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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Spinor Dynamics in Pristine and Mn 2+ -Doped CsPbBr 3 NC: Role of Spin–Orbit Coupling in Ground- and Excited-State Dynamics

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for optoelectronic and light-emitting devices because of their photoluminescence (PL) emission properties, which can be tuned/optimized by (I) surface passivation and (II) doping. (I) Surface passivation of the NC affects PL capabilities, as an underpassivated surface can introduce trap states, which reduces PL quantum yields. (II) Doping NCs and quantum dots with transition-metal ions provides stable optical transitions. Doping perovskite NCs with Mn 2+ ions provides high-intensity 4 T 1 → 6 A 1 optical transitions in addition to the bright intrinsic NC emission. In this study, we use noncollinear density functional theory (DFT) to investigate the roles of surface passivation and doping on the PL emission stability of perovskite NCs. Two models are investigated: (i) a pristine NC and (ii) a NC doped with the Mn 2+ ion. The noncollinear DFT includes spin–orbit coupling (SOC) between different spin states and produces spin adiabatic molecular orbitals. These orbitals are used to calculate the transition dipoles between electronic states, oscillator strengths, radiative transition rates, and emission spectra. It was found that the noncollinear spin basis with SOC slows down hole relaxation in the doped NC by 2 orders of magnitude compared to spin-polarized basis. This is attributed to “spin-flip” transition from the perovskite NC to the Mn 2+ dopant and low-probability nonradiative d-d transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Geometric and Magnetic Structures of K 2 ReI 6 as an Antiferromagnetic Insulator with Ferromagnetic Spin-Canting Originated from Spin–Orbit Coupling

We present the results of a crystallographic analysis, magnetic characterization including neutron powder diffraction, and theoretical assessment of K 2 ReI 6 prepared using solvent reactions. K 2 ReI 6 crystallizes in the space group P 2 1 / n with an inversion center. Magnetic measurements of K 2 ReI 6 sample indicate dominant antiferromagnetic coupling with a Curie–Weiss temperature of θ W = –63.3(1) K, effective magnetic moment ~2.64 μ B /Re but show a weak ferromagnetism ordered at ~24 K. Neutron powder diffraction indicates long-range order of the Re spins below 24 K, with an ordered magnetic moment of 2.2(1) μ B /Re at 1.5 K. Therefore, a canted antiferromagnetic structure is concluded. The electronic structures using first-principles calculations suggest that the antiferromagnetic model of K 2 ReI 6 yields the lowest total energy and opens a band gap with ~1.0 eV width, which is consistent with the UV–vis–NIR optical measurements. After including the spin–orbit coupling (SOC) into the calculation, the band degeneracies slightly shift without influencing the band gap. Furthermore, the results imply that K 2 ReI 6 is an antiferromagnetic insulator with weak ferromagnetic spin-canting resulting from strong SOC-entangled ground state S = 3/2.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Density Functional Calculations of Native Defects in CH 3 NH 3 PbI 3 : Effects of Spin–Orbit Coupling and Self-Interaction Error

We know that native point defects play an important role in carrier transport properties of CH3NH3PbI3. However, the nature of many important defects remains controversial due partly to the conflicting results reported by recent density functional theory (DFT) calculations. In this Letter, we show that self-interaction error and the neglect of spin–orbit coupling (SOC) in many previous DFT calculations resulted in incorrect positions of valence and conduction band edges, although their difference, which is the band gap, is in good agreement with the experimental value. Moreover, this problem has led to incorrect predictions of defect-level positions. Hybrid density functional calculations, which partially correct the self-interaction error and include the SOC, show that, among native point defects (including vacancies, interstitials, and antisites), only the iodine vacancy and its complexes induce deep electron and hole trapping levels inside of the band gap, acting as nonradiative recombination centers.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Diffusion of NiH on Ni(111) and of Ni with Adsorbed H on Ni(111) in the Context of Ni Coarsening in Solid Oxide Cells

In the Ni-based hydrogen electrode of a solid oxide cell (SOC), Ni coarsening is an important degradation mechanism and could be enhanced by NiH diffusing on the Ni particle surfaces. Here, in this work, the average lifetime and diffusion distance of NiH on Ni(111) are computed using density-functional theory and kinetic Monte Carlo methods. It is found that NiH is extremely short-lived and, thus, cannot promote coarsening in the SOC. Also, the diffusion of Ni on Ni(111) is shown to be at most slightly accelerated by H along NiH dissociation paths involving the movement of Ni with a nearby H. Based on this result, coarsening is not likely to be dramatically accelerated by the diffusion of Ni with H on Ni(111). However, support is provided for the experimental procedure of measuring the product of surface coverage and single-species diffusivity of Ni on Ni(111) in a hydrogen-rich atmosphere.

