Showing papers on "Catalysis published in 2013"
TL;DR: Structural characterization and electrochemical studies confirmed that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics and low-loss electrical transport and possess a proliferated density of catalytic active sites, which make these metallic nanOSheets a highly competitive earth-abundant HER catalyst.
Abstract: Promising catalytic activity from molybdenum disulfide (MoS2) in the hydrogen evolution reaction (HER) is attributed to active sites located along the edges of its two-dimensional layered crystal structure, but its performance is currently limited by the density and reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst. Here we report dramatically enhanced HER catalysis (an electrocatalytic current density of 10 mA/cm2 at a low overpotential of −187 mV vs RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochemical studies confirmed that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics and low-loss electrical transport and possess a proliferated density of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make ...
2,899 citations
TL;DR: The catalytically active Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.
Abstract: Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.
2,441 citations
TL;DR: The synthesis of ultrathin nickel-iron layered double hydroxide nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs) induced the formation of NiFe-LDH, which exhibits higher electrocatalytic activity and stability for oxygen evolution than commercial precious metal Ir catalysts.
Abstract: Highly active, durable, and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions, including water-splitting and rechargeable metal–air batteries. Here, we report the synthesis of ultrathin nickel–iron layered double hydroxide (NiFe-LDH) nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs). Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-LDH. The crystalline NiFe-LDH phase in nanoplate form is found to be highly active for oxygen evolution reaction in alkaline solutions. For NiFe-LDH grown on a network of CNTs, the resulting NiFe-LDH/CNT complex exhibits higher electrocatalytic activity and stability for oxygen evolution than commercial precious metal Ir catalysts.
2,320 citations
TL;DR: Analyses indicate that the enhanced electrocatalytic activity of WS₂ is associated with the high concentration of the strained metallic 1T (octahedral) phase in the as-exfoliated nanosheets.
Abstract: Efficient evolution of hydrogen via electrocatalysis at low overpotentials is promising for clean energy production. Monolayered nanosheets of chemically exfoliated WS2 are shown to be efficient catalysts for hydrogen evolution at very low overpotentials. The enhanced catalytic performance is associated with the high concentration of the strained metallic octahedral phase in the exfoliated nanosheets.
2,249 citations
TL;DR: This work demonstrates the successfully synergistic regulations of both structural and electronic benefits by controllable disorder engineering and simultaneous oxygen incorporation in MoS2 catalysts, leading to the dramatically enhanced HER activity.
Abstract: Molybdenum disulfide (MoS2) has emerged as a promising electrocatalyst for catalyzing protons to hydrogen via the so-called hydrogen evolution reaction (HER). In order to enhance the HER activity, tremendous effort has been made to engineer MoS2 catalysts with either more active sites or higher conductivity. However, at present, synergistically structural and electronic modulations for HER still remain challenging. In this work, we demonstrate the successfully synergistic regulations of both structural and electronic benefits by controllable disorder engineering and simultaneous oxygen incorporation in MoS2 catalysts, leading to the dramatically enhanced HER activity. The disordered structure can offer abundant unsaturated sulfur atoms as active sites for HER, while the oxygen incorporation can effectively regulate the electronic structure and further improve the intrinsic conductivity. By means of controllable disorder engineering and oxygen incorporation, an optimized catalyst with a moderate degree of ...
2,001 citations
TL;DR: This communication presents a synthesis process to grow MoS2 and MoSe2 thin films with vertically aligned layers, thereby maximally exposing the edges on the film surface, and confirmed their catalytic activity in a hydrogen evolution reaction (HER), in which the exchange current density correlates directly with the density of the exposed edge sites.
Abstract: Layered materials consist of molecular layers stacked together by weak interlayer interactions. They often crystallize to form atomically smooth thin films, nanotubes, and platelet or fullerene-like nanoparticles due to the anisotropic bonding. Structures that predominately expose edges of the layers exhibit high surface energy and are often considered unstable. In this communication, we present a synthesis process to grow MoS2 and MoSe2 thin films with vertically aligned layers, thereby maximally exposing the edges on the film surface. Such edge-terminated films are metastable structures of MoS2 and MoSe2, which may find applications in diverse catalytic reactions. We have confirmed their catalytic activity in a hydrogen evolution reaction (HER), in which the exchange current density correlates directly with the density of the exposed edge sites.
