Stable, efficient iron electrodeposition via anion-directed control of Fe(II) coordination.

Authors

Abstract

Iron production accounts for > 90% of global metal production by weight, along with the highest energy consumption of any single manufacturing process. Electrodeposition technologies offer an attractive opportunity to economize and modularize iron production. However, Faradaic efficiency (FE) is generally low for aqueous processes due to parasitic hydrogen evolution, and common electrolytes utilizing FeCl2 and FeSO4 are unstable under ambient conditions and/or elevated pH. We find that the addition of citrate as a co-anion in Cl- and SO4-based electrolytes enables a balanced tradeoff between pH stability and FE. Citrate, a chelating agent of intermediate coordination strength, forms complexes with Fe2+ that stabilize the electrolyte at near-neutral pH ( 5) for up to 10 days, even at relatively low concentrations. At elevated pH, optimized electrolytes achieve > 95% FE at 10 mA/cm2 with minimal iron oxide formation, which stands in stark contrast to deposits generated in citrate-free electrolytes at lower pH. Overall, this work demonstrates that the presence of citrate co-anions and the resulting iron complexes that form enable stable, efficient electrolytes for high-purity iron electrodeposition. This anion coordination strategy represents a promising new direction for developing stable electrolytes for efficient metal electrodeposition.