Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Pt”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on IrPt3 by Materials Project

Pt3Ir is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ir is bonded to twelve equivalent Pt atoms to form IrPt12 cuboctahedra that share corners with twelve equivalent IrPt12 cuboctahedra, edges with twenty-four equivalent PtIr4Pt8 cuboctahedra, faces with six equivalent IrPt12 cuboctahedra, and faces with twelve equivalent PtIr4Pt8 cuboctahedra. All Ir–Pt bond lengths are 2.79 Å. Pt is bonded to four equivalent Ir and eight equivalent Pt atoms to form PtIr4Pt8 cuboctahedra that share corners with twelve equivalent PtIr4Pt8 cuboctahedra, edges with eight equivalent IrPt12 cuboctahedra, edges with sixteen equivalent PtIr4Pt8 cuboctahedra, faces with four equivalent IrPt12 cuboctahedra, and faces with fourteen equivalent PtIr4Pt8 cuboctahedra. All Pt–Pt bond lengths are 2.79 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiPt3 by Materials Project

Pt3Ni is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pt+0.67- is bonded to eight equivalent Pt+0.67- and four equivalent Ni2+ atoms to form PtNi4Pt8 cuboctahedra that share corners with twelve equivalent PtNi4Pt8 cuboctahedra, edges with eight equivalent NiPt12 cuboctahedra, edges with sixteen equivalent PtNi4Pt8 cuboctahedra, faces with four equivalent NiPt12 cuboctahedra, and faces with fourteen equivalent PtNi4Pt8 cuboctahedra. All Pt–Pt bond lengths are 2.74 Å. All Pt–Ni bond lengths are 2.74 Å. Ni2+ is bonded to twelve equivalent Pt+0.67- atoms to form NiPt12 cuboctahedra that share corners with twelve equivalent NiPt12 cuboctahedra, edges with twenty-four equivalent PtNi4Pt8 cuboctahedra, faces with six equivalent NiPt12 cuboctahedra, and faces with twelve equivalent PtNi4Pt8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrCoPt2 by Materials Project

CrCoPt2 crystallizes in the trigonal R3m space group. The structure is three-dimensional. Cr2+ is bonded in a distorted hexagonal planar geometry to three equivalent Co2+ and three equivalent Pt2- atoms. All Cr–Co bond lengths are 2.46 Å. All Cr–Pt bond lengths are 2.63 Å. Co2+ is bonded in a distorted hexagonal planar geometry to three equivalent Cr2+ and three equivalent Pt2- atoms. All Co–Pt bond lengths are 2.68 Å. There are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded in a 12-coordinate geometry to three equivalent Cr2+ and three equivalent Pt2- atoms. All Pt–Pt bond lengths are 2.94 Å. In the second Pt2- site, Pt2- is bonded to three equivalent Co2+ and nine Pt2- atoms to form a mixture of distorted face, edge, and corner-sharing PtCo3Pt9 cuboctahedra. All Pt–Pt bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HfPt4 by Materials Project

HfPt4 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to twelve Pt1- atoms to form HfPt12 cuboctahedra that share corners with four equivalent PtPt12 cuboctahedra, corners with eight HfPt12 cuboctahedra, edges with four equivalent PtPt12 cuboctahedra, a faceface with one PtPt12 cuboctahedra, and faces with five HfPt12 cuboctahedra. There are a spread of Hf–Pt bond distances ranging from 2.78–2.90 Å. In the second Hf4+ site, Hf4+ is bonded to twelve Pt1- atoms to form a mixture of corner and face-sharing HfPt12 cuboctahedra. There are a spread of Hf–Pt bond distances ranging from 2.83–2.85 Å. There are seven inequivalent Pt1- sites. In the first Pt1- site, Pt1- is bonded to twelve Pt1- atoms to form PtPt12 cuboctahedra that share corners with four equivalent PtPt12 cuboctahedra, edges with eight equivalent HfPt12 cuboctahedra, and faces with eight PtPt12 cuboctahedra. There are four shorter (2.84 Å) and eight longer (2.87 Å) Pt–Pt bond lengths. In the second Pt1- site, Pt1- is bonded in a distorted rectangular see-saw-like geometry to four equivalent Hf4+ atoms. In the third Pt1- site, Pt1- is bonded in a distorted rectangular see-saw-like geometry to four equivalent Hf4+ atoms. In the fourth Pt1- site, Pt1- is bonded in a distorted L-shaped geometry to two equivalent Hf4+ and four Pt1- atoms. Both Pt–Pt bond lengths are 2.87 Å. In the fifth Pt1- site, Pt1- is bonded in a distorted rectangular see-saw-like geometry to four Hf4+ atoms. In the sixth Pt1- site, Pt1- is bonded in a distorted square co-planar geometry to four equivalent Hf4+ atoms. In the seventh Pt1- site, Pt1- is bonded to twelve Pt1- atoms to form PtPt12 cuboctahedra that share corners with four equivalent PtPt12 cuboctahedra, corners with eight equivalent HfPt12 cuboctahedra, faces with two equivalent HfPt12 cuboctahedra, and faces with eight PtPt12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaGa3Pt by Materials Project

