Biological nitrogen fixation, which converts atmospheric dinitrogen to ammonia, is catalyzed mostly by Mo-nitrogenase and is a primary contributor to bioavailable nitrogen on early Earth. Mo-nitrogenase is believed to have evolved during the Archean, despite the extremely low concentration of dissolved Mo. However, it remains unclear whether Mo minerals could serve as a source of Mo to support the prevalence of Mo-nitrogenase on early Earth. Here, in this study, we investigated the bioavailability of molybdenite by incubating it with a metabolically ancient anoxygenic phototroph (Rhodopseudomonas palustris) under anoxic conditions. In the laboratory, R. palustris utilized molybdenum from molybdenite as a cofactor for nitrogen fixation. This bacterium extracted Mo from molybdenite by secreting molybdophores rhodopetrobactin A and B and by expressing Mo transport proteins. Surface-sensitive techniques demonstrated significant changes in surface chemistry of molybdenite after its interaction with cells. These findings provide novel explanations for the prevalence of Mo-nitrogenase on early Earth, with significant implications for nitrogen fixation in modern Mo-deficient environments.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2024

Solvent-mediated oxide hydrogenation in layered cathodes

Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. Here, we demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2024