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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A New Sodium Thioborate Fast Ion Conductor: Na 3 B 5 S 9

Abstract We report a new sodium fast‐ion conductor, Na 3 B 5 S 9 , that exhibits a high Na ion total conductivity of 0.80 mS cm −1 (sintered pellet; cold‐pressed pellet=0.21 mS cm −1 ). The structure consists of corner‐sharing B 10 S 20 supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well‐distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X‐ray diffraction and powder synchrotron X‐ray diffraction at variable temperatures, solid‐state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na‐ion mobility (predicted conductivity: 0.96 mS cm −1 ) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice—and existence of well‐connected Na ion migration pathways formed via face‐sharing polyhedra—in dictating Na ion diffusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Polymorphism and phase transitions in Na 2 U 2 O 7 from density functional perturbation theory

Polymorphism and phase transitions in sodium diuranate, Na 2 U 2 O 7 , are investigated with density functional perturbation theory (DFPT). Thermal properties of crystalline α-, β- and γ-Na 2 U 2 O 7 polymorphs are predicted from DFPT phonon calculations, i.e., the first time for the high-temperature γ-Na 2 U 2 O 7 phase (R$\bar{3}$ with combining macron]m symmetry). The standard molar isochoric heat capacities predicted within the quasi-harmonic approximation are C p (298.15K)= 219.4 and 220.9 J K -1 mol -1 mfor P21/a α-Na 2 U 2 O 7 and C2/m β-Na 2 U 2 O 7 , respectively. Gibbs free energy calculations reveal that α-Na 2 U 2 O 7 (P2 1 /a) and β-Na 2 U 2 O 7 (C2/m) are almost energetically degenerate at low temperature, with β-Na 2 U 2 O 7 becoming slightly more stable than α-Na 2 U 2 O 7 as temperature increases. Here these findings are consistent with XRD data showing a mixture of α and β phases after cooling of γ-Na 2 U 2 O 7 to room temperature and the observation of a sluggish α → β phase transition above ca. 600 K. A recently observed α-Na 2 U 2 O 7 structure with P21 symmetry is also shown to be metastable at low temperature. Based on Gibbs free energy, no direct β → γ solid-solid phase transition is predicted at high temperature, although some experiments reported the existence of such phase transition around 1348 K. This, along with recent experiments, suggests the occurrence of a multi-step process consisting of initial β-phase decomposition, followed by recrystallization into γ-phase as temperature increases.

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

Materials Data on Na(BH)6 by Materials Project

Na(BH)5BH crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four boranediylradical molecules and two Na(BH)5 clusters. In each Na(BH)5 cluster, Na is bonded in a 6-coordinate geometry to six H atoms. There are a spread of Na–H bond distances ranging from 2.28–2.54 Å. There are five inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the third B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fourth B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fifth B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. There are five inequivalent H sites. In the first H site, H is bonded in a water-like geometry to one Na and one B atom. In the second H site, H is bonded in a water-like geometry to one Na and one B atom. In the third H site, H is bonded in a distorted water-like geometry to one Na and one B atom. In the fourth H site, H is bonded in a distorted single-bond geometry to two equivalent Na and one B atom. In the fifth H site, H is bonded in a water-like geometry to one Na and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SeO3)4 by Materials Project

