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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Pt(NCl2)2 by Materials Project

Pt(NCl2)2 crystallizes in the monoclinic C2/c space group. The structure is zero-dimensional and consists of four Pt(NCl2)2 clusters. Pt2+ is bonded in a 6-coordinate geometry to two equivalent N1+ and four Cl1- atoms. Both Pt–N bond lengths are 1.96 Å. There are two shorter (2.35 Å) and two longer (2.62 Å) Pt–Cl bond lengths. N1+ is bonded in an L-shaped geometry to one Pt2+ and one Cl1- atom. The N–Cl bond length is 1.69 Å. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Pt2+ and one N1+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Pt2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt(NCl)2 by Materials Project

Pt(NCl)2 crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of two Pt(NCl)2 ribbons oriented in the (0, 1, 0) direction. Pt2+ is bonded in a distorted square co-planar geometry to two equivalent N and two equivalent Cl1- atoms. Both Pt–N bond lengths are 1.88 Å. Both Pt–Cl bond lengths are 2.43 Å. N is bonded in a 2-coordinate geometry to one Pt2+ and one Cl1- atom. The N–Cl bond length is 1.66 Å. Cl1- is bonded in a distorted bent 120 degrees geometry to one Pt2+ and one N atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pt(NCl)4 by Materials Project

Pt(NCl)4 crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two Pt(NCl)4 sheets oriented in the (0, 0, 1) direction. Pt2+ is bonded in an octahedral geometry to four equivalent N+0.50+ and two equivalent Cl1- atoms. All Pt–N bond lengths are 1.96 Å. Both Pt–Cl bond lengths are 2.40 Å. N+0.50+ is bonded in a distorted T-shaped geometry to one Pt2+ and two equivalent Cl1- atoms. Both N–Cl bond lengths are 2.13 Å. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Pt2+ atom. In the second Cl1- site, Cl1- is bonded in a square co-planar geometry to four equivalent N+0.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomically dispersed Pt single sites and nanoengineered structural defects enable a high electrocatalytic activity and durability for hydrogen evolution reaction and overall urea electrolysis

The scarcity and high cost of PGM electrocatalysts are the key bottleneck in the mass-scale commercialization of many electrolysis technologies. Bifunctional single-atom electrocatalysts (SACs) are promising alternatives for PGM electrocatalysts in next-generation electrolysis technologies because of their superior intrinsic activity and perfect atom utilization. Regulating the coordination environment of platinum atomic sites identifies their electrocatalytic performance. Therefore, exploring more appropriate supports could facilitate the construction of active and durable electrocatalysts with ultralow noble metal content. Herein, we report on a reliable approach for producing a novel type of SACs composed of atomically dispersed Pt active sites stabilized on defective NiCo layered double hydroxide (Pt/D-NiCo LDH) nanosheets as an ultralow-Pt hybrid electrocatalyst for hydrogen evolution reaction (HER), urea oxidation reaction (UOR), and full urea-water electrolysis. The optimized Pt 1 /D NiCo LDH-24 SAC displays a remarkable HER and UOR performance where it yields a current density of 10 mA cm -2 at 37 mV and 1.25 V vs. RHE for HER and UOR, respectively. Finally, symmetrical urea electrolyzer constructed of Pt 1 /D-NiCo LDH-24 electrodes attains 10 mA cm -2 at a cell voltage of 1.32 V vs. RHE, demonstrating superior activity and durability over 60 h operation when compared to commercial Pt/C( + )||RuO 2 ( - ) system.

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

Diastereoselective Hydrogenation of Tetrasubstituted Olefins using a Heterogeneous Pt‐Ni Alloy Catalyst

