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1.
Artigo em Inglês | MEDLINE | ID: mdl-32725851

RESUMO

Graphitic carbon nitride quantum dots (g-CNQDs) are highly promising photoresponsive materials. However, synthesis of monodispersed g-CNQDs remains challenging. Here we report the dual function of MOF [Cu3BTC2] (HKUST-1) as a catalyst and template simultaneously to prepare g-CNQDs at mild conditions. Cyanamide (CA), a graphitic carbon nitride precursor, catalytically dimerized inside the MOF larger cavities at 90 oC and condensed into g-CNQDs at 120 oC in a controlled fashion. The HKUST-1 template was stable at the reaction conditions leading to uniform g-CNQDs with particle size of 2.22 ± 0.68 nm. The as prepared g-CNQDs showed photoluminescence emission with 3.1% quantum yield. Depending on this concept (MOF dual functionality) for catalyzing CA polycondensation (open metal sites (OMSs) effect) and controlling the produced particle size (pore templating effect) in addition to MOF tunable porosity, it is expected to produce unique g-CNQDs with controllable size, morphology, and surface functionality.

2.
Inorg Chem ; 2020 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-32578989

RESUMO

Reaction of the Cu(I) sources, [Cu5](Mes)5 and [(iDipp)CuOtBu] (Mes = mesityl; iDipp = 1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene) with the Zn(I) complex [Zn2](Cp*)2 leads to a mixture of intermetallic Cu/Zn clusters with a distribution of species that is dependent on the stoichiometric ratio of the reactants, the reaction time, as well as the temperature. Systematic and careful investigation of the product mixtures rendered the isolation of two new clusters possible, i.e., the Zn-rich, red cluster 1, [CuZn10](Cp*)7 = [Cu(ZnZnCp*)3(ZnCp*)4], as well as the Cu-rich, dark-green cluster 2 [Cu10Zn2](Mes)6(Cp*)2. Structure and bonding of these two species was rationalized with the help of density functional theory calculations. Whereas 1 can be viewed as an 18-electron Cu center coordinated to four ZnCp* and three ZnZnCp* one-electron ligands (with some interligand bonding interaction), compound 2 is better to be described as a six-electron superatom cluster. This unusual electron count is associated with a prolate distortion from a spherical superatom structure. This unexpected situation is likely to be associated with the ZnCp* capping units that offer the possibility to strongly bind to the top and the bottom of the cluster in addition to the bridging mesityl ligands stabilizing the Cu core of the cluster.

3.
Phys Chem Chem Phys ; 22(18): 10368, 2020 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-32347862

RESUMO

Correction for 'Micro-spectroscopy of HKUST-1 metal-organic framework crystals loaded with tetracyanoquinodimethane: effects of water on host-guest chemistry and electrical conductivity' by Miguel Rivera-Torrente et al., Phys. Chem. Chem. Phys., 2019, 21, 25678-25689.

4.
Inorg Chem ; 2020 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-32191447

RESUMO

The reactivity of GaCp* toward different Ni0 olefin complexes is investigated. The reaction of GaCp* with [Ni(cdt)] (cdt = all-trans-1,5,9-cyclododecatriene) leads to simple adduct formation and the 18 valence electron (ve) compound [Ni(GaCp*)(cdt)] (1). In contrast, [Ni2(dvds)3] (dvds = 1,1,3,3-tetramethyl-1,3-divinyldisiloxane) is converted to the undercoordinated and highly reactive 16 ve complex [Ni(GaCp*)(dvds)] (2), which represents an intermediate in the formation of the propeller-shaped M7 cluster [Ni4Ga3](Cp*)3(dvds)2 (3). Extensive characterization of the latter compound by experimental and computational means reveals the Cp* transfer from Ga to Ni. Therefore, the title compound can be best expressed by the structural formula [(µ2-GaCp*)(Ni2)(µ2-GaNiCp*)2(dvds)2]. The flexible dvds ligands stabilize this arrangement via alkene-Ni and O-Ga interactions. Furthermore, compound 2 exhibits a fast GaCp* ligand exchange with external GaCp*, which is rather unexpected for the [TM(ECp*)a] compounds; they usually do not undergo substitution reactions with two electron donor ligands like CO, phosphines, or GaCp*.