Na(SeO3)4 crystallizes in the monoclinic Pc space group. The structure is one-dimensional and consists of two Na(SeO3)4 ribbons oriented in the (1, 0, 0) direction. Na is bonded to six O atoms to form distorted NaO6 octahedra that share a cornercorner with one SeO4 tetrahedra and an edgeedge with one SeO4 tetrahedra. There are a spread of Na–O bond distances ranging from 2.32–2.90 Å. There are four inequivalent Se sites. In the first Se site, Se is bonded to four O atoms to form SeO4 tetrahedra that share a cornercorner with one NaO6 octahedra and an edgeedge with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 73°. There are a spread of Se–O bond distances ranging from 1.63–1.86 Å. In the second Se site, Se is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.62 Å) and two longer (1.63 Å) Se–O bond length. In the third Se site, Se is bonded in a trigonal non-coplanar geometry to three O atoms. There are a spread of Se–O bond distances ranging from 1.65–1.85 Å. In the fourth Se site, Se is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.62 Å) and two longer (1.63 Å) Se–O bond length. There are twelve inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Na and one Se atom. In the second O site, O is bonded in a distorted water-like geometry to one Na and one Se atom. In the third O site, O is bonded in a bent 120 degrees geometry to one Na and one Se atom. In the fourth O site, O is bonded in a single-bond geometry to one Se atom. In the fifth O site, O is bonded in a single-bond geometry to one Se atom. In the sixth O site, O is bonded in a bent 120 degrees geometry to one Na and one Se atom. In the seventh O site, O is bonded in a single-bond geometry to one Se atom. In the eighth O site, O is bonded in a bent 120 degrees geometry to one Na and one Se atom. In the ninth O site, O is bonded in a single-bond geometry to one Se atom. In the tenth O site, O is bonded in a 2-coordinate geometry to one Na and two Se atoms. In the eleventh O site, O is bonded in a single-bond geometry to one Se atom. In the twelfth O site, O is bonded in a single-bond geometry to one Se atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(MoSe)3 by Materials Project

Na(MoSe)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Na is bonded in a 12-coordinate geometry to three Mo and nine Se atoms. All Na–Mo bond lengths are 3.66 Å. There are a spread of Na–Se bond distances ranging from 3.28–3.50 Å. There are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. In the third Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. There are three inequivalent Se sites. In the first Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms. In the second Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms. In the third Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(GaAu2)2 by Materials Project

Na(Au2Ga)2 is beta Plutonium-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Na is bonded in a 1-coordinate geometry to eleven Au and five Ga atoms. There are a spread of Na–Au bond distances ranging from 3.03–3.58 Å. There are a spread of Na–Ga bond distances ranging from 3.24–3.52 Å. There are four inequivalent Au sites. In the first Au site, Au is bonded in a 4-coordinate geometry to three equivalent Na, three Au, and three Ga atoms. There are a spread of Au–Au bond distances ranging from 2.84–3.05 Å. There are a spread of Au–Ga bond distances ranging from 2.61–2.72 Å. In the second Au site, Au is bonded in a 12-coordinate geometry to three equivalent Na, five Au, and four Ga atoms. There are a spread of Au–Au bond distances ranging from 2.96–3.04 Å. There are a spread of Au–Ga bond distances ranging from 2.67–2.86 Å. In the third Au site, Au is bonded in a 12-coordinate geometry to three equivalent Na, three Au, and three Ga atoms. There are one shorter (2.82 Å) and one longer (2.83 Å) Au–Au bond lengths. There are a spread of Au–Ga bond distances ranging from 2.69–3.18 Å. In the fourth Au site, Au is bonded in a 11-coordinate geometry to two equivalent Na, five Au, and four Ga atoms. There are a spread of Au–Ga bond distances ranging from 2.62–2.87 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to two equivalent Na and seven Au atoms. In the second Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Na and seven Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na by Materials Project

Na is beta Polonium-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded to six equivalent Na atoms to form a mixture of distorted corner and edge-sharing NaNa6 pentagonal pyramids. All Na–Na bond lengths are 3.43 Å. In the second Na site, Na is bonded to six equivalent Na atoms to form a mixture of corner, edge, and face-sharing NaNa6 octahedra. The corner-sharing octahedral tilt angles are 46°.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Metal Sulfide Ion Exchangers: High Acid Stability of Na 2 x Mg 2 y – x Sn 4– y S 8 (NMS) and Topotactic Conversion to 2D Solid Acids with Semiconducting Character

