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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Effect of Pt vacancies on magnetotransport of Weyl semimetal candidate GdPtSb epitaxial films

Here, we examine the effects of Pt vacancies on the magnetotransport properties of Weyl semimetal candidate GdPtSb films, grown by molecular beam epitaxy on c-plane sapphire. Rutherford backscattering spectrometry and x-ray diffraction measurements suggest that phase-pure GdPt x ⁢Sb films can accommodate up to 15% of Pt vacancies (x = 0.85), which act as acceptors, as measured by the Hall effect. Two classes of electrical transport behavior are observed. Pt-deficient films display metallic temperature-dependent resistivity (dρ/dT > 0). The longitudinal magnetoresistance (LMR, magnetic field B parallel to electric field E) is more negative than transverse magnetoresistance (TMR, B⁢⊥⁢E), consistent with the expected chiral anomaly for a Weyl semimetal. The combination of Pt-vacancy disorder and doping away from the expected Weyl nodes, however, suggests that conductivity fluctuations may explain the negative LMR rather than chiral anomaly. Samples closer to stoichiometry display the opposite behavior: semiconductorlike resistivity (dρ/dT > 0) and more negative TMR than LMR. Hysteresis and other nonlinearities in the low-field Hall effect and magnetoresistance suggest that spin-disorder scattering and possible topological Hall effect may dominate the near-stoichiometric samples. Our findings highlight the complications of transport-based identification of Weyl nodes but point to possible topological spin textures in GdPtSb.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Pt-Ni/WC Alloy Nanorods Arrays as ORR Catalyst for PEM Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) among the other types of fuel cell technology are attractive power sources, especially for electric vehicle applications. While significant progress and plausible prospects of PEMFCs have been achieved, there are still some challenges related to the performance, durability, and cost that need to be overcome to make them economically viable for widespread commercialization. Our strategy is to develop thin films of high-active and stable catalyst coated on vertically aligned nanorod arrays of conductive and stable support. In this work, we fabricated tungsten carbide (WC) nanorods as support and coated them with a platinum-nickel (Pt-Ni) alloy shell denoted as Pt-Ni/WC catalysts. The Pt- Ni/WC nanorods were deposited on glassy carbon disks as well as on silicon substrates for evaluation of their electrocatalytic oxygen reduction reaction (ORR) activity and physical properties. Cyclic voltammetry experiments using rotating disk electrode were performed in perchloric acid (0.1 M HClO4) electrolyte at room temperature to characterize the ORR activity and stability of Pt-Ni/WC nanorods catalysts. Scanning electron microscopy and X-ray diffraction techniques were utilized to study the morphology and crystallographic properties, respectively.

Begum, Mahbuba↗
DOE OSTI2022

Continuous Production of Carbon-Supported and Surfactant-Free Pt-M (M=Fe, Co, Ni, and Cu) Nanocrystals for Catalyzing Oxygen Reduction

Scalable production of carbon-supported Pt-M (M=Co, Ni, and Fe) alloy nanocrystals is of great importance for their practical application as catalysts towards the oxygen reduction reaction (ORR), a process key to the operation of proton-exchange membrane fuel cells. Here we report the use of a fluidic device for the in situ nucleation and growth of Pt-M nanocrystals on a commercial carbon support in a continuous and scalable fashion. The use of dimethylformamide not only enables well dispersion of the carbon powders for the creation of a homogeneous reaction mixture but also helps reduce metal precursors for the heterogeneous nucleation and growth of nanocrystals on the carbon surface. The size, shape, and composition of the nanocrystals can all be tuned by changing the metal precursors added into the reaction mixture, resulting in Pt-M nanocrystals uniformly distributed across the surface of the carbon support. Among the nanocrystals, the carbon-supported Pt-Co nanocrystals show the highest ORR specific and mass activities at 0.9 V, demonstrating 11.4- and 8.8-fold enhancements over the state-of-the-art commercial Pt/C catalyst.

