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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Sub-micrometer sized yttrium oxide fibers prepared through hydrothermal reaction

Research highlights: {yields} Y{sub 2}O{sub 3} fibers were synthesized by hydrothermal reaction followed by calcination. {yields} Y(OH){sub x}Cl{sub 3-x}.yH{sub 2}O was received from hydrothermal reaction. {yields} Y{sub 2}O{sub 3} fibers showed outstanding high-temperature stability. -- Abstract: Yttrium oxide fibers have been synthesized via hydrothermal reaction and subsequent thermal treatment using yttrium chloride as precursor. The products before and after the thermal treatment were characterized by powder X-ray diffractions (XRD), scanning electron microscopy (SEM), ion-chromatograph analysis, and thermogravimetry and differential thermal analysis (TG-DTA). The fiber diameter ranged from 100 to 300 nm, while the length was up to tens of microns. It was found that the chemical composition and morphology of the products were closely related to the pH value of reaction solution, and fibrous products could be obtained at pH 9.5-10.25. These oxide fibers exhibited outstanding high-temperature stability, which maintained their morphology at temperature up to 1400 {sup o}C.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Removal of Tc-99, Zr-95, and Nb-95, From Solutions Obtained After Dissolution of Irradiated Mo Targets

Decontamination of 99 Tc, Nb, and Zr impurities in dissolved irradiated Mo disks can be accomplished using Fe(II) precipitation. Here, we report bench-scale experiments and large-scale demonstrations on removal of 99 Tc (0.1 mM), 95 Nb, and 95 Zr from dissolved Mo disk simulant solutions. Tc removal is accomplished through the reduction and simultaneous immobilization of Tc(VII) by Fe(II), producing an insoluble, Tcincorporated Fe(II)-Fe(III) solid that is removed by filtration. Large-scale testing showed that Tc (97.6% ± 1.7%) is removed without affecting 99 Mo yields. Other important side reaction product impurities in irradiated Mo targets, namely various isotopes of Nb and Zr, are also removed (>99%) in this process. The effects of metal (Fe, Tc, Mo) concentrations, Fe(II)/Fe(III) ratio, pH, temperature, Fe addition method, and hydrogen peroxide addition were tested. The minimum amount of Fe(II) needed to remove up to 99% Tc is 10 mM and the optimal pH value for simultaneous removal of Tc, Nb, and Zr impurities is pH 13.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Surface Modification of a MXene by an Aminosilane Coupling Agent

MXenes, two–dimensional (2D) transition metal carbides and/or nitrides, possess surface termination groups such as hydroxyl, oxygen, and fluorine, which are available for surface functionalization. Their surface chemistry is critical in many applications. This article reports amine functionalization of Ti 3 C 2 T x MXene surface with [3–(2–aminoethylamino)–propyl]trimethoxysilane (AEAPTMS). Characterization techniques such as X–ray photoelectron spectroscopy verify the success of the surface functionalization and confirm that the silane coupling agent bonds to Ti 3 C 2 T x surface both physically and chemically. The functionalization changes the MXene surface charge from –35 to +25 mV at neutral pH, which allows for in situ preparation of self–assembled films. Further, surface charge measurements of the functionalized MXene at different pH values show that the functionalized MXene has an isoelectric point at a pH around 10.7, and the highest reported positive surface charge of +62 mV at a pH of 2.58. Furthermore, the existence of a mixture of different orientations of AEAPTMS and the simultaneous presence of protonated and free amine groups on the surface of Ti 3 C 2 T x are demonstrated. As a result, the availability of free amine groups on the surface potentially permits the fabrication of crosslinked electrically conductive MXene/epoxy composites, dye adsorbents, high–performance membranes, and drug carriers. Surface modifications of this type are applicable to many other MXenes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Chloride facilitates Mn(III) formation during photoassembly of the Photosystem II oxygen-evolving complex

The Mn 4 Ca oxygen-evolving complex (OEC) in Photosystem II (PSII) is assembled in situ from free Mn 2+ , Ca 2+ , and water. In an early light-driven step, Mn 2+ in a protein high-affinity site is oxidized to Mn 3+ . Using dual-mode electron paramagnetic resonance spectroscopy, we observed that Mn 3+ accumulation increases as chloride concentration increases in spinach PSII membranes depleted of all extrinsic subunits. At physiologically relevant pH values, this effect requires the presence of calcium. Here, when combined with pH studies, we conclude that the first Mn 2+ oxidation event in OEC assembly requires a deprotonation that is facilitated by chloride.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Structural alteration of hexagonal birnessite by aqueous Mn(II): Impacts on Ni(II) sorption

