FePt Alloy Research Articles

RETRACTED: Fe3+ partitioning between clinopyroxene and silicate melt at 1–2.5 GPa: Implications for Fe3+ content of MORB and OIB source mantle

Pyroxene is the chief reservoir of Fe 3+ in upper mantle peridotite, but experiments exploring pyroxene/melt Fe 3+ partitioning ( D Fe3+ pyx/liq ) have been restricted to 100 kPa and pyroxene with low alumina. Here we present Fe 3+ partitioning experiments between clinopyroxenes (cpx) and mafic melt at elevated pressures (1–2.5 GPa). Experiments were conducted with f O2 buffered and modulated by Ru + RuO 2 and Fe-Pt alloy capsules, respectively, between ΔQFM −2.7 and +5.1. Fe 3+ /Fe T of both cpx and melt were determined by Fe K -edge X-ray absorption near edge structure spectroscopy. The experimentally synthesized cpx compositions (Al 2 O 3 = 2.36–6.01 wt.%, CaO = 19.33–22.21 wt.%) approximate those expected in basalt source regions. We find that Fe 3+ is moderately incompatible in cpx and D Fe3+ cpx/liq correlates with cpx Al 2 O 3 content, increasing from 0.05 ± 0.09 to 0.81 ± 0.04. D Fe3+ cpx/liq also increases with increasing f O2 . Comparison between experimentally synthesized cpx with those from natural peridotites indicates influences of both temperature and composition on Fe 3+ /Fe T for cpx in spinel and garnet peridotites. The combined effects of decreased pyroxene Al 2 O 3 concentration and pyroxene mode with progressive partial melting of peridotite diminishes the bulk partition coefficients of Fe 3+ , leading to greater Fe 2 O 3 contents in high degree partial melts, and this accounts for an inverse relationship between Na 2 O and Fe 2 O 3 observed in mid-ocean ridge basalts (MORB). Comparison to numerical experiments with pMELTS and the model of Jennings and Holland (2015) show that these models overpredict D Fe3+ cpx/liq for partial melting of the mantle, and so they do not accurately determine the relationship between the f O2 and Fe 2 O 3 of peridotite in basalt source regions. To estimate the Fe 3+ /Fe T ratio of the mantle source of MORB, we modeled liquid Fe 2 O 3 during isentropic batch melting of peridotite at three potential temperatures (1320 °C, 1400 °C, and 1440 °C) for peridotitic sources with Fe 3+ /Fe T ratios between 0.02–0.06. A source with an Fe 3+ /Fe T ratio of 0.038 ± 0.007 matches most of the span of natural MORB. This ratio is similar to that typical of continental lithospheric mantle sampled by xenoliths, but lower than that surmised by several recent experimental and thermodynamic studies. Considering this source Fe 3+ /Fe T but extending the partial melting calculations to higher pressures (2.5–4 GPa) reveals that bulk D Fe3+ perid/liq significantly decreases for garnet peridotite relative to spinel peridotite because the cpx become significantly less aluminous with increasing pressure. This results in high pressure partial melts with greater liquid Fe 3+ /Fe T ratios. Therefore, elevated Fe 3+ /Fe T ratios observed from some oceanic island basalts (OIB), such as those from Hawaii and Iceland, reflect in part the differences in conditions of melting and may not require mantle source regions more oxidized than those that produce MORB.

Segregation tendency and properties of FeRh1-xPtx alloys

In this work, the phase stability and properties of FeRh1-xPtx alloys (x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1) are studied within the framework of the density functional theory implemented in the VASP software package. It is found that the antiferromagnetic spin configurations AFM-II and AFM-III are energetically favorable for FeRh1-xPtx with a Pt content in the range of 0 < x ≤ 0.625 and 0.625 < x < 1, correspondingly. While, binary FePt alloy is ordered ferromagnetically. It is shown that compounds with 0 < x ≤ 0.625 are found to be stable with respect to decomposition into stable binary FeRh and FePt compounds at zero and finite temperatures. In the case of compositions with x = 0.75 and 0.875, their stability against segregation is predicted at finite temperatures. An increase in temperature enhances the stabilization of FeRh1-xPtx with respect to decomposition into two-component mixture.