Metal sulfide ion exchange materials (MSIEs) are of interest for nuclear waste remediation applications. Here, we report the high stability of two structurally related metal sulfide ion exchange materials, Na 2x Mg 2y–x Sn 4–y S 8 (Mg-NMS) and Na 2 SnS 3 (Na-NMS), in strongly acid media, in addition to the preparation of Na 2x Ni 2y–x Sn 4–y S 8 (Ni-NMS). Their formation progress during synthesis is studied with in-situ methods, with the target phases appearing in <15 min, reaction completion in <12 h, and high yields (75–80%). Upon contact with nitric or hydrochloric acid, these materials topotactically exchange Na + for H + , proceeding in a stepwise protonation pathway for Na 5.33 Sn 2.67 S 8 . Na-NMS is stable in 2 M HNO 3 and Mg-NMS is stable in 4 M HNO 3 for up to 4 h, while both NMS materials are stable in 6 M HCl for up to 4 days. However, the treatment of Mg-NMS and Na-NMS with 2–6 M H 2 SO 4 reveals a much slower protonation process since after 4 h of contact both NMS and HMS are present in the solution. The resultant protonated materials, H 2x Mg 2y–x Sn 4–y S 8 and H 4x [(H y Na y–1 ) 1.33x Sn 4––1.33x ]S 8 , are themselves solid acids and readily react with and intercalate a variety of organic amines, where the band gap of the resultant adduct is influenced by amine choice and can be tuned within the range of 1.88(5)–2.27(5) eV. The work function energy values for all materials were extracted from photoemission yield spectroscopy in air (PYSA) measurements and range from 5.47 (2) to 5.76 (2) eV, and the relative band alignments of the materials are discussed. DFT calculations suggest that the electronic structure of Na 2 MgSn 3 S 8 and H 2 MgSn 3 S 8 makes them indirect gap semiconductors with multi-valley band edges, with carriers confined to the [MgSn 3 S 8 ] 2– layers. Light electron effective masses indicate high electron mobilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Recent Progress on Dominant Sulfide‐Type Solid‐State Na Superionic Conductors for Solid‐State Sodium Batteries

Abstract Over the past decade, solid‐state batteries have garnered significant attentions due to their potentials to deliver high energy density and excellent safety. Considering the abundant sodium (Na) resources in contrast to lithium (Li), the development of sodium‐based batteries has become increasingly appealing. Sulfide‐based superionic conductors are widely considered as promising solid eletcrolytes (SEs) in solid‐state Na batteries due to the features of high ionic conductivity and cold‐press densification. In recent years, tremendous efforts have been made to investigate sulfide‐based Na‐ion conductors on their synthesis, compositions, conductivity, and the feasibility in batteries. However, there are still several challenges to overcome for their practical applications in high performance solid‐state Na batteries. This article provides a comprehensive update on the synthesis, structure, and properties of three dominant sulfide‐based Na‐ion conductors (Na 3 PS 4 , Na 3 SbS 4 , and Na 11 Sn 2 PS 12 ), and their families that have a variety of anion and cation doping. Additionally, the interface stability of these sulfide electrolytes toward the anode is reviewed, as well as the electrochemical performance of solid‐state Na batteries based on different types of cathode materials (metal sulfides, oxides, and organics). Finally, the perspective and outlook for the development and practical utilization of sulfide‐based SE in solid‐state batteries are discussed.

Guo, Xiaolin↗
DOE OSTI2020

Materials Data on Na(AsO3)2 by Materials Project

Na(AsO3)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Na is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Na–O bond distances ranging from 2.35–2.75 Å. There are two inequivalent As sites. In the first As site, As is bonded to four O atoms to form corner-sharing AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–59°. There are a spread of As–O bond distances ranging from 1.71–1.76 Å. In the second As site, As is bonded to six O atoms to form AsO6 octahedra that share corners with three equivalent AsO4 tetrahedra and an edgeedge with one AsO6 octahedra. There are a spread of As–O bond distances ranging from 1.78–1.97 Å. There are six inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to two As atoms. In the second O site, O is bonded in a distorted T-shaped geometry to one Na and two equivalent As atoms. In the third O site, O is bonded in a distorted single-bond geometry to two equivalent Na and one As atom. In the fourth O site, O is bonded in a trigonal planar geometry to one Na and two As atoms. In the fifth O site, O is bonded in a trigonal planar geometry to one Na and two As atoms. In the sixth O site, O is bonded in a distorted trigonal planar geometry to two equivalent Na and one As atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SeO3)2 by Materials Project