5.
Artigo em Inglês | MEDLINE | ID: mdl-31986002

RESUMO

Metal-organic frameworks with open metal sites are promising materials for gas separations. Particularly, the M2(dobdc) (dobdc4- = 2,5-dioxidobenzenedicarboxylate, M2+ = Co2+, Mn2+, Fe2+, ...) framework has been the Drosophila of this research field and has delivered groundbreaking results in terms of sorption selectivity. However, many studies focus on perfect two-component mixtures and use theoretical models, e.g., the ideal adsorbed solution theory, to calculate selectivities. Within this work, we shed light on the comparability of these selectivities with values obtained from propane/propene multicomponent measurements on the prototypical Co2(dobdc) framework, and we study the impact of impurities like water on the selectivity. Despite the expected capacity loss, the presence of water does not necessarily lead to a decreased selectivity. Density functional theory calculations of the binding energies prove that the water molecules adsorbed to the metal centers introduce new binding sites for the adsorbates.

6.
Angew Chem Int Ed Engl ; 59(14): 5837-5843, 2020 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-31912955

RESUMO

Metal-organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a "strain modulation" approach has been applied through the use of surface-mounted NiFe-MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm-2 at an overpotential of only ≈210 mV. It demonstrates operational long-term stability even at a high current density of 500 mA cm-2 and exhibits the so far narrowest "overpotential window" ΔEORR-OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.

7.
ACS Appl Mater Interfaces ; 12(1): 1024-1035, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31809022

RESUMO

Host-guest interactions control the fundamental processes in porous materials for many applications such as gas storage and catalysis. The study of these processes, however, is not trivial, even if the material is crystalline. In particular, metal-organic frameworks (MOFs) represent a complex situation since guest molecules can interact with different parts of the organic linkers and the metal clusters and may alter the details of the pore structure and system properties. A prominent example is the so-called retrofitted MOF material TCNQ@Cu3(BTC)2 that has attracted a lot of attention due to its electronic properties induced by the host-guest interactions. Only recently, structural evidence has been presented for a bridging binding mode of TCNQ to two Cu paddlewheel units; however, many issues regarding the redox chemistry of Cu3(BTC)2 and TCNQ are currently unsolved. Herein, we report a powerful spectroscopic approach to study the host-guest chemistry of this material. Combining IR spectroscopy in the presence of CO and EPR spectroscopy, we found that the intrinsic Cu(I) defects of the host react with the guest, forming TCNQ radical anions. This chemistry has profound implications, in particular, with respect to the performance of TCNQ@Cu3(BTC)2 as an electronic conductor. A decreasing availability of open Cu(II) sites with increasing TCNQ loading proves the coordinative binding of TCNQ to the paddlewheel nodes, and a heterogeneous structure is formed with different TCNQ arrangements and pore environments at low TCNQ loadings. Finally, the combined use of spectroscopic characterization techniques has proven to be, in general, a powerful approach for studying the complex chemistry of host-guest materials.

