Dispersed Platinum Research Articles

Atomically Dispersed Transition Metal-Nitrogen-Carbon Electrocatalysts: Design, Synthesis, Characterization, Reactivity and Durability

Platinum group metal-free (PGM-free) catalysts have been targeted as possible Earth Abundant Elements solution to many electrochemical energy conversion technologies. Special attention has been given to PGM-free electrocatalysis with atomically dispersed (AD) transition metal moieties decorated over nitrogen-doped carbonaceous materials (a.k.a. M-N-C catalysts). Major applications for M-N-Cs are in cathode catalysts for oxygen reduction reaction (ORR). 1 These materials are employed across the pH-range: in proton exchange membrane fuel cells (PEMFC), biological (microbial) fuel cells (MFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). We have successfully introduced M-N-C catalysts synthesized by sacrificial support method (SSM) as a hard template approach based on high temperature pyrolysis.2 In most cases a secondary pyrolysis is being performed to promote AD display of the transition metal.3 This talk will address structure-to-property correlations for M-N-C catalysts in ORR based on electrochemical activity obtained in rotating ring-disk electrodes (RRDE) with those spectroscopic and microscopic observations and density functional theory (DFT) calculations of oxygen binding on AD transition metal. We will discuss the role of the AD transition metal, participation of the surface N-groups as co-catalysts/alternative active sites and the possible role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor. M-N-C catalysts performance in single membrane electrode assembly (MEA) fuel cells will also be discussed in the context of its surface chemistry and materials structure/morphology. We will focus on local hydrophobicity of SSM-based M-N-C electrocatalystsand its impact on the MEA performance.A broad spectrum of AD transition metal decorated MNCs have been synthesized and evaluated for catalytic activity in ORR (and other processes). The use of such materials as “active supports” for highly dispersed platinum or platinum alloy nanoparticles will be discussed. New developments in synthesis protocols enabling “green chemistry” scalable solutions will be discussed.

Carbon-bridged atomically dispersed platinum on MOF-derived ZnO/C for selective photocatalytic oxidation of NO into Nitrates and Nitrites

Using nanoclusters and single atoms with unique activity to replace nanoparticles is a promising strategy to enhance catalyst activity. However, stable loading of nanoclusters and single atoms remain a challenge. This paper reports atomically dispersed Pt bridged with metal-organic framework (MOF)-derived ZnO/C through carbon atoms (Pt–ZnO/C), by impregnation combined with calcination, for photocatalytic oxidation of NO. The MOF-derived ZnO/C has a larger specific surface area than pure ZnO. The presence of C enhances the visible light absorption, promotes the migration of photogenerated carriers, and more importantly facilitates the stabilization of Pt single atoms through Pt–C interactions. The Pt species present in the Pt–ZnO/C catalysts in the form of single atoms and nanoclusters. The Pt–ZnO/C catalysts show high NO conversion rates and selectivity towards NO3−/NO2− ions formation. Specifically, the NO conversion rate of 81.9% is much higher than those of ZnO/C (31.4%) and Pt nanoparticles loaded ZnO/C (Pt NPs-ZnO/C, 58.6%). In addition, the selectivity of NO3−/NO2− (i.e., 98.6%) formation over the Pt–ZnO/C catalyst is much higher than that of NO2 (i.e., 1.4%). Furthermore, the photocatalysis tests and ESR results suggest that the Pt single atoms and nanoclusters can enhance the oxidation of NO by promoting the production of O2•- and OH•. The DFT results also reveal that single Pt atoms promote the adsorption of O2 and H2O to form O2•- and OH•. More importantly, OH• can promote the selective oxidation of NO to NO3−/NO2− ions. In addition, the projected density of states of single Pt atoms loaded on the ZnO/C catalysts show that the presence of C atom bridge favors the stability of single Pt atoms because of the interaction between C and Pt atoms. This work provides a new strategy for the design of single-atom-loaded metal oxide catalysts.

Catalytic hydrogenation of Cl-oxyanion pollutants in water

Pt and Pd catalysts supported on alumina have been tested and characterised for the catalytic hydrogenation of chlorates at room temperature and atmospheric pressure. Metallic nanoparticles are the catalytic active species, obtaining better results with the Pt than with the Pd catalysts. It is observed that the activity of the Pt catalysts depends on the metal precursor used for their preparation and the calcination temperature as these factors lead to different platinum dispersion on the alumina surface. The best results were obtained with the catalysts prepared from metal precursors containing Cl atoms and calcined at lower temperatures, as smaller metallic crystallites are formed. The chlorate reduction profiles displayed a pseudo-first order kinetic towards chlorate. The optimised catalyst was tested for the reduction of the different Cl-oxyanions, proving that the reaction rate depends on the chlorine valence of the ion following this order: ClO4- < ClO3- < ClO2-. This is due to the different molecular geometry of the anions that results in different stability of the ClOx-. The optimised catalyst was fully stable in successive uses, being active for the simultaneous reduction of chlorate, chlorite and bromate in water.

