Platinum Nanoparticle Catalysts Research Articles

Supported Platinum Nanoparticles Catalyzed Carbon-Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity.

Supported platinum nanoparticle catalysts are known to convert polyolefins to high-quality liquid hydrocarbons using hydrogen under relatively mild conditions. To date, few studies using platinum grafted onto various metal oxide (MxOy) supports have been undertaken to understand the role of the acidity of the oxide support in the carbon-carbon bond cleavage of polyethylene under consistent catalytic conditions. Specifically, two Pt/MxOy catalysts (MxOy = SrTiO3 and SiO2-Al2O3; Al = 3.0 wt %, target Pt loading 2 wt % Pt ∼1.5 nm), under identical catalytic polyethylene hydrogenolysis conditions (T = 300 °C, P(H2) = 170 psi, t = 24 h; Mw = ∼3,800 g/mol, Mn = ∼1,100 g/mol, Đ = 3.45, Nbranch/100C = 1.0), yielded a narrow distribution of hydrocarbons with molecular weights in the range of lubricants (Mw = < 600 g/mol; Mn < 400 g/mol; Đ = 1.5). While Pt/SrTiO3 formed saturated hydrocarbons with negligible branching, Pt/SiO2-Al2O3 formed partially unsaturated hydrocarbons (<1 mol % alkenes and ∼4 mol % alkyl aromatics) with increased branch density (Nbranch/100C = 5.5). Further investigations suggest evidence for a competitive hydrocracking mechanism occurring alongside hydrogenolysis, stemming from the increased acidity of Pt/SiO2-Al2O3 compared to Pt/SrTiO3. Additionally, the products of these polymer deconstruction reactions were found to be independent of the polyethylene feedstock, allowing the potential to upcycle polyethylenes with various properties into a value-added product.

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity.

Exfoliated M-Al layered double hydroxide (M-Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co-Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co-Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co-Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co-Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation.

Carbon-Free, Connected Core-Shell Nanoparticle Catalysts with Advanced Oxygen-Reduction Performances for PEFCs

As the world faces diminishing non-renewable energy sources and a surge in global pollution, establishing a hydrogen and low-carbon economy has become crucial. Polymer electrolyte fuel cells (PEFCs) hold great promise as a sustainable energy source with the potential for high efficiency, and clean power generation in both stationary and mobile applications. However, the conventional platinum nanoparticle catalysts on carbon support (Pt/C) used for the oxygen reduction reaction (ORR) at the cathode shows sluggish ORR activity, leading to high cost and inferior PEFC performance. Moreover, the carbon-supports used for the Pt catalysts are susceptible to degradation caused by carbon-corrosion during start-stop operations, which can severely compromise the overall performance of the PEFCs. Hence, in order to significantly enhance the commercial viability of PEFCs, considerable progress must be made in terms of cost, performance, and durability.Previously our group has reported carbon-free, connected Pt-alloy catalysts to address the above issues. This catalyst is composed of connected Pt-alloy nanonetworks with high electronic conductivity and exhibits enhanced ORR activity, high start-stop durability, and thin catalyst layers. Specifically, this catalyst exhibited 9 times higher specific activity than that of the commercial Pt/C, making it an excellent candidate for cathode catalyst applications.[1,2] However, high-temperature annealing process is required to develop connected networks between the Pt-alloy nanoparticles, resulting in larger crystallite sizes and reduced surface areas. This limitation has prevented connected Pt-alloy catalysts from achieving significant improvement in mass activity.In this work, we have proposed a novel synthesis method that enables the development of connected core-shell nanoparticle catalysts without any high-temperature treatment. This method eliminates the particle growth and exhibit a high surface area, making it highly effective for ORR applications. Here, a carbon-free catalyst with a core-shell nanonetwork structure having a non-Pt (Pd) core and Pt shell was developed. Additionally, the relationship between the thickness of the Pt-shell layer and ORR activity was investigated.Connected core-shell catalysts with Pd nanoparticles as core and Pt as atomic shell (Pd@Pt) were synthesized in a one-pot polyol process that does not require high-temperature annealing as shown in Fig. 1. The formation of connected Pd@Pt core-shell nanonetworks (< 10 nm) was confirmed by TEM and STEM-EDX analysis. Also, the structure of Pt shell on core metals was successfully tuned by controlling the reaction temperature and time, precursor ratio, etc. Here, the number of the Pt layers on the surface of the connected Pd@Pt core-shell catalysts were varied from 1–6 atomic layers and the results show that the ORR mass activity was notably enhanced in the catalyst with a moderate shell thickness ranging from 2.5 to 3.5 Pt atomic layers. This suggests that connected Pd@Pt catalyst with a moderate Pt layer achieves both high surface area and ORR specific activity. The high surface area of the developed catalysts is attributed to a new synthesis method that does not use high temperature annealing and a low Pt core-shell structure. The improvement in ORR specific activity can be attributed to the more suitable d-band center position of the Pt shell, which is influenced by strain and ligand effects resulting from the Pd core. The ORR performance of the carbon-free connected Pd@Pt catalyst showed 2–4 times enhancement in electrochemical surface area (ECSA) and 1.5–3 times improvement in ORR mass activity compared to the connected Pt-alloy catalysts prepared using high-temperature annealing. Further, high durability of the connected core-shell catalyst against load cycles (0.6 ↔1.0 V) at 60 °C in acidic electrolyte solution was also demonstrated, indicating that a high stability nanonetwork connected by Pt atomic shell.In summary, we have successfully demonstrated a new synthesis method for the formation of connected core-shell nanoparticles by Pt atomic shell without high-temperature annealing and prepared a carbon-free, connected Pd@Pt core-shell catalyst with advanced ORR performance, highlighting its great potential as a cathode catalyst. Acknowledgement The part of this presentation is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