Ni coarsening↗
DOE OSTI2019

Quantitative El-Sayed Rules for Many-Body Wave Functions from Spinless Transition Density Matrices

One-particle transition density matrices and natural transition orbitals enable quantitative description of electronic transitions and interstate properties involving correlated many-body wave functions within molecular orbital framework. In this work we extend the formalism to the analysis of tensor properties, such as spin–orbit couplings (SOCs), which involve states of different spin projection. By using spinless density matrices and Wigner–Eckart’s theorem, the approach allows one to treat the transitions between states with arbitrary spin projections in a uniform way. In addition to a pictorial representation of the transition, the analysis also yields quantitative contributions of hole-particle pairs into the overall many-body matrix elements. Specifically, it helps to rationalize the magnitude of computed SOCs in terms of El-Sayed’s rules. The capabilities of the new tool are illustrated by the analysis of the equation-of-motion coupled-cluster calculations of two transition metal complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Spin Reorientation in Antiferromagnetic Layered FePt 5 P

FePt 5 P, a substitutional variant of the anti-CeCoIn 5 structure type in the space group P4/mmm, was synthesized by a high-temperature solid-state method and structurally characterized by X-ray diffraction. FePt 5 P contains layers of FePt 12 clusters formed by magnetically active Fe and heavy Pt with strong spin-orbit coupling (SOC); the layers are separated by P atoms. The various Fe–Pt distances in FePt 12 clusters generate complex magnetic orders in FePt 5 P. According to temperature-dependent magnetic and specific heat measurements, FePt 5 P shows a stripe-type antiferromagnetic order at T N ≈ 90 K, which is also confirmed by resistivity measurements. Furthermore, a spin reorientation occurs at ~74 and ~68 K in and out of the ab plane based on the specific heat measurements. The temperature-dependent neutron powder diffraction patterns demonstrate the antiferromagnetic order in FePt 5 P, and the spins orientate up to 58.4° with respect to the c axis at 10 K. First-principles calculations of FePt 5 P show the band splitting at the Fermi level by strong SOC and the s–d hybridization between P and Fe/Pt electrons enhances the structural stability and affects the magnetic ordering.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electrochemical Sodiation Mechanism in Magnetite Nanoparticle-Based Anodes: Understanding of Nanoionics-Based Sodium Ion Storage Behavior of Fe 3 O 4

We report electrochemical ion storage behaviors of Fe 3 O 4 nanoparticles, as a representative transition metal oxide for an environmentally benign and low-cost anode for a sodium-ion battery, are thoroughly investigated through a combination of electrochemical analysis and diagnostics of Fe 3 O 4 electrode cells, X-ray-based and spectroscopic analysis of material structure evolution as functions of depth of discharge (DoD) and state of charge (SoC), and first principle modeling. The gravimetric capacity is found to be 50 mA h/g for bulk Fe 3 O 4 (50 nm average crystallite size) and 100 mA h/g--about a tenth of the theoretical prediction for complete conversion--for Fe 3 O 4 nanoparticles (8.7 nm average particle size), respectively. A fundamental and mechanistic study of material evolution as functions of DoD and SoC shows that Fe 3 O 4 does not allow electrochemical incorporation of Na + ions into the empty cation positions of the inverse spinel structure, leading to our assertion that electrochemical intercalation of Na + ions to conversion of the Fe 3 O 4 anode in sodium-ion batteries is nonviable. A density functional theory investigation points to the impracticality of the intercalation of Na + ions into Fe 3 O 4 and further validates our experimental findings. We propose several possible mechanisms corresponding to the observed low capacity, including formation of solid electrolyte interphases with unfavorable properties and adsorption of Na + ions onto surfaces of nanoparticles and/or at heterointerfaces in Fe 3 O 4 composite electrodes in a NaPF 6 -based electrolyte system.