LaPtGa3 crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. La is bonded in a 12-coordinate geometry to four equivalent Pt and twelve Ga atoms. All La–Pt bond lengths are 3.44 Å. There are eight shorter (3.33 Å) and four longer (3.44 Å) La–Ga bond lengths. Pt is bonded to four equivalent La and eight Ga atoms to form distorted PtLa4Ga8 tetrahedra that share corners with four equivalent GaLa4Ga4Pt4 cuboctahedra, corners with twelve equivalent PtLa4Ga8 tetrahedra, edges with two equivalent GaLa4Ga4Pt4 cuboctahedra, faces with four equivalent GaLa4Ga4Pt4 cuboctahedra, and faces with four equivalent PtLa4Ga8 tetrahedra. There are four shorter (2.59 Å) and four longer (3.08 Å) Pt–Ga bond lengths. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 2-coordinate geometry to four equivalent La, two equivalent Pt, and three Ga atoms. There are one shorter (2.53 Å) and two longer (2.59 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded to four equivalent La, four equivalent Pt, and four equivalent Ga atoms to form GaLa4Ga4Pt4 cuboctahedra that share corners with twelve equivalent GaLa4Ga4Pt4 cuboctahedra, corners with four equivalent PtLa4Ga8 tetrahedra, edges with two equivalent PtLa4Ga8 tetrahedra, faces with four equivalent GaLa4Ga4Pt4 cuboctahedra, and faces with four equivalent PtLa4Ga8 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3B7PtO20 by Materials Project

K3PtB7O20 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of K–O bond distances ranging from 2.76–3.26 Å. In the second K site, K is bonded to seven O atoms to form distorted KO7 pentagonal bipyramids that share a cornercorner with one PtO6 octahedra. The corner-sharing octahedral tilt angles are 62°. There are a spread of K–O bond distances ranging from 2.70–2.98 Å. Pt is bonded to six O atoms to form PtO6 octahedra that share a cornercorner with one KO7 pentagonal bipyramid and corners with two BO4 tetrahedra. There are a spread of Pt–O bond distances ranging from 1.85–2.04 Å. There are five inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There is two shorter (1.37 Å) and one longer (1.38 Å) B–O bond length. In the second B site, B is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.36 Å) and two longer (1.38 Å) B–O bond length. In the third B site, B is bonded to four O atoms to form BO4 tetrahedra that share a cornercorner with one PtO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. There are a spread of B–O bond distances ranging from 1.42–1.54 Å. In the fourth B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.38 Å. In the fifth B site, B is bonded to four O atoms to form BO4 tetrahedra that share a cornercorner with one PtO6 octahedra and a cornercorner with one BO4 tetrahedra. The corner-sharing octahedral tilt angles are 62°. There are a spread of B–O bond distances ranging from 1.45–1.55 Å. There are thirteen inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to one K, one Pt, and one B atom. In the second O site, O is bonded in a bent 120 degrees geometry to one Pt and one B atom. In the third O site, O is bonded in a trigonal planar geometry to one Pt and two B atoms. In the fourth O site, O is bonded in a distorted bent 120 degrees geometry to one K and two B atoms. In the fifth O site, O is bonded in a distorted bent 120 degrees geometry to one K and two B atoms. In the sixth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the seventh O site, O is bonded in a bent 120 degrees geometry to two equivalent K and two B atoms. In the eighth O site, O is bonded in a single-bond geometry to one K and one B atom. In the ninth O site, O is bonded in a distorted single-bond geometry to one K and one B atom. In the tenth O site, O is bonded in a distorted single-bond geometry to two K and one B atom. In the eleventh O site, O is bonded in a distorted single-bond geometry to three K and one Pt atom. In the twelfth O site, O is bonded in a 1-coordinate geometry to two K and one O atom. The O–O bond length is 1.24 Å. In the thirteenth O site, O is bonded in a distorted T-shaped geometry to three K atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2PtI5O2 by Materials Project