RuO2 Nanostructure as an Efficient and Versatile Catalyst for H2 Photosynthesis.

Photocatalytic H2 generation holds promise in the green production of alternative fuels and valuable chemicals. Seeking alternative, cost-effective, stable, and possibly reusable catalysts represents a timeless challenge for scientists working in the field. Herein, commercial RuO2 nanostructures were found to be a robust, versatile, and competitive catalyst in H2 photoproduction in several conditions. We employed it in a classic three-component system and compared its activities with those of the widely used platinum nanoparticle catalyst. We observed a hydrogen evolution rate of 0.137 mol h-1 g-1 and an apparent quantum efficiency (AQE) of 6.8% in water using EDTA as an electron donor. Moreover, the favorable employment of l-cysteine as the electron source opens possibilities precluded to other noble metal catalyst. The versatility of the system has also been demonstrated in organic media with impressive H2 production in acetonitrile. The robustness has been proved by the recovery of the catalyst by centrifugation and reusage alternatively in different media.

Plasma-synthesized platinum single atom and nanoparticle catalysts for high-current–density hydrogen evolution

“Green hydrogen” is the production of hydrogen through the electrolysis of water with renewable energy, which is an ideal form of hydrogen energy generation with zero carbon emissions. Platinum (Pt)-based catalysts have the highest catalytic efficiencies, but their application is limited by the high price and low reserves of Pt. Therefore, developing high-performance catalysts with low platinum loadings is a desirable way to reduce the cost of hydrogen production. Single atom platinum can achieve 100 % atomic utilization, but does not perform well at high current density. Here, we synthesized a catalyst composed of platinum single atoms and nanoparticles by nonthermal plasma technique. The catalyst exhibits an overpotential of 18, 89 and 130 mV at a current density of 10, 300 and 1000 mA cm−2, respectively. This performance far exceeds that of the commercial 20 wt% Pt/C and the loading is only one tenth (1.89 wt%). Nonthermal plasma technique offers an effective means to promote the synthesis of high-current hydrogen evolution reaction (HER) catalysts with low costs and the development of their industrialization.

Catalytic C–C bond formation over platinum nanoparticle catalyst on three-dimensional porous carbon

Three-dimensional porous carbon was prepared via a hard templating method using a colloidal crystal of monodispersed silica nanospheres (SNSs). Platinum nanoparticle catalyst on thus prepared porous carbon was prepared by a liquid-phase method using hydrogen hexachloroplatinate (IV) hexahydrate as Pt source in the presence of ethylene glycol. The prepared Pt catalyst on the carbon was characterized in detail and applied for the C-methylation reaction to elucidate the influence of the pore structure and morphology of the replicated porous carbon supports.

