Magnesium alloys are light structural materials and promising anode candidates for Mg-air batteries. However, application of Mg-air batteries is limited by poor performance at large current density and severe H₂ generation side reactions. In this study, we pioneered magnesium-rare earth Mg₃RE (RE=La, Ce, Pr and Nd) intermetallic compounds as anodes to provide higher power density and more stable discharge performance. Especially, Mg₃Pr alloy exhibits high discharge voltage of 0.91 V and peak power density of 54.4 mW cm⁻² at 60 mA cm⁻² with anodic efficiency of 60%, far better than other Mg alloys. We reveal an activation mechanism of Mg₃RE-based anodes during discharge, which significantly accelerates mass transfer process as well as enhances discharge activity. The results improve the performance of high-power Mg-air batteries and promote the value-added application of abundant rare earth elements such as Ce and La.

It has been well known that doping nano-scale catalysts can significantly improve both the kinetics and reversible hydrogen storage capacity of MgH₂. However, so far it is still a challenge to directly synthesize ultrafine catalysts (e.g., < 5 nm), mainly because of the complicated chemical reaction processes. Here, a facile one-step high-energy ball milling process is developed to in situ form ultrafine Ni nanoparticles from the nickel acetylacetonate precursor in the MgH₂ matrix. With the combined action of ultrafine metallic Ni and expanded graphite (EG), the formed MgH₂Ni-EG nanocomposite with the optimized doping amounts of Ni and EG can still release 7.03 wt.% H₂ within 8.5 min at 300 ℃ after 10 cycles. At a temperature close to room temperature (50 ℃), it can also absorb 2.42 wt.% H₂ within 1 h. It can be confirmed from the microstructural characterization analysis that the in situ formed ultrafine metallic Ni is transformed into Mg₂Ni/Mg₂NiH₄ in the subsequent hydrogen absorption and desorption cycles. It is calculated that the dehydrogenation activation energy of the MgH₂Ni-EG nanocomposite is also reduced obviously in comparison with the pure MgH₂. Our work provides a methodology to significantly improve the hydrogen storage performance of MgH₂ by combining the in situ formed and uniformly dispersed ultrafine metallic catalyst from the precursor and EG.

LiBH₄ has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity, which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversion via anodic oxidation reaction of direct borohydride fuel cells (DBFCs). However, the realization of practical hydrogen applications heavily depends on the effective synthesis of high-purity LiBH₄ and recycling of the spent fuels (LiBO₂·xH₂O). The present work demonstrates a convenient and high-efficiency solvent-free strategy for regenerating LiBH₄ with a maximum yield close to 80%, by retrieving its by-products with MgH₂ as a reducing agent under ambient conditions. Besides, the hydrogen released from the regeneration course can completely compensate the demand for consumed MgH₂. The isotopic tracer method reveals that the hydrogen stored in LiBH₄ comes from both MgH₂ and coordinated water bound to LiBO₂. Here, the expensive MgH₂ can be substituted with the readily available and cost-effective MgH₂−Mg mixtures to simplify the regeneration route. Notably, LiBH₄ catalyzed by CoCl₂ can stably supply hydrogen to proton exchange membrane fuel cell (PEMFC), thus powering a portable prototype vehicle. By combining hydrogen storage, production and utilization in a closed cycle, this work offers new insights into deploying boron-based hydrides for energy applications.