8.
ACS Appl Mater Interfaces ; 12(2): 2655-2661, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31840974

RESUMO

Defect engineering is a strategy for tailoring the properties of metal-organic frameworks (MOFs). Plenty of efforts have been devoted to study the defect chemistry and structures of bulk MOFs; however, the reported example of a defect-engineered surface-mounted MOF (SURMOF) thin film is rare. In this work, defects were incorporated in SURMOF thin films by using defect-generating linkers and taking advantage of the liquid-phase stepwise epitaxial layer-by-layer growth (LBL). Two methods based on the LBL, named mixing method and alternating method, are proposed for incorporating defects in the prototypical SURMOF HKUST-1 by partially substituting the parent H3btc (benzene-1,3,5-tricarboxylic acid) linker with a set of defect-generating linkers H2ip (isophthalic acid), H2OH-ip (5-hydroxyisophthalic acid), and H2pydc (3,5-pyridinedicarboxylic acid). The crystallinity and phase purity of the obtained "defected" SURMOFs were confirmed by X-ray diffraction, infrared reflection absorption spectroscopy, and Raman spectroscopy. The incorporation of the defect-generating linkers and the types of induced defects were characterized by ultraviolet-visible spectroscopy, time-of-flight secondary ion mass spectrometry, methanol adsorption, scanning electron microscopy, and 1H nuclear magnetic resonance spectroscopy (after digestion of the samples). These two methods provide avenues for controlling the defect formation in MOF thin films.

9.
Inorg Chem ; 59(1): 514-522, 2020 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-31874031

RESUMO

Heterometallic Ni/Zn complexes can serve as molecular models for the semihydrogenation of acetylene catalyzed by heterogeneous Ni/Zn phases. Pursuing this target, we present the synthesis of the series [Ni(ZnCp*)n(ZnMe)n(PEt3)4-n] (n = 1-3; 1, 2, 3) which is obtained via E/Zn exchange from [Ni(ECp*)n(PEt3)4-n] (n = 1-3, E = Al, Ga; P1, P2, P3). The isolation of the intermediate compound [Ni(GaCp*)(ZnCp*)(ZnMe)(PEt3)2] (2a) supports the assumption of a stepwise Ga/Zn exchange in the formation of 3. The dissociation behavior of PEt3 in 2 and 3 was investigated experimentally using variable temperature (VT) UV-vis spectroscopy indicating suppressed phosphine dissociation in both cases. For comparison, the absorption spectra of the saturated and unsaturated compounds were calculated using time dependent DFT calculations (TDDFT). Energy decomposition analysis with the natural orbital for chemical valence extension (EDA NOCV) calculations shows a bond strengthening of the Ni-P bond by successive substitution of the phosphines with (ZnR)2 units. The influence of different phosphines (PMe3, PEt3, PPh3, P(OEt)3) on Ni-P bond length and on Zn-Zn interactions in [Ni(ZnR)2n(PR')4-n] (R = Cp*, Me; R' = Me, Et, Ph, OEt) was also studied by DFT calculations. A correlation of increasing sterical demand of the phosphine ligand and a shortening of the Zn-Zn distances is observed.

10.
Phys Chem Chem Phys ; 21(46): 25678-25689, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31742269

RESUMO

Composite materials, consisting of a metal-organic framework (MOF) and a guest molecule, further denoted as guest@MOF composites, have gained strong interest due to the guest-induced tunability of the host properties, for example in sensing or electroconductivity applications. However, decoding the complexity of these guest@MOF composites and extracting structure-performance relationships are far from trivial and require the use of a gamut of characterization tools. In this work, we use various micro-spectroscopic tools both under static (ex situ) and dynamic (in situ) conditions to map the properties and diffusion behavior of TCNQ (7,7,8,8-tetracyanoquinodimethane) as a guest molecule in single HKUST-1 crystals as the host. Raman micro-spectroscopy allowed us to map the spatial distribution of TCNQ within HKUST-1 single crystals, thereby revealing a heterogeneous distribution of TCNQ after initial TCNQ-infiltration, concentrated at the crystal edges, and a homogeneous redistribution upon water vapor treatment. These insights are correlated to I-V scans at different temperatures and to electrochemical impedance spectroscopy (EIS), which allowed us to verify the different contributions to conductivity. These data showed changes in electrical conductivity after exposing the sample to moisture and air. In situ FT-IR micro-spectroscopy during treatment with moisturized nitrogen gas suggests lower transient diffusion rates for water inside TCNQ@HKUST-1 relative to pristine HKUST-1, likely due to steric hindrance of the pore-filling TCNQ molecules in the HKUST-1 framework. The application of micro-spectroscopic techniques is crucial to uncovering MOF intracrystal heterogeneities and yielding rationally-derived instructions for the improved design of guest@MOF systems.