1,976 citations
TL;DR: By partially oxidizingMoS2, it is found that the activity of 2H MoS2 is significantly reduced after oxidation, consistent with edge oxidation, and 1T MoS 2 remains unaffected after oxidization, suggesting that edges of the nanosheets are not the main active sites.
Abstract: We report chemically exfoliated MoS2 nanosheets with a very high concentration of metallic 1T phase using a solvent free intercalation method. After removing the excess of negative charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of hydrogen with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, we found that the activity of 2H MoS2 is significantly reduced after oxidation, consistent with edge oxidation. On the other hand, 1T MoS2 remains unaffected after oxidation, suggesting that edges of the nanosheets are not the main active sites. The importance of electrical conductivity of the two phases on the hydrogen evolution reaction activity has been further confirmed by using carbon nanotubes to increase the conductivity of 2H MoS2.
1,856 citations
TL;DR: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-Electron processes, which feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.
Abstract: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.
Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3
However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.
Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.
A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.
1,326 citations
TL;DR: It is demonstrated that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis, which contain a homogeneous distribution of metals with compositions that can be accurately controlled.
Abstract: Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe100-y-zCoyNizOx are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.
1,258 citations
TL;DR: The versatility of the perovskite structure is exploited to search for oxide catalysts that are both active and stable and can be explained by having the O p-band centre neither too close nor too far from the Fermi level, which is computed from ab initio studies.
Abstract: The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln₀.₅Ba₀.₅)CoO(₃-δ) (Ln=Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidation in alkaline solution. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O(₃-δ) which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band centre neither too close nor too far from the Fermi level, which is computed from ab initio studies.
1,150 citations
TL;DR: Chainmail for catalysts: a catalyst with iron nanoparticles confined inside pea-pod-like carbon nanotubes exhibits a high activity and remarkable stability as a cathode catalyst in polymer electrolyte membrane fuel cells (PEMFC), even in presence of SO(2).
Abstract: Chainmail for catalysts: a catalyst with iron nanoparticles confined inside pea-pod-like carbon nanotubes exhibits a high activity and remarkable stability as a cathode catalyst in polymer electrolyte membrane fuel cells (PEMFC), even in presence of SO(2). The approach offers a new route to electro- and heterogeneous catalysts for harsh conditions.
TL;DR: This poster presents a probabilistic procedure to evaluate the response of the H2O/O2 mixture to various pyrolysis conditions and shows promising results in both the horizontal and the vertical domain.
Abstract: Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy
TL;DR: Acceptorless dehydrogenation and related dehydrogenative coupling reactions have the potential for redirecting synthetic strategies to the use of sustainable resources, devoid of toxic reagents and deleterious side reactions, with no waste generation.
Abstract: Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.
TL;DR: The unprecedented performance of these NPM catalysts in ORR was attributed to their well-defined porous structures with a narrow mesopore size distribution, high Brunauer-Emmett-Teller surface area, and homogeneous distribution of abundant metal-Nx active sites.
Abstract: A family of mesoporous nonprecious metal (NPM) catalysts for oxygen reduction reaction (ORR) in acidic media, including cobalt–nitrogen-doped carbon (C–N–Co) and iron–nitrogen-doped carbon (C–N–Fe), was prepared from vitamin B12 (VB12) and the polyaniline-Fe (PANI-Fe) complex, respectively. Silica nanoparticles, ordered mesoporous silica SBA-15, and montmorillonite were used as templates for achieving mesoporous structures. The most active mesoporous catalyst was fabricated from VB12 and silica nanoparticles and exhibited a remarkable ORR activity in acidic medium (half-wave potential of 0.79 V, only ∼58 mV deviation from Pt/C), high selectivity (electron-transfer number >3.95), and excellent electrochemical stability (only 9 mV negative shift of half-wave potential after 10 000 potential cycles). The unprecedented performance of these NPM catalysts in ORR was attributed to their well-defined porous structures with a narrow mesopore size distribution, high Brunauer–Emmett–Teller surface area (up to 572 m2...
