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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Organic carbon oxidation state shapes fermentative methanogenic microbiomes and controls greenhouse gas fluxes

Organic compounds with a negative nominal oxidation state of carbon (NOSC) are thermodynamically recalcitrant in anaerobic ecosystems, but few studies have measured the influence of NOSC on carbon degradation rates, gaseous product yields, or microbiome composition. We amended anaerobic rice paddy sediment microcosms with water-soluble monomeric organic carbon compounds varying in NOSC. Consistent with thermodynamic and stoichiometric predictions, negative NOSC compounds are catabolized more slowly but produce more methane per mole of carbon. Negative NOSC microbiomes have higher alpha diversity, more syntrophs and methanogens, and fewer fermentative bacteria. Strikingly, fermentative bacterial taxa display genomically encoded NOSC catabolic preferences both in the lab and field. Negative NOSC-preferring fermenters have longer predicted doubling times, consistent with the thermodynamic recalcitrance of their preferred substrates. We propose that microbial NOSC catabolic preferences may reflect the thermodynamic niche of microorganisms and we anticipate that extending research on microbial catabolic preferences to a greater variety of organic carbon substrates and diverse microbiomes will improve our understanding of microbial carbon cycling and trait evolution.

Hu, Ruiwen↗
DOE OSTI2026

Membrane Degradation in PEM Fuel Cells: Part I. Modeling Gas Crossover and the Pt Band

Understanding chemical degradation of the proton-exchange membrane in fuel cells is crucial for extending their lifetimes. Herein, various degradation reactions reported in literature are organized and analyzed, including direct radical generation and an indirect (Fenton) pathway. To understand the transport of dissolved H 2 and O 2 crossover gases as they relate to membrane degradation, an agglomerate-scale model is introduced, treating gas, ionomer, and catalyst as discrete phases. The model reveals a key phenomenon: at working potentials, dissolved gases are mostly consumed at the interface between the catalyst layer and the membrane, leaving little gas to cross the membrane. Under open-circuit conditions, dissolved gases are not consumed and can then cross the membrane. This explains high H 2 O 2 concentrations and degradation rates seen in experiments but not captured in previous models. Following mixed-potential theory, crossover gases supply the hydrogen-oxidation and oxygen-reduction reactions, which occur simultaneously on individual Pt particles comprising the Pt band in the membrane, forming reactive species (H 2 O 2 , OH·). Results show crossover gas almost entirely reacts on the Pt band, allowing little to reach the opposite electrode. Furthermore, the micro-scale geometry of the catalyst-layer/membrane interface impacts the gas crossover at working potentials, indicating that cell construction affects membrane durability.

Johnson, Evan F. [Lawrence Berkeley National Labor↗
DOE OSTI2021

Aged and unaged pine wood pyrogenic organic matter: mineralization, elemental analysis and spectroscopy data (February 2020)

In this study, we used a pyrogenic organic matter (PyOM) degrading Streptomyces isolate – a globally common soil bacterium – to investigate the effects of physical (freeze-thaw and wet-dry), chemical (oxidation), and biological (microbial community incubation) ageing on the chemical properties and mineralizability of 350°C and 550°C pine wood PyOM. We used Fourier Transform Infrared spectroscopy (FTIR) and elemental analysis to characterize the aged and unaged PyOM, and cavity ring-down spectroscopy to trace CO2 emissions. The carbon (C) mineralization data from incubation of aged and unaged PyOM with the isolate are provided in co2cmg_picarro_022020.csv. This dataset contains raw carbon dioxide (CO2) data measured on the cavity ring-down spectroscopy over 1 month of incubation. The dataset also includes processed data such as cumulative CO2 emitted over multiple cycles of measurement and CO2 values normalized by the total carbon content in each PyOM treatment. The carbon, hydrogen and nitrogen elemental content of aged and unaged 350°C and 550°C pine wood PyOM are provided in CHN_pyom.csv. The relative peak heights measured during the FTIR analysis of aged and unaged PyOM are provided in ftir_peaks_rel.csv.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1986

Effect of crystallographical and geometrical changes of a ferrite head on magnetic signals during the sliding process with magnetic tape

This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.