25 ENERGY STORAGE↗
DOE OSTI2024

Monitoring Redox Processes in Lithium-Ion Batteries by Laboratory-Scale Operando X-ray Emission Spectroscopy

Tracking changes in the chemical state of transition metals in alkali-ion batteries is crucial to understanding the redox chemistry during operation. X-ray absorption spectroscopy (XAS) is often used to follow the chemistry through observed changes in the chemical state and local atomic structure as a function of the state-of-charge (SoC) in batteries. In this study, we utilize an operando X-ray emission spectroscopy (XES) method to observe changes in the chemical state of active elements in batteries during operation. Operando XES and XAS were compared by using a laboratory-scale setup for four different battery systems: LiCoO 2 (LCO), Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 (NMC111), Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (NMC811), and LiFePO 4 (LFP) under a constant current charging the battery in 10 h (C/10 charge rate). We show that XES, despite narrower chemical shifts in comparison to XAS, allows us to fingerprint the battery SOC in real time. We further demonstrate that XES can be used to track the change in net spin of the probed atoms by analyzing changes in the emission peak shape. As a test case, the connection between net spin and the local chemical and structural environment was investigated by using XES and XAS in the case of electrochemically delithiated LCO in the range of 2–10% lithium removal.

25 ENERGY STORAGE↗
DOE OSTI2025

Exploring the Electrochemical Stability Window of an All-Solid-State Composite Cathode via a Novel Operando Tender XPS Setup

All-solid-state batteries (ASSBs) have the potential to provide greater energy density than conventional batteries based on liquid electrolytes. Here, an operando ASSB cell setup for tender X-ray photoelectron spectroscopy (XPS) was developed, and the interface of a Ni-rich layered transition metal oxide cathode active material (CAM) and an Li 6 PS 5 Cl (LPSCl) solid electrolyte (SE) was evaluated during initial charge/discharge cycles. After validating the cell performance against a conventional pouch cell operated at high compression, intermittent galvanostatic cycling was performed, and XPS data were recorded as a function of state of charge (SOC). Upon the initial charge of the cell to ≈3.3 V Li , the LPSCl appears to decompose into LiCl, Li 3 PS 4 , and polysulfides, whose amount gradually increases with potential. Upon further charge, at a potential higher than ≈3.8 V Li , initially, present sulfate and sulfite impurities decompose, and at ≈74% SOC (corresponding to a cathode potential of ≈4.10 V Li ), surface reconstruction of the CAM particles due to lattice oxygen release is detected. In addition, at potentials beyond ≈4.6 V Li , a decrease of the S 1s counts of the sum of the LPSCl, the thiophosphate, and polysulfide species suggests the formation of elemental sulfur that is lost via sublimation into the vacuum chamber.

25 ENERGY STORAGE↗
DOE OSTI2020

Cobalt-Group 13 Complexes Catalyze CO 2 Hydrogenation via a Co(-I)/Co(I) Redox Cycle