TL;DR: Rate measurements are reported on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals, and it is found that carbon monoxide oxidation inceria-based catalysts is greatly enhanced at the cia- metal interface sites for a range of group VIII metal catalysts.
Abstract: Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support
TL;DR: Li et al. as mentioned in this paper constructed stable zinc-air batteries using novel catalysts for oxygen reduction and evolution reactions, but their realization is hampered by the lack of efficient and robust air catalysts.
Abstract: Metal-air batteries are promising for energy storage because of their high theoretical energy density, but their realization is hampered by the lack of efficient and robust air catalysts. Li et al. construct stable zinc-air batteries using novel catalysts for oxygen reduction and evolution reactions.
TL;DR: Graphene was doped with both boron and nitrogen at well-defined doping sites to induce a synergistic effect that boosts its catalytic activity for oxygen reduction.
Abstract: Don't be a dope: be a double dope! Graphene was doped with both boron and nitrogen at well-defined doping sites to induce a synergistic effect that boosts its catalytic activity for oxygen reduction (see structure). The excellent catalytic performance of the new metal-free catalyst is comparable to that of commercial Pt/C.
TL;DR: This Account discusses how to obtain highly promising M-N-C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800-1000 °C and controls the formation of different nanostructures during the synthesis of M-n-C catalysts.
Abstract: Platinum-based catalysts represent a state of the art in the electrocatalysis of oxygen reduction reaction (ORR) from the point of view of their activity and durability in harnessing the chemical energy via direct electrochemical conversion. However, because platinum is both expensive and scarce, its widespread implementation in such clean energy applications is limited. Recent breakthroughs in the synthesis of high-performance nonprecious metal catalysts (NPMCs) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this Account, we discuss how we can obtain highly promising M–N–C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800–1000 °C. The activity and durability of resulting catalysts depend greatly on the selection of precursors and synthesis chemistry. In addition, they correlate quite well with the catalyst nanostructure. While chemists have presented n...
TL;DR: A group of first-row transition metal dichalcogenides (ME2, M = Fe, Co, Ni; E = S, Se) were introduced as non-precious HER catalysts in an acidic electrolyte.
Abstract: A group of first-row transition metal dichalcogenides (ME2, M = Fe, Co, Ni; E = S, Se) are introduced as non-precious HER catalysts in an acidic electrolyte. They exhibit excellent catalytic activity especially in their nanoparticle form. These compounds expand and enrich the family of high performance HER catalysts.
TL;DR: The reported new syntheses with NP parameter-tuning capability should pave the way for future development of highly efficient catalysts for applications in fuel cells, metal-air batteries, and even in other important chemical reactions.
Abstract: Advances in chemical syntheses have led to the formation of various kinds of nanoparticles (NPs) with more rational control of size, shape, composition, structure and catalysis. This review highlights recent efforts in the development of Pt and non-Pt based NPs into advanced nanocatalysts for efficient oxygen reduction reaction (ORR) under fuel-cell reaction conditions. It first outlines the shape controlled synthesis of Pt NPs and their shape-dependent ORR. Then it summarizes the studies of alloy and core-shell NPs with controlled electronic (alloying) and strain (geometric) effects for tuning ORR catalysis. It further provides a brief overview of ORR catalytic enhancement with Pt-based NPs supported on graphene and coated with an ionic liquid. The review finally introduces some non-Pt NPs as a new generation of catalysts for ORR. The reported new syntheses with NP parameter-tuning capability should pave the way for future development of highly efficient catalysts for applications in fuel cells, metal-air batteries, and even in other important chemical reactions.
TL;DR: The continuously tuned electronic structure of lithiated MoS2 is correlated with the corresponding enhanced hydrogen evolution reaction activity, and thus the electronic structure–catalytic activity relationship is constructed.
Abstract: The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li+ ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity.
TL;DR: It is demonstrated that the HOR can be enhanced more than fivefold compared to state-of-the-art platinum catalysts, and it is proposed that the more oxophilic sites on Ir and PtRu material electrodes facilitate the adsorption of OHad species.