Miyoshi, K.↗
NASA NTRS2001

Radiation Response of Emerging FeRAM Technology

The test results of measurements performed on two different sizes of ferroelectric random access memory (FeRAM) suggest the degradation is due to the low radiation tolerance of sense amplifiers and reference voltage generators which are based on commercial complementary metal oxide semiconductor (CMOS) technology. This paper presents total ionizing dose (TID) testing of 64Kb Ramtron FM1608 and 256Kb Ramtron FM1808.

Nguyen, D. N.↗
DOE OSTI2023

Degradation Mechanisms in TOPCon/POLO Solar Cells

This presentation shows how Poly-Si/SiO2 contacts show a post firing degradation/regeneration cycle. The following conclusions were made: 1) cycle changes surface passivation (Jo), but not the bulk lifetime; 2) cycle time depends on anneal temperature in light or dark (higher T, faster cycle); 3) 400 degrees Celsius anneal eliminates the cycle - only generation occurs; 4) cycle time and magnitude is not correlated with Tfire; 5) contact passivation is stable after cycling; 6) fundamental nature of defect(s) responsible is not known; 7) TOPCon cells/modules, if constructed well, seem to show minimal degradation issues (PVEL, Jolywood, Jinko, ET Solar), and 8) NREL/ASU are studying TOPCon cells and UC Davis has a molecular dynamics model for TOPCon.

degradation↗
DOE OSTI2026

Microstructure and Composition of Passivating Interfaces in Silicon Heterojunction Solar Modules Weathered in Different Climates

Sanyo/Panasonic patented silicon heterojunction with intrinsic thin layer (HIT) solar cells in the 1990's, which demonstrated world record photovoltaic (PV) efficiency around 2014 and inspired the newer generations of silicon heterojunction technology (SHJ) as well as the current world record back-contact PV cell designs. The high-quality passivation strategy, utilizing ultra-thin layers of hydrogenated amorphous silicon (a-Si:H), leads to high voltages and long carrier lifetimes, but these qualities may degrade over time as the modules operate outdoors. Here, we investigate local microstructure and composition at the interface layers of cells from HIT modules weathered in a hot, humid climate (Florida, USA) and temperate climate (Colorado, USA) for 10 years. We employ a comprehensive set of high-resolution electron microscopy imaging and spectroscopy to directly resolve structure and composition in these cells down to the nanoscale. We show features such as alignment of the In2O3 transparent conducting oxide and a-Si:H layers on the textured c-Si facets, interfacial oxidation at the a-Si:H/c-Si and In2O3/a-Si:H interfaces, and twinned c-Si resulting from epitaxial growth into the a-Si:H layer. Our results raise potential degradation mechanisms in these outdoor-weathered modules, but the root cause of electrical loss remains uncertain due to the very small changes in aged samples. This study shows that many atomic scale features at the In2O3/a-Si:H/c-Si interfaces are surprisingly robust, and the electrical losses with aging may either be attributed to other pathways or be very sensitive to the subtle chemical and microstructural features observed here.

14 SOLAR ENERGY↗
DOE OSTI2026

Molecularly engineered ZnO–carbon nanosheets from fumaric acid precursors for efficient photocatalytic water purification

The photocatalytic breakdown of organic contaminants is crucial for the development of water purification technology. Zinc oxide (ZnO) is an extensively researched photocatalyst; however, its efficacy is hindered by rapid charge recombination and limited utilization of UV irradiation. Resolving these issues necessitates integrating ZnO with conductive carbon phases via scalable, low-temperature synthesis. We provide a molecularly designed sol–gel method that converts zinc–fumarate coordination networks into two-dimensional ZnO–carbon nanosheets utilizing solely aqueous precursors and mild annealing temperatures (400–600 °C). This method utilizes fumaric acid as a dicarboxylate linker and polyvinylpyrrolidone (PVP) as a structural carbon source to produce ultrathin wurtzite ZnO nanosheets embedded inside an amorphous carbon matrix. The resultant ZnO-C hybrid achieves nearly complete methylene blue degradation within 10 min under UV-A illumination, demonstrating first-order kinetics and outstanding recyclability. Compared with commercial ZnO, the ZnO–C nanosheets exhibit comparable rapid photocatalytic degradation, enhanced adsorption behavior, a porous nanosheet morphology, and an integrated ZnO–carbon interfacial structure. These findings provide a viable molecular-templating approach to fabricating various metal oxide–carbon photocatalysts and underscore substantial enhancements in semiconductor efficacy in eco-friendly water treatment systems.