11.
Beilstein J Nanotechnol ; 10: 1754-1767, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31501747

RESUMO

NiGa is a catalyst for the semihydrogenation of alkynes. Here we show the influence of different dispersion times before microwave-induced decomposition of the precursors on the phase purity, as well as the influence of the time of microwave-induced decomposition on the crystallinity of the NiGa nanoparticles. Microwave-induced co-decomposition of all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in the ionic liquid [BMIm][NTf2] selectively yields small intermetallic Ni/Ga nanocrystals of 5 ± 1 nm as derived from transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and supported by energy-dispersive X-ray spectrometry (EDX), selected-area energy diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). NiGa@[BMIm][NTf2] catalyze the semihydrogenation of 4-octyne to 4-octene with 100% selectivity towards (E)-4-octene over five runs, but with poor conversion values. IL-free, precipitated NiGa nanoparticles achieve conversion values of over 90% and selectivity of 100% towards alkene over three runs.

12.
Chem Asian J ; 14(20): 3474-3501, 2019 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-31430417

RESUMO

Rational design and synthesis of efficient electrocatalysts are important constituents in addressing the currently growing provision issues. Typical reactions, which are important to catalyze in this respect, include CO2 reduction, the hydrogen and oxygen evolution reactions as well as the oxygen reduction reaction. The most efficient catalysts known up-to-date for these processes usually contain expensive and scarce elements, substantially impeding implementation of such electrocatalysts at a larger scale. Metal-organic frameworks (MOFs) and their derivatives containing affordable components and building blocks, as an emerging class of porous functional materials, have been recently attracting a great attention thanks to their tunable structure and composition together with high surface area, just to name a few. Up to now, several MOFs and MOF-derivatives have been reported as electrode materials for the energy-related electrocatalytic application. In this review article, we summarize and analyze current approaches to design such materials. The design strategies to improve the Faradaic efficiency and selectivity of these catalysts are discussed. Last but not least, we discuss some novel strategies to enhance the conductivity, chemical stability and efficiency of MOF-derived electrocatalysts.

13.
J Am Chem Soc ; 141(35): 13962-13969, 2019 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-31398974

RESUMO

The generation and matrix stabilization of ligand-free, small platinum nanoclusters (NCs) Pt12±x is presented. The metal-organic framework-template approach is based on encapsulating CO-ligated, atom-precise Pt9 Chini clusters [{Pt3(CO)6}3]2- into the zeolitic imidazolate framework ZIF-8. The selective formation of the air-stable inclusion compound [NBu4]2[{Pt3(CO)6}4]@ZIF-8 of defined atomicity Pt12 and with Pt loadings of 1-20 wt % was monitored by UV/vis and IR spectroscopy and was confirmed by high-resolution transmission electron microscopy (HR-TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (PXRD). Thermally induced decarbonylation at 200 °C yields the composite material Ptn@ZIF-8 with a cluster atomicity n close to 12, irrespective of the Pt loading. The PtNCs retain their size even during annealing at 300 °C for 24 h and during catalytic hydrogenation of 1-hexene at 25 °C in the liquid phase. The Ptn@ZIF-8 material can conveniently be used for storing small PtNCs and their further processing. Removal of the protective ZIF-8 matrix under acidic conditions and transfer of the PtNCs to carbon substrates yields defined aggregation to small Pt nanoparticles (1.14 ± 0.35 nm, HR-TEM), which have previously shown exceptional performance in the electrocatalytic oxygen reduction reaction (ORR).