High-performance long-term driving proton exchange membrane fuel cell implemented with chemically ordered Pt-based alloy catalyst at ultra-low Pt loading

In proton exchange membrane fuel cells (PEMFCs), it is very important to develop a cathode catalyst with high oxygen reduction reaction activity and high chemical stability while reducing the Pt content. Alloying Pt with transition metals is one of options to achieve this goal, but it generally suffers from stability issues caused by transition metals. We demonstrate a mass-producible carbon layer-protected and chemically ordered PtFe alloy cathode nanocatalyst of about 4 nm size with high activity, stability, and Pt utilization efficiency. The catalyst is prepared via a facile and easily scaled synthesis route where the formation of PtFe nanoparticles, phase transition from chemically disordered to chemically ordered PtFe phase, and carbon layer-covering occurs simultaneously. The synthesized catalyst with the highest degree of phase transition to chemically ordered PtFe achieves a mass activity of 848 A gPt−1 at 0.9 V on rotating disk electrode, and maintains its performance over 30,000 stability test cycles. The PEMFC with this catalyst also stably performs 0.8 A cm−2 at 0.66 V (1.1 A cm−2 at 0.6 V) over 30,000 stability test cycles at an ultra-low total Pt loading of 0.100 mgPt cm−2, far exceeding the 2025 US Department of Energy (DOE) stability target.

Self-Assembly Ultrathin Fe-Terephthalic Acid as Synergistic Catalytic Platforms for Selective Hydrogenation

Self-Assembly Ultrathin Fe-Terephthalic Acid as Synergistic Catalytic Platforms for Selective Hydrogenation

The Mineralogy of Pt-Fe alloys and phase relations in the Pt–Fe binary system

ABSTRACT A revised Pt–Fe phase diagram is proposed to replace those used in the materials science literature (e.g., Okamoto 2004), and to improve the one of Cabri &amp; Feather (1975) by adding high-temperature phase equilibria data published in the mineralogical literature. The projected solid-solution fields at room temperature in the pure Pt–Fe system lie at the following approximate compositions: for γ(Pt,Fe) from Pt to Pt0.78Fe0.22, for Pt3Fe from Pt3.04Fe0.96 to Pt2.64Fe1.36, for PtFe from Pt1.16Fe0.84 to Pt0.67Fe0.33, and for PtFe3 from Pt1.26Fe2.94 to Pt0.68Fe3.32. The phase relations and phase boundaries are discussed and evaluated for Pt-Fe alloys occurring in pristine intrusive rocks and ores as well as in eluvial and placer deposits derived from the former by physical and chemical weathering over long periods of geologic time. In spite of the variable concentrations of minor and trace elements, the natural Pt-Fe alloy minerals correlate well with phase relations in the pure Pt–Fe binary system.

Pt-Fe nanoalloy: Structure evolution study and catalytic properties in water gas shift reaction

In the present work we studied the properties of Pt0.5Cu0.5, Pt0.5Fe0.5, Pt0.33Ag0.67, Pt0.6Au0.4 nanoalloys in water gas shift (WGS) reaction for the first time. Cu, Fe, Ag, Au were chosen as modifiers due to the low catalytic activity in undesirable side reactions of carbon oxides methanation. Nanoalloys were synthesized via corresponding double complex salts decomposition, which provided the selective formation of bimetallic nanoparticles. A simulated reformate gas mixture, containing (vol.%) 10 CO, 15 CO2, 30 H2O and 45 H2, was used to evaluate the activity of these systems. Only Pt0.5Fe0.5 nanopowder was active, while Pt-FeOx metal-oxide composite was inert. The positive effect of Pt-Fe alloying on WGS performance was also confirmed for silica supported catalysts. TG and XRD in situ analysis reveal that Pt0.5Fe0.5 is stable toward oxidation under WGS reaction conditions (T < 350°C, reductive atmosphere), while Pt-FeOx undergoes partial reduction but without formation of Pt-Fe alloy nanoparticles.