Abstract Stereoselective hydrogenation of tetrasubstituted olefins is an attractive method to access compounds with two contiguous stereocenters. However, homogeneous catalysts for enantio‐ and diastereoselective hydrogenation exhibit low reactivity toward tetrasubstituted olefins due to steric crowding between the ligand scaffold and the substrate. Monometallic heterogeneous catalysts, on the other hand, provide accessible surface active sites for hindered olefins but exhibit unpredictable and inconsistent stereoinduction. In this work, we develop a Pt−Ni bimetallic alloy catalyst that can diastereoselectively hydrogenate unactivated, sterically‐bulky tetrasubstituted olefins, utilizing the more oxophilic Ni atoms to adsorb a hydroxyl directing group and direct facially‐selective hydrogen addition to the olefin via the Pt atoms. Structure‐activity studies on several Pt−Ni compositions underscore the importance of exposing a uniform PtNi alloy surface to achieve high diastereoselectivity and minimize side reactions. The optimized Pt−Ni/SiO 2 catalyst exhibits good functional group tolerance and broad scope for tetrasubstituted olefins in a cyclopentene scaffold, generating cyclopentanol products with three contiguous stereocenters. The synthetic utility of the method is demonstrated in a four‐step synthesis of (1R,2S)‐(+)‐cis‐methyldihydrojasmonate with high yield and enantiopurity.

Chemistry↗
DOE OSTI2024

NO Reduction with CO on Low‐loaded Platinum‐group Metals (Rh, Ru, Pd, Pt, and Ir) Atomically Dispersed on Ceria

Abstract Low‐loaded platinum‐group single‐atom catalysts on CeO 2 (M 1 /CeO 2 ) were synthesized via high‐temperature atom trapping (AT) and tested for the NO+CO reaction under dry and wet conditions. The activity of these catalysts for NO+CO reaction follows the order Rh>Pd≈Ru>Pt>Ir. For Rh, Ru, and Pd single‐atom catalysts, the N 2 O byproduct is formed but not clearly observed in Ir and Pt cases, which may result from the higher reaction temperature (>200 °C) required for Pt and Ir catalysts. The presence of water can promote the activity of these M 1 /CeO 2 catalysts for the NO+CO reaction. Under wet conditions, significant NH 3 formation occurred during the reaction, which is due to the co‐existence of water‐gas‐shift reaction on these catalysts. Compared with Pt, Pd and Ir, the Rh and Ru single‐atom catalysts show higher selectivity to NH 3 species, resulting from the hydride species on the surface. Among all tested catalysts, Ru 1 /CeO 2 shows the highest production of ammonia and highest CO conversion due to excellent water‐gas‐shift activity, whereas Pd 1 /CeO 2 shows lowest ammonia production. Rh 1 /CeO 2 shows the best low temperature NO reduction activity among all tested catalysts.

Tian, Jinshu↗
DOE OSTI2025

Durability of Pt-Alloy Catalyst for Heavy-Duty Polymer Electrolyte Fuel Cell Applications under Realistic Conditions

As an emerging technology, polymer electrolyte fuel cells (PEFCs) powered by clean hydrogen can be a great source of renewable power generation with flexible utilization because of high gravimetric energy density of hydrogen. To be used in real-life applications, PEFCs need to maintain their performance for long-term use under a wide range of conditions. Therefore, it's important to understand the degradation of the PEFC under protocols that are closely related to the catalyst lifetime. Alloying Pt with transitional metal improves catalyst activity. It is also crucial to understand Pt alloys degradation mechanisms to improve their durability. To study durability of Pt alloys, accelerated stress tests (ASTs) are performed on Pt-Co catalyst supported on two types of carbon. Two different AST protocols were being studied: Membrane Electrolyte Assembly (MEA) AST based on the protocol introduced by the Million Mile Fuel Cell Truck consortium in 2023 and Catalyst AST, adopted from the U.S. Department of Energy (DoE).

25 ENERGY STORAGE↗
DOE OSTI2022

Nanoporous Pt(Au) Alloys for the Enhanced, Non–enzymatic Detection of Hydrogen Peroxide under Biofouling Conditions

The non-enzymatic electrochemical sensing of hydrogen peroxide (H 2 O 2 ) is described. This study utilized a 3D bicontinuous nanoporous platinum-gold alloy-based sensor (NP-Pt(Au) electrode), which has a morphology that resembles a molecular sieve. SEM and CV were used to evaluate the morphological and electrochemical characteristics of the NP-Pt(Au) electrodes. The cathodic voltammetric response of H 2 O 2 was enhanced at the NP-Pt(Au) as compared to planar Pt electrodes. Further, the nanoporous electrode was able to maintain the H 2 O 2 voltammetric profile even in the presence of the biofouling agent, serum albumin. Its application as a non-enzymatic sensor for the amperometric measurement of H 2 O 2 was explored.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In-situ monitoring of atomically dispersed Pt sites supported on OMS-2 during CO 2 activation