K2PtO2I5 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. K is bonded in a distorted bent 120 degrees geometry to two equivalent O and two I atoms. There are one shorter (2.68 Å) and one longer (2.70 Å) K–O bond lengths. There are one shorter (3.70 Å) and one longer (3.76 Å) K–I bond lengths. Pt is bonded to six I atoms to form corner-sharing PtI6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are a spread of Pt–I bond distances ranging from 2.67–2.92 Å. O is bonded in a trigonal non-coplanar geometry to two equivalent K and one I atom. The O–I bond length is 1.90 Å. There are four inequivalent I sites. In the first I site, I is bonded in a 1-coordinate geometry to one Pt and one O atom. In the second I site, I is bonded in a 3-coordinate geometry to two equivalent K and one Pt atom. In the third I site, I is bonded in a distorted single-bond geometry to one Pt atom. In the fourth I site, I is bonded in a rectangular see-saw-like geometry to two equivalent K and two equivalent Pt atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KPt3 by Materials Project

KPt3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. K is bonded to twelve equivalent Pt atoms to form a mixture of distorted face and corner-sharing KPt12 cuboctahedra. There are six shorter (3.18 Å) and six longer (3.28 Å) K–Pt bond lengths. Pt is bonded in a 4-coordinate geometry to four equivalent K and six equivalent Pt atoms. There are two shorter (2.72 Å) and four longer (2.78 Å) Pt–Pt bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe2Pt by Materials Project

Fe2Pt is beta-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Fe is bonded to nine equivalent Fe and three equivalent Pt atoms to form distorted FeFe9Pt3 cuboctahedra that share corners with three equivalent PtFe6Pt6 cuboctahedra, corners with nine equivalent FeFe9Pt3 cuboctahedra, edges with nine equivalent PtFe6Pt6 cuboctahedra, edges with fifteen equivalent FeFe9Pt3 cuboctahedra, faces with six equivalent PtFe6Pt6 cuboctahedra, and faces with twelve equivalent FeFe9Pt3 cuboctahedra. There are three shorter (2.36 Å) and six longer (2.62 Å) Fe–Fe bond lengths. All Fe–Pt bond lengths are 2.69 Å. Pt is bonded to six equivalent Fe and six equivalent Pt atoms to form PtFe6Pt6 cuboctahedra that share corners with six equivalent FeFe9Pt3 cuboctahedra, corners with six equivalent PtFe6Pt6 cuboctahedra, edges with six equivalent PtFe6Pt6 cuboctahedra, edges with eighteen equivalent FeFe9Pt3 cuboctahedra, faces with six equivalent PtFe6Pt6 cuboctahedra, and faces with twelve equivalent FeFe9Pt3 cuboctahedra. All Pt–Pt bond lengths are 2.62 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PH30Pt2C10I2NCl2 by Materials Project