Ozcan, Muca [ORNL] (ORCID:0000000320020474)↗
NASA NTRS2011

The Effect of Photon Source on Heterogeneous Photocatalytic Oxidation of Ethanol by a Silica-Titania Composite

The objective of this study was to distinguish the effect of photon flux (i.e., photons per unit time reaching a surface) from that of photon energy (i.e., wavelength) of a photon source on the silica-titania composite (STC)-catalyzed degradation of ethanol in the gas phase. Experiments were conducted in a bench-scale annular reactor packed with STC pellets and irradiated with either a UV-A fluorescent black light blue lamp ((gamma)max=365 nm) at its maximum light intensity or a UV-C germicidal lamp ((gamma)max=254 nm) at three levels of light intensity. The STC-catalyzed oxidation of ethanol was found to follow zero-order kinetics with respect to CO2 production, regardless of the photon source. Increased photon flux led to increased EtOH removal, mineralization, and oxidation rate accompanied by lower intermediate concentration in the effluent. The oxidation rate was higher in the reactor irradiated by UV-C than by UV-A (38.4 vs. 31.9 nM/s) at the same photon flux, with similar trends for mineralization (53.9 vs. 43.4%) and reaction quantum efficiency (i.e., photonic efficiency, 63.3 vs. 50.1 nmol CO2 (mu)mol/photons). UV-C irradiation also led to decreased intermediate concentration in the effluent . compared to UV-A irradiation. These results demonstrated that STC-catalyzed oxidation is enhanced by both increased photon flux and photon energy.

Coutts, Janelle L.↗
NASA NTRS2016

Thermochemistry of CaO-MgO-Al2O3-SiO2 (CMAS) and Advanced Thermal and Environmental Barrier Coating Systems

CaO-MgO-Al2O3-SiO2 (CMAS) oxides are constituents in a broad number of materials and minerals which have recently inferred to discussions in materials science, planetary science, geochemistry and cosmochemistry communities. In materials science, there is increasing interest in the degradation studies of thermal (TBC) and environmental (EBC) barrier coatings of gas turbines by molten CMAS. These coatings have been explored to be applied on silicon-based ceramics and composites which are lighter and more temperature capable hot-section materials of gas turbines than the current Ni-based superalloys. The degradation of the coatings occurs when CMAS minerals carried by the intake air into gas turbines, e.g. in aircraft engines, reacts at high temperatures (1000C) with the coating materials. This causes premature failure of the static and rotating components of the turbine engines. We discuss some preliminary results of the reactions between CMAS and Rare-Earth (RE Y, Yb and Gd) oxide stabilized ZrO2 systems, and stability of the resulting oxides and silicates.

CaO-MgO-Al2O3-SiO2 (CMAS)↗
DOE OSTI2020

Degradation & Performance Studies of ALD-Stabilized Nano-Composite SOFC Cathodes

This work showed, definitively, for the first time, that zirconia Atomic Layer Deposited (ALD) overcoats improve the stability of Solid Oxide Fuel Cell (SOFC) cathodes by chemically gettering interfacial Sr that has segregated out of lanthanum strontium cobalt iron oxide (LSCF). The optimum ALD ZrO 2 overcoat thickness was found to be ≥5 nm and <10 nm. Gadolinium doped ceria (GDC) pre-infiltration was also shown, for the first time, to improve SOFC cathode stability through the chemical getting of Sr at the LSCF-backbone and LSCF-gas interfaces. Due to the fact that it can be performed easily in air on large-area electrodes, GDC pre-infiltration is likely more commercially viable than ALD ZrO 2 overcoating as an interfacial Sr gettering technique. Combining ZrO 2 overcoating with GDC pre-infiltration was not successful because the GDC nano-particles gettered the ZrO 2 overcoat instead of the interfacial Sr.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1977