Surfactant-assisted synthesis of platinum nanoparticle catalysts for proton exchange membrane fuel cells

High-performance platinum nanoparticle catalysts (Pt–NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mgPt−1 and specific activity (SA) of 0.077 mA cm−2, higher than those of commercial Pt/C (0.023 A mgPt−1 and 0.035 mA cm−2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm−2, which is about 1.24 times larger than that of commercial Pt/C.

Scalable Synthesis of Pt/SrTiO3 Hydrogenolysis Catalysts in Pursuit of Manufacturing-Relevant Waste Plastic Solutions.

An improved hydrothermal synthesis of shape-controlled, size-controlled 60 nm SrTiO3 nanocuboid (STO NC) supports, which facilitates the scalable creation of platinum nanoparticle catalysts supported on STO (Pt/STO) for the chemical conversion of waste polyolefins, is reported herein. This synthetic method (1) establishes that STO nucleation prior to the hydrothermal treatment favors nanocuboid formation, (2) produces STO NC supports with average sizes ranging from 25 to 80 nm with narrow size distributions, and (3) demonstrates how SrCO3 formation and variation in solution pH prevent the formation of STO NCs. The STO synthesis was scaled-up and conducted in a 4 L batch reactor, resulting in STO NCs of comparable size and morphology (m = 22.5 g, davg = 58.6 ± 16.2 nm) to those synthesized under standard hydrothermal conditions in a lab-scale 125 mL autoclave reactor. Size-controlled STO NCs, ranging in roughly 10 nm increments from 25 to 80 nm, were used to support Pt deposited through strong electrostatic adsorption (SEA), a practical and scalable solution-based method. Using SEA techniques and an STO support with an average size of 39.3 ± 6.3 nm, a Pt/STO catalyst with 3.6 wt % Pt was produced and used for high-density polyethylene hydrogenolysis under previously reported conditions (170 psi H2, 300 °C, 96 h; final product: Mw = 2400, Đ = 1.03). As a well-established model system for studying the behavior of heterogeneous catalysts and their supports, the Pt/STO system detailed in this work presents a unique opportunity to simultaneously convert waste plastic into commercially viable products while gaining insight into how scalable inorganic synthesis can support transformative manufacturing.

One-Pot Facile Synthesis of Noble Metal Nanoparticles Supported on rGO with Enhanced Catalytic Performance for 4-Nitrophenol Reduction.

In this study, reduced graphene oxide (rGO)-supported noble metal (gold, silver, and platinum) nanoparticle catalysts were prepared via the one-pot facile co-reduction technique. Various measurement techniques were used to investigate the structures and properties of the catalysts. The relative intensity ratios of ID/IG in rGO/Au, rGO/Ag, rGO/Pt, and GO were 1.106, 1.078, 1.047, and 0.863, respectively. The results showed the formation of rGO and that noble metal nanoparticles were decorated on rGO. Furthermore, the catalytic activities of the designed nanocomposites were investigated via 4-nitrophenol. The catalysts were used in 4-nitrophenol reduction. The catalytic performance of the catalysts was evaluated using the apparent rate constant k values. The k value of rGO/Au was 0.618 min−1, which was higher than those of rGO/Ag (0.55 min−1) and rGO/Pt (0.038 min−1). The result proved that the rGO/Au catalyst exhibited a higher catalytic performance than the rGO/Ag catalyst and the rGO/Pt catalyst. The results provide a facile method for the synthesis of rGO-supported nanomaterials in catalysis.

The effect of non-spherical platinum nanoparticle sizes on the performance and durability of proton exchange membrane fuel cells