Pt2C9PNH28I2CH2Cl2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four dichloromethane molecules and four Pt2C9PNH28I2 clusters. In each Pt2C9PNH28I2 cluster, there are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to three C+2.40-, one N3-, and two I1- atoms to form distorted PtC3I2N octahedra that share a cornercorner with one PC3N tetrahedra and a faceface with one PtC3I2N octahedra. There are one shorter (2.06 Å) and two longer (2.07 Å) Pt–C bond lengths. The Pt–N bond length is 2.37 Å. There are one shorter (2.84 Å) and one longer (2.86 Å) Pt–I bond lengths. In the second Pt2- site, Pt2- is bonded to three C+2.40-, one N3-, and two I1- atoms to form distorted PtC3I2N octahedra that share a cornercorner with one PC3N tetrahedra and a faceface with one PtC3I2N octahedra. There are one shorter (2.06 Å) and two longer (2.07 Å) Pt–C bond lengths. The Pt–N bond length is 2.36 Å. There are one shorter (2.83 Å) and one longer (2.86 Å) Pt–I bond lengths. There are nine inequivalent C+2.40- sites. In the first C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. There is one shorter (1.09 Å) and two longer (1.10 Å) C–H bond length. In the second C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. All C–H bond lengths are 1.10 Å. In the third C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. All C–H bond lengths are 1.10 Å. In the fourth C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. All C–H bond lengths are 1.10 Å. In the fifth C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. All C–H bond lengths are 1.10 Å. In the sixth C+2.40- site, C+2.40- is bonded in a distorted trigonal non-coplanar geometry to one Pt2- and three H1+ atoms. All C–H bond lengths are 1.10 Å. In the seventh C+2.40- site, C+2.40- is bonded to one P5+ and three H1+ atoms to form distorted corner-sharing CPH3 tetrahedra. The C–P bond length is 1.80 Å. There is one shorter (1.09 Å) and two longer (1.10 Å) C–H bond length. In the eighth C+2.40- site, C+2.40- is bonded to one P5+ and three H1+ atoms to form distorted corner-sharing CPH3 tetrahedra. The C–P bond length is 1.80 Å. All C–H bond lengths are 1.10 Å. In the ninth C+2.40- site, C+2.40- is bonded to one P5+ and three H1+ atoms to form distorted corner-sharing CPH3 tetrahedra. The C–P bond length is 1.80 Å. There is one shorter (1.09 Å) and two longer (1.10 Å) C–H bond length. P5+ is bonded to three C+2.40- and one N3- atom to form PC3N tetrahedra that share corners with two PtC3I2N octahedra. The corner-sharing octahedra tilt angles range from 53–55°. The P–N bond length is 1.65 Å. N3- is bonded in a 2-coordinate geometry to two Pt2-, one P5+, and one H1+ atom. The N–H bond length is 1.03 Å. There are twenty-eight inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the fifteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the sixteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the seventeenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the eighteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the nineteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twentieth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-first H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-second H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-third H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-fourth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-fifth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-sixth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-seventh H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. In the twenty-eighth H1+ site, H1+ is bonded in a single-bond geometry to one C+2.40- atom. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a 2-coordinate geometry to two Pt2- atoms. In the second I1- site, I1- is bonded in a distorted L-shaped geometry to two Pt2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Creating Favorable Pt/Co Interfaces via a Two‐Step Approach for Constructing Highly Durable PtCo Intermetallic Fuel Cell Catalysts

Structurally ordered PtCo intermetallics are one of the most promising oxygen-reduction catalysts in proton exchange membrane fuel cells (PEMFCs) due to their intrinsically improved catalytic activity and stability relative to PtCo solid-solution alloys. However, increasing the heating temperature to achieve a desirable high degree of ordering results in severe particle agglomeration and low mass activity and stability. Herein, a two-step synthesis approach is developed to create an L1 2 -Pt 3 Co intermetallic structure with an increased ordering degree and well-dispersed ultrafine particles. The first step of the synthesis yields ultrafine Pt nanoparticles that are well-dispersed on the ZIF-8-derived carbon support. The second adsorption step enables us to fine-tune the Pt and Co interfaces, assisted by optimal amino acids, to establish a favorable Co-rich environment around fine Pt nanoparticles, facilitating Co diffusion into the Pt crystalline under mild thermal conditions (<800 °C). In conclusion, this two-step ordered L1 2 -Pt 3 Co catalyst is systematically evaluated using membrane electrode assemblies under heavy-duty vehicle (HDV) conditions and demonstrated exceptional performance and durability, retaining 1.35 A cm -2 only a 7% loss in current density at 0.7 V after an extensive accelerated stress test of 150,000 voltage cycles.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Probing Heterogeneous Degradation of Catalyst in PEM Fuel Cells under Realistic Automotive Conditions with Multi-Modal Techniques

The heterogeneity of polymer electrolyte fuel cell catalyst degradation is studied under varied relative humidity and types of feed gas. Accelerated stress tests (ASTs) are performed on four membrane electrode assemblies (MEAs) under wet and dry conditions in an air or nitrogen environment for 30 000 square voltage cycles. The largest electrochemically active area loss is observed for MEA under wet conditions in a nitrogen gas environment AST due to constant upper potential limit of 0.95 V and significant water content. The mean Pt particle size is larger for the ASTs under wet conditions compared to dry conditions, and the Pt particle size under land is generally larger than under the channel. Observations from ASTs in both conditions and gas environments indicate that water content promotes Pt particle size growth. ASTs under wet conditions and an air environment show the largest difference in Pt particle size growth for inlet versus outlet and channel versus land, which can be attributed to larger water content at outlet and under land compared to inlet and under channel. From X-ray fluorescence experiments Pt particle size increase is a local phenomenon as Pt loading remains relatively uniform across the MEA.

