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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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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Flowable conducting particle networks in redox-active electrolytes for grid energy storage

This paper reports a new hybrid approach toward achieving high volumetric energy and power densities in an electrochemical flow capacitor for grid energy storage. The electrochemical flow capacitor suffers from high self-discharge and low energy density because charge storage is limited to the available surface area (electric double layer charge storage). Here, we examine two carbon materials as conducting particles in a flow battery electrolyte containing the VO 2+ /VO 2 + redox couple. Highly porous activated carbon spheres (CSs) and multi-walled carbon nanotubes (MWCNTs) are investigated as conducting particle networks that facilitate both faradaic and electric double layer charge storage. Charge storage contributions (electric double layer and faradaic) are distinguished for flow-electrodes composed of MWCNTs and activated CSs. A MWCNT flow-electrode based in a redox-active electrolyte containing the VO 2+ /VO 2 + redox couple demonstrates 18% less self-discharge, 10 X more energy density, and 20 X greater power densities (at 20 mV s -1 ) than one based on a non-redox active electrolyte. Additionally, a MWCNT redox-active flow electrode demonstrates 80% capacitance retention, and >95% coulombic efficiency over 100 cycles, indicating the feasibility of utilizing conducting networks with redox chemistries for grid energy storage.

25 ENERGY STORAGE↗
DOE OSTI2015

A high-fidelity multiphysics model for the new solid oxide iron-air redox battery part I: Bridging mass transport and charge transfer with redox cycle kinetics

A high-fidelity two-dimensional axial symmetrical multi-physics model is described in this paper as an effort to simulate the cycle performance of a recently discovered solid oxide metal-air redox battery (SOMARB). The model collectively considers mass transport, charge transfer and chemical redox cycle kinetics occurring across the components of the battery, and is validated by experimental data obtained from independent research. In particular, the redox kinetics at the energy storage unit is well represented by Johnson-Mehl-Avrami-Kolmogorov (JIVIAK) and Shrinking Core models. The results explicitly show that the reduction of Fe3O4 during the charging cycle limits the overall performance. Distributions of electrode potential, overpotential, Nernst potential, and H-2/H2O-concentration across various components of the battery are also systematically investigated. (C) 2015 Elsevier B.V. All rights reserved.

Jin, XF↗
DOE OSTI2019

Redox and volatility of Tc(CO)3 + compounds in waste glass melting

The behavior of non-pertechnetate (Tc(I)) species was studied by preparing three portions of dried low-activity waste-glass simulated feed, combining it with either the [fac-Tc(CO) (OH)] “tetramer,” the [fac-Tc(CO) (OH)(H O) ] “monohydroxo,” or the [fac-Tc(CO) Cl ] “trichloro,” and then heating samples to 600, 800, and 1000 °C. For the feeds and the heat-treated samples, Tc concentrations were measured by liquid scintillation counting (LSC) after NaOH and HNO fusion, and the results were used to determine the Tc volatility. For unheated samples and samples heated to 600 °C, the speciation of Tc was measured by X-ray absorption near-edge structure (XANES) analysis, while partitioning of Tc in the glass-forming melt was determined by leaching the samples in water and measuring the Tc concentration of the leachate. The current results are discussed in connection with previously reported data for Tc(VII) and Tc(IV) species to rationalize the potential mechanism on how different speciation of Tc affect its retention in glass. 3 4 3 2 2 3 3 3 2-