Influence of Oxygen and Nitrogen Doping on the Structure and Magnetic Properties of Fept Alloy: First Principle Calculations

Influence of Oxygen and Nitrogen Doping on the Structure and Magnetic Properties of Fept Alloy: First Principle Calculations

Highly Efficient Ptfe Alloy Catalyst for Electrocatalytic Methanol Oxidation with High Resistance to Co

Highly Efficient Ptfe Alloy Catalyst for Electrocatalytic Methanol Oxidation with High Resistance to Co

First-principles study of electronic structure and magnetic properties of L10-ordered FeNi, FePd, and FePt alloys

The structural, electronic, and magnetic properties of three spin configurations of L10-ordered FeM alloys (M = Ni, Pd, or Pt) were studied using the first-principles method. The calculations were carried out using Quantum ESPRESSO package within the framework of Density Functional Theory (DFT). The exchange-correlation functional potentials were studied using local density approximation (LDA) of Perdew-Zunger (PZ), the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE), Perdew and Wang 91 (PW91), and Perdew-Burke-Ernzerhof revised for solids (PBEsol). We found that the PBE approximation has the most accurate results for lattice parameters compared to the experimental values. Furthermore, our results reveal that the most stable spin configuration for the considered alloys is the ferromagnetic configuration, where all spins are aligned perpendicular to the (001) plane. However, in FePd and FePt alloys, a small variation in the tetragonality ratio c/a (from 0.98 to 0.92) can transform them from ferromagnetic to antiferromagnetic state. In an antiferromagnetic state, a pseudogap is observed just below fermi energy for each alloy. Moreover, our calculations reveal large magnetocrystalline anisotropies for FePt alloy in the order of 3 meV/f.u. On the other hand, FePd and FeNi show relatively lower values in the range of 0.18–0.42 meV/f.u. Finally, Heisenberg exchange interactions are calculated from first-principles and Green's functions formalism.

Huge Baltic project adds PE, later PP

To improve performance of membrane electrode assembly (MEA) at large current density region, efficient mass transfer at the cathode is desired, for which a feasible strategy is to lower catalyst layer thickness by constructing high loading Pt-alloy catalysts on carbon. But the high loading may induce unwanted particle aggregation. In this work, H-PtNi/C with 33% (mass) Pt loading on carbon and monodisperse distribution of 3.55 nm PtNi nanoparticles, was prepared by a bimodal-pore route. In electrocatalytic oxygen reduction reaction (ORR), H-PtNi/C displays an activity inferior to the low Pt loading catalyst L-PtNi/C (13.3% (mass)) in the half-cell. While in H2-O2 MEA, H-PtNi/C delivers the peak power density of 1.51 W·cm−2 and the mass transfer limiting current density of 4.4 A·cm−2, being 21% and 16% higher than those of L-PtNi/C (1.25 W·cm−2, 3.8 A·cm−2) respectively, which can be ascribed to enhanced mass transfer brought by the thinner catalyst layer in the former. In addition, the same method can be used to prepare PtFe alloy catalyst with a high-Pt loading of 36% (mass). This work may lead to a range of catalyst materials for the large current density applications, such as fuel cell vehicles.

Doping‐Modulated Strain Enhancing the Phosphate Tolerance on PtFe Alloys for High‐Temperature Proton Exchange Membrane Fuel Cells

AbstractIn high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs), the poisoning of Pt by phosphoric species severely affects the kinetics of the oxygen reduction reaction, which restricts their commercialized application. Herein, for the first time, the phosphate tolerance of PtFe ordered intermetallic alloys is enhanced by a doping‐modulated strain strategy via employing a low amount of Cu as a dopant to boost HT‐PEMFCs. This Cu doping facilitates the formation of compressive strain in PtFe crystals, consequently altering the electronic structure of electrocatalysts and then benefiting for weakening the adsorption energy between phosphoric acid and Pt surfaces. In addition, the high temperature phosphate adsorption tests also reveal that the dopant of Cu in Pt based electrocatalysts can improve the tolerance of phosphoric acid. The HT‐PEMFCs assembled by those cathodic electrocatalysts with the low‐Pt loading of 0.5 mgPt cm−2 achieve a preeminent peak power of 793.5 and 432.6 mW cm−2 under the condition of H2–O2 and H2–air atmosphere, respectively, or nearly 1.53 and 1.34 times higher as compared with commercial Pt/C electrocatalysts. Moreover, those electrocatalysts also exhibit robust stability under harsh condition in H2–O2 atmosphere with negligible activity loss for at least 100 h, exceeding most of other reported ORR electrocatalysts.