Ceria–Zirconia Supported Platinum Catalysts for Water Gas Shift Reaction: Influence of Support Composition

The study is presented on the influence of the composition of a ceria-zirconia support on the structure and the activity in water gas shift reaction of platinum catalysts (Pt/Ce0.75Zr0.25O2 и Pt/Ce0.4Zr0.5Y0.05La0.05O2). The structure diagnostics of the samples were performed using high-resolution transmission electron microscopy, powder X-ray diffraction, CO chemisorption and X-ray atomic pair distribution function method. It was shown that the catalysts contain highly dispersed platinum particles not exceeding 2 nm in size. Platinum particles supported on Ce0.75Zr0.25O2 are smaller due to the higher specific surface area of the support. The catalysts Pt/Ce0.75Zr0.25O2 and Pt/Ce0.4Zr0.5Y0.05La0.05O2 proved to have similar efficiency while having the same platinum content. It was assumed that the catalysts supported on Ce0.4Zr0.5Y0.05La0.05O2 demonstrate a slightly higher turnover frequency per platinum surface atom, but it is likely compensated by the difference in the supported metal particle size.

Dual-site catalysts featuring platinum-group-metal atoms on copper shapes boost hydrocarbon formations in electrocatalytic CO2 reduction

Copper-based catalyst is uniquely positioned to catalyze the hydrocarbon formations through electrochemical CO2 reduction. The catalyst design freedom is limited for alloying copper with H-affinitive elements represented by platinum group metals because the latter would easily drive the hydrogen evolution reaction to override CO2 reduction. We report an adept design of anchoring atomically dispersed platinum group metal species on both polycrystalline and shape-controlled Cu catalysts, which now promote targeted CO2 reduction reaction while frustrating the undesired hydrogen evolution reaction. Notably, alloys with similar metal formulations but comprising small platinum or palladium clusters would fail this objective. With an appreciable amount of CO-Pd1 moieties on copper surfaces, facile CO* hydrogenation to CHO* or CO-CHO* coupling is now viable as one of the main pathways on Cu(111) or Cu(100) to selectively produce CH4 or C2H4 through Pd-Cu dual-site pathways. The work broadens copper alloying choices for CO2 reduction in aqueous phases.

Re‐Dispersion of Platinum From CNTs Substrate to α‐MoC1 ‐ x to Boost the Hydrogen Evolution Reaction (Small 21/2023)

Hydrogen Evolution Reaction In article number 2207146, Rui Gao, Chuan Shi, and co-workers present Pt atoms to redisperse on α-MoC1−x substrate from carbon nanotubes, which creates dual active interfaces of Pt species dispersed over carbon nanotubes and α-MoC1−x. Benefiting from the strong electronic interaction between the Pt atom and α-MoC1−x, the utilization efficiency of the Pt atom is evidently enhanced, providing practical solutions to enhance platinum dispersion, and thereby enhancing the catalytic activity in hydrogen production.

Combining Highly Dispersed Amorphous MoS3 with Pt Nanodendrites as Robust Electrocatalysts for Hydrogen Evolution Reaction.

Surface modification of electrocatalysts to obtain new or improved electrocatalytic performance is currently the main strategy for designing advanced nanocatalysts. In this work, highly dispersed amorphous molybdenum trisulfide-anchored Platinum nanodendrites (denoted as Pt-a-MoS3 NDs) are developed as efficient hydrogen evolution electrocatalysts. The formation mechanism of spontaneous in situ polymerization MoS4 2- into a-MoS3 on Pt surface is discussed in detail. It is verified that the highly dispersed a-MoS3 enhances the electrocatalytic activity of Pt catalysts under both acidic and alkaline conditions. The potentials at the current density of 10mA cm-2 (η10 ) in 0.5msulfuric acid (H2 SO4 ) and 1mpotassium hydroxide (KOH) electrolyte are -11.5 and -16.3mV, respectively, which is significantly lower than that of commercial Pt/C (-20.2mV and -30.7mV). This study demonstrates that such high activity benefits from the interface between highly dispersed a-MoS3 and Pt sites, which act as the preferred adsorption sites for the efficient conversion of hydrion (H+ ) to hydrogen (H2 ). Additionally, the anchoring of highly dispersed clusters to Pt substrate greatly enhances the corresponding electrocatalytic stability.

