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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Surface Lattice-Embedded Pt Single-Atom Catalyst on Ceria-Zirconia with Superior Catalytic Performance for Propane Oxidation

Tuning the metal–support interaction and coordination environment of single-atom catalysts can help achieve satisfactory catalytic performance for targeted reactions. Herein, via the facile control of calcination temperatures for Pt catalysts on pre-stabilized Ce 0.9 Zr 0.1 O 2 (CZO) support, Pt single atoms (Pt 1 ) with different strengths of Pt–CeO 2 interaction and coordination environment were successfully constructed. With the increase in calcination temperature from 350 to 750 °C, a stronger Pt–CeO 2 interaction and higher Pt-O-Ce coordination number were achieved due to the reaction between PtO x and surface Ce 3+ species as well as the migration of Pt 1 into the surface lattice of CZO. The Pt/CZO catalyst calcined at 750 °C (Pt/CZO-750) exhibited a surprisingly higher C 3 H 8 oxidation activity than that calcined at 550 °C (Pt/CZO-550). Here, through systematic characterizations and reaction mechanism study, it was revealed that the higher concentration of surface Ce 3+ species/oxygen vacancies and the stronger Pt–CeO 2 interaction on Pt/CZO-750 could better facilitate the activation of oxygen to oxidize C 3 H 8 into reactive carbonate/carboxyl species and further promote the transformation of these intermediates into gaseous CO 2 . The Pt/CZO-750 catalyst can be a potential candidate for the catalytic removal of hydrocarbons from vehicle exhaust.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Construction of a Pt‐CeO x Interface for the Electrocatalytic Hydrogen Evolution Reaction

Abstract The creation of metal‐metal oxide interfaces is an important approach to fine‐tuning catalyst properties through strong interfacial interactions. This article presents the work on developing interfaces between Pt and CeO x that improve Pt surface energetics for the hydrogen evolution reaction (HER) within an alkaline electrolyte. The Pt‐CeO x interfaces are formed by depositing size‐controlled Pt nanoparticles onto a carbon support already coated with ultrathin CeO x nanosheets. This interface structure facilitates substantial electron transfer from Pt to CeO x , resulting in decreased hydrogen binding energies on Pt surfaces, and water dissociation for the HER, as predicted by the density functional theory (DFT) calculations. Electrochemical testing indicates that both Pt specific activity and mass activity are improved by a factor of 2 to 3 following the formation of Pt‐CeO x interfaces. This study underscores the significance and potential of harnessing robust interfacial effects to enhance electrocatalytic reactions.

25 ENERGY STORAGE↗
DOE OSTI2016

An experimental and theoretical study of glycerol oxidation to 1,3-dihydroxyacetone over bimetallic Pt-Bi catalysts

It is important to utilize glycerol, the main by-product of biodiesel, to manufacture value-added chemicals such as 1,3-dihydroxyacetone (DHA). In the present work, the performance of five different catalysts (Pt-Bi/AC, Pt-Bi/ZSM-5, Pt/MCM-41, Pt-Bi/MCM-41, and Pt/Bi-doped-MCM-41) was investigated experimentally, where Pt-Bi/MCM-41 was found to exhibit the highest DHA yield. To better understand the experimental results and to obtain insight into the reaction mechanism, density functional theory (DFT) computations were conducted to provide energy barriers of elementary steps. Both experimental and calculated results show that for high DHA selectivity, Bi should be located in an adatom-like configuration Pt, rather than inside Pt. A favorable pathway and catalytic cycle of DHA formation were proposed based on the DFT results. A cooperative effect, between Pt as the primary component and Bi as a promoter, was identified for DHA formation. Both experimental and theoretical considerations demonstrate that Pt-Bi is efficient to convert glycerol to DHA selectively.

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

Selective Catalytic Behavior Induced by Crystal–Phase Transformation in Well–Defined Bimetallic Pt–Sn Nanocrystals

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt–Sn phase. Colloidal chemistry offers a route for the synthesis of Pt–Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt 3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt 3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt 3 Sn/Al 2 O 3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L1 2 -ordered superlattice. Contrary to PtSn, H 2 cofeeding has no effect on the Pt 3 Sn deactivation rate. Finally, the results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure–performance relationship on emerging bimetallic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effect of particle size and adsorbates on the L{sub 3}, L{sub 2} and L{sub 1} x-ray absorption near edge structure of supported Pt nanoparaticles.