14.
Inorg Chem ; 58(16): 10837-10845, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31386356

RESUMO

Metal-organic framework nanosheets (MONs) are attracting increasing attention as a diverse class of two-dimensional materials derived from metal-organic frameworks (MOFs). The principles behind the design of layered MOFs that can readily be exfoliated to form nanosheets, however, remain poorly understood. Here we systematically investigate an isoreticular series of layered MOFs functionalized with alkoxy substituents in order to understand the effect of substituent alkyl chain length on the structure and properties of the resulting nanosheets. A series of 2,5-alkoxybenzene-1,4-dicarboxylate ligands (O2CC6H2(OR)2CO2, R = methyl-pentyl, 1-5, respectively) was used to synthesize copper paddle-wheel MOFs. Rietveld and Pawley fitting of powder diffraction patterns for compounds Cu(3-5)(DMF) showed they adopt an isoreticular series with two-dimensional connectivity in which the interlayer distance increases from 8.68 Å (R = propyl) to 10.03 Å (R = pentyl). Adsorption of CO2 by the MOFs was found to increase from 27.2 to 40.2 cm3 g-1 with increasing chain length, which we attribute to the increasing accessible volume associated with increasing unit-cell volume. Ultrasound was used to exfoliate the layered MOFs to form MONs, with shorter alkyl chains resulting in higher concentrations of exfoliated material in suspension. The average height of MONs was investigated by AFM and found to decrease from 35 ± 26 to 20 ± 12 nm with increasing chain length, with the thinnest MONs observed being only 5 nm, corresponding to five framework layers. These results indicate that careful choice of ligand functionalities can be used to tune nanosheet structure and properties, enabling optimization for a variety of applications.

15.
Dalton Trans ; 48(31): 11743-11748, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31298254

RESUMO

A prospective connection between Hume-Rothery inspired TM/E (TM = transition metal; E = Al, Ga, Zn) complexes and clusters with the related solid-state intermetallic TM/E compounds is presented with respect to the industrially relevant catalytic semihydrogenation of acetylene. The theoretical study dealing with [Ni(ER)n(C2Hx)4-n] (x = 2, 4; R = CH3, C5Me5,) calculated on the DFT level of theory shows intriguing structural and electronic properties of the examined complexes. Different Ni-E complexes show preferred binding of C2H2 over C2H4 in bridging positions between Ni and E depending on the [Ni(ER)n] fragment. These findings render molecular TM/E systems, such as Ni/Zn, promising candidates to mimic key intermediates of intermetallic catalysts applied in heterogeneous hydrogenation reactions. We put these findings into the context of existing synthetic results and illustrate different experimental approaches to obtain compounds of the general formula [TMaEb](Cp*)c(UHC)d (UHC = unsaturated hydrocarbon ligands) as potential surface models.

16.
J Am Chem Soc ; 141(29): 11594-11602, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31298851

RESUMO

Coordination polymers show great potential for the tailored design of advanced photonic applications by employing crystal chemistry concepts. One challenge for achieving a rational design of nonlinear optically active MOF materials is deriving fundamental structure-property relations of the interplay between the photonic properties and the spatial arrangements of optically active chromophores within the network. We here investigate two-photon-absorption (TPA)-induced photoluminescence of two new MOFs based on a donor-acceptor tetraphenylphenylenediamine (tPPD) chromophore linker (H4TPBD) and Zn(II) and Cd(II) as metal centers. The TPA efficiencies are controlled by the network topologies, degree of interpenetration, packing densities, and the specific spatial arrangement of the chromophores. The effects can be rationalized within the framework of established excited-state theories of molecular crystals. The results presented here demonstrate the key effect of chromophore orientation on the nonlinear optical properties of crystalline network compounds and allow for establishing quantitative design principles for efficient TPA materials.