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms, Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction.

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg-1 Pt and 11.7 ± 0.6 A mg-1 Cat at -50mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.

Genesis of Active Pt/CeO2 Catalyst for Dry Reforming of Methane by Reduction and Aggregation of Isolated Platinum Atoms into Clusters.

Atomically dispersed metal catalysts offer the advantages of efficient metal utilization and high selectivities for reactions of technological importance. Such catalysts have been suggested to be strong candidates for dry reforming of methane (DRM), offering prospects of high selectivity for synthesis gas without coke formation, which requires ensembles of metal sites and is a challenge to overcome in DRM catalysis. However, investigations of the structures of isolated metal sites on metal oxide supports under DRM conditions are lacking, and the catalytically active sites remain undetermined. Data characterizing the DRM reaction-driven structural evolution of a cerium oxide-supported catalyst, initially incorporating atomically dispersed platinum, and the corresponding changes in catalyst performance are reported. X-ray absorption and infrared spectra show that the reduction and agglomeration of isolated cationic platinum atoms to form small platinum clusters/nanoparticles are necessary for DRM activity. Density functional theory calculations of the energy barriers for methane dissociation on atomically dispersed platinum and on platinum clusters support these observations. The results emphasize the need for in-operando experiments to assess the active sites in such catalysts. The inferences about the catalytically active species are suggested to pertain to a broad class of catalytic conversions involving the rate-limiting dissociation of light alkanes.

Restructured zeolites anchoring singly dispersed bimetallic platinum and zinc catalysts for propane dehydrogenation

Restructuring of a heterogeneous catalyst under reaction conditions is a common phenomenon. Severe restructuring of a catalyst can result in deactivation in many catalytic systems—for example, the catalytic dehydrogenation of propane to propylene. Herein, we report the utilization of catalyst restructuring to improve activity and stability for the propane dehydrogenation reaction. A bimetallic platinum and zinc (Pt1Znm) catalyst protected by an in situ restructured silicalite-1 zeolite is prepared. The catalyst yields outstanding activity (initial conversion of ∼69.2%, initial selectivity of ∼91.1%) with high stability at 580°C, which is better than several commercial catalysts. Characterization shows the singly dispersed bimetallic sites of Pt1Znm serve as the catalytic sites during the reaction. Moreover, the less-stable silicalite-1 zeolite undergoes restructuring during the dehydrogenation reaction, forming a crucial protective layer on the Pt1Znm bimetallic nanocatalysts.

Re-Dispersion of Platinum From CNTs Substrate to α-MoC1-x to Boost the Hydrogen Evolution Reaction.

Developing high-performance electrocatalysts toward hydrogen evolution reaction (HER) is important for clean and sustainable hydrogen energy, yet still challenging. Herein, an α-MoC1-x induced redispersing strategy to construct a superior HER electrocatalyst (Pt/CNTs-N+α-MoC1-x ) by mechanical mixing of α-MoC1-x with Pt/CNTs-N followed by thermal reduction is reported. It is found that thermo-activation treatment enables partial Pt atoms to redisperse on α-MoC1-x substrate from carbon nanotubes, which creates dual active interfaces of Pt species dispersed over carbon nanotubes and α-MoC1-x . Benefiting from the strong electronic interaction between the Pt atom and α-MoC1-x , the utilization efficiency of the Pt atom and the zero-valence state of Pt is evidently enhanced. Consequently, Pt/CNTs-N+α-MoC1-x catalyst exhibits excellent HER activity with low overpotentials of 17 and 34 mV to achieve a current density of 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Density functional theory calculations further reveal that the synergistic effect between Pt and α-MoC1-x makes it accessible for the dissociation of water molecules and subsequent desorption of hydrogen atoms. This work reveals the crucial roles of α-MoC1-x additives, providing practical solutions to enhance platinum dispersion, and thereby enhance the catalytic activity in HER.