We studied the impacts of aqueous Mn(II) (1 mM) on the sorption of Ni(II) (200 μM) by hexagonal birnessite (0.1 g L- 1) at pH 6.5 and 7.5 with batch experiments and XRD, ATR-FTIR and Ni K-edge EXAFS analyses. In the absence of Mn(II)aq, sorbed Ni(II) was coordinated predominantly as triple corner-sharing complexes at layer vacancies at both pH values. Introduction of Mn(II)aq into Ni(II)-birnessite suspensions at pH 6.5 caused Ni(II) desorption and led to the formation of edge-sharing Ni(II) complexes. This was attributed to competitive displacement of Ni(II) from layer vacancies by either Mn(II) or by Mn(III) formed through interfacial Mn(II)-Mn(IV) comproportionation, and/or incorporation of Ni(II) into the birnessite lattice promoted by Mn(II)-catalyzed recrystallization of the sorbent. Similar to Mn(II)aq, the presence of HEPES or MES caused the formation of edge-sharing Ni(II) sorption complexes in Ni(II)-birnessite suspensions, which was attributed to partial reduction of the sorbent by the buffers. At pH 7.5, interaction with aqueous Mn(II) caused reductive transformation of birnessite into secondary feitknechtite that incorporated Ni(II), enhancing removal of Ni(II) from solution. These results demonstrate that reductive alteration of phyllomanganates may significantly affect the speciation and solubility of Ni(II) in anoxic and suboxic environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO{sub 3} ceramics

We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO{sub 3} ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 {sup o}C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO{sub 3} ceramics could be reduced to 1100 {sup o}C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO{sub 3} ceramics with a high permittivity ({epsilon}{sub r} = 2946 and {epsilon}{sub max} = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO{sub 3} ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ion Gating in Nanopore Electrode Arrays with Hierarchically Organized pH-Responsive Block Copolymer Membranes

Inspired by biological ion channels, artificial nanopore-based architectures have been developed for smart ion/molecular transport control with potential applications to iontronics and energy conversion. Advances in nanofabrication technology enable simple, versatile construction methods, and post-fabrication functionalization delivers nanochannels with unique ion transport-control attributes. Here, we characterize a pH-responsive, charge-selective dual-gating block copolymer (BCP) membrane composed of polystyrene-b-poly(4-vinylpyridine) (PS 48400 -b-P4VP 21300 ), capable of self-organizing into highly ordered nanocylindrical domains. Because the PS-b-P4VP membrane exhibits pH-dependent structural transitions, it is suitable for designing intelligent pH-gated biomimetic channels, for example, exhibiting on–off transport switching at pH values near the pK a of P4VP with excellent anion permselectivity at pH < pK a . Introducing the BCP membrane onto nanopore electrode arrays (BCP@NEAs) allows the BCP to serve as a pH-responsive gate controlling ion transfer into the NEA nanopores. Such selectively transported and confined ions are detected by using a 100 nm gap dual-ring nanoelectrode structure capable of enhancing current output by efficient redox cycling with an amplification factor >10 2 . In addition, BCP@NEAs exhibit extraordinary pH-gated ion selectivity, resulting in a 3380-fold current difference between anion and cation probes at pH 3.0. Furthermore, this hierarchically organized BCP-gated NEA system can serve as a template for the development of other stimulus-responsive ion gates, for example, those based on temperature and ligand gating, thus exploiting the intrinsic advantages of NEAs, such as enhanced sensitivity based on redox cycling, which may lead to technological applications such as engineered biosensors and iontronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Plasma-Initiated Graft Polymerization of Acrylic Acid onto Fluorine-Doped Tin Oxide as a Platform for Immobilization of Water-Oxidation Catalysts