• Developed and implemented a novel one-pot synthesis technique. • Synthesized non-spherical carbon-supported platinum nanoparticle catalysts. • Carried out physical, half- and full cell electrochemical characterizations. • Catalyst with 2 nm Pt size has excellent performance (> 1.1 W/cm 2 peak power density). • Catalyst with larger Pt size (5 nm) has excellent durability under AST. Platinum (Pt) nanoparticles with different sizes of 2 nm and 5 nm supported on functionalized high surface area carbon (HSC) have been successfully synthesized with a one-pot synthesis technique in large scale. Of the interest for the proton exchange membrane fuel cell applications, the synthesized supported catalysts are evaluated by physical characterizations, half-cell and scaled up single cell tests to study the impact of the catalyst sizes on cell performance and durability. Physical characterizations clearly demonstrate the sizes, shapes, crystallinity phases, and the total loading of the Pt nanoparticles on HSC. Half cell characterizations demonstrate higher electrochemical surface area, higher mass activity, and less durability for the working electrode prepared by the smaller Pt nanoparticle sizes (2 nm) than the larger Pt nanoparticles (5 nm). Scaled up single cell tests using air and hydrogen as the cathode and anode reactants demonstrate the membrane electrode assembly (MEA) prepared by smaller Pt nanoparticle sizes (2 nm) shows the maximum power density of 1.1 W/cm 2 , which is 7% higher than the maximum power density of MEA prepared by larger Pt nanoparticles (5 nm) under similar operational conditions. The 30,000 cycles of accelerated stress test on the membrane electrode assembly prepared by larger Pt nanoparticles (5 nm) demonstrates 13% drop at maximum power density, illustrating the excellent performance against degradation (ageing).

Stabilization of Pt on Carbon Supports Doped with Atomically-Dispersed Metal/Metal-Oxide Additives

The shift in focus of Proton Exchange Membrane Fuel Cell (PEMFC) development for use in heavy-duty truck applications has accelerated the need for highly durable and efficient Membrane Electrode Assemblies (MEA) in order to meet the long lifetime requirements (~30,000 hours of runtime or 1 million mile driving distance) and high efficiency to minimize the total cost of ownership dominated by the H2 fuel cost.1 These requirements for heavy-duty truck are far stringent compared to the light-duty vehicle applications (~8,000 hours of run time). This brings into focus the need to develop highly-durable catalyst and membrane materials to satisfy the longer lifetime demanded by heavy-duty trucks.The primary cause of cell voltage loss in an operating fuel cell largely arises from the electrochemical surface area (ECSA) loss of the Pt-based cathode catalyst layer. Two mechanisms, namely Pt migration/coalescence and dissolution/redeposition are responsible for the coarsening of Pt nanoparticles leading to surface area loss.2,3 In this presentation, we will explore the concept of using metal/metal-oxide (M/MOx) based dopants in the carbon support as additives to mitigate the Pt coarsening behavior. Specifically, we evaluate dopants that are in the form of M/MOx nanoclusters and/or atomically-dispersed M in the graphitic carbon lattice (M-Cy). We will discuss fuel cell MEA results by investigating the stability when subjected to accelerated voltage cycling tests along with a suite of ex situ characterizations to understand the chemical nature of the catalyst materials with dopants. Acknowledgements: This work is partially supported by U.S Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0008821. References Marcinkoski, J. et al. Hydrogen Class 8 Long Haul Truck Targets. Subsection of the Electrified Powertrain Roadmap. Technical Targets for Hydrogen-Fueled Long-Haul Tractor-Trailer Trucks. DOE Advanced Truck Technologies 1–31 (2019). Available at: https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf. Cherevko, S., Kulyk, N. & Mayrhofer, K. J. J. Durability of platinum-based fuel cell electrocatalysts: Dissolution of bulk and nanoscale platinum. Nano Energy 29, 275–298 (2016). Yu, K. et al. Degradation mechanisms of platinum nanoparticle catalysts in proton exchange membrane fuel cells: The role of particle size. Chem. Mater. 26, 5540–5548 (2014). Figure 1

Boosting the Role of Ir in Alleviating Corrosion of Carbon Support By Alloying with Pt

