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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2023

Siderophore-Mediated Mobilization of Manganese Limits Iron Solubility in Mixed Mineral Systems

Recent laboratory and field studies show the need to consider the formation of aqueous Mn(III)-siderophore complexes in manganese (Mn) and iron (Fe) geochemical cycling, a shift from the historical view that aqueous Mn(III) species are unstable and thus unimportant. In this study, we quantified Mn and Fe mobilization by desferrioxamine B (DFOB), a terrestrial bacterial siderophore, in single (Mn or Fe) and mixed (Mn and Fe) mineral systems. We selected manganite (γ-MnOOH), δ-MnO 2 , lepidocrocite (γ-FeOOH), and 2-line ferrihydrite (Fe 2 O 3 ·0.5H 2 O) as relevant mineral phases. We found that DFOB mobilized Mn(III) as Mn(III)-DFOB complexes to varying extents from both Mn(III,IV) oxyhydroxides but reduction of Mn(IV) to Mn(III) was required for the mobilization of Mn(III) from δ-MnO 2 . The initial rates of Mn(III)-DFOB mobilization from manganite and δ-MnO 2 were not affected by the presence of lepidocrocite but decreased by a factor of 5 and 10 for manganite and δ-MnO 2 , respectively, in the presence of 2-line ferrihydrite. Additionally, the decomposition of Mn(III)-DFOB complexes through Mn-for-Fe ligand exchange and/or ligand oxidation led to Mn(II) mobilization and Mn(III) precipitation in the mixed-mineral systems (~10% (mol Mn/mol Fe)). As a result, the concentration of Fe(III) mobilized as Fe(III)-DFOB decreased by up to 50% and 80% in the presence of manganite and δ-MnO 2 , respectively, compared to the single mineral systems. Our results demonstrate that siderophores, through their complexation of Mn(III), reduction of Mn(III,IV), and mobilization of Mn(II), can redistribute Mn to other soil minerals and limit the bioavailability of Fe in natural systems.

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DOE OSTI2025

Nanoporous Fe 2 O 3 and Soluble Fe(II) Intermediates Accelerate the Electrodeposition of Fe in NaOH(aq)

Electrochemical conversion of iron oxide to iron metal can enable low-cost batteries for long duration energy storage and zero-emissions ironmaking for steel. Iron oxides, such as hematite, can be electrochemically reduced to metallic iron in concentrated alkaline electrolytes at modest temperatures, but the relative influences of solid-state and dissolved intermediates at practical reaction rates remains unclear. Here, in this study, we prepare a homologous set of well-defined hematite particles to measure how the nanoscale morphology of oxides controls both their reactivity and apparent reduction mechanism in concentrated hydroxide. Correlated electron microscopy and rotating-ring-disk-electrode measurements revealed that nanoporous hematite and solid intermediates formed iron via a dissolution-redeposition pathway. In contrast, dense hematite particles directly formed iron metal via reactive fracture. While previous studies on iron electrowinning have primarily emphasized the role of particle diameter at the micron scale, these results demonstrate the importance of the dissolution-redeposition pathway to support rapid reaction rates and suggest that nanoscale porosity controls iron oxide reactivity at temperatures <100 °C. Therefore, iron-oxide-to-metal electrolyzers and fast-charging iron-air batteries supported by curtailed electricity can increase the rate of metal formation by accelerating fracture and dissolution in reactant oxides.

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