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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Variable Surface Termination and Ligand Passivation of Lead Sulfide Nanocrystals Synthesized with Excess Lead Chloride

The surface termination and ligand passivation of semiconducting nanocrystals (NCs) impact the stability, optical properties, and self-assembly of NCs. In this work, we definitively characterize the surface of lead sulfide (PbS) NCs synthesized from excess PbCl 2 . With a combination of small-angle neutron scattering (SANS), photoluminescence, and 1D and 2D NMR experiments, we show that the surface termination of PbS NCs depends on the presence of PbCl 2 during ligand exchange. When excess PbCl 2 is removed prior to ligand exchange, PbS[RNH 3 + Cl – ] NCs are obtained, which are terminated by a monolayer of PbCl x on the {100} PbS facet and passivated by oleylammonium chloride ligands. On the other hand, when excess PbCl 2 remains in solution during ligand exchange, lead oleate forms and attaches to the {111} PbS facets of PbS[RNH 3 + Cl – ] NCs, creating PbS@PbCl x NCs. PbS@PbCl x NCs are coated in an epitaxial layer of PbCl x on both the {100} PbS and {111} PbS facets, making them 0.3–0.4 nm larger on average than PbS[RNH 3 + Cl – ] NCs with identical absorption wavelengths. Additionally, PbS@PbCl x NCs have a consistently higher photoluminescence quantum yield and longer photoluminescence lifetimes than PbS[RNH 3 + Cl – ] NCs. This study clarifies the surface structure of PbS NCs synthesized from excess PbCl 2 , highlighting ligand exchange strategies and reconciling observations from across the literature.

Anions↗
DOE OSTI2023

Synthesis of PbS/CdS/Cu 2-x S core/shell/shell quantum dots for rapid NIR emission.

Nanoscale semiconductors, known as quantum dots (QDs), possess unique size-tunable optical and electrical properties. With continued research into quantum information storage and quantum communication, the need for near-infrared single photon emitters and absorbers has gained prominence. Lead sulfide QDs have only recently been explored as a reliable near-infrared single photon emitters with the addition of a protective cadmium sulfide shell. Despite the increased air and room temperature stability of these QDs, long photon emission times have limited widespread application. This work examines the enhanced photon emission due to the Purcell effect provided by the layering of copper sulfide. In particle, this work synthesized lead sulfide cores in the 10 nm range, successfully layered cadmium sulfide through cation exchange, and attempted the cation exchange of copper sulfide, as identified with near-infrared absorbance spectra, transmission electron microscopy, and photoluminescence spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Synthetic Control of Water-Stable Hybrid Perovskitoid Semiconductors

Hybrid metal-halide perovskites and their derived materials have emerged as the next-generation semiconductors with a wide range of applications, including photovoltaics, light-emitting devices, and other optoelectronics. Over the past decade, numerous single-crystalline perovskite derivatives have been synthesized and developed. However, the synthetic methods for these derivatives mainly rely on acidic crystallization conditions. This approach leads to crystals comprising metal halide building blocks, which show problematic stability when directly exposed to water. In this study, a methodology is developed for synthesizing hybrid metal-halide compounds using lead iodide and the zwitterionic bifunctional molecule cysteamine (CYS), to form various perovskitoid structures under a broad pH range. Interestingly, the different pH conditions alter the coordination environment of lead halides, leading to lead-sulfide and lead-nitride covalent bond formation. This modification significantly enhances their stability when in direct contact with water, lasting for months. Photoluminescence measurements and first principal density functional theory (DFT) calculations reveal that the perovskitoids synthesized under basic and acidic pH conditions exhibit a direct bandgap nature, while those synthesized under neutral conditions display an indirect bandgap. This approach opens new avenues for manipulating synthetic methods to develop water-stable hybrid semiconductors suitable for a wide range of applications, such as solid-state light emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Interfacial Charge Transfer in Lead Sulfide/Cadmium Sulfide Quantum Dot–Monolayer Molybdenum Disulfide Heterostructures