Structurally ordered PtFe intermetallic embedded in N-doped carbon as a highly active and durable electrocatalyst for oxygen reduction reaction

The structurally ordered PtM with surface coating layers strategy has drawn increasing attention. In this work, we synthesize a structurally ordered PtFe@NC-X-PDA catalyst modified with nitrogen-doped carbon coating layers by confined space annealing strategy. Compared with the current commercial Pt/C catalyst, the structurally ordered PtFe@NC-X-PDA catalyst shows better catalytic activity and stability. Especially, the mass activity and specific activity of the synthesized PtFe@NC-0.06-PDA sample with the optimized poly-dopamine feeding mass content (0.06 g) exhibit 9.95 and 11.53 times higher than that of commercial Pt/C catalyst. In addition, after 20,000 CV cycles, the PtFe@NC-0.06-PDA sample achieves the minimum activity loss (7%). The PtFe alloy catalyst with the different thickness NC shell (PtFe@NC-X-PDA) possesses the enhanced ORR activity and stability owing to the protection of nitrogen carbon shell (NC) and the strong electronic interaction of the ordered PtFe NPs. The improved ORR activity and stability of the structurally ordered PtFe@NC-X-PDA catalyst provide a promising direction for the development of fuel cells.

High grade ores of the Onverwacht platinum pipe, eastern Bushveld, South Africa

ABSTRACT The platiniferous dunite pipes are discordant orebodies in the Bushveld Complex. The Onverwacht pipe is a large body (&amp;gt;300 m in diameter) of magnesian dunite (Fo80–83) that crosscuts a sequence of cumulates in the Lower Critical Zone of the Bushveld Complex. In a pipe-in-pipe configuration, the main dunite pipe at Onverwacht hosts a carrot-shaped inner pipe of Fe-rich dunite pegmatite (Fo46–62) which comprises the platinum-bearing orebody. The latter was ca. 18 m in diameter and a mining depth of about 320 m was reached. In the present work, a variety of ore samples were studied by whole-rock geochemistry, including analyses of platinum group elements, ore microscopy, and electron probe microanalysis. Olivine of the ore zone displays considerable chemical variation (range 46–62 mol.% Fo) and may represent either a continuum, or different batches of magma, or vertical or horizontal zonation within the ore zone. Chromite is principally regarded to be a consanguineous component of the pipe magma that crystallized in situ and simultaneously with olivine. The Onverwacht mineralization is Pt-dominated (&amp;gt;95% of the platinum group elements) and the ore is virtually devoid of sulfides. Platinum-dominated platinum group minerals predominate, followed by Rh-, Pd-, and Ru-species. Pt-Fe alloys are most frequent, followed by Pt-Rh-Ru-arsenides and -sulfarsenides, platinum group element antimonides, and platinum group element sulfides. Our hypothesis on the genesis of the Onverwacht pipe and its mineralization is as follows: After near-consolidation of the layered series of the Critical Zone, the magnesian dunite pipe of Onverwacht was formed by upward penetration of magmas that replaced the existing cumulates initially by infiltration, followed by the development of a central channel where large volumes of magma flowed through. Fractional crystallization of olivine within the deeper magma chamber and/or during ascent of the melt resulted in the formation of a consanguineous, residual, more iron-rich melt. This melt also contained highly mobile, supercritical, water-bearing fluids and was continuously enriched in platinum group elements and other incompatible elements. In several closing pulses, the platinum group element-enriched residual melts crystallized and sealed the inner ore pipe. Crystallization of the melt resulted in the coeval formation of Fe-rich olivine, chromite, and platinum group minerals. The non-sulfide platinum group element mineralization was introduced in the form of nanoparticles and small droplets of platinum group minerals, which coagulated to form larger grains during evolution of the mineralizing system. The suspended platinum group minerals acted as collectors of other platinum group elements and incompatible elements during generation and ascent of the melt. With decreasing temperature, the platinum group mineral grains annealed and recrystallized, leading to the formation of composite platinum group mineral grains, complex intergrowths, or lamellar exsolution bodies. On further cooling, platinum group minerals overgrowing Pt-Fe alloys formed by reaction of leached elements and ligands like Sb, As, and S mobilized by supercritical magmatic/hydrothermal fluids. Redistribution of platinum group elements/platinum group minerals apparently only occurred on the scale of millimeters to centimeters. Finally, surface weathering led to the local formation of platinum group element oxides/hydroxides by oxidation of reactive precursor platinum group minerals.