Luksic, SA↗
DOE OSTI2018

Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils

In this paper, oscillating redox conditions are a common feature of humid tropical forest soils, driven by an ample supply and dynamics of reductants, high moisture, microbial oxygen consumption, and finely textured clays that limit diffusion. However, the net result of variable soil redox regimes on iron (Fe) mineral dynamics and associated carbon (C) forms and fluxes is poorly understood in tropical soils. Using a 44-day redox incubation experiment with humid tropical forest soils from Puerto Rico, we examined patterns in Fe and C transformations under four redox regimes: static anoxic, "flux 4-day" (4d oxic, 4d anoxic), "flux 8-day" (8d oxic, 4d anoxic) and static oxic. Prolonged anoxia promoted reductive dissolution of Fe-oxides, and led to an increase in soluble Fe(II) and amorphous Fe oxide pools. Preferential dissolution of the less-crystalline Fe pool was evident immediately following a shift in bulk redox status (oxic to anoxic), and coincided with increased dissolved organic C, presumably due to acidification or direct release of organic matter (OM) from dissolving Fe(III) mineral phases. The average nominal oxidation state of water-soluble C was lowest under persistent anoxic conditions, suggesting that more reduced organic compounds were metabolically unavailable for microbial consumption under reducing conditions. Anoxic soil compounds had high H/C values (and were similar to lignin-like compounds) whereas oxic soil compounds had higher O/C values, akin to tannin- and cellulose-like components. Cumulative respiration derived from native soil organic C was highest in static oxic soils. These results show how Fe minerals and Fe-OM interactions in tropical soils are highly sensitive to variable redox effects. Shifting soil oxygen availability rapidly impacted exchanges between mineral-sorbed and aqueous C pools, increased the dissolved organic C pool under anoxic conditions implying that the periodicity of low-redox events may control the fate of C in wet tropical soils.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Assessment of the flagellar redox potential in Chlamydomonas reinhardtii using a redox-sensitive fluorescent protein, Oba-Qc

Highlights: • In vivo flagellar redox potential of Chlamydomonas reinhardtii was assessed. • Non-ratiometric redox biosensor was induced into flagella at the constant amount. • The standard curve could be drawn from the in vitro experiments. • Fluorescence of live cells was compared with the standard curve for quantification. • The in vivo redox potential changes depending on the light conditions for culture. Cellular reducing-oxidizing (redox) potential is mainly determined by the concentration ratio between reduced and oxidized glutathiones. It is normally kept at a moderately reduced state but affected to some extent by metabolic activities such as respiration and/or photosynthesis. Changes in redox potential induce many cellular activities collectively called redox responses. For an understanding of the dynamics of the cellular redox responses, redox potential must be accurately assessed in vivo. In this study, we developed a method to measure the in vivo redox potential in the green alga Chlamydomonas reinhardtii, using Oba-Qc, a recently developed redox-monitoring protein. Taking advantage of the periodic flagellar assembly, we introduced Oba-Qc molecules into the flagella at a constant density. Fluorescence signals from flagella in live cells, calibrated against the fluorescence from the samples in buffers of known redox potentials, determined the redox potential to be ∼-250 mV in the light and ∼-280 mV in the dark. Introduction of a sensor protein fused with a structural protein that assembles at a constant density will be also applicable for measurements of various kinds cellular signals in flagella.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Quantitative Decoupling of Oxygen-Redox and Manganese-Redox Voltage Hysteresis in a Cation-Disordered Rock Salt Cathode

Pronounced voltage hysteresis in Li-excess cathode materials is commonly thought to be associated with oxygen redox. However, these materials often possess overlapping oxygen and transition-metal redox, whose contributions to hysteresis between charge and discharge are challenging to distinguish. In this work, a two-step aqueous redox titration is developed with the aid of mass spectrometry (MS) to quantify oxidized lattice oxygen and Mn 3+/4+ redox in a representative Li-excess cation-disordered rock salt—Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO). Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, thereby allowing Mn and O redox capacities to be decoupled. The decoupled O and Mn redox coulombic efficiencies are close to 100% for the LMTO cathode, indicating high charge-compensation reversibility. As incremental Mn and O redox capacities are quantitatively decoupled, each redox voltage hysteresis is further evaluated. Overall, LMTO voltage hysteresis arises not only from an intrinsic charge-discharge voltage mismatch related to O redox, but also from asymmetric Mn-redox overvoltages. The results reveal that O and Mn redox both contribute substantially to voltage hysteresis. In conclusion, this work further shows the potential of designing new analytical workflows to experimentally quantify key properties, even in a disordered material having complex local coordination environments.