We investigate the ultrafast interfacial charge transfer dynamics in mixed-dimensional PbS/CdS quantum dot (QD)–monolayer MoS 2 heterostructures exhibiting a type-II band alignment. These 0D–2D heterostructures were assembled using oleic acid-capped PbS/CdS QDs with systematically varied core sizes deposited onto molecular beam epitaxy-grown monolayer MoS 2 . Steady-state and time-resolved optical spectroscopies revealed pronounced bidirectional charge transfer between the 0D and 2D components, involving both electron and hole exchange across the interface. The quenching of the monolayer MoS 2 A-exciton bleach and the modifications of its decay dynamics provide direct evidence for efficient hole transfer from photoexcited MoS 2 into the PbS QD core. Concurrently, attenuation of the QD ground-state bleach and the emergence of ultrafast decay components confirmed electron transfer from photoexcited QDs to monolayer MoS 2 . Both hole and electron transfer processes are dependent on the QD core size, with smaller cores enabling faster transfer rates and higher efficiencies due to enhanced band offsets and interfacial coupling. The complementary insights gained from transient absorption and time-resolved photoluminescence measurements clarify the mechanisms governing interfacial carrier exchange and highlight the importance of both hole and electron transfer as key components in the functioning of such 0D–2D heterostructures. This study underscores the potential of 0D–2D semiconductor heterostructures for advanced optoelectronic and light-energy conversion applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Coupling of Infrared Active Colloidal Quantum Dots and Amorphous Selenium for Fast and Sensitive Photodetection

Colloidal quantum dot (CQD) based infrared (IR) photodetectors offer facile wavelength tunability in the IR and low-cost fabrication. However, owing to their large surface areas, CQDs intrinsically have significant surface traps critically affecting the speed of CQD photodetectors, typically mediated through tedious surface passivation efforts. In this report, an alternative strategy involving coupling of near-IR photoactive lead sulfide CQDs with a thermally evaporated amorphous selenium (a-Se) hole transport layer is proposed. By separating the detector into a photon absorbing CQD region and a charge transport a-Se region, the study takes advantage of the extremely low noise, predominantly hole-only transport process in a-Se. Here, a high 3 dB bandwidth of 2.5 MHz and a competitive specific detectivity of 2.5 × 10 11 Jones at room temperature are demonstrated at 980 nm. This report serves as a first demonstration of strong coupling between an IR active CQD absorber and a-Se, which paves the path to obtain fast and highly photoresponsive IR photodetection in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ultrafast Symmetry Control in Photoexcited Quantum Dots

Symmetry control is essential for realizing unconventional properties, such as ferroelectricity, nonlinear optical responses, and complex topological order, thus it holds promise for the design of emerging quantum and photonic systems. Nevertheless, fast and reversible control of symmetry in materials remains a challenge, especially for nanoscale systems. Here, reversible symmetry changes are unveiled in colloidal lead chalcogenide quantum dots on picosecond timescales. Using a combination of ultrafast electron diffraction and total X-ray scattering, in conjunction with atomic-scale structural modeling and first-principles calculations, it is revealed that symmetry-broken lead sulfide quantum dots restore to a centrosymmetric phase upon photoexcitation. The symmetry restoration is driven by photoexcited electronic carriers, which suppress lead off-centering for about 100 ps. Furthermore, the change in symmetry is closely correlated with the electronic properties, and the bandgap transiently red-shifts in the symmetry-restored quantum dots. Overall, this study elucidates reversible symmetry changes in colloidal quantum dots, and more broadly defines a new methodology to optically control symmetry in nanoscale systems on ultrafast timescales.

36 MATERIALS SCIENCE↗
DOE OSTI2023

An artificial intelligence’s interpretation of complex high-resolution in situ transmission electron microscopy data

Complicated nano- and atomic-scale processes with sub-angstrom spatial resolution and millisecond time resolution visualized by in situ transmission electron microscopy (TEM) are often highly dynamical and time consuming to analyze and interpret. Here, we report how variational autoencoders (VAEs) can provide an artificial intelligence’s interpretation of high-resolution in situ TEM data by condensing and deconvoluting complicated atomic-scale dynamics into a latent space with reduced dimensionality. We designed a VAE model with high latent dimensions capable of deconvoluting information from complex high-resolution TEM data. We demonstrate how this model, with high latent dimensions trained on atomically resolved TEM images of lead sulfide (PbS) nanocrystals, is able to capture movements and perturbations of periodic lattices in both simulated and real in situ TEM data. Importantly, the VAE model shows the capability of detecting and deconvoluting dynamical nanoscale physical processes, such as the rotation of crystal lattices and intra-particle ripening during the annealing of semiconductor nanocrystals.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Overcoming efficiency and cost barriers for large-area quantum dot photovoltaics through stable ink engineering