Pt nano-particles from about 1 to 10 nm have been prepared on silica, alkali-silica, alumina, silica-alumina, carbon and SBA-15 supports. EXAFS spectra of the reduced catalysts in He show a contraction of the Pt-Pt bond distance as particle size is decreased below 3 nm. The bond length decreased as much as 0.13 {angstrom} for 1 nm Pt particles. Adsorption of CO and H{sub 2} lead to a increase in Pt-Pt bond distance to that near Pt foil, e.g., 2.77 {angstrom}. In addition to changes in the Pt bond distance with size, as the particle size decreases below about 5 nm there is a shift in the XANES to higher energy at the L{sub 3} edge, a decrease in intensity near the edge and an increase in intensity beyond the edge. We suggest these features correspond to effects of coordination (the decrease at the edge) and lattice contraction (the increase beyond the edge). At the L{sub 2} edge, there are only small shifts to higher energy at the edge. However, beyond the edge, there are large increases in intensity with decreasing particle size. At the L{sub 1} edge there are no changes in position or shape of the XANES spectra. Adsorption of CO and H{sub 2} also lead to changes in the L{sub 3} and L{sub 2} edges, however, no changes are observed at the L1 edge. Density Functional Theory and XANES calculations show that the trends in the experimental XANES can be explained in terms of the states available near the edge. Both CO and H{sub 2} adsorption result in a depletion of states at the Fermi level but the creation of anti-bonding states above the Fermi level which give rise to intensity increases beyond the edge.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Revealing the dynamics of the alloying and segregation of Pt-Co nanoparticles via in-situ environmental transmission electron microscopy

Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes. So far, the mechanisms leading to the size and composition heterogeneity, as well as the phase segregation behavior in Pt-Co nanoparticles (NPs) are still not well understood. Here, via in-situ environmental transmission electron microscopy, the formation dynamics and segregation behaviors of Pt-Co alloyed NPs during the thermal treatment were investigated. It is found that Pt-Co NPs on zeolitic imidazolate frameworks-67-derived nanocarbon (NC) are formed consecutively through both particle migration coalescence and the Ostwald ripening process. The existence of Pt NPs is found to affect the movement of Co NPs during their migration. With the help of theoretical calculations, the correlations between the composition and migration of the Pt and Co during the ripening process were uncovered. Herein, these complex alloying processes are revealed as key factors leading to the heterogeneity of the synthesized Pt-Co alloyed NPs. Under oxidation environment, the Pt-Co NPs become surface faceted gradually, which can be attributed to the oxygen facilitated relatively higher segregation rate of Co from the (111) surface. This work advances the fundamental understanding of design, synthesis, and durability of the Pt-based nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effect of reductive treatments on Pt behavior and NOx storage in lean NOx trap catalysts

Lean NOx trap (LNT) catalysts represent a promising approach to meet increasingly stringent NOx emission regulations on diesel and other lean-burn engines. Pt material properties, including dispersion and particle size, are known to be important factors in determining NOx uptake performance, since Pt provides active sites for NO oxidation to NO2 necessary for storing NOx as nitrates, and for the reduction of nitrates to N2. In this work, the physicochemical properties of Pt in Pt-BaO/Al2O3 LNT catalysts, such as the Pt accessible surface area and particle size, were investigated by using various tools, such as irreversible volumetric H2 chemisorption, high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD), following successive reductive treatments at elevated temperatures. NOx uptake activities were also measured to establish a relationship between the properties of Pt and NOx storage following identical high-temperature reductive treatments. We find that the reductive treatments of Pt-BaO/Al2O3 lean NOx trap catalysts at temperatures up to 500 ºC promote a significant increase in NOx uptake explained, in part, by an induced close interaction between Pt and BaO phases in the catalyst, thus enabling facilitation of the NOx storage process.

