Trimethyl Phosphate Enables More Reversible Iron Metal Anodes in Aqueous Electrolytes

High Resolution Image Download MS PowerPoint Slide The cycling life of Fe metal anodes in aqueous electrolytes is limited by the hydrogen evolution reaction and irreversible interfacial chemistry. Here, we show that trimethyl phosphate (TMP) as a cosolvent improves the reversibility of Fe metal anodes in aqueous FeCl 2 electrolytes through coupled solvation and interfacial effects. Synchrotron spectroscopic analyses and molecular dynamics simulations reveal that TMP enters the second solvation shell of Fe 2+, where its phosphoryl (P=O) group forms hydrogen bonds with aqua ligands in the first shell. This interaction weakens first-shell Fe-H 2 O coordination and draws chloro ligands closer to the Fe 2+ center. At the iron surface, TMP alters interfacial evolution during cycling and suppresses the buildup of resistive iron oxide. Together, these effects promote more reversible Fe deposition, increasing the average Coulombic efficiency from 89.0 to 96.7%, as measured by the Aurbach reservoir method.