The bottom-up construction of electronics from colloidal quantum dots (CQDs) could innovate nanotechnology manufacturing through printing. However, the unstable and expensive semiconductive CQD inks make the scaling up of CQD electronics challenging. Here, in this study, we develop a strategy for engineering the solution chemistry of lead sulfide (PbS) CQD inks prepared from a low-cost direct synthesis method. By creating an iodine-rich environment in weakly coordinating solvents, we convert the iodoplumbates into functional anions, which condense into a robust surface shell. The fully charged electrostatic surface layer prevents aggregation and epitaxial fusion of CQDs, yielding stable inks. By eliminating the fusion-induced inter-band states, we print a compact CQD film with uniformity in three dimensions, flattened energy landscape and improved carrier transport. We achieved a certified efficiency of 13.40% on 0.04 cm 2 cells, with a 300-fold increase in active area, scaling up to a 12.60 cm 2 module with a certified efficiency of 10%.

14 SOLAR ENERGY↗
DOE OSTI2025

Hydrothermal Liquefaction of Structurally Diverse Lignins: Insights into Biocrude Yield, Fuel Properties, and Reaction Mechanisms

Lignin holds significant promise as a feedstock for biocrude production via hydrothermal liquefaction (HTL). Although lignin HTL has been widely studied, the specific depolymerization pathways associated with distinct lignin structures remain largely unexplored. This study investigates the HTL of four structurally diverse lignins: alkaline (AL), dealkaline (DAL), organosolv (OL), and lignosulfonate (LS) across 270–310 °C to elucidate structure-specific mechanisms governing biocrude yield and composition. AL and OL achieved the highest yields (16.8 ± 0.3% and 16.8 ± 2.5%), with AL-derived biocrude showing the highest carbon content (70.2 ± 0.0%) and HHV (31.0 ± 0.2 MJ/kg). In contrast, DAL and LS produced lower yields and inferior fuel quality due to higher sulfur content and lower carbon enrichment. The structures of AL and DAL, containing fewer methoxy groups, produced guaiacol-rich biocrudes (46.6% and 69.5%). Methylation in AL formed alkyl guaiacols and veratroles, while DAL favored side-chain oxidation. OL retained complex structures, forming syringols and desaspidinol, which contributed to heavier biocrude compounds. Sulfonate groups in LS were stabilized mostly as sulfides, leading to elevated sulfur content. These findings provide mechanistic insight into how lignin structure governs HTL behavior, enabling targeted control of biocrude yield and quality for renewable fuel production.

biocrude↗
DOE OSTI2025

Mineralogical evidence for hydrothermal alteration of Bennu samples

Samples of asteroid (101955) Bennu delivered by the OSIRIS-REx mission offer the opportunity to study pristine planetary materials unchanged by exposure to the terrestrial environment. Here we use a combination of X-ray diffraction and various electron microscopy techniques to explore the detailed mineralogy of Bennu samples and determine the alteration history of the planetesimal protolith from which they originated. The samples consist largely of hydrated sheet-silicate minerals, namely nanoscale serpentine and saponite of varied grain size, which are decorated with micro- to nanoscale Fe-sulfides, magnetite and carbonates. We observe sheet silicates parallel and normal to sulfide surfaces and as inclusions in sulfides; sulfur-rich veins transecting the sheet-silicate matrix; zoned carbonates and phosphates and sulfide and magnetite grains exhibiting embayment. The mineralogical evidence indicates alteration of accreted minerals by a fluid that evolved with time, leading to etching, dissolution and reprecipitation. Sulfide compositions indicate alteration at ~25 °C, similar to conditions inferred for asteroid (162173) Ryugu and Ivuna-type (CI) chondrite meteorites. The fluid probably evolved from neutral to alkaline, culminating with the precipitation of highly soluble salts. We conclude that Bennu’s protolith comprised mainly nanometre to micrometre silicates, with fewer chondrules and calcium–aluminium-rich inclusions than those of most chondrite groups.