The Co(-I) dihydrogen complexes, [(η 2 -H 2 )CoML]-, where ML is the group 13 metalloligand, N(o-(NCH 2 PiPr 2 )C 6 H 4 ) 3 M, and M is Al, Ga, or In, were previously reported ( J. Am. Chem. Soc. 2017, 139, 6570-6573). In this work, the related Co(-I) end-on dinitrogen adducts, [(N 2 )CoML]-, were isolated and investigated as precatalysts for CO 2 hydrogenation. The Co–Ga catalyst was highly active, achieving 19,200 formate turnovers with an initial turnover frequency of 27,000 h –1 under 34 atm of 1:1 CO 2 /H 2 and using Verkade’s proazaphosphatrane as a base at ambient temperature. The Co–Al catalyst was moderately active, while the Co–In complex was inactive. Hence, tuning the group 13 ion greatly influences the catalytic activity at the Co site. To elucidate the role of the group 13 support, experimental and theoretical mechanistic studies of the Co–Ga and Co–Al catalysts were conducted. The Co(-I) H 2 species are potent hydride donors with estimated thermodynamic hydricities (ΔG° H– ) of 32.0(1) and 37.4(1) kcal/mol in CH 3 CN for M = Al and Ga, respectively. By acting as masked Co(I) dihydrides, the Co(-I) H 2 species operate via an unusual Co(-I)/Co(I) redox cycle. After hydride transfer to CO 2 , the resulting intermediate is the Co(I) hydride complex, HCoML, which was independently synthesized and structurally characterized for M = Al and Ga. The Gibbs free energy for H 2 binding, ΔG° bind (1 atm), to generate (η 2 -H 2 )HCoML was slightly more favorable for HCoGaL (-4.2(1) kcal/mol) than for HCoAlL (-2.7(1) kcal/mol). In the subsequent step, the deprotonation reaction to regenerate the initial catalyst was much more favorable for (η 2 -H 2 )HCoGaL (pK a of 31.4, CH 3 CN) than for (η 2 -H 2 )HCoAlL (pK a of 34.3). Finally, the straightforward substitution of Al with Ga perturbs the energy profile of the catalytic reaction (|ΔΔG° H– | = 5.4 kcal/mol, |ΔΔG° bind | = 1.5 kcal/mol, and |ΔΔG° K a | = 4.0 kcal/mol) and thus provides a thermodynamic rationale for the higher catalytic efficiency of Co–Ga over Co–Al.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Operando Bragg Coherent Diffraction Imaging of LiNi 0.8 Mn 0.1 Co 0.1 O 2 Primary Particles within Commercially Printed NMC811 Electrode Sheets

Due to complex degradation mechanisms, disparities between the theoretical and practical capacities of lithium-ion battery cathode materials persist. Specifically, Ni-rich chemistries such as LiNi 0.8 Mn 0.1 Co 0.1 O 2 (or NMC811) are one of the most promising choices for automotive applications; however, they continue to suffer severe degradation during operation that is poorly understood, thus challenging to mitigate. Here in this paper we use operando Bragg coherent diffraction imaging for 4D analysis of these mechanisms by inspecting the individual crystals within primary particles at various states of charge (SoC). Although some crystals were relatively homogeneous, we consistently observed non-uniform distributions of inter- and intracrystal strain at all measured SoC. Pristine structures may already possess heterogeneities capable of triggering crystal splitting and subsequently particle cracking. During low-voltage charging (2.7–3.5 V), crystal splitting may still occur even during minimal bulk deintercalation activity; and during discharging, rotational effects within parallel domains appear to be the precursor for the nucleation of screw dislocations at the crystal core. Ultimately, this discovery of the central role of crystal grain splitting in the charge/discharge dynamics may have ramifications across length scales that affect macroscopic performance loss during real-world battery operation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Giant Topological Hall Effect in van der Waals Heterostructures of CrTe 2 /Bi 2 Te 3

Discoveries of the interfacial topological Hall effect (THE) provide an ideal platform for exploring the physics arising from the interplay between topology and magnetism. The interfacial topological Hall effect is closely related to the Dzyaloshinskii-Moriya interaction (DMI) at an interface and topological spin textures. However, it is difficult to achieve a sizable THE in heterostructures due to the stringent constraints on the constituents of THE heterostructures, such as strong spin-orbit coupling (SOC). Here, we report the observation of a giant THE signal of 1.39 mu Omega.cm in the van der Waals heterostructures of CrTe 2 /Bi 2 Te 3 fabricated by molecular beam epitaxy, a prototype of two-dimensional (2D) ferromagnet (FM)/topological insulator (TI). This large magnitude of THE is attributed to an optimized combination of 2D ferromagnetism in CrTe 2 , strong SOC in Bi 2 Te 3 , and an atomically sharp interface. Furthermore, our work reveals CrTe 2 /Bi 2 Te 3 as a convenient platform for achieving large interfacial THE in hybrid systems, which could be utilized to develop quantum science and high-density information storage devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Entropy-Tailored Fast-Charging Sodium Layered Cathodes