The discovery of new and versatile strategies for the immobilization of molecular water-oxidation catalysts (WOCs) is crucial for developing clean energy conversion devices [e.g., (photo)electrocatalytic cells for water splitting]. The traditional approach for surface attachment to transparent conductive oxides [e.g., fluorine doped tin oxide (FTO)] is via synthetic modification of the ligand architecture to incorporate functional groups such as carboxylic acids (-COOH) or phosphonates (-PO 3 H 2 ) prior to immobilization. However, challenges arising from desorption and the cumbersome derivatizations steps have limited the scope and applications of surface-bound WOCs. Herein, we report the successful immobilization of underivatized Ru(II)-based WOCs (Ru–Cat1 = [Ru(tpy) (bpy) (H 2 O)] 2+ (tpy = 2,2':6'2"–terpyridine and bpy = 2,2;-bipyridine) and Ru–Cat2 = [Ru(Mebimpy) (bpy) (H 2 O)] 2+ (Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) pyridine)) and the Ru(II) polypyridyl chromophore Ru–C3 = [Ru(bpy) 3 ] 2+ onto a FTO plasma-grafted poly(acrylic acid) surface (PAA|FTO). Various characterization techniques such as attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and cyclic voltammetry measurements provide evidence for the plasma-induced grafted PAA|FTO film and immobilization. Surface stability and electrocatalytic properties of these new hybrid composite films upon cycling were investigated at different pH values. Immobilized Ru–Cat1 and Ru–Cat2 onto PAA|FTO displayed pH-dependent (RuIII/RuII) couples and onset potentials indicative of PCET (proton-coupled electron transfer) reactions. Based on cyclic voltammetry results and spectroscopic monitoring, the immobilized WOCs Ru–Cat1 and Ru–Cat2 exhibited a higher surface stability in neutral aqueous solutions relative to Ru–C3 upon electrochemical oxidation. Furthermore, we attribute the surface PCET and stability to the presence of a water ligand in the coordination sphere of immobilized Ru–Cat1 and Ru–Cat2 which can H-bond with negatively charged carboxylate groups of the cross-linked PAA brushes. Our findings demonstrate that the plasma-grafted polymeric network onto FTO offers a versatile platform to directly anchor unmodified homogeneous WOCs or chromophores for potential applications in solar-to-fuel energy conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Modulation of PEDOT:PSS pH for efficient inverted perovskite solar cells with reduced potential loss and enhanced stability

Inverted p-i-n perovskite solar cells (PVSCs) using PEDOT:PSS as the hole-transporting layer (HTL) is one of the most widely adopted device structures thus far due to its facile processability and good compatibility for high throughput manufacturing processes. However, most of the PEDOT:PSS-based CH 3 NH 3 PbI 3 PVSCs reported to date suffered an inferior open-circuit voltage (V OC ) (0.88-0.95 V) compared to that (1.05-1.12 V) obtained for common CH 3 NH 3 PbI 3 PVSCs, revealing a severe potential loss issue. Herein, we describe a simple method to alleviate this problem by tuning the pH value of PEDOT:PSS with a mild base, imidazole. Accompanied by the pH modulation, the blended imidazole concurrently tailors the surface texture and electronic properties of PEDOT:PSS to promote the quality and crystallization of the perovskite film deposited on top of it and enable better energy-level alignment at this corresponding interface. Consequently, the PVSC using this modified PEDOT:PSS HTL yields an enhanced power conversion efficiency (PCE) of 15.7% with an enlarged V OC of 1.06 V and improved long-term stability. Lastly, these outperform the pristine device showing a PCE of 12.7% with a much smaller V OC of 0.88 V and unsatisfactory environmental stability.

14 SOLAR ENERGY↗
DOE OSTI2021

Structure of the electrical double layer at the ice–water interface

The surface of ice in contact with water contains sites that undergo deprotonation and protonation and can act as adsorption sites for aqueous ions. Therefore, an electrical double layer should form at this interface and existing models for describing the electrical double layer at metal oxide–water interfaces should be able to be modified to describe the surface charge, surface potential, and ionic occupancy at the ice–water interface. I used a surface complexation model along with literature measurements of the zeta potential of ice in brines of various strength and pH to constrain equilibrium constants. I then made predictions of ion site occupancy, surface charge density, and partitioning of counterions between the Stern and diffuse layers. The equilibrium constant for cation adsorption is more than 5 orders of magnitude larger than the other constants, indicating that this reaction dominates even at low salinity. Deprotonated OH sites are predicted to be slightly more abundant than dangling O sites, consistent with previous work. Surface charge densities are on the order of ±0.001 C/m2 and are always negative at the moderate pH values of interest to atmospheric and geophysical applications (6–9). In this pH range, over 99% of the counterions are contained in the Stern layer. This suggests that diffuse layer polarization will not occur because the ionic concentrations in the diffuse layer are nearly identical to those in the bulk electrolyte and that electrical conduction and polarization in the Stern layer will be negligible due to reduced ion mobility.