Na(SeO3)2 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. Na is bonded in a 5-coordinate geometry to five O atoms. There are a spread of Na–O bond distances ranging from 2.32–2.90 Å. There are two inequivalent Se sites. In the first Se site, Se is bonded in a 4-coordinate geometry to four O atoms. There are a spread of Se–O bond distances ranging from 1.65–2.49 Å. In the second Se site, Se is bonded in a tetrahedral geometry to four O atoms. There are a spread of Se–O bond distances ranging from 1.64–1.82 Å. There are six inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Na and one Se atom. In the second O site, O is bonded in a distorted bent 120 degrees geometry to one Na and two Se atoms. In the third O site, O is bonded in a linear geometry to one Na and one Se atom. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Na and one Se atom. In the fifth O site, O is bonded in a distorted single-bond geometry to two Se atoms. In the sixth O site, O is bonded in a bent 150 degrees geometry to one Na and one Se atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Solvent-free and low temperature synthesis of chalcogenide Na superionic conductors for solid-state batteries

Sodium chalcogenide ionic conductors are attractive candidates as solid electrolytes (SEs) in solid-state Na metal batteries. They show the advantages of high ionic conductivity of 10 –4 –10 –2 S cm –1 at room temperature and great chemical stability in air. However, simple, efficient, and scalable approaches for the synthesis of chalcogenide solid electrolytes (SEs) are required. In this work, we report a solvent-free mixing to form dry intermediate products, which are subjected to different treatments (electron-beam assisted method or low temperature heating (≤150 °C)) to produce pure phase of Na 3 SbS 4-y Se y (0 ≤ y < 2) chalcogenides. Heavy Se-doping in Na 3 SbS 4 results in the tetragonal-to-cubic phase transition as well as a significant change of Sb-S bonding in Raman spectra. Among all chalcogenide SEs, Na 3 SbS 3 Se showed the highest ionic conductivity of 3.75 × 10 –4 S cm –1 at room temperature, 47% higher than that of pristine Na 3 SbS 4 . Moreover, the Se-dopant also enhanced the electrochemical stability towards Na metal in solid-state batteries. The solid-state Na||FeS 2 battery with Na 3 SbS 3 Se SE displayed long-term cycling ability up to 1,000 cycles within the voltage window of 1.0–2.7 V and retained a specific capacity of 105 mAh g –1 after 600 cycles. As a result, this technique promotes the practical applications of chalcogenide SEs in solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2025

Synthesis and post-heating treatment of inorganic NaF·Na 3 SbS 4 solid electrolytes

Sulfide-type sodium (Na) solid electrolytes (SEs) with halide doping have attracted serious interest due to their high ionic conductivity and great potential in solid-state Na batteries. While other halogens such as Cl, Br, I have been studied to enhance Na-ion transport in sulfide-type SEs, the introduction of fluorine (F) is rarely investigated. Moreover, synthetic parameters such as heating treatment temperatures strongly influence the structure and conductive properties of halide-doped sulfide SEs. Herein, we prepared xNaF·(1-x)Na 3 SbS 4 nanocomposites with varying concentration of F using a low-temperature (150 °C) heating method, and studied the effects of post-heating treatment on structure and conductivity. In-situ neutron diffraction was employed to investigate the structural evolution of X-doped Na 3 SbS 4 (X = F, Cl) during the post-heating treatment and cooling process. In addition, the post-heating treatment at 300 °C leads to increased ionic conductivity of xNaF·(1-x)Na 3 SbS 4 nanocomposites with various F contents. After 300 °C post-heating treatment, 0.2NaF·0.8Na 3 SbS 4 exhibited the highest conductivity of 0.48 mS cm –1 at room temperature. Moreover, improved electrochemical stability was also observed in Na-Sn symmetric cells, specially, with prolonged stable cycling for 300 h and much lower polarization voltage (<0.35 V). Furthermore, this work highlights the importance of post-heating treatment on the structural evolution and its role in exploring new halide-incorporated sulfide-type SEs, promoting the development of inorganic solid-state ionic conductors.