O3-type layered transition metal (TM) oxides are widely used as cathode materials for Na-ion batteries due to their high energy density potential, enabled by the state of charge (SoC)-dependent transition from octahedral (O-type) to prismatic (P-type) structures during Na-ion (de)sodiation. However, the O–P transition is often criticized for compromising the Na-ion mobility and limiting the cycle life. Herein, we reveal the intrinsic correlation between O–P transitions, oxygen behaviors, and Na-ion kinetics. We demonstrate that a compositionally versatile, entropy-tailored approach can promote preferred transitions (characterized by large lattice parameter deviations in the O-type region and rapid O–P biphasic reactions), enhancing Na-ion migration, as revealed by in situ high-energy synchrotron X-ray diffraction (HEXRD). Additionally, irreversible oxygen loss at high SoC is effectively mitigated, while TM migration and surface reconstruction are greatly suppressed, further accelerating Na-ion transport and stabilizing the structure, as confirmed by X-ray absorption spectroscopy (XAS) and theoretical analyses. The result is an exceptionally high rate capability of 88.7 mAh g –1 at 20 C (2.4 A g –1 ) with a superior normalized retention of 72.6%, accompanied by a prolonged lifetime with 74.3% retention after 1000 cycles. In conclusion, this work advances the understanding of the chemistry–property relationships in O3-type layered cathodes and broadens the prospects for fabricating high-power-density electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Excited-State Dynamics of a CsPbBr 3 Nanocrystal Terminated with Binary Ligands: Sparse Density of States with Giant Spin–Orbit Coupling Suppresses Carrier Cooling

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light-emitting devices due to optoelectronic properties that can be tuned/optimized via halide composition, surface passivation, doping, and confinement. Compared to bulk materials, certain excited-state properties in NCs can be adjusted by electronic confinement effects such as suppressed hot carrier cooling and enhanced radiative recombination. In this paper, we use spinor Kohn–Sham orbitals (SKSOs) with spin–orbit coupling (SOC) interaction as a basis to compute excited-state dissipative dynamics simulations on a fully passivated CsPbBr 3 NC atomistic model. Redfield theory in the density matrix formalism is used to describe electron–phonon interactions which drive hot carrier cooling and nonradiative recombination ( k nonrad ). Radiative recombination ( k rad ) is calculated through oscillator strengths using SKSO basis. From k rad and k rad + k nonrad , we compute a theoretical photoluminescence quantum yield (PLQY) of 53%. Computed rates of hot carrier cooling ( k cooling ≈ 10 –1 1/ps) compare favorably with what has been reported in the literature. Interestingly, we observe that hot electron cooling slows down near the band edge, which we attribute to large SOC in the conduction band combined with strong confinement, which creates subgaps above the band edge. This slow carrier cooling could potentially impact hot carrier extraction before complete thermalization in photovoltaics (PVs). Implications of this work suggest that strong/intermediate confined APbX 3 NCs are better suited to applications in PVs due to slower carrier cooling near the conduction band edge, while intermediate/weak confined NCs are more appropriate for light-emitting applications, such as LEDs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Contrasting Responses of Soil Inorganic Carbon to Afforestation in Acidic Versus Alkaline Soils

Afforestation is recommended as an effective approach for carbon sequestration and environmental benefits. However, it remains less clear, and sometimes controversial, regarding how afforestation may impact soil inorganic carbon (SIC), a crucial component of the ecosystem carbon pool. Here, using field data from 619 afforested plots and 163 control plots across northern China, we investigated the relative and absolute differences in SIC between afforested and corresponding control plots. Our results suggested that afforestation increased SIC in acidic soils, while decreased SIC in alkaline soils. Fitting a linear mixed model and further a structure equation model, we found that afforestation-induced soil pH change was the most significant factor regulating SIC responses. In particular, SIC was more sensitive to pH change in more arid areas, where both soil pH and SIC stocks were high. Other factors could indirectly affect SIC responses to afforestation through modulating soil pH and soil organic carbon (SOC) dynamics. Moreover, afforestation-induced SIC changes also varied considerably among different species of tree plantations and across different soil depths. Importantly, in plantations of Pinus sylvestris var. mongholica, Pinus tabuliformis, and Populus spp., changes in SIC caused by afforestation were even comparable to that in SOC. Overall, our findings provide a data-based understanding on the comprehensive soil carbon dynamics following afforestation and its underlying mechanisms. With the increased use of afforestation and reforestation as nature-based solutions to climate change, their associated impacts on SIC need to be taken into account, especially in SIC-rich areas.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

The Importance of Accounting for Landscape Position When Investigating Grasslands: A Multidisciplinary Characterisation of a California Coastal Grassland