Daigle, Hugh (ORCID:0000000260628321)↗
DOE OSTI2011

Proton management as a design principle for hydrogenase-inspired catalysts

The properties of the hydrogenase-inspired [Ni(PNP)2]2+ (PNP ¼ Et2PCH2NMeCH2PEt2) catalyst for homogeneous hydrogen oxidation in acetonitrile solution are explored from a theoretical perspective for hydrogen production. The defining characteristic of this catalyst is the presence of pendent bases in the second coordination sphere that function as proton relays between the solution and the metal center. DFT calculations of the possible intermediates along proposed catalytic pathways are carried out and used to construct coupled Pourbaix diagrams of the redox processes and free-energy profiles along the reaction pathways. Analysis of the coupled Pourbaix diagrams reveals insights into the intermediate species and the mechanisms favored at different pH values of the solution. Consideration of the acid-base behavior of the metal hydride and H2 adduct species imposes additional constraints on the reaction mechanism, which can involve intramolecular as well as intermolecular proton-coupled electron-transfer steps. The efficacy of the catalyst is shown to depend critically on the pKa values of these potential intermediates, as they control both the species in solution at a given pH and the freeenergy profile of reaction pathways. Optimal relationships among these pKa values can be identified, and it is demonstrated that ‘‘proton management’’, i.e., the manipulation of these pKa values (e.g., through choice of metal or substituents on ligands), can serve as a design principle for improved catalytic behavior. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

Small, Yolanda A↗
DOE OSTI2016

Molecular origins of the zeta potential

The zeta potential (ZP) is an oft-reported measure of the macroscopic charge state of solid surfaces and colloidal particles in contact with solvents. However, the origin of this readily measurable parameter has remained divorced from the molecular-level processes governing the underlying electrokinetic phenomena, which limits its usefulness. Here, we connect the macroscopic measure to the microscopic realm through nonequilibrium molecular dynamics simulations of electroosmotic flow between parallel slabs of the hydroxylated (110) rutile (TiO 2 ) surface. These simulations provided streaming mobilities, which were converted to ZP via the commonly used Helmholtz-Smoluchowski equation. A range of rutile surface charge densities (0.1 to –0.4 C/m 2 ), corresponding to pH values between about 2.8 and 9.4, in RbCl, NaCl, and SrCl 2 aqueous solutions, were modeled and compared to experimental ZPs for TiO 2 particle suspensions. Simulated ZPs qualitatively agree with experiment and show that “anomalous” ZP values and inequalities between the point of zero charge derived from electrokinetic versus pH titration measurements both arise from differing co- and counterion sorption affinities. We show that at the molecular level the ZP arises from the delicate interplay of spatially varying dynamics, structure, and electrostatics in a narrow interfacial region within about 15 Å of the surface, even in dilute salt solutions. This contrasts fundamentally with continuum descriptions of such interfaces, which predict the ZP response region to be inversely related to ionic strength. In reality the properties of this interfacial region are dominated by relatively immobile and structured water. Furthermore, viscosity values are substantially greater than in the bulk, and electrostatic potential profiles are oscillatory in nature.

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

Tank 48H Tetraphenylborate Mitigation: Simulant Studies using Sodium Permanganate

Tank 48H currently holds legacy material containing organic tetraphenylborate (TPB) compounds from the operation of the In-Tank Precipitation (ITP) process. TPB was added during the ITP process to precipitate the otherwise soluble cesium as insoluble cesium TPB (CsTPB), but excessive benzene generation from TPB degradation curtailed this treatment method. The contents of Tank 48H, which include approximately 26.000 kg of potassium TPB (KTPB) and trace CsTPB, are not compatible with the waste treatment facilities at the Savannah River Site (SRS) since the organic content and the associated flammability issues pose a challenge to the salt processing and sludge processing facilities within the liquid waste system. An in-tank process to remove (or decompose) TPB safely would be of great value. Previous testing at Savannah River National Laboratory (SRNL) demonstrated the destruction of glycolate via chemical oxidation using sodium permanganate with simulated and radioactive waste. Scoping tests were performed to study the destruction of TPB to determine if the contents of Tank 48H would be amenable to the same type of destruction. Partial destruction of TPB was observed in Tank 48H simulants under mild conditions (e g., pH 11, room temperature) with no definitive indication of benzene generation. To build upon the success of the scoping tests, an additional study was requested to provide a better understanding of the underlying chemistry for Tank 48H content destruction using sodium permanganate. Three experiments were performed with Tank 48H simulants at 40 °C to determine the efficacy of using sodium permanganate for TPB destruction. Three starting pH values were selected: 1) pH 11 for comparison with the previous work at room temperature, 2) pH 10 as the minimum pH recommended by the Corrosion Control Program (CCP) for in-tank processing, and 3) pH 8 to determine the effectiveness of TPB destruction at near neutral pH. While below the allowable pH for the CCP, the experiment at pH 8 was performed to study the TPB-Permanganate reaction under more extreme conditions and further verify the potential for out-of-tank processing.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Quantifying Acute Fuel and Respiration Dependent pH Homeostasis in Live Cells Using the mCherryTYG Mutant as a Fluorescence Lifetime Sensor

