In Situ Hydrogenation Strategy for Ultrahigh-Power Magnesium-Air Batteries

Magnesium-air batteries offer high energy density and intrinsic safety, yet their practical deployment is hindered by rapid passivation that suppresses kinetics. Here, we develop an in situ hydrogenation strategy that embeds uniformly dispersed cerium hydride (CeH_2.73) nanodomains within magnesium, reprogramming dissolution from localized corrosion to a spatially uniform mode. The CeH_2.73 phase establishes a hydride-regulated reaction pathway, acting as a weak-cathodic catalytic unit that enriches local electron density and activates neighboring magnesium. During discharge, partial oxidation of CeH_2.73 yields CeH_2.73-CeO₂ clusters, enabling rapid interfacial turnover and constructing a percolating pore-channel architecture that shortens ion/electron transport pathways and refreshes reactive surfaces. This dynamic hydride-oxide conversion prevents passivation even under high current densities. Consequently, under an ultrahigh current density of 200 mA cm^-2, the CeH_2.73|Mg anode delivers an energy density of 396 Wh kg^-1 and a peak power density of 140 mW cm^-2, representing the highest energy and power output reported for Mg-air anodes in this extreme high-current regime, while maintaining stability across 0 °C, 80 °C and low-oxygen seawater environments. In seawater batteries, the CeH_2.73|Mg||AgCl cell achieves a peak power density exceeding 200 mW cm^-2. These results establish hydride phase engineering as a generalizable strategy for high-power, wide-temperature metal-air energy systems.