Electrochemistry↗
DOE OSTI2015

Isotopic Probe Illuminates the Role of the Electrode Surface in Proton Coupled Hydride Transfer Electrochemical Reduction of Pyridinium on Pt(111)

A recently proposed mechanism for electrochemical CO 2 reduction on Pt (111) catalyzed by aqueous acidic pyridine solutions suggests that the observed redox potential of ca. -600 mV vs. SCE is due to the one-electron reduction of pyridinium through proton coupled electron transfer (PCET) to form H atoms adsorbed on the Pt surface (H ads ). The initial pyridinium reduction was probed isotopically via deuterium substitution. A combined experimental and theoretical analysis found equilibrium isotope effects (EIE) due to deuterium substitution at the acidic pyridinium site. A shift in the cathodic cyclic voltammetric half wave potential of -25 mV was observed, consistent with the theoretical prediction of -40 mV based on the recently proposed reaction mechanism where pyridinium is essential to establish a high concentration of Bronsted acid in contact with the substrate CO 2 and with the Pt surface. A prefeature in the cyclic voltammogram was examined under isotopic substitution and indicated an H-ads intermediate in pyridinium reduction. In conclusion, the theoretical prediction and observation of an BM supported the assignment of the cathodic wave to the proposed reduction of pyridinium through PCET forming H ads and eventually H 2 on the Pt surface.

08 HYDROGEN↗
DOE OSTI2010

SISGR: Theoretically Relating the Surface Composition of Pt Alloys to their Performance as the Electrocatalysts of Low-Temperature Fuel Cells

The main goal of this project is to gain fundamental knowledge about the relation between surface composition and catalytic performance of Pt alloy catalysts for oxygen reduction reaction (ORR). Specific objectives are: to develop and improve a first-principles based multiscale computation approach to simulating surface segregation phenomena in Pt alloy surfaces; to evaluate the surface electronic structure and catalytic activity of Pt alloy catalysts and; to relate the surface composition to the catalytic performance of Pt alloy catalysts.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2018

Investigation of continuous Pt-monolayer deposition method on stable non-noble metals and other stable materials (Final Report)

The objective of the project is for BNL to investigate the method of depositing continuous Pt monolayer on non-noble metals and other stable materials under PEM fuel cell operating condition. The motivation of this research is to develop a novel Pt monolayer catalyst for O 2 reduction reaction. This leads to ultra-low Pt loading (<0.1 mg/cm 2 ) for PEM fuel cell catalyst. The deposited Pt-monolayer will be tested to determine their activity and stability under potential cycling conditions. Project involves exploring approaches to increase the catalyst's activity and stability against oxidation under fuel cell operating conditions.

99 GENERAL AND MISCELLANEOUS↗
NASA NTRS1991

Microstructural and magnetic characterization of rapidly solidified and annealed Pt-Co-B alloys

Significant increases in intrinsic coercivity (Hic) of Pt-Co alloys have been obtained by the addition of boron and the application of rapid solidification processing. After rapid solidification by double anvil splat quenching with subsequent annealing at 650 C for 30 min, an alloy of Pt42Co45B13 exhibits an Hic as high as 14 kOe. Annealing of the Pt-Co-B influences the L1(0) superlattice structure and grain size of the matrix, the crystal structure and size of Co-boride precipitate, and the distribution of magnetic domain walls. A microstructural analysis shows that the maximum H(ic) occurs when Co borides, having the Co3B structure, are within the single magnetic domain size. The magnetic hardening mechanism in Pt-Co-B is believed to be a combination of inhibited magnetic domain nucleation and difficult reverse magnetic domain growth caused by the interaction of the magnetically anisotropic Co borides with the L1(0) Pt-Co matrix.

Qiu, N.↗
NASA NTRS2008

Low-Pt-Content Anode Catalyst for Direct Methanol Fuel Cells

Combinatorial experiments have led to the discovery that a nanophase alloy of Pt, Ru, Ni, and Zr is effective as an anode catalyst material for direct methanol fuel cells. This discovery has practical significance in that the electronic current densities achievable by use of this alloy are comparable or larger than those obtained by use of prior Pt/Ru catalyst alloys containing greater amounts of Pt. Heretofore, the high cost of Pt has impeded the commercialization of direct methanol fuel cells. By making it possible to obtain a given level of performance at reduced Pt content (and, hence, lower cost), the discovery may lead to reduction of the economic impediment to commercialization.