Supergene mobilization and redistribution of platinum-group elements in the Merensky Reef, eastern Bushveld Complex, South Africa

ABSTRACT Near-surface supergene ores of the Merensky Reef in the Bushveld Complex, South Africa, contain economic grades of platinum-group elements, however, these are currently uneconomic due to low recovery rates. This is the first study that investigates the variation in platinum-group elements in pristine and supergene samples of the Merensky Reef from five drill cores from the eastern Bushveld. The samples from the Richmond and Twickenham farms show different degrees of weathering. The whole-rock platinum-group element distribution was studied by inductively coupled plasma-mass spectrometry and the platinum-group minerals were investigated by reflected-light microscopy, scanning electron microscopy, and electron microprobe analysis. In pristine (“fresh”) Merensky Reef samples, platinum-group elements occur mainly as discrete platinum-group minerals, such as platinum-group element-sulfides (cooperite–braggite) and laurite as well as subordinate platinum-group element-bismuthotellurides and platinum-group element-arsenides, and also in solid solution in sulfides (especially Pd in pentlandite). During weathering, Pd and S were removed, resulting in a platinum-group mineral mineralogy in the supergene Merensky Reef that mainly consists of relict platinum-group minerals, Pt-Fe alloys, and Pt-oxides/hydroxides. Additional proportions of platinum-group elements are hosted by Fe-hydroxides and secondary hydrosilicates (e.g., serpentine group minerals and chlorite). In supergene ores, only low recovery rates (ca. 40%) are achieved due to the polymodal and complex platinum-group element distribution. To achieve higher recovery rates for the platinum-group elements, hydrometallurgical or pyrometallurgical processing of the bulk ore would be required, which is not economically viable with existing technology.

Redox-controlled chalcophile element geochemistry of the Polaris Alaskan-type mafic-ultramafic complex, British Columbia, Canada

ABSTRACT The Early Jurassic Polaris Alaskan-type intrusion in the Quesnel accreted arc terrane of the North American Cordillera is a zoned, mafic-ultramafic intrusive body that contains two main styles of magmatic mineralization of petrologic and potential economic significance: (1) chromitite-associated platinum group element (PGE) mineralization hosted by dunite (±wehrlite); and (2) sulfide-associated Cu-PGE-Au mineralization hosted by olivine (±magnetite) clinopyroxenite, hornblendite, and gabbro-diorite. Dunite-hosted PGE mineralization is spatially associated with thin discontinuous layers and schlieren of chromitite and chromitiferous dunite and is characterized by marked enrichments in iridium-subgroup PGE (IPGE) relative to palladium-subgroup PGE (PPGE). Discrete grains of platinum group minerals (PGM) are exceedingly rare, and the bulk of the PGE are inferred to reside in solid solution within chromite±olivine. The absence of Pt-Fe alloys in dunite of the Polaris intrusion is atypical, as Pt-enrichment of dunite-hosted chromitite is widely regarded as a characteristic feature of Alaskan-type intrusions. This discrepancy appears to be consistent with the strong positive dependence of Pt solubility on the oxidation state of sulfide-undersaturated magmas. Through comparison with experimentally determined PGE solubilities, we infer that the earliest (highest temperature) olivine-chromite cumulates of the Polaris intrusion crystallized from a strongly oxidized ultramafic parental magma with an estimated log f(O2) &amp;gt; FMQ+2. Parental magmas with oxygen fugacities more typical of volcanic arc settings [log f(O2) ∼ FMQ to ∼ FMQ+2] are, in turn, considered more favorable for co-precipitation of Pt-Fe alloys with olivine and chromite. More evolved clinopyroxene- and hornblende-rich cumulates of the Polaris intrusion contain low abundances of disseminated magmatic sulfides, consisting of pyrrhotite and chalcopyrite with minor pentlandite, pyrite, and rare bornite (≤12 wt.% total sulfides), which occur interstitially or as polyphase inclusions in silicates and oxides. The sulfide-bearing rocks are characterized by strong primitive mantle-normalized depletions in IPGE and enrichments in Cu-PPGE-Au, patterns that resemble those of other Alaskan-type intrusions and primitive arc lavas. The absolute abundances and sulfur-normalized whole-rock concentrations (Ci/S, serving as proxy for sulfide metal tenor) of chalcophile elements, including Cu/S, in sulfide-bearing rocks are highest in olivine clinopyroxenite. Sulfide saturation in the relatively evolved magmas of the Polaris intrusion, and Alaskan-type intrusions in general, appears to be intimately tied to the appearance of magnetite. Fractional crystallization of magnetite during the formation of olivine clinopyroxenite at Polaris resulted in reduction of the residual magma to log f(O2) ≤ FMQ+2, leading to segregation of an immiscible sulfide melt with high Cu/Fe and Cu/S, and high PGE and Au tenors. Continued fractionation resulted in sulfide melts that were progressively more depleted in precious and base chalcophile metals. The two styles of PGE mineralization in the Polaris Alaskan-type intrusion are interpreted to reflect the evolution of strongly oxidized, hydrous ultramafic parental magma(s) through intrinsic magmatic fractionation processes that potentially promote sulfide saturation in the absence of wallrock assimilation.