Intracellular pH plays a key role in physiology, and its measurement in living specimens remains a crucial task in biology. Fluorescent protein-based pH sensors have gained widespread use, but there is limited spectral diversity for multicolor detection, and it remains a challenge to measure absolute pH values. In this work we demonstrate that mCherryTYG is an excellent fluorescence lifetime pH sensor that significantly expands the modalities available for pH quantification in live cells. We first report the 1.09 Å X-ray crystal structure of mCherryTYG, exhibiting a fully matured chromophore. We next determine that it has an extraordinarily large dynamic range with a 2 ns lifetime change from pH 5.5 to 9.0. Critically, we find that the sensor maintains a pK a of 6.8 independent of environment, whether as the purified protein in solution or expressed in live cells. Furthermore, the lifetime measurements are robustly independent of total fluorescence intensity and scatter. We demonstrate that mCherryTYG is a highly effective sensor using time-resolved fluorescence spectroscopy on live-cell suspensions, which has been previously overlooked as an easily accessible approach for quantifying intracellular pH. As a red fluorescent sensor, we also demonstrate that mCherryTYG is spectrally compatible with the ATeam sensor and EGFP for simultaneous dual-color measurements of intracellular pH, ATP, and extracellular pH. In a proof-of-concept, we quantify acute respiration-dependent pH homeostasis that exhibits a stoichiometric relationship with the ATP-generating capacity of the carbon fuel choice in E. coli . Broadly speaking, our work presents a previously unemployed methodology that will greatly facilitate continuous pH quantification.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Ni and Cr addition to alloy waste forms to reduce radionuclide environmental releases

Reference alloy waste forms (RAW) were fabricated and underwent hybrid corrosion/immersion testing to parameterize the ANL analytical oxidative-dissolution model to enable the calculation of fractional release rates and to determine the effectiveness of Ni and Cr trim additions in reducing release rates of radionuclide surrogates. Figure 1 shows the prototypical multiphase microstructure of the alloys with each phase type contributing about equally to the exposed surface area. The waste forms tested at SRNL were variations of the RAW-6 formulation that uses HT9 as the main alloy component, and are meant to enable evaluation of the impact of Ni and Cr trim additions on the release rates of actinides and Tc-99. The test solutions were deaerated alkaline and acidic brines, ranging in pH 3 to pH 10, representing potential repositories with those conditions. The testing approach consisted of 4 major steps; 1) bare surface corrosion measurements at pH values of 3, 5, 8, and 10, 2) hybrid potentiostatic hold/exposure measurements at pH 3, 3) measurement of radionuclide concentrations and relations to anodic current from potentiostatic holds, and 4) identification of corroding phases using SEM/EDS of electrodes.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Fine Aerosol Acidity and Water during Summer in the Eastern North Atlantic

