doped with 5 wt % NiO@KNbO3 exhibits the most superior hydrogen storage performance, with a hydrogen absorption capacity of 4.95 wt % H2 within 5 min at 150 ℃ and 1.5 MPa H2 pressure. Furthermore, H2 release started approximately at 175 °C with 5.96 wt % H2 at 300 °C. The composite's H2 desorption activation energy was decreased to 71.75 kJ/mol. The Mg2NiH4/Mg2Ni generated in situ can serve as a "hydrogen pump" by creating numerous activation sites and pathways for hydrogen diffusion, thereby facilitating H2 dissociation during the process of hydrogen absorption. Additionally, the NiO@KNbO3-doped MgH2 samples exhibited excellent integrated hydrogen storage properties due to the combined effect of KNbO3 and the in situ formed NbO. The study provides clear evidence that NiO@KNbO3, a bimetallic oxide, can effectively enhance the hydrogen storage performance of MgH2 as an additive. Furthermore, the straightforward synthesis of NiO@KNbO3 offers guidance for the development of high-performance oxide catalysts that can improve the properties of MgH2.