25 ENERGY STORAGE↗
DOE OSTI2025

Quantum Monte Carlo Approaches to Na Intercalation on Bilayer Graphene

We have performed Quantum Monte Carlo (QMC) simulations on Na-intercalated bilayer graphene to study the evolution of electronic and optical properties upon Na intercalation into hard carbon layers. The objective was to model the optimal configuration of Na intercalation into a hard carbon matrix containing graphene regions. Our study showed that Na intercalation can be energetically stabilized at large interlayer distances (over 6 Å) in both AA- and AB-stacked bilayer graphene. In the QMC results, we found a significant band gap opening at the equilibrium interlayer distance of Na-intercalated bilayer graphene, while corresponding density functional theory (DFT) results showed no gap. This difference between DFT and QMC results indicates that the gap opening induced by Na intercalation into a hard carbon is underestimated within the DFT framework. In addition, a zigzag configuration of Na atoms was found to be energetically stable at interlayer distances up to 10 Å, leading us to predict the existence of a local minimum of Na intercalation at large interlayer distance. These computation and modeling results can provide guidance on how to synthesize and optimize hard carbon with bilayer graphene regions that permit a zigzag intercalation configuration that will maximize and stabilize sodium hosting.

Binding energy↗
DOE OSTI2020

Expansion of the Na 3 M III (Ln/An) 6 F 30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework

Abstract Na n MAn 6 F 30 is an extremely versatile framework structure for incorporating tetravalent actinides (An) and cerium along with divalent or trivalent d‐metals (M); moreover, the structure exhibits a high resistance to harsh chemical conditions. This extreme robustness can potentially be exploited for the sequestration of plutonium in a stable matrix; however, no Na n MPu 6 F 30 compounds have been reported so far. Herein, we present four new plutonium fluorides that have been prepared as single crystals by mild hydrothermal synthesis methods. Structural characterizations revealed their compositions to be Na 3 AlPu 6 F 30 , Na 3 FePu 6 F 30 , Na 3 CoPu 6 F 30 , and Na 2.4 Mn 1.6 Pu 6 F 30 . Surprisingly, in the plutonium series, it was found that Co 2+ and Mn 2+ precursors oxidized to form Na 3 Co III Pu 6 F 30 and Na 2.4 Mn II/III 1.6 Pu 6 F 30 , whereas the analogous reactions for cerium result in reduction of the transition metal, even when beginning with a M 3+ precursor. While cerium is often used as a surrogate for plutonium, this work serves as an example that deviations between their chemistries do occur.

Pace, Kristen A.↗
DOE OSTI2021

The impact of alkali‐ion intercalation on redox chemistry and mechanical deformations: Case study on intercalation of Li, Na, and K ions into FePO 4 cathode