Narayanan, Sekharipuram↗
DOE OSTI2011

PT AND PT/NI "NEEDLE" ELETROCATALYSTS ON CARBON NANOTUBES WITH HIGH ACTIVITY FOR THE ORR

Platinum and platinum/nickel alloy electrocatalysts supported on graphitized (gCNT) or nitrogen doped carbon nanotubes (nCNT) are prepared and characterized. Pt deposition onto carbon nanotubes results in Pt 'needle' formations that are 3.5 nm in diameter and {approx}100 nm in length. Subsequent Ni deposition and heat treatment results in PtNi 'needles' with an increased diameter. All Pt and Pt/Ni materials were tested as electrocatalysts for the oxygen reduction reaction (ORR). The Pt and Pt/Ni catalysts showed excellent performance for the ORR, with the heat treated PtNi/gCNT (1.06 mA/cm{sup 2}) and PtNi/nCNT (0.664 mA/cm{sup 2}) showing the highest activity.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and CO-stripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2011

X-ray Absorption Spectroscopy of Bimetallic Pt-Re Catalysts for Hydrogenolysis of Glycerol to Propanediols

Bimetallic Pt-Re nanoparticles supported on Norit carbon were effective at converting aqueous glycerol to 1,3 (34 %) and 1,2 (33 %) propanediol at 443 K under 4 MPa of H{sub 2}. Results from X-ray absorption spectroscopy and analytical transmission electron microscopy confirmed that the nanoparticles were indeed bimetallic, with a particle size less than 2 nm in diameter. The Pt L{sub III} near edge spectra indicated that the Pt was reduced to the metallic state by treatment in H{sub 2} at 473 K, but that a partial positive charge remained on the Re. These oxidized Re species could be associated with charged Re atoms dispersed on the carbon support because spillover of H atoms from Pt was required to reduce Re in the bimetallic particles.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Faceting of Nanoscale Pt and Au Particles for Applications in Catalysis

In an effort to reduce the world's dependence on fossil fuels as well as lower green house gas emissions, proton exchange membrane fuel cells (PEMFC) have been considered by many as a prime candidate for both mobile and stationary alternative energy sources. The principal limiting factor for efficiency in fuel cells is the oxygen reduction reaction (ORR) which is driven by platinum based catalyst materials. Numerous methods have been developed to synthesize particles that make more efficient use of the active surfaces by tuning shapes, sizes and facets. For example, it was recently demonstrated that selectivity can be tuned by controlling particle shape in the case of promoting trans olefin isomerization to their cis counterparts using close-packed Pt (111), Pt (557) and Pt (100) surfaces as opposed to a more open Pt (110), which favored the trans-counterparts. Furthermore, it has been reported that certain facets exhibit improved ORR activity while others may decrease activity at the bulk phase single crystal level. Here, we will present a study of various wet chemical reduction methods targeting specific morphologies and the resulting electrochemical activity. Determining the effects of synthetic parameters on the final product via transmission electron microscopy (TEM), small angle x-ray scattering (SAXS) and wide angle x-ray scattering (WAXS) provides mechanistic insight on growth kinetics, while electrochemical studies correlate physical properties to performance. Understanding structure and activity relationships will allow us to intuitively design next generation materials with enhanced properties.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

The catalytic behavior of precisely synthesized Pt–Pd bimetallic catalysts for use as diesel oxidation catalysts

The demands of stricter diesel engine emission regulations have created challenges for current exhaust systems. With advances in low-temperature internal combustion engines and their operations, advances must also be made in vehicle exhaust catalysts. Most current diesel oxidation catalysts use heavy amounts of precious group metals (PGMs) for hydrocarbon (HC), CO, and NO oxidation. These catalysts are expensive and are most often synthesized with poor bimetallic interaction and dispersion. In this paper, the goal was to study the effect of aging on diesel emission abatement of Pt–Pd bimetallic nanoparticles precisely prepared with different morphologies: well dispersed core–shell vs. well dispersed homogeneously alloyed vs. poorly dispersed, poorly alloyed particles. Alumina and silica supports were studied. Particle morphology and dispersion were analyzed before and after hydrothermal treatments by XRD, EDX, and STEM. Reactivity as a function of aging was measured in simulated diesel engine exhaust. While carefully controlled bimetallic catalyst nanoparticle structure has a profound influence on initial or low temperature catalytic activity, the differences in behavior disappear with higher temperature aging as thermodynamic equilibrium is achieved. The metallic character of Pt-rich alumina-supported catalysts is such that behavior rather closely follows the Pt–Pd metal phase diagram. Nanoparticles disparately composed as well-dispersed core–shell (via seq-SEA), well-dispersed homogeneously alloyed (via co-SEA), and poorly dispersed, poorly alloyed (via co-DI) end up as well alloyed, large particles of almost the same size and activity. With Pd-rich systems, the oxidation of Pd also figures into the equilibrium, such that Pd-rich oxide phases appear in the high temperature forms along with alloyed metal cores. Finally, the small differences in activity after high temperature aging can be attributed to the synthesis methods, sequential SEA and co-DI which give rise, after aging, to a bimetallic surface enriched in Pd.