Zega, T J↗
DOE OSTI2024

Vapor Infiltration Synthesis of Indium Sulfide Magic Size Cluster

The energetically favorable formation of atomically precise clusters, known as magic size clusters, in the solution phase enables a precision nanoscale synthesis with exquisite uniformity. Here, we report the synthesis of magic size clusters via vapor infiltration of atomic layer deposition precursors directly in a polymer thin film. Sequential infiltration of trimethylindium vapor and hydrogen sulfide gas into poly(methyl methacrylate) leads to the formation of clusters with uniform properties consistent with a magic size cluster-In 6 S 6 (CH 3 ) 6 . While an increase in cluster size might be expected with additional sequential infiltration cycles of the reactive In and S precursors, uniform properties consistent with magic size clusters form in multiple polymers under a range of processing conditions. Ultraviolet-visible absorption spectra of In 6 S 6 (CH 3 ) 6 are largely independent of the number of sequential infiltration cycles and exhibit air stability, both of which are attributed to an energetically favorable synthetic pathway that is evaluated with density functional theory.

atomic layer deposition↗
DOE OSTI2026

Probing Interfacial Reaction Pathways in Atomic Layer Deposition on Sulfide Superionic Conductors

Sulfide superionic conductors (e.g., argyrodite Li 6 PS 5 Cl, LPSCl) are extremely promising for all solid-state batteries, but poor atmospheric stability and high interfacial reactivity limit widespread adoption. Coating LPSCl powders with ultrathin coatings using atomic layer deposition (ALD) mitigates these problems, protecting against atmospheric degradation and reducing reactivity with Li metal, yielding more stable cycling. Despite significant promise, the ALD mechanism is unknown, hampering the development of new coating chemistries. In this study, we elucidate the mechanism for Al 2 O 3 ALD on LPSCl using trimethyl aluminum (TMA) and H 2 O by combining in situ Fourier transform infrared spectroscopy, ex situ solid-state magic angle spinning nuclear magnetic resonance, UV Raman spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. We determine that ALD Al 2 O 3 nucleates promptly via TMA reaction with native —OH, —SH, and PS 3 -OH groups to form transient C–Al–O(S) species that are rapidly hydrolyzed during the subsequent H 2 O exposure. This reversible transformation maintains surface nucleophilicity and prevents sulfide decomposition. The resulting layer-by-layer growth leads to highly conformal Al 2 O 3 coatings on LPSCl that are readily scalable to ≥ 50 g quantities using a rotating drum fixture. This detailed understanding of ALD surface reactions provides critical insights guiding the selection of future ALD chemistries with improved performance.

atomic layer deposition↗
DOE OSTI2024

Effects of catholyte aging on high-nickel NMC cathodes in sulfide all-solid-state batteries

Sulfide solid-state electrolytes (SSEs) in all-solid-state batteries (SSBs) are recognized for their high ionic conductivity and inherent safety. The LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode offers a high thermodynamic potential of approximately 3.8 V vs. Li/Li + and a theoretical specific capacity of 200 mA h g −1 . However, the practical utilization of NMC811 in sulfide SSBs faces significant interfacial challenges. The oxidation instability of sulfide solid electrolytes against NMC811 and the formation of the cathode electrolyte interphase (CEI) during cycling lead to degradation and reduced cell performance. Volumetric changes in NMC during lithiation and de-lithiation can also cause detachment from sulfide electrolytes or internal particle cracking. Despite extensive galvanostatic cycling studies to address the issues, the calendar life of sulfide SSBs remains poorly understood. Here, we systematically studied the effects of four different catholytes on the calendar aging of LiNbO 3 (LNO)-coated NMC811, including Li 6 PS 5 Cl (LPSCl), Li 3 InCl 6 –Li 6 PS 5 Cl (LIC–LPSCl), Li 3 YCl 6 –Li 6 PS 5 Cl (LYC–LPSCl), and Li 10 GeP 2 S 12 (LGPS). Our results indicate that LPSCl provides optimal capacity retention when stored at high state-of-charge (SOC) at room temperature, but the LIC–LPSCl cathode shows significant capacity degradation and chemical incompatibility. We also established an effective electrochemical calendar aging testing protocol to simulate daily usage, enabling quick inference of the calendar life of SSBs. In conclusion, this new testing approach accelerates materials selection strategies for high-nickel NMC composite cathodes in sulfide SSBs.