Abstract Batteries made of charge carriers from Earth‐crust abundant materials (e.g., Na, K, and Mg) have received extensive attention as an alternative to Li‐ion batteries for grid storage. However, a lack of understanding of the behavior of these larger ions in the electrode materials hinders the development of electrode structures suitable for these large ions. In this study, we investigate the impact of alkali ions (Li, Na, and K) on the redox chemistry and mechanical deformations of iron phosphate composite cathodes by using electrochemical techniques and in situ digital image correlation. Na‐ion and Li‐ion intercalation demonstrate a nearly linear correlation between electrochemical strains and the state of charge and discharge. The strain development shows nonlinear dependance on the state of charge and discharge for K ions. Strain rate calculations show that K ion intercalation results in a progressive increase in the strain rate for all cycles. Li and Na intercalation induce nearly constant strain rates with the exception of the first discharge cycle of Na intercalation. When the same amount of ions are inserted into the electrode, the electrode shows the lowest strain generation upon Li intercalation compared to larger alkali ions. Na and K ions induce similar volumetric changes in the electrode when the state of charge and discharge is around 30%. Although the electrode experiences larger absolute strain generation at the end of the discharge cycles upon Na intercalation, strain rates were found to be greater for K ions. Potential‐dependent behaviors also demonstrate more sluggish redox reactions during K intercalation, compared to Li and Na. Our quantitative analysis suggests that the strain rate, rather than the absolute value of strain, is the critical factor in amorphization of the crystalline electrode.

25 ENERGY STORAGE↗
DOE OSTI2025

Uncertainty improvement of 22 Na based radioactive tracer dilution for determining total mass of pyroprocessing molten salt systems by 154 Eu removal

To determine the total salt mass of the molten salt systems for pyroprocessing spent nuclear fuels, a 22 Na based radioactive tracer dilution was studied in Idaho National Laboratory in recent years. This 22 Na based RTD technique was deemed feasible, but due to the gamma energy peak of 22 Na coinciding with one of the energy peaks of 154 Eu radioisotope in the molten salt, the uncertainty of the 22 Na radioactivity in the 22 Na-spiked salt samples was quite high. To improve the uncertainty of the 22 Na based RTD technique, we proposed to chemically remove the 154 Eu of the salt samples by DGA resin for gamma spectroscopy. The effectiveness of removing 154 Eu on uncertainty improvement was evaluated. Furthermore, it was found that (1) the 154 Eu fission product effect on the uncertainty and detection limit can be effectively eliminated by chemically removing the 154 Eu during the salt sample preparation and (2) the uncertainty of 22 Na radioactivity in the salt samples for electrorefining was significantly improved from 13% to 2%, showing the potential of practical engineering application of 22 Na based RTD as a safeguards technique for molten salt systems for pyroprocessing spent nuclear fuels.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Reverse water-gas shift: Na doping of m-ZrO 2 supported Pt for selectivity control

Reverse water-gas shift (RWGS) is a vital step in producing syngas for the chemical conversion of CO 2 to liquid transportation fuels and chemicals. Na-doping of m-ZrO 2 supported Pt catalysts allowed selectivity control by systematically increasing the ratio of relative rates of r CO /r CH4 . This was achieved by facilitating the formation of formate intermediate species, which precedes CO formation, and by suppressing the metallic Pt 0 active sites responsible for CH 4 formation. Here, a 2.5%Na-2%Pt/m-ZrO 2 catalyst was first tested for the forward water-gas shift (FWGS) reaction and found to have 50% higher CO conversion at 285°C compared to the undoped catalyst. Results of DRIFTS spectroscopy of adsorbed CO confirmed a formate ν(CH) band shift to lower wavenumbers (2870–2802 cm —1 ) with the addition of Na and more rapid forward formate decomposition in steam to H 2 and carbonate species, the precursor to CO 2 . This is consistent with C-H bond breaking being the rate limiting step of a FWGS mechanism occurring at the metal-support junction. Consistent with this, DRIFTS of RWGS in 4%CO 2 + 60%H 2 showed more facile formation of formate for the Na-doped catalyst and, once again, the ν(CH) band was shifted to lower wavenumbers (2874–2803 cm —1 ) with Na-doping. In addition, Na doping resulted in a systematic decrease in the Pt-carbonyl band in DRIFTS of adsorbed CO as well as DRIFTS of in-situ RWGS reaction tests, suggesting that Na blocked a fraction of on-top Pt sites, breaking up ensembles of Pt 0 responsible for methanation. The selectivity of the 2.5%Na-doped catalyst, unlike its undoped counterpart, was remarkably resistant to methanation (e.g., selectivity < 0.2% CH 4 with pressures of up to 20 bar).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