17.
Adv Mater ; 31(32): e1900820, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31155761

RESUMO

Metal-organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best-performing MOFs make them moisture-sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be overcome by developing stable hydrophobic MOFs whose chemical composition is tuned to ensure that their metal-ligand bonds persist even in the presence of moisture and water. However, the design and fabrication of such hydrophobic MOFs pose a significant challenge. Reported syntheses of hydrophobic MOFs are critically summarized, highlighting issues relating to their design, characterization, and practical use. First, wetting of hydrophobic materials is introduced and the four main strategies for synthesizing hydrophobic MOFs are discussed. Afterward, critical challenges in quantifying the wettability of these hydrophobic porous surfaces and solutions to these challenges are discussed. Finally, the reported uses of hydrophobic MOFs in practical applications such as hydrocarbon storage/separation and their use in separating oil spills from water are summarized. Finally, the state of the art is summarized and promising future developments of hydrophobic MOFs are highlighted.

18.
J Am Chem Soc ; 141(26): 10504-10509, 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31184478

RESUMO

The modular building principle of metal-organic frameworks (MOFs) presents an excellent platform to explore and establish structure-property relations that tie microscopic to macroscopic properties. Negative thermal expansion (NTE) is a common phenomenon in MOFs and is often ascribed to collective motions that can move through the structure at sufficiently low energies. Here, we show that the introduction of additional linkages in a parent framework, retrofitting, is an effective approach to access lattice dynamics experimentally, in turn providing researchers with a tool to alter the NTE behavior in MOFs. By introducing TCNQ (7,7,8,8-tetracyanoquinodimethane) into the prototypical MOF Cu3BTC2 (BTC = 1,3,5-benzenetricarboxylate; HKUST-1), NTE can be tuned between αV = -15.3 × 10-6 K-1 (Cu3BTC2) and αV = -8.4 × 10-6 K-1 (1.0TCNQ@Cu3BTC2). We ascribe this phenomenon to a general stiffening of the framework as a function of TCNQ loading due to additional network connectivity, which is confirmed by computational modeling and far-infrared spectroscopy. Our findings imply that retrofitting is generally applicable to MOFs with open metal sites, opening yet another way to fine-tune properties in this versatile class of materials.

19.
Dalton Trans ; 48(32): 12031-12039, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31237287

RESUMO

This work presents the first full series of mixed precious-group metal-organic frameworks (MPG-MOFs) using ruthenium and rhodium. The obtained crystalline, highly porous and thermally robust materials were characterized by means of powder X-ray diffraction, N2/CO2 sorption isotherms, thermogravimetry, spectroscopy methods (IR, Raman, UV/VIS-, NMR and XPS) and as well by high resolution transmission electron microscopy (HR-TEM) with elemental mapping (HAADF-EDS). Additionally, the assignment of spectroscopic data is supported by computational (time dependent)-density functional theory methods. The materials turned out to consist of homogeneously dispersed Ru2 and Rh2 paddlewheel units being linked by benzenetricarboxylate (BTC) to yield a framework that is isoreticular to [Cu3(BTC)2] (HKUST-1, Hong Kong University of Science and Technology). However, acetate (OAc) is incorporated as an intrinsic component which compensates for missing BTC-linker defects and some Cl is coordinated to the Ru centre at an apical position. The exact empirical formula of the MPG-MOFs is derived as [RuxRh3-x(BTC)2-a(OAc)b(Cl)c].

20.
Angew Chem Int Ed Engl ; 58(28): 9596-9600, 2019 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-31050857

RESUMO

High oxygen reduction (ORR) activity has been for many years considered as the key to many energy applications. Herein, by combining theory and experiment we prepare Pt nanoparticles with optimal size for the efficient ORR in proton-exchange-membrane fuel cells. Optimal nanoparticle sizes are predicted near 1, 2, and 3 nm by computational screening. To corroborate our computational results, we have addressed the challenge of approximately 1 nm sized Pt nanoparticle synthesis with a metal-organic framework (MOF) template approach. The electrocatalyst was characterized by HR-TEM, XPS, and its ORR activity was measured using a rotating disk electrode setup. The observed mass activities (0.87±0.14 A mgPt -1 ) are close to the computational prediction (0.99 A mgPt -1 ). We report the highest to date mass activity among pure Pt catalysts for the ORR within similar size range. The specific and mass activities are twice as high as the Tanaka commercial Pt/C catalysis.

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