The degradation of PEMFC is a very complex phenomenon and is affected by various factors. Among the components of PEMFC, an electrode composed of a carbon-supported platinum nanoparticle catalyst (Pt/C) plays an important role in determining the durability of PEMFC. Typically, PEMFCs have an operating voltage range of 0.5–1.0V. During long-term operation under these conditions, Pt nanoparticles agglomerate, reducing the active surface area and gradually reducing electrode performance. On the other hand, abnormal conditions such as low fuel and start/shutdown (SU/SD) cycles produce abnormally high potentials above 1.4V at the electrodes. At this high potential, the carbon support corrodes to form carbon dioxide (C + 2H2O → CO2 + 4H + + 4e–, E0 = 0.207 V), leading to loss of supported Pt nanoparticles and rapid decay or catastrophic failure of electrode performance. Automotive PEMFCs, which are more often exposed to the aforementioned abnormal conditions, have a shorter life (almost thousands of hours) than stationary PEMFCs (nearly tens of thousands of hours). This clearly means that these dynamic conditions will decisively affect the degradation of PEMFC.Extensive research efforts have been made to mitigate the corrosion of carbon supports to improve the durability of PEMFC. First, it improves the corrosion resistance of these materials by modifying the surface properties and crystallinity of carbon. Second, corrosion-resistant and electrically conductive oxides and transition metal carbides have been explored as alternative supports for Pt nanoparticles to remove carbon from the electrode. Electrodes without supports, such as nanostructured thin film electrodes, have also been proposed to remove carbon from the electrode. On the other hand, operating procedures or plant balances (BOPs) have been developed to avoid exposure to cell reversal or reverse current conditions. Despite these studies, the lifetime of automotive PEMFCs is limited due to carbon corrosion, but this is not the only issue. Nevertheless, the mitigation of carbon corrosion remains an important challenge.With a new approach, iridium oxide (IrO2) is incorporated into the Pt/C electrode as an additive that protects carbon from corrosion with the help of sacrificial oxidation of water (or oxygen evolution reaction, OER) demonstrating improved durability in both half-cell and single-cell tests. However, the function of the OER catalyst was not clear in terms of composition and distribution, which is a prerequisite for further improvement of cathode durability. This study aims to gain a mechanical understanding of OER functional Ir-containing Pt/C electrodes. Carbon-supported Pt–Ir alloy catalysts (PtxIry/C) are synthesized in various compositions and are exposed to potential cycles from 1.0 to 1.5 VRHE compared to Pt/C and mixtures of Pt/C and Ir/C (Pt/C + Ir/C, Pt-Ir ratio 85:15). Pt85Ir15/C has been proven to be more resistant to carbon corrosion than Pt/C as well as Pt/C+Ir/C due to Ir atomically distributed in Pt85Ir15/C. The corrosion behavior of the carbon support is thoroughly investigated by the identical location transmission electron microscopy (IL-TEM), differential electrochemical mass spectrometry (DEMS), and X-ray photoelectron spectroscopy (XPS). As a cathode catalyst, Pt85Ir15/C exhibits much higher oxygen reduction reaction (ORR) activity than Pt/C after potential cycles, which is associated with the formation of high-index facets of Pt as revealed by high-resolution TEM (HR-TEM) and inductively coupled plasma mass spectrometry connected to a scanning flow cell (SFC/ICP-MS). This study suggests that the atomic-level distribution of Ir is a key factor in effectively mitigating carbon corrosion and improving PEMFC durability.

(Invited) In Situ and Operando Synchrotron X-Ray Spectroscopy and Scattering Characterization of PEFC Cathode Catalysts

With wavelengths on the order of atomic dimensions and the ability to penetrate through low atomic number materials (e.g., Nafion® and carbon), hard X-rays, particularly those arising from synchrotron sources with high brilliance, are ideal for the atomic-level characterization of polymer electrolyte fuel cell (PEFC) catalysts in situ, in aqueous environments that mimic PEFC conditions, and operando, in the membrane-electrode assembly (MEA) environment. Two particularly valuable X-ray techniques for this purpose are X-ray absorption spectroscopy (XAS) and small angle X-ray scattering (SAXS) or anomalous SAXS (ASAXS), which allows discrimination of scattering from the absorbing element. Analysis of the X-ray spectrum near the absorption edge of interest (i.e., the near edge or XANES region) provides information on the oxidation state and electronic structure (e.g., d-band vacancy) of the material, properties that have been associated with catalyst activity. The extended region of the XAS spectrum (EXAFS) yields information on the atomic structure and coordination environment of the absorbing element (i.e., number and identity of nearest neighbors and distances between atoms). Unlike X-ray diffraction, XAS is particularly useful for characterization of platinum nanoparticle catalysts and of single-site platinum-group metal-free catalysts, such as Fe-N-C catalysts. However, EXAFS can be limited in the information it can provide regarding the bonding geometries, but absorption in the pre-edge region, which is sensitive to bonding geometry, can provide this essential information. SAXS and ASAXS are well-established techniques for probing particle sizes and particle size distributions on the nanometer level. While not as widely-used in the fuel cell community as XAS, SAXS and ASAXS are well-suited to examining nanoparticle fuel cell catalysts, which typically have particle diameters of 2-5 nm.This presentation will discuss the information that can be obtained from X-ray spectroscopy and scattering techniques and provide examples of application of these techniques to the study of platinum and platinum alloy nanoparticle catalysts and atomically-dispersed Fe-N-C and Co-N-C PEFC cathode catalysts. The utility of using a combination of XAS and ASAXS to study platinum alloy catalyst degradation and of the combination of information from XANES, EXAFS, and XAS pre-edge data to an Fe-N-C catalyst will be presented.Acknowledgements:This research was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO), through the Electrocatalysis Consortium (ElectroCat). This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. The authors thank Hoon Chung of Los Alamos National Laboratory for providing the Fe-N-C catalyst and Johnson Matthey Fuel Cells for providing the Pt and PtCo catalysts. This work was conducted at Argonne National Laboratory, a U.S. DOE Office of Science Laboratory operated for the U.S. DOE by UChicago Argonne, LLC, under Contract DE-AC02-06CH11357.