Atomically dispersed catalysts have drawn great interest lately, as they showcase a high density of active sites, selectivity, and high turnover frequencies in oxidation chemistry due to labile oxygen activation. In contrast, the applications of these catalysts have lagged in reduction reactions due to the ambiguity caused by the sintering and restructuring of active sites. To bridge this gap, the evolution of Pt 4+ isomorphically substituted into an octahedral molecular sieve structure (OMS-2) under reductive conditions was correlatively characterized using multiple in-situ analytical techniques such as ambient pressure X-ray photoelectron spectroscopy, environmental transmission electron microscopy, and solid-state nuclear magnetic resonance. The surface dynamics of the Pt single atoms were revealed during the Reverse Water Gas Shift (RWGS) reaction, where the active sites were identified as two-coordinated platinum single atoms. Under reaction, we show nonbinding atoms adjacent to the single atoms restructured the motif of the single atoms to Pt 2+ via ion mobility of potassium, increasing the activation energy by 25.6 kJ/mol. Here, this work also highlights the potential for increased stability of the single atom sites via isomorphic substitution of the metal oxide support, since the Pt-OMS-2 catalyst retained activity for about 33 h before deactivation, after which nanoparticles were observed in TEM images. This work offers a new perspective in single atom synthesis using the metal oxide as the host for the single atom site, instead of adatoms on the surface

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

DFT and microkinetic comparison of Pt, Pd and Rh-catalyzed ammonia oxidation

Ammonia oxidation is the heart of the Ostwald process and is important in emissions control. Catalytic behaviors are a function of conditions and are observed to vary across the platinum group metals (PGMs) Pt, Pd, Rh. Here, we combine density functional theory computations and microkinetic modeling to rationalize these dependencies. We compute reactions over model (2 1 1) and (1 1 1) surfaces of PGMs. Binding energies are similar on Pd and Pt and generally greater on Rh, while activation energies vary across all metals. Rates on (2 1 1) surfaces are greater than (1 1 1) surfaces. Additionally, the stepped Pt is most active and stepped Rh most selective to N 2 at ammonia slip conditions, while at Ostwald process conditions, stepped Pd is most active and stepped Pt most selective to NO. Degree of rate and selectivity control analysis provides insights into the reactions limiting performance of PGMs. Both activation barriers and surface coverages influence rates and selectivities.

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

Adsorption and activation of CO 2 on Pt/CeOx/TiO 2 (110): Role of the Pt-CeO x interface

The adsorption and dissociation of CO 2 on TiO 2 (110), CeO x /TiO 2 (110) and Pt/CeO x /TiO 2 (110) surfaces has been examined using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS). The substrates under study exhibited different degrees of complexity which were tested for the binding of the adsorbate and the cleavage of C-O bonds. The surfaces were prepared by depositing CeO x (0.1 ML) onto TiO 2 (110) to form a mixed oxide support, onto which Pt nanoparticles (0.2 ML) were deposited. This configuration yields a complex set of interfaces between metal and oxides and we have systematically titrated the active role of each component (Pt 4f, Ce 3d and Ti 2p regions) and the arising surface intermediates (C 1s and O 1s regions). CO 2 barely bonds to stoichiometric TiO 2 (110). It heals oxygen vacancies of this oxide surface (CO 2,gas → CO gas + O a ) and does not form stable carbonates. A stable carbonate was seen upon adsorption of CO 2 on CeO x /TiO 2 (110) and on this type of substrate the adsorbate also removed O vacancies leading to the oxidation of Ti 3+ and Ce 3+ sites. Pt nanoparticles dispersed on CeO x /TiO 2 (110) were highly effective for the binding and dissociation of CO 2 , with the formation of CO 3 , CO, C and CH x species on the Pt/CeO x /TiO 2 (110) system. The results of theoretical calculations based on density-functional theory (DFT) show that Pt/CeOx/TiO2(110) binds CO2 much stronger than surfaces of bulk platinum {(111), (100), (110)} or other late transition metals. On a Pt-CeO x interface, the molecule adsorbs with a bent configuration (~ 130° O-C-O bond angle) and with a substantial elongation (~ 0.1 Å) of the C-O bonds, facilitating its transformation into high value chemicals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural Insights into the Vapochromic Behavior of Pt- and Pd-Based Compounds