Mechanism for ultrafast electric-field driven skyrmion nucleation

We show how a Dzyaloshinskii-Moriya interaction can be generated in an ultrathin metal film from the induced internal electric field created by an ultrashort electromagnetic pulse. This interaction does not require structural inversion-symmetry breaking, and its amplitude can be tuned depending on the amplitude of the field. We perform first-principles calculations to estimate the strength of the field-induced magnetoelectric coupling for ferromagnetic Fe, Co, and Ni, and antiferromagnetic Mn, as well as FePt alloys. Last, using atomistic simulations, we demonstrate how an isolated antiferromagnetic skyrmion can be coherently nucleated from the collinear background by an ultrashort pulse in electric field on a 100-fs timescale.

Slag design and iron capture mechanism for recovering low-grade Pt, Pd, and Rh from leaching residue of spent auto-exhaust catalysts

Recovery of platinum group metals (PGMs) from secondary resources has attracted worldwide attention from environmental and economic points of view. Pyrometallurgical routes exhibit the superiority in terms of efficiency and contamination control compared to hydrometallurgical process. However, traditional pyrometallurgical processes face the challenges of excessive flux and energy consumption. In this paper, an iron capture process was proposed to recover low-grade PGMs from leaching residue of spent auto-exhaust catalysts. Slag design was explored aimed at reducing the addition amount of flux. The optimized smelting conditions were as follows: 1400 °C for 30 min, adding 40.0 wt% CaO, 22.7 wt% Na2CO3, 5.0 wt% Na2B4O7, 5.0 wt% CaF2, 15.0 wt% Fe, and 5.0 wt% C. The concentrations of Pt, Pd and Rh remaining in the smelting slag were 0.83 g/t, 4.99 g/t, and 1.47 g/t, respectively. Furthermore, the 50 kg-scale experiment implied positive economic feasibility because of saving flux dosage and smelting time. The capture mechanism was revealed by investigating the formation of the metals phase and slag phase. Matrix formed slag phase and separate with metals phase owing to differences in chemical bonding, density, viscosity, and surface tension. PGMs were proved solubilized in α-Fe as substitutional solid solutions. The formation energies for FePt, FePd, and FeRh alloys were −4.149 eV, −4.040 eV, and −4.360 eV, respectively. Finally, the obtained CaO-SiO2-Al2O3-Na2O glass slag was used for producing glass ceramics. To sum up, the iron capture process realized low energy and material consumption, high recovery efficiency of PGMs, and resource utilization of the glass slag.

Conversion of Pt nanoparticles encapsulated within MIL-101(Fe) to FePt intermetallic nanoparticles supported on carbon promotes formic acid electrooxidation

Pt-based catalysts have limited usefulness in direct formic acid fuel cells (DFAFCs) due to their susceptibility to CO poisoning. Combining Pt with Fe atoms is an effective approach for suppressing Pt poisoning by CO. In this work, we fabricate novel carbon-supported FePt alloy nanoparticles (FePt@C) by pyrolyzing Pt nanoparticles encapsulated within mesoporous MIL-101(Fe) (Pt@MIL-101(Fe)). The resulting FePt nanoparticles (Fe3Pt (111)) possess a lower CO adsorption energy (0.64 eV) than the (111) surfaces of Pt, indicating that the FePt nanoparticles are far less susceptible to CO poisoning. The mass activity and current density of a 9.6 wt% FePt@C catalyst are 4.2 and 4.5 times, respectively, higher than those of a commercial Pt/C catalyst. Furthermore, the 9.6 wt% FePt@C catalyst exhibits excellent durability, with only a 0.1% loss of mass activity after 1000 cycles. These results should guide the development of improved anode catalysts for DFAFCs based on MOF precursors.