Highly dispersed Pt with CoFeP hollow nanocages for efficient oxygen evolution reaction

The strong binding energy of Pt with oxygen intermediates results in its low OER efficiency at the anode. Herein, Pt-doped CoFeP (Pt-CoFeP) material has been synthesized using CoFe-PBA as precursor through facile etching and phosphating processes. Interestingly, Pt-CoFeP with hollow cage framework exhibits large surface area after etching, which plays a domain-limiting role for the high dispersion of platinum atoms and facilitates the oxygen evolution reaction (OER). The target sample Pt-CoFeP only needs low overpotentials of 311.7 and 343.1 mV to deliver the current density of 10 and 50 mA cm-2, which is superior to commercial RuO2. The excellent activity can be attributed to large specific surface area in hollow framework and highly dispersed platinum atoms. And its great durability is evaluated through chronoamperometry measurement for 12 hours. This work provides a potential method to design electrocatalysts with complex structure loaded with highly dispersed Pt particles derived from Prussian blue analogues (PBAs) for water splitting.

Enhancing the low-temperature CO oxidation over Pt/Y2O3 catalyst: The effects of Pt dispersion and support basicity on the catalytic performance

High metal dispersion supported catalysts have attracted extensive attention due to their high atom utilization and excellent activities in various catalytic reactions. In this work, Pt/Y2O3-HT was synthesized via a wet-impregnation method modified by hydrothermal process. Compared with Pt/Y2O3 without hydrothermal modification, CO oxidation activity of Pt/Y2O3-HT was significantly improved. The comprehensive experiment results demonstrate that hydrothermal aging at 200 °C could enhance basicity of yttria support by increasing the number of strong basic sites (low coordination surface O2−) and greatly improve dispersion of platinum at atomic level (about 30% and 82% platinum single atom for Pt/Y2O3 and Pt/Y2O3-HT, respectively). Moreover, in-situ DRIFTS results further indicate that hydrothermal treatment could alleviate CO adsorption rate on Pt atoms and clusters to provide more site for the adsorption of oxygen. Our work may provide a new insight for the mechanism of the effect of hydrothermal pretreatment on CO oxidation.

Construction of hierarchical core-shell Pt/USY@MSA bifunctional catalysts for hydroisomerization of n-hexadecane

Hydroisomerization of long-chain n-alkanes is an indispensable process in the upgrading of fuel oil and lubricants to meet the state of art regulations. In this work, a novel core-shell structural material comprising USY zeolite core and mesoporous aluminosilicate (MSA) shell, denoted as USY@MSA, was fabricated by virtue of a desilication and recrystallization approach. Comprehensive characterizations demonstrate that the USY@MSA composite exhibits a hierarchical pore architecture and a gradient acidity. Due to the confinement effect of the mesoporous aluminosilicate shell, highly dispersed platinum particles were selectively deposited on the shell, generating a nanoscale distance with acidic sites of USY zeolite core. In the hydroisomerization of n-hexadecane, the Pt/USY@MSA composite catalyst outperforms the conventional Pt/USY and desilicated Pt/USY-ds catalysts, effectively suppressing the cracking side reactions and producing higher selectivity to branched isomers.

PLATINUM ON REDUCED GRAPHENE OXIDE NANOSHEETS OBTAINED UNDER MICROWAVE IRRADIATION, USING REDUCING AGENTS

Hydrophobic catalysts used in catalytic detritiation process of heavy water consist of platinum impregnated on charcoal (commercial material) and PTFE. For this type of material, Pt is found as agglomerates leading to an increase of hydrophilicity in the final catalyst and also, to a low number of functional groups for isotopic exchange. Therefore, in order to avoid these drawbacks, another type of platinum-based material was considered, with a higher platinum dispersion which would lead to an increase number of functional groups for the isotopic exchange process. There are different methods to synthesize Pt on graphene composites, but using microwaves involves advantages like fewer stages and shorter time to produce. The obtaining method uses reduction of H2PtCl6 in the presence of ethylene glycol and other reducing agents (NaBH4 and KOH) and graphene oxide suspension. Samples were then microstructurally investigated using SEM, BET, X-ray diffraction, RAMAN and TGA.

Preparation of Nanocrystalline Nb-Doped SnO2 on Mesoporous Carbon for PEFC Electrocatalysts

Platinum-based nanoparticles decorated on carbon supports (Pt/C) are widely used as electrocatalysts in polymer electrolyte fuel cells (PEFCs). Meanwhile, SnO2 is more stable than carbon at high potentials in cathodic environments. Highly durable Pt/SnO2/C electrocatalysts have therefore previously been developed using carbon nanomaterials as an electron-conducting backbone and SnO2 as a stable support layer for highly dispersed platinum nanoparticles. Here, we report on the development of Pt/SnO2/C electrocatalysts based on mesoporous carbon (MC) scaffolds. The electron conduction pathway through SnO2 was minimized by reducing the SnO2 loading. The use of Pt/SnO2/MC electrocatalysts resulted in high activity towards the oxygen reduction reaction (ORR) as well as excellent start-stop voltage cycling durability in half-cell conditions.