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

Implementing hydrogen oxidation reaction on Pt for controlling counter electrode processes

The search for active, stable, and durable materials for electrochemical energy technologies requires increasing levels of precision to establish true structure-function relationships and guide materials design from atomic and molecular scale. This increases the level of control required over the experimental system for proper materials evaluation. The choice of counter electrode material become crucial, as Pt dissolution at high voltages may cause contamination to the working electrode, especially when studying reductive processes in reactions such as oxygen reduction reaction (ORR), H 2 evolution reaction (HER), and the CO 2 reduction reaction. The learnings from “old school” electrochemistry groups lead us to leverage H 2 reactions over Pt to construct a counter electrode system with controlled potential that eliminates Pt ion contamination concerns. In here we discuss the construction of such Pt|H 2 counter electrode where key experimental aspects such as the H 2 flow rate and effective distribution determines the maximum current this counter electrode can accommodate before switching to high voltage and triggering Pt dissolution. Lastly, we demonstrate the use of the Pt|H 2 counter electrode in aqueous electrolytes during HER occurring on the working electrode at varying currents, showing that the Pt content in the cell remains below parts per trillion (ppt) up to 10 mA, and below 50 ppt at 100 mA up to 1 h of constant current hold. This work provides a guide to the implementation of Pt|H 2 counter electrodes to improve the precision of electrochemical experiments in search of highly active, selective, and durable materials for energy technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

NO{sub 2} gas sensing of flame-made Pt-loaded WO{sub 3} thick films

Unloaded WO{sub 3} and 0.25–1.0 wt% Pt-loaded WO{sub 3} nanoparticles for NO{sub 2} gas detection were synthesized by flame spray pyrolysis (FSP) and characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The BET surface area (SSA{sub BET}) of the nanoparticles was measured by nitrogen adsorption. The NO{sub 2} sensing properties of the sensors based on unloaded and Pt-loaded WO{sub 3} nanoparticles were investigated. The results showed that the gas sensing properties of the Pt-loaded WO{sub 3} sensors were excellent to those of the unloaded one. Especially, 0.25 wt% Pt-loaded WO{sub 3} sensor showed highest response to NO{sub 2} than the others at low operating temperature of 150 °C. - Graphical abstract: The response of 0.25 wt% Pt-loaded WO3 sensor was 637 towards NO{sub 2} concentration of 10 ppm at 150 °C. - Highlights: • Unloaded and Pt-loaded WO{sub 3} nanoparticles for NO{sub 2} gas detection were synthesized by flame spray pyrolysis (FSP). • Gas sensing properties of the Pt-loaded WO{sub 3} sensors were excellent to those of the unloaded one. • 0.25 wt% Pt-loaded WO{sub 3} sensor showed highest response to NO{sub 2} at low operating temperature of 150 °C.

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

Magnetic feature and near-infrared absorption of a [Pt(mnt){sub 2}]{sup -}based H-bond supramolecular crystal

A new salt [H{sub 2}DABCO][Pt(mnt){sub 2}]{sub 2} (1) (mnt{sup 2-}=maleonitriledithiolate and H{sub 2}DABCO{sup 2+} is diprotonated 1,4-diazabicyclo[2.2.2]octane) has been synthesized; its crystal structure, magnetic and near-IR absorption properties have been investigated. Two different [Pt(mnt){sub 2}]{sup -} anions form the strong π-dimers, labeled as Pt(1)-dimer and Pt(2)-dimer, with quite shorter Pt…Pt and S…S distances and molecular plane-to-plane distance (<3.5 Å) within a dimer. The [Pt(mnt){sub 2}]{sub 2}{sup 2-} π-dimers are connected through the cations in the strong H-bond manner to form three-dimensional H-bond supramolecular crystal. The salt shows weak paramagnetism in 1.99–300 K and this is due to the existence of strong antiferromagnetic coupling within a π-dimer. In addition, a small thermal hysteresis loop is observed at ca. 120 K, indicating that a phase transition probably occurs that is further confirmed by variable-temperature IR spectra. Another fascinating functionality of 1 is the intense near-IR absorption in the region of 750–2500 nm, and this near-IR absorption feature makes it to be a promising optical material. - Graphical abstract: A H-bond supramolecular crystal of [H{sub 2}DABCO][Pt(mnt){sub 2}]{sub 2} shows a magnetic phase transition at ca. 120 K with sizable thermal hysteresis loop and intense near-IR absorption in the region of 750–2500 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis of Pt nanoparticles on electrochemically reduced graphene oxide by potentiostatic and alternate current methods