25 ENERGY STORAGE↗
DOE OSTI2022

Ru-promoted perovskites as effective redox catalysts for CO2 splitting and methane partial oxidation in a cyclic redox scheme

The current study reports AxA’1-xByB’1-yO3- perovskite redox catalysts (RCs) for CO2-splitting and methane partial oxidation (POx) in a cyclic redox scheme. Strontium (Sr) and iron (Fe) were chosen as A and B site elements with A’ being lanthanum (La), samarium (Sm) or yttrium (Y), and B’ being manganese (Mn), or titanium (Ti) to tailor their equilibrium oxygen partial pressures (P_(O_2 ) s) for CO2-splitting and methane partial oxidation. DFT calculations were performed for predictive optimization of the oxide materials whereas experimental investigation confirmed the DFT predicted redox performance. The redox kinetics of the RCs improved significantly by 1 wt.% ruthenium (Ru) impregnation without affecting their redox thermodynamics. Ru impregnated LaFe0.375Mn0.625O3 (A=0, A’=La, B=Mn, and B’=0) was the most promising RC in terms of its superior redox performance (CH4/CO2 conversion >90% and CO selectivity~ 95%) at 800oC. Long-term redox testing over Ru impregnated LaFe0.375Mn0.625O3 indicated stable performance during the first 30 cycles following with a ~25% decrease in the activity during the last 70 cycles. Air treatment was effective to reactivate the redox catalyst. Detailed characterizations revealed the underlying mechanism for redox catalyst deactivation and reactivation. Furthermore, this study not only validated a DFT guided mixed oxide design strategy for CO2 utilization but also provides potentially effective approaches to enhance redox kinetics as well as long-term redox catalyst performance.

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

Reactivity of Redox Cycled Fe-bearing Subsurface Sediments Towards Hexavalent Chromium Reduction

Structural Fe(II) in clay minerals and natural sediments is known to reduce Cr(VI) to Cr(III), but the effect of redox-cycled Febearing natural sediments on Cr(VI) reduction kinetics is poorly understood. The objective of this study was to understand the kinetics and mechanisms of Cr(VI) reduction by Fe(II) in redox cycled natural sediment. Fe-bearing sediment was collected from the Ringold formation in the 300 area of Hanford, Washington, United States. Fe redox cycling of the sediment was accomplished via four cycles of bioreduction of structural Fe(III) in Hanford sediment and air oxidation of the resulting Fe(II). Bio-produced Fe(II) in Hanford sediment from each redox cycle was utilized to reduce Cr(VI) at three temperatures (10, 20 and 30° C). The initial rate of Cr(VI) reduction generally increased with each redox cycle, which was more pronounced at high temperatures. The amount of Fe(II) oxidized to the amount of Cr(VI) reduced was close to the expected stoichiometric ratio of 3. Aqueous concentrations of Si, Al, and Fe revealed some dissolution of the sediment after reaction with Cr(VI). Xray diffraction (XRD) and scanning electron microscopy (SEM) detected secondary mineral formation. Mössbauer data showed that the oxidation of Fe(II) was coupled with the reduction of Cr(VI) but no Feoxides/ oxyhydroxides formed. Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), XANES, and EXAFS were performed for representative reduced Cr solids that formed from reduction of Cr(VI) by sediment-associated Fe(II) at 30oC. TEM revealed that the d-spacing of Cr-reacted montmorillonite at 30° C, a dominant Fe-bearing mineral in Hanford sediment, expanded from 10 Å to 13 Å. This layer expansion was likely due to intercalation of reduced Cr(III) into the interlayer space of the montmorillonite structure. EELS exhibited an L2 absorption peak at 586.0 eV and an L3 absorption peak at 577.0 eV, suggestive of Cr(III) in a hydroxide mineral phase. Similarly, XANES and EXAFS analyses confirmed Cr(VI) reduction to Cr(OH)3 at 30° C and indicated an edge-sharing coordination of the Cr(III) octahedra to 2-3 other Cr or metal ions. This study has important implications for understanding the reactivity of clay-rich sediment towards Cr(VI) reduction at contaminated sites and the stability of the reduced Cr(III).

Bishop, Michael E.↗