Mesostructured cellular foam silica supported Au–Pt nanoalloy: Enrichment of d-state electrons for promoting the catalytic synergy

A mesostructured cellular foam (MCF) silica was applied to support gold (Au) – platinum (Pt) alloy nanoparticles (NPs) for benzyl alcohol partial oxidation. A catalytic synergy on bimetallic gold (Au)-platinum (Pt) nanoparticle (NP) catalyst, referring to that introducing Au to Pt leading to a higher catalytic performance has been observed. However, the essence of this synergistic effect is still under debate. In this work, a series of MCF supported Au–Pt NP catalysts are designed to reveal the essence . Well-developed porous structure of MCF support eliminated the mass transfer limitation and intrinsic catalytic activity was obtained. The improved catalytic performance on bimetallic catalyst is attributed to the geometric and electronic changes of active sites after formation of Au–Pt alloy NPs. Compared with monometallic catalyst, the formation of Au–Pt alloy results in the changes of particle size and lattice structure. Electronic property analyses confirmed the increase of d state electrons on Au–Pt alloy NPs, which are calculated from s-p-d hybridization and intra-atomic charge redistribution, leading to the increased abundance of transferable d electrons near Fermi level and further enhancing the catalytic activity. These findings gain new insights into the catalytic synergy of bimetallic nanoparticles and shed light on the optimization of these catalysts. The catalytic synergy of mesostructured cellular foam silica supported bimetallic Au–Pt catalysts for benzyl alcohol oxidation is attributed to the increased abundance of transferable d electrons near Fermi level which are calculated from s-p-d hybridization and intra-atomic charge redistribution. • Mesostructured cellular foam silica support Au–Pt alloy nanoparticles were prepared by a facile one-pot method. • The formation of Au–Pt alloy nanoparticles results in particle size variation and lattice distortions. • Electron polarization leads to the increase of transferable d-orbital electrons on Au and Pt atoms. • The catalytic activity on Au–Pt alloy catalyst was enhanced through accelerating the O 2 activation.

Nanoparticulate Pt-catalyzed hydrogenation of Yb films: Towards hydrides with higher hydrogen compositions

• Moderate condition synthesis of β-YbH 3− δ was achieved by nanoparticulate Pt-catalyzed hydrogenation. • Hydrogenation using the Pt nanoparticle catalyst capping method demonstrated room-temperature synthesis of α-YbH 2± δ . • Thermodynamic kinetics in syntheses of β-YbH 3− δ and α-YbH 2± δ were analyzed. It is more difficult to synthesize β-phase ytterbium trihydride (β-YbH 3− δ ) under moderate conditions than other rare-earth metal trihydrides because it requires a valence change from a fully occupied 4 f shell ( 4 f 14 ) in Yb 2+ to an unclosed shell ( 4 f 13 ) in Yb 3+ . We synthesized β-YbH 3− δ at ambient pressure through hydrogenation of a Yb film capped with platinum (Pt) nanoparticle (NP) catalysts. In addition, Pt NP capping enabled us to synthesize α-phase Yb dihydride (α-YbH 2± δ ) at room temperature. The difficulty of trihydrogenating Yb to β-YbH 3− δ is explained by kinetic analyses based on temperature and time dependences of molar fractions of α-YbH 2± δ and β-YbH 3− δ . Pt NP capping can be used to synthesize other hydrogen-rich rare-earth metal hydrides under ambient pressure and lower temperatures.