Reduced graphene oxide (RGO) has been synthesized on Pt wires by means of a potentiodynamic method between + 0.6 V and − 1.4 V for 20 scans. Cyclic voltammetry characterization of the coatings showed the typical capacitative behavior of graphene. Pt nanoparticles were synthesized on Pt–RGO electrodes by means of potentiostatic methods and a comparison between different synthesis potentials (− 0.16, 0, + 0.2 and + 0.4 V) for the same synthesis charge (mC·cm{sup −2}) was established. The electrodes obtained were characterized in 0.5 M H{sub 2}SO{sub 4} solution to observe the characteristic oxidation and reduction processes of the Pt surface. A 0.5 M H{sub 2}SO{sub 4}/0.5 M CH{sub 3}OH solution was used to measure the catalytic properties of the deposits against methanol oxidation. The most appropriate potential to perform the synthesis was 0 V followed by − 0.16 V and + 0.2 V. The morphology of the coatings varied depending on the potential applied as observed by scanning electron microscopy. Alternate current methods were also used to synthesize Pt nanoparticles and compare the results with the traditional potentiostatic method. Different frequencies were used: 0.1, 1, 10, 100, 1000 and 10 000 Hz. Alternate current synthesis is more efficient than traditional potentiostatic methods, obtaining more electroactive coatings with less effective synthesis time. - Highlights: • Reduced graphene oxide has been obtained by electrochemical reduction on Pt wires. • Pt nanoparticles have been obtained potentiostatically at different potentials. • Pt nanoparticles have been obtained by ac methods with different frequencies. • ac synthesis is a better synthesis method than potentiostatic synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Atomic Layer Deposition of Pt on the Surface Deactivated by Fluorocarbon Implantation: Investigation of the Growth Mechanism

Selective atomic layer deposition (ALD) using surface-controlled reactivity is attracting a great deal of attention as a simple bottom-up patterning process that can provide both continued dimensional scaling and accurate pattern placement for next-generation nanoelectronics. Previously, we reported topographically selective deposition through Pt ALD using a MeCpPtMe 3 precursor and an O 2 counter reactant on fluorocarbon (CF x )-modified surfaces; however, gradual loss of selectivity in the CF x -modified regions was observed during the Pt ALD process. This work develops a fundamental understanding of the microscopic growth mechanisms of Pt ALD on the CF x -modified surface using a combination of experimental analyses and theoretical methods. The Pt growth characteristics on the CF x surface are investigated within a temperature window from 225 to 350 °C, and the results show a sharp sensitivity to growth temperature, with significant Pt growth occurring at temperatures above 300 °C. Through density functional theory (DFT) calculations, the reaction energies for adsorption of oxygen and the MeCpPtMe 3 precursor as well as formation of reaction products of CF x degradation are determined. Based on experimental results in conjunction with the DFT calculations, we show that while lower temperature Pt ALD (<300 °C) on CF x -modified surfaces can be significantly retarded because of a lack of MeCpPtMe 3 chemisorption, the surface reaction pathways for Pt ALD on CF x -modified surfaces at temperatures above 300 °C can proceed through oxygen adsorption and CF 4 desorption followed by Pt nucleation in CF x -degraded regions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Elucidating the Nanoparticle–Metal Organic Framework Interface of Pt@ZIF-8 Catalysts

