MgH₂, albeit with slow desorption kinetics, has been extensively studied as one of the most ideal solid hydrogen storage materials. Adding such catalyst as Ni can improve the desorption kinetics of MgH₂, whereas the catalytic role has been attributed to different substances such as Ni, Mg₂Ni, Mg₂NiH_0.3, and Mg₂NiH₄. In the present study, Ni nanoparticles (Ni-NPs) supported on mesoporous carbon (Ni@C) have been synthesized to improve the hydrogen desorption kinetics of MgH₂. The utilization of Ni@C largely decreases the dehydrogenation activation energy from 176.9 to 79.3 kJ mol⁻¹ and the peak temperature of dehydrogenation from 375.5 to 235 °C. The mechanism of Ni catalyst is well examined by advanced aberration-corrected environmental transmission electron microscopy and/or x-ray diffraction. During the first dehydrogenation, detailed microstructural studies reveal that the decomposition of MgH₂ is initially triggered by the Ni-NPs, which is the rate-limiting step. Subsequently, the generated Mg reacts rapidly with Ni-NPs to form Mg₂Ni, which further promotes the dehydrogenation of residual MgH₂. In the following dehydrogenation cycle, Mg₂NiH₄ can rapidly decompose into Mg₂Ni, which continuously promotes the decomposition of MgH₂. Our study not only elucidates the mechanism of Ni catalyst but also helps design and assemble catalysts with improved dehydriding kinetics of MgH₂.

Lithium-oxygen (Li-O₂) batteries have been considered as an ideal solution to solving the global energy crisis. Silver (Ag) and Ag-based catalyst have been extensively studied due to their high catalytic activities in Li-O₂ batteries. However, it remains a challenge to track the catalytic mechanism during the charge/discharge process. Here, a nanoscale processing method was used to assemble a Li-O₂ nanobattery in an aberration-corrected environmental transmission electron microscope (ETEM), where a single Ag nanowire (NW) was used as catalyst for O₂ electrode. A visualization of the lithium ion insertion process during the electrochemical reactions was achieved in this nanobattery. Numerous Ag nanoparticles (NPs) were observed on the surface of the Ag NW, which were covered by the discharge product Li₂O₂. By simultaneously studying the evolution of the interface and the phase transformation, it can be concluded that these Ag NPs wrapped around Ag NW acted as catalyst during the subsequent charge/discharge reaction. Based on these studies, Ag NPs decorated on porous carbon were synthesized, and it can simultaneously improve the cycling stability (100 cycles) and the maximum specific capacity (17,371 mAh·g⁻¹ at a current density of 100 mA·g⁻¹) in a coin cell Li-O₂ battery. This study suggests that nanoscale Ag may be a promising catalyst for Li-O₂ battery.