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

Electrochemical Degradation of Pt–Ni Nanocatalysts: An Identical Location Aberration-Corrected Scanning Transmission Electron Microscopy Study

The evolution of Pt–Ni nanoparticles supported on amorphous carbon is investigated before and after electrochemical potential cycling (0.6-1.1 V), using aberration-corrected scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). During voltage cycling and due to the dissolution of nanoparticles, single ions/atoms and ionic/atomic clusters emerge and diffuse across the carbon support toward larger nanoparticles, where they redeposit. We observe that the preferred locations for the dissolution are the steps and corners of the nanoparticles. On the other hand, the redeposition process happens often on {111} type planes. In addition, contrary to the conventional view, where larger particles grow isotropically from smaller ones, this research work shows that anisotropic growth of smaller particles occurs during potential cycling. The reason for this behavior seems to be related to the fact that smaller particles with thicker Pt-rich shells trigger the nucleation and deposition of Pt.

catalysts↗
DOE OSTI2020

Materials Data on Pt(OF3)2 by Materials Project

PtF6O2 is Tetraauricupride structured and crystallizes in the cubic Ia-3 space group. The structure is zero-dimensional and consists of eight oxygen molecules and eight PtF6 clusters. In each PtF6 cluster, Pt is bonded in an octahedral geometry to six equivalent F atoms. All Pt–F bond lengths are 1.92 Å. F is bonded in a single-bond geometry to one Pt atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt(NCl)2 by Materials Project

Pt(NCl)2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of two cis-diaminedichloroplatinum molecules. Pt2+ is bonded in a distorted rectangular see-saw-like geometry to two N and two Cl1- atoms. There is one shorter (1.77 Å) and one longer (1.78 Å) Pt–N bond length. There are one shorter (2.37 Å) and one longer (2.41 Å) Pt–Cl bond lengths. There are two inequivalent N sites. In the first N site, N is bonded in a single-bond geometry to one Pt2+ atom. In the second N site, N is bonded in a single-bond geometry to one Pt2+ atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Pt2+ atom. In the second Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Pt2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt(NCl2)2 by Materials Project

Pt(NCl2)2 is alpha Niobium phosphide-derived structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is zero-dimensional and consists of two nsc119876 molecules. Pt2+ is bonded in a distorted octahedral geometry to two equivalent N1+ and four equivalent Cl1- atoms. Both Pt–N bond lengths are 1.99 Å. All Pt–Cl bond lengths are 2.34 Å. N1+ is bonded in a distorted single-bond geometry to one Pt2+ atom. Cl1- is bonded in a single-bond geometry to one Pt2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt(I3N2)2 by Materials Project

Pt(N2I3)2 is Copper structured and crystallizes in the orthorhombic Pnnm space group. The structure is zero-dimensional and consists of two Pt(N2I3)2 clusters. Pt2+ is bonded in an octahedral geometry to six I1- atoms. There are a spread of Pt–I bond distances ranging from 2.54–2.82 Å. N1+ is bonded in a bent 120 degrees geometry to two I1- atoms. There are one shorter (1.99 Å) and one longer (2.39 Å) N–I bond lengths. There are three inequivalent I1- sites. In the first I1- site, I1- is bonded in a 3-coordinate geometry to one Pt2+ and two equivalent N1+ atoms. In the second I1- site, I1- is bonded in a distorted bent 150 degrees geometry to one Pt2+ and two equivalent N1+ atoms. In the third I1- site, I1- is bonded in a single-bond geometry to one Pt2+ atom.

36 MATERIALS SCIENCE↗