Composites of metal nanoparticles encapsulated in metal–organic frameworks (NP@MOFs) have emerged as heterogeneous catalysts for regioselective reactions. While numerous NP@MOF composite combinations have been synthesized, characterization of the nanoparticle–MOF interface and the encapsulated nanoparticle surface have yet to be determined. In this work, Pt@ZIF-8 synthesized by the controlled encapsulation method was chosen as a representative NP@MOF, and in situ characterization methods coupled with density functional theory (DFT) calculations were used to probe the nanoparticle surface. CO adsorption diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that Pt@ZIF-8 exhibits red-shifted linear- and bridge-bound CO peaks and a linear peak associated with cationic Pt. DFT calculations and 1H NMR suggest that these sites arise from the binding and electronic donation of the MOF linker, 2-methylimidazole, to the Pt surface. DRIFTS under argon reveals that linker fragments may be present on the Pt nanoparticle surface, suggesting a reaction between the nanoparticle and the MOF linker during controlled encapsulation synthesis. Finally, CO oxidation reveals via DRIFTS that the red-shifted linear CO and bridging CO sites are active sites, while the cationic Pt is not. Overall, these results show that Pt@ZIF-8 contains unique Pt surface sites and indicate that the nanoparticle–MOF interface contains a heterogeneous mixture of framework 2-methylimidazole, free-standing 2-methylimidazole, and linker fragments. These findings expose the complex nature of the nanoparticle surface in NP@MOF composites and demonstrate the importance of characterizing their surface to understand their catalytic behavior.

Whitford, Cassandra L. (ORCID:0000000282237516)↗
DOE OSTI2017

Tuning Nb–Pt Interactions To Facilitate Fuel Cell Electrocatalysis

High stability, availability of multiple oxidation states, and accessibility within a wide electrochemical window are the prime features of Nb that make it a favorable candidate for electrocatalysis, especially when it is combined with Pt. However, Nb has been used as a support in the form of oxides in all previously reported Pt–Nb electrocatalysts, and no Pt–Nb alloying phase has been demonstrated hitherto. Herein, we report a multifunctional Pt–Nb composite (PtNb/NbOx-C) where Nb exists both as an alloying component with Pt and as an oxide support and is synthesized by means of a simple wet chemical method. In this work, the Pt–Nb alloy phase has been firmly verified with the help of multiple spectroscopic methods. This allows for the experimental evidence of the theoretical prediction that Pt–Nb alloy interactions improve the oxygen reduction reaction (ORR) activity of Pt. In addition, such a combination of multiphase Nb brings up myriad features encompassing increased ORR durability, immunity to phosphate anion poisoning, enhanced hydrogen oxidation reaction (HOR) activity, and oxidative carbon monoxide (CO) stripping, making this electrocatalyst useful in multiple fuel cell systems.

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

Structure Sensitivity of Acetylene Semi-Hydrogenation on Pt Single Atoms and Subnanometer Clusters

Oxide-supported Pt-group single atoms and clusters in the subnanometer size regime maximize the metal utilization and have shown extraordinary catalytic properties for many reactions including selective hydrogenation. Establishing relations between the metal nuclearity and electronic and catalytic properties is crucial for catalyst design. Here, we varied the nuclearity of Pt supported on TiO 2 from single atoms to subnanometer clusters to larger nanoparticles to develop such relations for acetylene hydrogenation. We show that, in contrast to the low selectivity on large Pt nanoparticles, in the subnanometer size regime, Pt exhibits remarkably high selectivity to ethylene. Through a combination of X-ray photoelectron spectroscopy and calorimetry, we demonstrate that the origin of high selectivity is the decreased electron density on Pt and destabilization of C 2 H 4 as the Pt nuclearity decreases. However, as the Pt nuclearity decreased, the activity for H 2 activation and acetylene hydrogenation decreased, indicating a trade-off between activity and selectivity. Lastly, the results show that, while different properties emerge in the subnanometer regime, Pt supported on TiO 2 appears to be bound by similar scaling and Brønsted–Evans–Polanyi relationships as on metal surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Rutile-Deposited Pt–Pd clusters: A Hypothesis Regarding the Stability at 50/50 Ratio