Preparation of a platinum nanoparticle catalyst located near photocatalyst titanium oxide and its catalytic activity to convert benzyl alcohols to the corresponding ethers.

A novel platinum nanoparticle catalyst closely located near the surface of titanium oxide, PtNP/TiO2, has been prepared. This catalyst has both the properties of a photocatalyst and a metal nanoparticle catalyst, and acquired environmentally friendly catalytic activity, which cannot be achieved by just one of these catalysts, to afford ethers from benzyl alcohols under the wavelength of 420 nm.

Homogeneously supported PtGa NPs on nitrogen-doped mesoporous carbon as an enhanced ORR electro-catalyst

Platinum (Pt) nanoparticle catalysts show excellent performance for oxygen reduction reaction (ORR), but the high cost of Pt directly limits the commercialization of Pt-based catalysts. Supported PtGa alloy nanoparticles (NPs) with modified surface property and reactivity through ligand, strain and/or ensemble effects are considered as promising inexpensive low-Pt candidates. In this article, we report a PtGa nanoparticles with a size of 3.8 ± 0.4 nm anchored on nitrogen-doped mesoporous carbon (PtGa@NMC) for an efficient ORR electrocatalyst in alkaline electrolytes. The half-wave potential (E1/2) values of PtGa@NMC (0.92 V vs RHE) positively shift ~30 mV compared to commercial Pt/C in 1 M KOH solution. And it has outstanding long-term durability by the result of accelerated durability tests (ADTs) and chronoamperometry (CA). Considering high performance and excellent stability, PtGa@NMC presents the possibility of replacing contemporary Pt-based catalysts.

Classification of platinum nanoparticle catalysts using machine learning

Computer simulations and machine learning provide complementary ways of identifying structure/property relationships that are typically targeting toward predicting the ideal singular structure to maximize the performance in a given application. This can be inconsistent with experimental observations that measure the collective properties of entire samples of structures that contain distributions or mixture of structures, even when synthesized and processed with care. Metallic nanoparticle catalysts are an important example. In this study, we have used a multi-stage machine learning workflow to identify the correct structure/property relationships of Pt nanoparticles relevant to oxygen reduction, hydrogen oxidation, and hydrogen evolution reactions. By including classification prior to regression, we identified two distinct classes of nanoparticles and subsequently generated the class-specific models based on experimentally relevant criteria that are consistent with observations. These multi-structure/multi-property relationships, predicting properties averaged over a large sample of structures, provide a more accessible way to transfer data-driven predictions into the lab.

Water management implications for ALD-modified polymer electrolyte membrane fuel cell catalysts

Device testing of polymer electrolyte membrane fuel cell catalysts is essential for electrocatalyst development, yet most reported catalysts fabricated with nanoceramic coatings via atomic layer deposition (ALD) have not been thoroughly examined in this fashion. Platinum nanoparticle catalysts supported on functionalized XC72 carbon black that had been modified with sub-monolayer WN films and subjected to various thermal treatments were incorporated into membrane electrode assemblies and tested for oxygen reduction reaction activity in a fuel cell. The mass activities of the catalysts calculated at low current densities had comparable trends to those previously recorded in aqueous half-cell testing; however, significant deviations in catalyst performance became apparent at high current densities in the mass transport region of the polarization curves. The poor performance of the ALD-modified catalysts was attributed to water flooding induced by the low hydrophobicity of these catalyst layers, as determined by contact angle measurements on the cathode surfaces. It was seen that hydrophobicity was increased by thermal treatment and removal of surface groups known to be prone to hydrogen bonding, thereby improving the catalyst performance in the mass transport region. A heat-treated WN-coated ALD catalyst was found to have superior performance to commercial Pt/C. The field of research on fuel cell catalyst design via ALD is rapidly expanding, and this work demonstrates the importance of understanding the impact of ALD-deposited nanostructures on materials properties beyond the pure electrocatalytic activity.

Hollow PtFe Alloy Nanoparticles Derived from Pt-Fe3 O4 Dimers through a Silica-Protection Reduction Strategy as Efficient Oxygen Reduction Electrocatalysts.

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO2 -coated Pt-Fe3 O4 nanoparticle dimers supported on carbon at 900 °C, followed by SiO2 shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO2 protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO2 coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.