25 ENERGY STORAGE↗
DOE OSTI2023

Underlying Substrate Effect on Electrochemical Activity for Hydrogen Evolution Reaction with Low‐Platinum‐Loaded Catalysts

Platinum is known as the best catalyst for the hydrogen evolution reaction (HER) but the scarcity and high cost of Pt limit its widespread applicability. Herein, the role of the underlying substrate on the HER activity of dispersed Pt atoms is uncovered. A direct current magnetron sputtering technique is utilized to deposit transition metal (TM) thin films of W, Ti, and Ta as underlying substrates for extremely low loading of Pt (<1.5 at%). The electrocatalytic performance of as‐synthesized samples for the HER is examined in both alkali and acidic media. The results show that despite the low loading of Pt, the Pt/TM catalysts produce hydrogen at a rate comparable to that of pristine bulk Pt. Pt/TM catalysts also display good stability with less than 5% decay in performance after 10 h of continuous HER operation. Based on the computational study, the excellent performance is attributed to the modified electronic properties of the Pt atoms, offering ideal binding energy for HER due to interaction with the underlying substrates. This work provides a robust and industry‐friendly route toward designing efficient catalytic systems for important electrochemical reactions such as HER and others.

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

Decoding anomalous grain growth at room temperature during pressure-induced phase transformations

Significant grain growth is observed during the high-pressure phase transformations (PTs) at room temperature in various materials. The main focus here is grain growth from a few hundred nanometers to 10 μm within an hour during α → ω PT in Zr. No existing theory explains this phenomenon since without PT, Zr nanocrystals do not grow at room temperature even for up to 10 years. Here, in this study, a multistep mechanism for the grain growth during α → ω PT in Zr is suggested. Phase interfaces (PI) and grain boundaries (GBs) coincide and move together as a combined PI-GBs under the action of the combined thermodynamic driving force. Such a combined motion changes the diffusional grain growth mechanism to the transformational one and the martensitic mechanism of PT to a reconstructive one via an intermediate disordered phase. The primary condition is that the GB energy of the ω phase is smaller than that of the α phase, which promotes the nucleation of ω-Zr and is consistent with the absence of the reverse PT and reduction in the PT pressure with reducing grain size. Several intermediate steps for such motion are suggested and justified kinetically. Nonhydrostatic stresses due to volume reduction in the growing ω grain promote continuous growth of the existing ω grain instead of a new nucleation at other GBs. In situ synchrotron Laue diffraction experiments confirm the main predictions of the theory. The suggested mechanism provides a new insight into synergistic interaction between PTs and microstructure evolution.

anomalous grain growth during phase transformation↗
DOE OSTI2026

Processing iridium foil targets for the production of radioplatinum isotopes

Dissolving noble metals remains challenging because of their high reduction potentials and tendency to passivate as oxides. This barrier is acute for iridium metal targets used to produce platinum radioisotopes, where post-irradiation processing is costly and hazardous with conventional routes. Here, we report a rapid alkali-fusion method that converts Ir metal directly into chloride media compatible with downstream separations. In the process, an Ir foil is fused with Na 2 O 2 and KCl at temperatures above the KCl melting point; the molten salt enhances heat transfer and facilitates O 2− /Na + transport to the Ir surface, overcoming Ir's oxidation resistance. The fused cake is then cooled and leached in 10 M HCl, yielding Ir in solution without specialized microwave digestion or HF. Pt separation from bulk Ir was evaluated using extraction-chromatography resins. A newly formulated ionic-liquid resin containing Cyphos IL 104 (E104) was compared with two commercial resins (TrisKem TK200 and TK201). All resins achieved >90 % Ir recovery. Pt co-recovery depended on resin chemistry: TK200 recovered 85.9 % Pt, TK201 recovered 54.1 % Pt, and E104 recovered 72.9 % Pt. This study introduces a fast, scalable dissolution route for solid Ir targets and demonstrates resin choices that tune Ir/Pt separation, lowering the barrier to routine production and purification of Pt radioisotopes.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Parallel transport dynamics for mixed quantum states with applications to time-dependent density functional theory