Mixed Pt–Pd clusters deposited on oxides have been of great interest to catalysis. Clusters containing Pt and Pd in roughly equal proportions were found to be unusually stable against sintering, one of the major mechanisms of catalyst deactivation. After aging of such catalysts, the 50/50 Pt–Pd and Pd–O clusters appeared to be the two most prevalent phases. The reason for the enhanced stability of these equally proportioned clusters has remained unclear. In the following, sintering of mixed Pt–Pd clusters on TiO2(110) for various initial atomic concentrations of Pt and Pd and at a range of catalytically relevant temperatures was simulated. It is confirmed that equally mixed clusters have the relatively highest survival rate. Surprisingly, subnanoclusters containing Pt and Pd in all proportions have very similar geometries and chemical bonding, revealing no apparent explanation for favoring the 1:1 Pt/Pd ratio. However, it was discovered that at high temperatures, the 50/50 clusters have considerably more thermally accessible isomers than clusters containing Pt and Pd in other proportions. Hence, one of the reasons for stability is entropic stabilization. Electrostatics also plays a key role as a subtle charge redistribution, and a shift of electron density to the slightly more electronegative Pt results in the partially charged atoms being further stabilized by intracluster Coulomb attraction; this effect is greatest for 1:1 mixtures.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

The role of hydrogen during Pt–Ga nanocatalyst formation

Hydrogen is a critical element during the in situ assembly of tailored catalytic materials, and serves as key ingredient in multifarious chemical reactions promoted by these catalysts. Despite intensive debate for several decades, the existence and nature of hydrogen-involved mechanisms – such as hydrogen-spillover, surface migration – have not been unambiguously proven and elucidated up to date. In this work, Pt–Ga alloy formation is used as a probe reaction to study the behavior and atomic transport of H and Ga, starting from Pt nanoparticles on hydrotalcite-derived Mg(Ga)(Al)O x supports. In situ XANES spectroscopy, time-resolved TAP kinetic experiments, HAADF-STEM imaging and EDX mapping are combined to probe Pt, Ga and H in a series of H 2 reduction experiments up to 650 °C. Mg(Ga)(Al)O x by itself dissociates hydrogen, but these dissociated hydrogen species do not induce significant reduction of Ga 3+ cations in the support. Only in the presence of Pt, partial reduction of Ga 3+ into Ga δ+ is observed, suggesting that different reaction mechanisms dominate for Pt- and Mg(Ga)(Al)O x -dissociated hydrogen species. This partial reduction of Ga 3+ is made possible by Pt-dissociated H species which spillover onto non-reducible Mg(Al)O x or partially reducible Mg(Ga)(Al)O x and undergo long-range transport over the support surface. Moderately mobile Ga δ+ O x migrates towards Pt clusters, where Ga δ+ is only fully reduced to Ga 0 on condition of immediate stabilization inside Pt–Ga alloyed nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effects of crystal phase and composition on structurally ordered Pt–Co–Ni/C ternary intermetallic electrocatalysts for the formic acid oxidation reaction

In this paper, to enhance the electrocatalytic performance of the formic acid oxidation reaction (FAOR), structurally ordered face-centered tetragonal (fct) Pt–Co–Ni/C intermetallic nanoparticles were synthesized via an impregnation reduction method, followed by post heat-treatment. It was found that an ordered intermetallic PtCo phase prevails rather than PtNi as the principal part for the ternary Pt–Co–Ni alloy after being annealed at high temperature, namely, Ni atoms merely serve as the substitute for Co in the lattice of Pt–Co–Ni intermetallics possessing the same atomic stack as PtCo intermetallics. In addition, there is a limitation for Ni to replace Co for the intermetallic PtCo phase, otherwise, most likely excessive Ni would replace the Pt atoms and damage the atomically ordered structure. Benefiting from the ordered structural features and rational introduction of the third transition metal to modify the distance between Pt and Pt atoms, the Pt–Co–Ni/C ordered intermetallic nanoparticles exhibit an enhancement in catalytic activity for the FAOR compared with Pt/C, the PtNi/C alloy and ordered intermetallic PtCo/C nanoparticles. Furthermore, the presence of Ni in the ordered intermetallic Pt–Co–Ni/C catalyst leads to a noticeable improvement in durability compared with the ordered intermetallic PtCo/C catalyst. Finally, the present work reveals opportunities for the rational design of ternary electrocatalysts with enhanced catalytic performance for fuel cell applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