Abstract Grasslands are one of the most common land‐cover types, providing important ecosystem services globally, yet few studies have examined grassland critical‐zone functioning throughout hillslopes. This study characterised a coastal grassland over a small hillslope at Point Reyes National Seashore, California, using multidisciplinary techniques, combining remotely‐sensed, geophysical, plant, and soil measurements. Clustering techniques delineated the study area into four landscape zones, up‐, mid‐, and down‐slope, and a bordering riparian ecotone, which had distinct environmental properties that varied spatially across the site, with depth, and time. Soil moisture increased with depth and down slope towards a bordering riparian zone, and co‐varied with soil CO 2 flux rates both spatially and temporally. This highlighted three distinct controls of soil moisture on soil respiration: CO 2 fluxes were inhibited by high moisture content in the down‐slope during the wet winter months, and converged across landscape positions in the dry summer months, while also displaying post‐rain pulses. The normalised difference vegetation index (NDVI) ranged from 0.32 (September)–0.80 (April) and correlated positively with soil moisture and aboveground biomass, moving down slope. Yet, NDVI, aboveground biomass, and soil moisture were not correlated to soil organic carbon (SOC) content (0.4%–4.5%), which was highest in the mid‐slope. The SOC content may instead be linked to shifts in dominant grassland species and their rhizosphere properties with landscape position. This multidisciplinary characterisation highlighted significant heterogeneity in grassland properties with landscape position, and demonstrated an approach that could be used to characterise other critical‐zone environments on hillslopes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Climate Change Will Increase Biomass Proportion of Global Forest Carbon Stocks Under an SSP5–8.5 Climate Trajectory

Abstract A large amount of carbon is stored in global forests. However, the fraction of carbon stored as plant biomass versus soil organic carbon (SOC) varies among forest types, and potential changes over the 21st century are uncertain. Here, we used extensive data derived from inventories and remote sensing and Coupled Model Intercomparison Project Phase 6 (CMIP6) models to examine the current and 21st century dynamics in the proportion of biomass and SOC across global forests. We found that precipitation, elevation, soil, and wildfire were the primary controls of these differences in carbon pools. Under the SSP5–8.5 climate scenario, CMIP6 models project that the ratio of biomass to ecosystem carbon in global forests will increase across the 21st century, with the largest increases in boreal forests (95 ± 37%) compared to moist tropical forests (16 ± 15%). Changes in forest carbon pools resulting in greater biomass fraction will affect disturbance, and ecosystem carbon and energy balances, all of which interact with the climate system.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

ELM‐MOSART‐DOC: A Large‐Scale Riverine Dissolved Organic Carbon Model and Its Application Over the United States

Riverine dissolved organic carbon (DOC), primarily sourced from soil organic carbon (SOC), plays a crucial role in regional and global carbon cycles. However, the complexities of the underlying mechanisms and limited observations present significant challenges for predictive understanding of DOC at regional or larger scales. Recently, we developed a machine learning‐based (ML) map of DOC transformation rates, bridging the gap between SOC and DOC leaching flux and simplifying terrestrial DOC representation. Building on this advancement, we introduce ELM‐MOSART‐DOC, a DOC module integrated into the riverine component of the Energy Exascale Earth System Model (E3SM)—the Model for Scale Adaptive River Transport (MOSART). ELM‐MOSART‐DOC simulates DOC transport and transformation across both headwater streams and river networks, including those managed. Model validation demonstrates the ability of ELM‐MOSART‐DOC to accurately capture long‐term average DOC concentrations, with Kling‐Gupta Efficiency (KGE) scores of 0.58 and 0.76 at large and local stations, respectively. We further assess the impact of reservoirs through different simulation schemes, revealing that reservoirs significantly alter DOC fluxes by regulating streamflow patterns and promoting DOC mineralization. Model simulations indicate that reservoirs reduce total DOC flux from the Mississippi River into the ocean by 7.5%, with the long‐term average annual export decreasing from 3.34 to 3.14 teragrams (Tg) per year. ELM‐MOSART‐DOC integrates process‐based modeling with ML parameterization to enhance the predictive understanding of riverine biogeochemical processes. This approach reduces uncertainties in modeling regional and global carbon cycle ESMs and provides new insights into carbon cycling and its implications for global environmental change.

Li, Lingbo [Univ. of Houston, TX (United States); ↗