Direct simulation of the von Neumann dynamics for a general (pure or mixed) quantum state can often be expensive. One prominent example is the real-time time-dependent density functional theory (rt-TDDFT), a widely used framework for the first principle description of many-electron dynamics in chemical and materials systems. Practical rt-TDDFT calculations often avoid the direct simulation of the von Neumann equation, and solve instead a set of Schrödinger equations, of which the dynamics is equivalent to that of the von Neumann equation. However, the time step size employed by the Schrödinger dynamics is often much smaller. Here, in order to improve the time step size and the overall efficiency of the simulation, we generalize a recent work of the parallel transport (PT) dynamics for simulating pure states [An, Lin, Multiscale Model. Simul. 18, 612, 2020] to general quantum states. The PT dynamics provides the optimal gauge choice, and can employ a time step size comparable to that of the von Neumann dynamics. Going beyond the linear and near adiabatic regime in previous studies, we find that the error of the PT dynamics can be bounded by certain commutators between Hamiltonians, density matrices, and their derived quantities. Such a commutator structure is not present in the Schrödinger dynamics. We demonstrate that the parallel transport-implicit midpoint (PT-IM) method is a suitable method for simulating the PT dynamics, especially when the spectral radius of the Hamiltonian is large. The commutator structure of the error bound, and numerical results for model rt-TDDFT calculations in both linear and nonlinear regimes, confirm the advantage of the PT dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Durable hybrid electrocatalysts for proton exchange membrane fuel cells

The low durability of carbon-based non-precious metal electrocatalysts hinders their practical applications in proton exchange membrane fuel cells (PEMFCs). In this study, we rationally design a hybrid Pt-Fe-N-C electrocatalyst with unprecedented durability. It consists of abundant Pt and Fe single atoms homogeneously dispersed on the nitrogen-doped carbon support and a small amount of Pt-Fe alloy nanoparticles. A PEMFC with Pt-Fe-N-C as the cathode shows a larger peak power density (0.75 W cm -2 ) than that with Fe-N-C as the cathode (0.50 W cm -2 ). The remarkable durability of Pt-Fe-N-C is reflected from no noticeable drop in the half-wave potential after 70000 potential cycles between 0.6 and 1.0 V in the liquid cell, and 80% current retention after 85 h of potential hold at 0.4 V in the fuel cell. This work demonstrates the feasibility of improving the durability of Fe-N-C material via ultra-low Pt doping and makes non-precious metal electrocatalysts be close to achieving commercial metrics.

25 ENERGY STORAGE↗
DOE OSTI2025

Development of a Transferable Density-Functional Tight-Binding Model for Organic Molecules at the Water/Platinum Interface

A computationally efficient and transferable approach for modeling reactions at metal/water interfaces could significantly accelerate our understanding and ultimately the development of new catalytic transformations, particularly in the context of the emerging field of biomass conversion. Here, we present a parametrization of Pt–X (X = H, O, C) density-functional tight-binding (DFTB) for addressing this need. We first constructed Pt–H, Pt–O, and Pt–C repulsive potential splines. These pairwise parameters were then augmented to include many-body interactions using the Chebyshev Interaction Model for Efficient Simulation (ChIMES). We compare the geometrical and energetic performances of both DFTB and DFTB/ChIMES methods with DFT reference data across a variety of organic molecules at the platinum surface from nanoparticles to single-crystal surfaces. DFTB shows limited transferability between extended crystal surfaces and small nanoparticles. This transferability is significantly improved through the introduction of three-body interactions with Pt in DFTB/ChIMES, which provides consistent results across various systems, with reductions in the RMSD from around 30 kcal/mol in DFTB to around 10 kcal/mol. We demonstrate the stability and reliability of the obtained parameters by performing metadynamic simulations for the adsorption of phenol on Pt(111). We observe that DFTB itself is undersolvating the surface, leading to only one or two chemisorbed water molecules in a c(4 × 6) unit cell. In contrast, DFTB/ChIMES leads to a coverage of about 0.5 ML and successfully captures the chemisorbed mode of phenol at both the solid/liquid and the solid/gas interfaces. Furthermore, in agreement with experimental measurements, the adsorption at the solid/liquid interface is significantly weaker than that at the solid/gas interface. As a result, we highlight that even with DFTB, where we can accumulate dynamics for more than 1 ns for a given system, the simulations are not fully converged.

Adsorption↗