Aerosol pH governs many important atmospheric processes that occur in the marine boundary layer, including regulating halogen and sulfur chemistries, and nutrient fertilization of surface ocean waters. In this study, we investigated the acidity of PM1 over the eastern North Atlantic during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) aircraft campaign. The ISORROPIA-II thermodynamic model was used to predict PM1 pH and water. We first investigated the sensitivities of PM1 pH and water predictions to gas-phase NH3 and HNO3 concentrations. Our sensitivity analysis indicated that even though NH3 and HNO3 were present at very low concentrations in the eastern North Atlantic during the campaign, PM1 pH calculations can still be sensitive to NH3 concentrations. Specifically, NH3 was needed to constrain the pH of populations of PM1 that had low mass concentrations of NH4+ and non-volatile cations (NVCs). We next assumed that gas-phase NH3 and HNO3 concentrations during the campaign were 0.15 and 0.09 µg m−3, respectively, based on previous measurements conducted in the eastern North Atlantic. Using the assumption that PM1 were internally mixed (i.e., bulk PM1), we determined that PM1 pH ranged from 0.3–8.6, with a mean pH of 5.0 ± 2.3. The pH depended on both Hair+ and Wi. Hair+ was controlled primarily by the NVCs/SO42− molar ratio, while Wi was controlled by the SO42− mass concentration and RH. Changes in pH with altitude were driven primarily by changes in SO42−. Since aerosols in marine atmospheres are rarely internally mixed, the scenario where non-sea salt species and sea-salt species were present in two separate aerosol modes in the PM1 (i.e., completely externally mixed) was also considered. Smaller pH values were predicted for the aerosol mode comprised only of non-sea salt species compared to the bulk PM1 (difference of around 1 unit on average). This was due to the exclusion of sea-salt species (especially hygroscopic alkaline NVCs) in this aerosol mode, which led to increases in Hair+ values and decreases in Wi values. This result demonstrated that assumptions of aerosol mixing states can impact aerosol pH predictions substantially, which will have important implications for evaluating the nature and magnitude of pH-dependent atmospheric processes that occur in the marine boundary layer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Charge Transport at Ti-Doped Hematite (001)/Aqueous Interfaces

Solid-state transport and electrochemical properties of Ti-doped hematite (001) epitaxial thin films (6.0, 8.3, and 16.6 at% Ti) were probed to achieve a better understanding of doped hematite for photoelectrochemical (PEC) applications. Room temperature resistivity measurements predict a resistivity minimum near 10 at% Ti doping, which can be rationalized as maximizing charge compensating Fe2+ concentration and Fe3+ electron accepting percolation pathways simultaneously. Temperature dependent resistivity data are consistent with small polaron hopping, revealing an activation energy that is Ti concentration dependent and commensurate with previously reported values (≈ 0.11 eV). In contact with inert electrolyte, linear Mott-Schottky data at various pH values indicate that there is predominantly a single donor for Ti-doped hematite at 6.0 at% Ti and 16.6 at% Ti concentrations. Two slope Mott-Schottky data at pH extremes indicate the presence of a second donor or surface state in the 8.3 at% Ti-doped film, with an energy level ≈ 0.7 eV below the Fermi level. Mott-Schottky plots indicate pH and Ti concentration dependent flatband potentials of -0.4 to -1.1 V vs. Ag/AgCl, commensurate with previously reported data. Flatband potentials exhibited super-Nernstian pH dependence ranging from -69.1 to -101.0 mV/pH. Carrier concentration data indicate that the Fermi energy of the Ti-doped system is Ti concentration dependent, with a minimum of 0.15 eV near 10 at% Ti. These energy level data allow us to construct an energy band diagram for Ti-doped hematite electrode/electrolyte interfaces, and to determine a Ti-doping concentration t

Environmental Molecular Sciences Laboratory↗
DOE OSTI2021

Experimental Investigation of a Novel Membrane-Based Condensing Heat Exchanger for High Efficiency Furnaces

Building space heating consumes approximately one-third of all global natural gas end use. Higher-efficiency (i.e., condensing) furnaces constitute only about 30% of the annual furnace shipments in the United States because the condensing heat exchangers must use highly expensive, corrosion-resistant materials to be protected from acidic components in the furnace flue gas stream. Increasing the market share of high-efficiency furnaces will reduce greenhouse gas emissions. This study developed and tested a benchtop prototype of a novel membrane-based heat exchanger (MHX) for high-efficiency furnaces to achieve nonacidic condensation via nanoporous membranes. Test results show that both sensible and latent heat were recovered by the MHX, and the fraction of latent heat recovery ranged from about 25% to 45% over the range of operating conditions evaluated. The amount of water condensed through the MHX increased with the increase of flue gas flow rate and decreased with increasing coolant temperature. The fraction of latent heat recovery decreased with the increase of flue gas flow rate and coolant temperature. The pH value of condensed water from the MHX was only mildly acidic, varying from 5.3 to 5.6 without any additional treatment, about 2.0 to 2.3 pH points higher (i.e., less acidic) than typical values for the condensate from conventional condensing furnaces. Therefore, feasibility of the MHX was experimentally verified, and the MHX could enable wider market penetration of highly energy-efficient condensing furnaces by reducing costs associated with managing the acid condensation compared with conventional condensing furnaces, possibly enabling the use of existing vent systems when replacing noncondensing furnaces (due to higher flue gas exit temperatures), and possibly reducing furnace first costs.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