Anionic complexes having vapochromic behavior are investigated: [K(H 2 O)][M(ppy)(CN) 2 ], [K(H 2 O)][M(bzq)(CN) 2 ], and [Li(H 2 O) n ][Pt(bzq)(CN) 2 ], where ppy = 2-phenylpyridinate, bzq = 7,8-benzoquinolate, and M = Pt(II) or Pd(II). These hydrated potassium/lithium salts exhibit a change in color upon being heated to 380 K, and they transform back into the original color upon absorption of water molecules from the environment. The challenging characterization of their structure in the vapochromic transition has been carried out by combining several experimental techniques, despite the availability of partially ordered and/or impure crystalline material. Room-temperature single-crystal and powder X-ray diffraction investigation revealed that [K(H 2 O)][Pt(ppy)(CN) 2 ] crystallizes in the Pbca space group and is isostructural to [K(H 2 O)][Pd(ppy)(CN) 2 ]. Variable-temperature powder X-ray diffraction allowed the color transition to be related to changes in the diffraction pattern and the decrease in sample crystallinity. Water loss, monitored by thermogravimetric analysis, occurs in two stages, well separated for potassium Pt compounds and strongly overlapped for potassium Pd compounds. Furthermore, the local structure of potassium compounds was monitored by in situ pair distribution function (PDF) measurements, which highlighted changes in the intermolecular distances due to a rearrangement of the crystal packing upon vapochromic transition.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A Study of How LaFeO 3 and CaTiO 3 Supports Affect the Oxidation, Hydrogenation, and Methane Steam Reforming Activity of Pt and Ni Catalysts

The structure and catalytic properties of Pt and Ni supported on thin films of LaFeO 3 and CaTiO 3 , prepared by Atomic Layer Deposition (ALD), were investigated. X-Ray diffraction (XRD) and scanning transmission electron microscopy (STEM) show that reduction at 1073 K causes Pt-Fe intermetallic compound formation for Pt/LaFeO 3 . For Pt/CaTiO 3 , 1073-K reduction induces local decomposition of the CaTiO 3 with migration of Ti to the Pt. Reduced Pt/LaFeO 3 and Pt/CaTiO 3 exhibited CO-oxidation activity similar to that for Pt supported on MgAl 2 O 4 but were much less active for propane oxidation and hydrogenation of 1-hexene and toluene. In contrast, Ni/CaTiO 3 behaved similarly to a conventional supported Ni catalyst for the methane-steam-reforming (MSR) and 1-hexene hydrogenation. There was also no evidence for local decomposition of the perovskite in the vicinity of the Ni particles. Furthermore, the results obtained in this study demonstrate that metal-perovskite interactions that affect reactivity are specific to each component.

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

Elucidation of the Active Site for the Oxygen Evolution Reaction on a Single Pt Atom Supported on Indium Tin Oxide

Single-atom catalysts (SACs) have attracted attention for their high catalytic activity and selectivity, but the nature of their active sites under realistic reaction conditions, involving various ligands, is not well understood. In this study, we use Density Functional Theory calculations and grand canonical basin hopping to theoretically investigate the active site for the oxygen evolution reaction (OER) on single Pt atom supported on Indium Tin Oxide, including the influence of the electrochemical potential. We show that the ligands on the Pt atom change from Pt-OH in the absence of electrochemical potential to PtO(OH) 4 in electrochemical conditions. This change of the chemical state of Pt is associated to a decrease of 0.3V for the OER overpotential. This highlights the importance of accurately identifying the nature of the active site under reaction conditions and the impact of adsorbates on the electrocatalytic activity. This theoretical investigation enhances our understanding of SACs for OER.

