Isotopic Engineering of Water Reactivity for Stable Aqueous Iron-Metal Batteries

The development of aqueous iron-metal batteries (AIBs) is critically hindered by the severe parasitic hydrogen evolution reaction (HER) at the anodes and the resulting structural degradation of the cathode. Moving beyond conventional additive-based approaches, this work presents a kinetically targeted strategy to suppress HER and enhance overall cell stability through an isotope-engineered deuterated water (D₂O)-based electrolyte. Leveraging the intrinsic differences in zero-point energy between deuterium and hydrogen, D₂O features a substantially higher activation energy barrier for water dissociation, effectively taming the reactivity of the problematic Fe anode. Concurrently, control experiments in Fe metal-free configurations reveal that this isotope effect extends a vital secondary stabilization to the cathode host, establishing a cooperative, dual-side protection mechanism. Consequently, the D₂O-based electrolyte enables a highly reversible iron anode with an average Coulombic efficiency of 99.6% and grants Fe||MoS₂ full cells a stable lifespan of 2000 cycles with an 87.6% capacity retention at 0.5 A g^-1. This work highlights the potential of isotopic modulation as a targeted, high-efficacy strategy for stabilizing high-performance aqueous batteries.