Simultaneously deposited Pt-alloy nanoparticles over graphene nanoplatelets via supercritical carbon dioxide deposition for PEM fuel cells

One of the main barriers to the commercialization of polymer electrolyte membrane fuel cell (PEMFC) systems is the cost, which is largely due to the need of platinum (Pt)-containing catalysts. In order to overcome this issue, several methods have been developed. One of them is the supported electrocatalysts prepared by combining a low cost second metal with Pt. Motivated by this idea, in this study, nano-sized Pt-M (M = Ni, Fe, Cu) binary electrocatalysts were synthesized on the graphene nanoplatelets (GNPs) via supercritical fluid deposition (SFD) technique in order to decrease the cost and increase the activity of the catalysts. Because, the unusual properties of supercritical fluids (SFs), including tunable solvent strength, high diffusivity, low viscosity, and low surface tension, offer significant advantages over conventional techniques for materials processing. In this regard, compared to the other SFs, carbon dioxide (CO2) has received much more attention due to its easy accessibility to the supercritical state, relative benignity to the environment, chemical inertness, low toxicity, low cost. The supercritical carbon dioxide (scCO2) deposition technique involves firstly the dissolution of the metal precursor onto the support material, and then conversion of the metal precursor to its metallic form by means of thermal or chemical conversion. Synthesis of supported bimetallic nanoparticles (NPs) via scCO2 can be sequentially or simultaneously. Herein, we investigated the development of Pt-M (PtCu, PtNi, PtFe) alloy NPs on GNPs by scCO2 deposition via simultaneous addition of metal precursors. Subsequently, these catalysts were characterized by employing various characterization techniques and systems such as X-Ray Diffaction (XRD), Thermogravimetric Analysis (TGA), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), Transmission Electron Microscopy (TEM), Raman Spectroscopy, Cyclic Voltammetry (CV), Rotating Disk Electrode (RDE) and PEM Fuel Cell performance tests. The obtained results revealed the formation of bimetallic catalysts within the size ranges from 1.6 to 2.1 nm. Furthermore, CV results demonstrate that PtNi/GNPs catalyst exhibit significantly high catalytic activity toward the PEM fuel cell reaction in comparison with the PtFe/GNPs and PtCu/GNPs. Also, PtNi/GNPs catalyst show about 2–4 times higher durability than the PtFe/GNPs and PtCu/GNPs catalysts in the accelerated degradation tests (ADTs). All results suggested that the PtNi/GNPs catalyst has great potential for PEM fuel cell applications.

Dependence of the Growth Mode in Epitaxial FePt Films on Surface Free Energy.

Epitaxial thin films of L10-ordered FePt alloys are one of the most important materials in magnetic recording and spintronics applications due to their large perpendicular magnetic anisotropy (PMA). The key to the production of these required superior properties lies in the control of the growth mode of the films. Further, it is necessary to distinguish between the effect of lattice mismatch and surface free energy on the growth mode because of their strong correlation. In this study, the effect of surface free energy on the growth mode of FePt epitaxial films was investigated using MgO, NiO, and MgON surfaces with almost the same lattice constant to exclude the effect of lattice mismatch. It was found that the growth mode can be tuned from a three-dimensional (3D) island mode on MgO to a more two-dimensional (2D)-like mode on MgON and NiO. Contact angle measurements revealed that MgON and NiO show larger surface free energy than MgO, indicating that the difference in the growth mode is due to their larger surface free energy. In addition, MgON was found to induce not only a flat surface as FePt grown on SrTiO3 (STO), which has a small lattice mismatch, but also a larger PMA than that of STO/FePt. As larger lattice mismatch is favored to induce a higher PMA into the FePt films, MgO substrates are exclusively used, but 3D island growth is indispensable. This work demonstrates that tuning the surface free energy enables us to achieve a large PMA and flat film surface in FePt epitaxial films on MgO. The results also indicate that modifying the surface free energy is pertinent for the flexible functional design of thin films.