Cross Linking and Degradation Mechanisms in Model Sealant Candidates

Model compounds were investigated as to which type of heterocyclic ring is the most advantageous for curing sealants based on perfluoroalkylether chains. The relative thermal, thermal oxidative, hydrolytic, and fuel stability of potential crosslinks were determined. Specifically substituted materials were synthesized and evaluation of their stabilities in air, inert atmosphere, water, and Jet-A fuel at 235 and 325 C was made. Three heterocyclic ring systems were considered, namely, triazine, 1,2,4- and 1,3,4-oxadiazoles.

Paciorek, K. L.↗
DOE OSTI2025

Structure-dependent mechanisms for plastic degradation in the marine environment

The visible and invisible accumulation of waste plastic in our oceans is a consequence of rapidly increasing inputs and very slow degradation rates. In general, this combination of effects results in long residence times. Nevertheless, the abiological degradation rate of a specific synthetic plastic varies widely, depending on its structural characteristics at the molecular, mesoscopic, and macroscopic levels. This chapter summarizes factors that determine these rates of degradation, and describes their principal mechanisms, for several of the major types of waste plastic found in the oceans. Mechanical forces cause cracking and flaking that break macroplastics into microplastics and even smaller fragments with increasing surface-to-volume ratios. Chemical degradation rates increase with surface area, influenced by intrinsic variations in crystallinity and the presence of additives, as well as extrinsic factors such as temperature, pH, and UV light intensity. Since polyolefin-based plastics are less dense than seawater and lack hydrolysable bonds in their polymer backbones, they accumulate close to the surface of the ocean where photo-oxidation is the principal cause of C–C bond cleavage in the polymer backbone. In contrast, polyesters and polyamides are denser than seawater and they sink, experiencing less exposure to solar irradiation. However, they can also degrade by slow hydrolysis of the C–O or C–N bonds intrinsic to the polymer structures.

Maciulis, Nicholas A.↗
DOE OSTI2025

Manganese‐Based Spinel Cathodes: A Promising Frontier for Solid‐State Lithium‐Ion Batteries

Recently, all-solid-state lithium-ion batteries (ASSLIBs), which exhibit improved safety and enhanced energy density compared to conventional commercialized lithium-ion batteries (LIBs), thereby have garnered extensive research interest. Among the promising cathode candidates, Mn-based spinel cathodes LiMn 2 O 4 (LMO) and LiNi 0.5 Mn 1.5 O 4 (LNMO), with the unique characteristics of low cost, structural stability, and 3D Li-ion diffusion channels, have demonstrated excellent performance in LIBs and presented great potential in ASSLIBs applications. However, several challenges, including structural degradations, poor interfacial contact, large interfacial resistance, and Mn-dissolution/diffusion during the electrochemical cycling, hinder their practical applications and commercialization in the ASSLIBs. Particularly, the high-voltage LNMO cathodes suffer from the challenge of electrochemical incompatibility with most of the solid-state electrolytes (SSEs). Herein, the spinel structure, the electrochemical behavior, and the structural degradation of the LMO/LNMO are explored. The characteristics and recent progress of the mitigating strategies to the challenges of various SSEs, including polymer-, oxide-, composite-, sulfide-, halide-, and LiPON-based SSEs, are introduced when paired with LMO/LNMO. Finally, the directions for future research to advance Mn-based spinel cathodes and fulfill the requirements of the next-generation ASSLIBs are also discussed.

