<i>In Situ</i> Hydrogenation Strategy for Ultrahigh-Power Magnesium-Air Batteries.

Abstract

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 <i>in situ</i> 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.