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

Ultrasmooth Epitaxial Pt Thin Films Grown by Pulsed Laser Deposition

Platinum (Pt) thin films are useful in applications requiring high-conductivity electrodes with excellent thermal and chemical stability. Ultrasmooth and epitaxial Pt thin films with single-crystalline domains have the added benefit of providing ideal templates for the subsequent growth of heteroepitaxial structures. Here, we grow epitaxial Pt (111) electrodes (ca. 30 nm thick) on sapphire (α-Al 2 O 3 (0001)) substrates with pulsed laser deposition. This versatile technique allows control of the growth process and fabrication of films with carefully tailored parameters. X-ray scattering, atomic-force microscopy, and electron microscopy provide structural characterization of the films. Various gaseous atmospheres and temperatures were explored to achieve epitaxial growth of films with low roughness. A two-step (500 °C/300 °C) growth process was developed, yielding films with improved epitaxy without compromising roughness. The resulting films possess ultrasmooth interfaces (<3 Å) and high electrical conductivity (6.9 × 10 6 S/m). Finally, Pt films were used as current collectors and templates to grow lithium manganese oxide (LiMn 2 O 4 (111)) epitaxial thin films, a cathode material used in Li-ion batteries. In conclusion, using a solid-state ionogel electrolyte, the films were highly stable when electrochemically cycled in the 3.5-4.3 V vs Li/Li + range.

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

A Novel Magnetic Material by Design: Observation of Yb 3+ with Spin-1/2 in Yb x Pt 5 P

The localized f-electrons enrich the magnetic properties in rare-earth-based intermetallics. Among those, compounds with heavier 4d and 5d transition metals are even more fascinating because anomalous electronic properties may be induced by the hybridization of 4f and itinerant conduction electrons primarily from the d orbitals. Here, we describe the observation of trivalent Yb 3+ with S = 1/2 at low temperatures in Yb x Pt 5 P, the first of a new family of materials. Yb x Pt 5 P (0.23 ≤ x ≤ 0.96) phases were synthesized and structurally characterized. They exhibit a large homogeneity width with the Yb ratio exclusively occupying the 1a site in the anti-CeCoIn 5 structure. Moreover, a sudden resistivity drop could be found in Yb x Pt 5 P below ~0.6 K, which requires further investigation. First-principles electronic structure calculations substantiate the antiferromagnetic ground state and indicate that two-dimensional nesting around the Fermi level may give rise to exotic physical properties, such as superconductivity. Yb x Pt 5 P appears to be a unique case among materials.

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

Comparing Intrinsic Catalytic Activity and Practical Performance of Ni- and Pt-Based Alkaline Anion Exchange Membrane Water Electrolyzer Cathodes

The stringent cost and performance requirements of renewable hydrogen production systems dictate that electrolyzers benefit from the use of nonprecious catalysts only if they deliver the same level of activity and durability as their precious metal counterparts. Here we report on recent work to understand interrelationships between the intrinsic activity of Ni- and Pt-based electrolyzer cathode catalysts and their performance in zero-gap alkaline water electrolyzer assemblies. Our results suggest that nanoparticulate Ni–Mo exhibits HER activity that is roughly 10-fold lower than Pt–Ru on the basis of turnover frequency under low (≤100 mV) polarization conditions. We further found that the HER activity of Ni–Mo/C cathodes is inhibited by aryl piperidinium anionexchange ionomers bearing bicarbonate counter-anions. After addressing this poisoning effect, we produced electrolyzer assemblies based on Ni–Mo/C cathodes that delivered indistinguishable current density vs cell potential relationships compared to otherwise identical assemblies with Pt–Ru cathodes. This result indicates that the contribution of the cathode to the total cell polarization is small, even for the less active Ni–Mo/C catalyst, and further implies that Pt-based cathodes can indeed be replaced by nonprecious alternatives with no loss in performance.

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

What Makes Au Nanospheres Superior to Octahedral and Cubic Counterparts for the Deposition of a Pt Monolayer Shell?

This study demonstrates that Au nanospheres are advantageous over their octahedral and cubic counterparts as seeds in the synthesis of Au@Pt core−shell nanocrystals with a monolayer shell. In combination with experimental characterization, we show through training a machine-learned interatomic potential that the Au nanospheres exhibit a large fraction of lowcoordination atoms which are uniformly distributed over the surface. The corresponding high-index facets, including {211}, {311}, {331}, {210}, and {310}, on a spherical seed promote nucleation while greatly shortening the diffusion distance for adatoms. In addition, the high-index facets are instrumental in retaining the deposited Pt atoms on the outermost surface by retarding their inter-diffusional exchange with the underlying Au atoms. By switching from a monolayer made of pure Pt to those made of Pt−Au alloys, we can optimize both the activity and selectivity of the nanocrystals toward the two-electron oxygen reduction reaction for the electrochemical synthesis of H 2 O 2 . This method should be extendible to the fabrication of other core−shell nanocatalysts with desired monolayer shells for various catalytic reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