Dou, Yu [Concordia University, Montreal, QC (Canad↗
DOE OSTI2021

Material Interactions in Severe Accidents – Benchmarking the MELCOR V2.2 Eutectics Model for a BWR-3 Mark-I Station Blackout: Part II – Uncertainty Analysis

Single case comparisons between severe accident simulations can provide detailed insights into severe accident model behavior, however, they cannot offer insights into model uncertainty, sensitivity to uncertain parameters, or underlying model biases.Here in this analysis, the single case benchmark comparison of the MELCOR material interaction models for a station blackout (SBO) scenario of a boiling water reactor (BWR) using representative Fukushima Daiichi Unit 1 boundary conditions is expanded to include an uncertainty analysis. As part of this uncertainty analysis, 1200 simulations are performed for each material interaction model (2400 total), with random sampling of 14 uncertain MELCOR input parameters. Input parameters are selected for their impact on models representing core degradation processes. These include candling, fuel rod failure, debris quenching and dryout. The analysis performed here is not a traditional “best-estimate” uncertainty analysis that uses best-estimate parameters or identifies best-estimate figure of merit distributions. Instead, it is an exploratory uncertainty analysis that identifies and interrogates underlying model form biases of the two material interaction models (eutectics and interactive materials models). Uniform distributions are applied to all uncertain parameters to ensure coverage of the model parameter uncertainty space. Key findings from this study include underlying model form biases exhibited by material interaction models, and notable differences in accident progression outcomes between the material interaction models. This uncertainty study extends and confirms the conclusions from the first part of this study, which compared the impact of material interaction modeling on simulation of a short-term station blackout scenario with representative Fukushima Daiichi Unit I boundary conditions. In particular, this study confirms that the eutectics model generally exhibits accelerated degradation and failure of fuel components, the core plate, and the lower head. The eutectics model also has a tendency to exhibit a greater degree of core degradation, greater debris mass formation, and larger debris mass ejection. Finally, the eutectics model exhibits higher maximum temperatures for fuel, cladding, particulate debris, oxidic molten pool, and metallic molten pool components than the interactive materials model; interactive materials model simulations exhibit a soft “limitation” on maximum temperatures that is related to the temperature at which material relocation occurs.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Diffusion-limited hydrolysis in polymeric materials

Polymer degradation under aggressive environmental stressors often develops heterogeneities due to diffusion-limited reaction phenomena. This is well established for diffusion-limited oxidation (DLO), which is known to occur for most polymeric materials at elevated temperatures but has been less summarized for the conditions of diffusion-limited hydrolysis (DLH). Here, an overview of hydrolysis for several materials and a computational model, analogous to the underlying equations for DLO, able to define this diffusion-reaction system is presented. A systematic study of the influence of various parameters, such as water diffusivity, reaction rate and order, and a more in-depth focus on residual isocyanate hydrolysis in a polymeric methylene diphenyl diisocyanate (pMDI) based polyurethane (PU) foam is given. For this system, we present experimental data for model ‘input’ parameters and discuss predictions for different conditions. We conceptually compare the behavior of diffusion-limited oxidation to that of diffusion-limited hydrolysis (DLH). With the mathematical framework and key material properties presented herein, any DLH phenomena following Fickian diffusion behavior can be understood, modeled, and predicted.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Sm 0.5 Sr 0.5 CoO 3-δ Surface Modification of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ -Ce 0.9 Gd0.1 2-δ Composite Oxygen Electrodes for Solid Oxide Electrochemical Cells

La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- δ -Ce 0.9 Gd 0.1 O 2- δ (LSCF-GDC) composite oxygen electrodes have been widely used in intermediate temperature (<700 °C) solid oxide cells, with composite usually providing better electrochemical performance than single-phase LSCF. However, LSCF-based electrodes are often observed to degrade over time due to Sr segregation. Here we present an impedance spectroscopy study comparing the degradation behaviors of LSCF-GDC and Sm 0.5 Sr 0.5 CoO 3- δ (SSC) infiltrated LSCF-GDC electrodes. The LSCF-GDC polarization resistance increases by ~5 times over ~1000 h at 650 °C. In contrast, the SSC-infiltrated electrode shows similar initial polarization resistance but much more stable performance. The impedance modeling results show that the improved stability is associated with the low frequency oxygen dissociative adsorption/desorption process. The results suggest that this adsorption/desorption process slows due to increased Sr segregation on LSCF over time, and that SSC does not degrade significantly due to Sr surface segregation.

Electrochemistry↗