Impact of platinum loading and dispersion on the catalytic activity of Pt/SnO2 and Pt/α-Fe2O3

The Pt/SnO2 (SP-samples) and Pt/α-Fe2O3 (FP-samples) with platinum loadings between 1 and 10 mol% were synthesized mechanochemically starting from platinum(II) acetylacetonate dissolved in toluene and from SnO2 and α-Fe2O3 powders obtained from tin(II) and iron(II) acetates. The STEM results show that the ultrasmall platinum nanoparticles (PtNPs) are well dispersed on the SnO2 and α-Fe2O3 supports. The PtNPs size distributions calculated with lognormal functions ranged from 1.0 to 1.3 nm. The results of temperature programmed reduction in hydrogen showed maxima at 120–160 °C due to the reduction of PtOx to Pt0. The Pt-4f-XPS results showed that the dispersed platinum on the SnO2 and α-Fe2O3 supports consisted of all three oxidation states of platinum: Pt4+, Pt2+ and Pt0. The average oxidation state of platinum as a function of molar fraction of Pt loading in the SP samples varies from 1.69 to 2.11, whereas the oxidation state of Pt in the FP samples varies more linearly and steeply from 1.42 to 2.58. The synthesized samples showed high catalytic activity for the reduction of 4-nitropenol (4-NP) to 4-aminophenol (4-AP), which can be explained by the high dispersion of non-aggregated ultrasmall PtNPs with a size of about 1 nm on the SnOx and FeOx supports.

Effect of Platinum Precursor on the Properties of Pt/N-Graphene Catalysts in Formic Acid Decomposition

Properties of a novel catalytic material, Pt/N-graphene, in gas-phase decomposition of formic acid to obtain pure hydrogen were studied. The graphene powder doped with nitrogen atoms was used as the carbon support. The following methods were used to characterize the synthesized catalysts: X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), EXAFS and CO chemisorption. It was determined that the platinum precursor substantially affects the state of the metal in the Pt/N-graphene catalysts. When Pt(NO3)4 was used as the precursor, platinum on the catalyst surface was in the form of nanocrystals. Meanwhile, the use of H2PtCl6 led to the formation of atomically dispersed platinum stabilized on the surface of N-graphene. Carbon structures containing defects in the graphene layer surrounded by four nitrogen atoms had strong interactions with platinum atoms and acted as the sites where atomic platinum was stabilized.

Metallic Strontium as a Precursor of the Al2O3/SrCO3 Xerogels Obtained by the One-Pot Sol-Gel Method.

Two series of binary xerogel systems of Sr/Al with molar ratios of 0.1, 0.25, 0.5, and 1.0 were synthesized by the sol–gel technique with metallic strontium component as a precursor. The influence of the metallic precursor on the properties of the final xerogel was determined. The properties of the gels were determined on the basis of X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), low temperature nitrogen adsorption, transmission, and scanning electron microscopy with Energy Dispersive X-ray Spectroscopy (TEM, SEM, and SEM/EDS). The Al2O3/SrCO3 xerogels were tested as supports for platinum catalysts. Hydrogen chemisorption was used to determine the platinum dispersion of the Pt/Al2O3-SrCO3 systems. The original method of synthesis allows to obtain highly dispersed and stable strontium carbonate phases that allow for obtaining a high (42–50%) dispersion of platinum nanoparticles.

Highly dispersed platinum deposited on nitrogen-doped vertical graphene array for efficient electrochemical hydrogen evolution

The electrochemical hydrogen evolution is a key technology for future renewable energy conversion and storage. Platinum is the most efficient catalyst for hydrogen evolution reaction (HER), but its mass activity should be boosted further. Herein, we deposited platinum on nitrogen-doped vertical graphene through an atomic layer deposition method. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy confirmed that the platinum was highly dispersed on the array substrate. On account of the array structure and high dispersion of platinum, the synthesized catalyst exhibited high HER performance with a low overpotential of 42 mV at 10 mA cm−2 and a low Tafel slope of 52.2 mV dec−1. Significantly, the synthesized catalyst exhibited a high mass activity of 4.45 A mg−1 Pt, which was ∼13 times higher than that of commercial Pt/C.