25 ENERGY STORAGE↗
DOE OSTI2026

Evaluation of NETL’s Self-Healing Metallic Coating for Internal Corrosion Protection of Natural Gas Pipelines: Field Test

Steel pipelines are a safe, reliable, and affordable way to transport natural gas. However, the presence of impurities (e.g., water, carbon dioxide, and hydrogen sulfide) in the natural gas can cause internal corrosion, which can lead to pipeline leaks and failure. This paper reports on field tests of an innovative self-healing, corrosion-resistant, metallic coating developed at the National Energy Technology Laboratory (NETL) for protecting the interior surfaces of pipelines.

carbon dioxide (CO2)↗
DOE OSTI2026

Fluorinated Glyme Solvents to Extend Lithium-Sulfur Battery Life (Final Technical Report, Unlimited)

This project investigated a number of partially fluorinated glymes (PFGs) as electrolyte cosolvents to improve the performance of lithium-sulfur (Li-S) batteries. A major issue in Li-S cells is the electrochemical reaction of sulfur in the cathode to form lithium polysulfides (LPS) that dissolve in the electrolyte. Those LPS are electrochemically and chemically reactive at the lithium anode, resulting in lithium sulfide deposition on the anode and also electrochemical reaction at both the anode and cathode, leading to a “polysulfide shuttle” and reduced coulombic efficiency (CE) and self-discharge of the cell. PFGs reduce the solubility of LPS while maintaining good solubility of lithium salts such as LiTFSI. By adjusting the amount of PFG as cosolvent in the electrolyte, we showed that the solubility of LPS in the electrolyte can be tuned. (It is not desirable to completely eliminate LPS in the electrolyte, as they facilitate electrochemical reaction of the electrically insulating S 8 and Li 2 S within the cathode by shuttling charge between them and the conductive carbon.) Another issue in Li-S cells is degradation of the Li anode over many cycles of stripping (discharge) and plating (charge). We showed that PFGs have a beneficial effect on the physical morphology of the Li anode, SEI formation, and the CE of a Li-Li cell. Among the many PFGs tested, we found the best performance from PFGs designated PFG2 and PFG5, and these two PFGs were thoroughly studied. A systematic coin-cell study of electrolyte solvents of 90:10, 80:20, or 70:30 DME:PFG (DME = 1,2-dimethoxyethane) revealed some systematic trends: a higher percentage of PFG solvent led to substantially longer cycle life, but at the same time reduced specific capacity (mAh/g(S)) and cell capacity at higher rates. These studies used LiFSI as the electrolyte salt, as it was found to extend cycle life compared to LiTFSI. Finally, the addition of a small amount of 1,3-dioxolane (DOL) to the electrolyte was found to be beneficial. The overall optimal electrolyte solution was found to be 0.6 M LiFSI + 0.5 M LiNO 3 in 75:5:20 DME/DOL/PFG (either PFG2 or PFG5).

25 ENERGY STORAGE↗
DOE OSTI2024

Impact of mineral and non-mineral sources of iron and sulfur on the metalloproteome of Methanosarcina barkeri

Methanogens often inhabit sulfidic environments that favor the precipitation of transition metals such as iron (Fe) as metal sulfides, including mackinawite (FeS) and pyrite (FeS 2 ). These metal sulfides have historically been considered biologically unavailable. Nonetheless, methanogens are commonly cultivated with sulfide (HS - ) as a sulfur source, a condition that would be expected to favor metal precipitation and thus limit metal availability. Recent studies have shown that methanogens can access Fe and sulfur (S) from FeS and FeS 2 to sustain growth. As such, medium supplied with FeS 2 should lead to higher availability of transition metals when compared to medium supplied with HS - . Here, we examined how transition metal availability under sulfidic (i.e., cells provided with HS - as sole S source) versus non-sulfidic (cells provided with FeS 2 as sole S source) conditions impact the metalloproteome of Methanosarcina barkeri Fusaro. To achieve this, we employed size exclusion chromatography coupled with inductively coupled plasma mass spectrometry and shotgun proteomics. Significant changes were observed in the composition and abundance of iron, cobalt, nickel, zinc, and molybdenum proteins. Among the differences were alterations in the stoichiometry and abundance of multisubunit protein complexes involved in methanogenesis and electron transport chains. Furthermore, our data suggest that M. barkeri utilizes the minimal iron-sulfur cluster complex and canonical cysteine biosynthesis proteins when grown on FeS 2 but uses the canonical Suf pathway in conjunction with the tRNA-Sep cysteine pathway for iron-sulfur cluster and cysteine biosynthesis under sulfidic growth conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Arctic Permafrost Thawing Enhances Sulfide Oxidation

Permafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw-induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO 2 ) is relatively unconstrained. Resolving this uncertainty is important as thaw-driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean-atmosphere system and increase pCO 2 , producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate (SO 4 2- ) sulfur ( 34 S/ 32 S) and oxygen ( 18 O/ 16 O) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO 2 . Calculations found that approximately 80% of SO 4 2- in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, 34 S/ 32 S ratios, 13 C/ 12 C ratios of dissolved IC, and sulfur X-ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO 2 over timescales shorter than carbonate compensation (~10 4 yr) and, for mainstem samples, higher values of pCO 2 over timescales longer than carbonate compensation but shorter than the residence time of marine (~10 7 yr). Furthermore, the absolute concentrations of and Mg 2+ in the Koyukuk River, as well as the ratios of SO 4 2- and Mg 2+ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale-dependent feedback on warming.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Methanogens acquire and bioaccumulate nickel during reductive dissolution of nickelian pyrite

ABSTRACT Nickel (Ni) is a key component of the active site metallocofactors of numerous enzymes required for methanogenesis, including [NiFe]-hydrogenase, carbon monoxide dehydrogenase, and methyl CoM reductase, leading to a high demand for Ni among methanogens. However, methanogens often inhabit euxinic environments that favor the sequestration of nickel as metal-sulfide minerals, such as nickelian pyrite [(Ni,Fe)S 2 ], that have low solubilities and that are not considered bioavailable. Recently, however, several different model methanogens ( Methanosarcina barkeri , Methanococcus voltae , Methanococcus maripaludis ) were shown to reductively dissolve pyrite (FeS 2 ) and to utilize dissolution products to meet iron and sulfur biosynthetic demands. Here, using M. barkeri Fusaro, and laboratory-synthesized (Ni,Fe)S 2 that was physically isolated from cells using dialysis membranes, we show that trace nickel (<20 nM) abiotically solubilized from the mineral can support methanogenesis and limited growth, roughly fivefold less than the minimum concentration known to support methanogenesis. Furthermore, when provided direct contact with (Ni,Fe)S 2 , M. barkeri promoted the reductive dissolution of (Ni,Fe)S 2 and assimilated solubilized nickel, iron, and sulfur as its sole source of these elements. Cells that reductively dissolved (Ni,Fe)S 2 bioaccumulated approximately fourfold more nickel than those grown with soluble nickel and sulfide but had similar metabolic coupling efficiencies. While the mechanism for Ni uptake in archaeal methanogens is not known, homologs of the bacterial Nik uptake system were shown to be ubiquitous across methanogen genomes. Collectively, these observations indicate that (Ni,Fe)S 2 is bioavailable in anoxic environments and that methanogens can convert this mineral into nickel-, iron-, and sulfur-containing metalloenzymes to support methanogenesis and growth. IMPORTANCE Nickel is an essential metal, and its availability has changed dramatically over Earth history due to shifts in the predominant type of volcanism in the late Archean that limited its availability and an increase in euxinic conditions in the early Proterozoic that favored its precipitation as nickel sulfide minerals. Observations presented herein indicate that the methanogen, Methanosarcina barkeri , can acquire nickel at low concentration (<20 nM) from soluble and mineral sources. Furthermore, M. barkeri was shown to actively reduce nickelian pyrite; use dissolution products to meet their iron, sulfur, and nickel demands; and bioaccumulate nickel. These data help to explain how M. barkeri (and possibly other methanogens and anaerobes) can acquire nickel in contemporary and past anoxic or euxinic environments.

(NiFe)S2↗