Abstract: The development of hydrogen-based energy sources as viable alternatives to fossil-fuel technologies has revolutionized clean energy production using fuel cells However, to date, the slow rate of the hydrogen oxidation reaction (HOR) in alkaline environments has hindered advances in alkaline fuel cell systems Here, we address this by studying the trends in the activity of the HOR in alkaline environments We demonstrate that it can be enhanced more than fivefold compared to state-of-the-art platinum catalysts The maximum activity is found for materials (Ir and Pt₀₁Ru₀₉) with an optimal balance between the active sites that are required for the adsorption/dissociation of H₂ and for the adsorption of hydroxyl species (OHad) We propose that the more oxophilic sites on Ir (defects) and PtRu material (Ru atoms) electrodes facilitate the adsorption of OHad species Those then react with the hydrogen intermediates (Had) that are adsorbed on more noble surface sites
TL;DR: A broad range of aryl electrophiles, which are conventionally challenging, by applying palladium catalysts can now be coupled efficiently with boron reagents in the presence of nickel catalysts.
Abstract: In the transition-metal-catalyzed cross-coupling reactions, the use of the first row transition metals as catalysts is much more appealing than the precious metals owing to the apparent advantages such as cheapness and earth abundance. Within the last two decades, particularly the last five years, explosive interests have been focused on the nickel-catalyzed Suzuki–Miyaura reactions. This has greatly advanced the chemistry of transition-metal-catalyzed cross-coupling reactions. Most notably, a broad range of aryl electrophiles such as phenols, aryl ethers, esters, carbonates, carbamates, sulfamates, phosphates, phosphoramides, phosphonium salts, and fluorides, as well as various alkyl electrophiles, which are conventionally challenging, by applying palladium catalysts can now be coupled efficiently with boron reagents in the presence of nickel catalysts. In this review, we would like to summarize the progress in this reaction.
TL;DR: Recent progress in the design and synthetic strategies for ORR catalysts including controlling the shape and size of Pt and its bimetallic alloys, and controlling the surface composition and structure of core-shell, monolayer, and hollow porous structures are reviewed.
Abstract: An efficient oxygen reduction reaction (ORR) offers the potential for clean energy generation in low-temperature, proton-exchange membrane fuel cells running on hydrogen fuel and air. In the past several years, researchers have developed high-performance electrocatalysts for the ORR to address the obstacles of high cost of the Pt catalyst per kilowatt of output power and of declining catalyst activity over time. Current efforts are focused on new catalyst structures that add a secondary metal to change the d-band center and the surface atomic arrangement of the catalyst, altering the chemisorption of those oxygencontaining species that have the largest impact on the ORR kinetics and improving the catalyst activity and cost effectiveness.This Account reviews recent progress in the design of Pt-based ORR electrocatalysts, including improved understanding of the reaction mechanisms and the development of synthetic methods for producing catalysts with high activity and stability. Researchers have made several...
TL;DR: In this article, molybdenum carbide (β-Mo2C) nanoparticles are prepared by in situ carburization of ammonium molydate on carbon nanotubes and XC-72R carbon black without using any gaseous carbon source.
Abstract: In an attempt to tailor low-cost, precious-metal-free electrocatalysts for water electrolysis in acid, molybdenum carbide (β-Mo2C) nanoparticles are prepared by in situ carburization of ammonium molybdate on carbon nanotubes and XC-72R carbon black without using any gaseous carbon source. The formation of Mo2C is investigated by thermogravimetry and in situ X-ray diffraction. X-ray absorption analysis reveals that Mo2C nanoparticles are inlaid or anchored into the carbon supports, and the electronic modification makes the surface exhibit a relatively moderate Mo–H bond strength. It is found that carbon nanotube-supported Mo2C showed superior electrocatalytic activity and stability in the hydrogen evolution reaction (HER) compared to the bulk Mo2C. An overpotential of 63 mV for driving 1 mA cm−2 of current density was measured for the nanotube-supported Mo2C catalysts; this exceeds the activity of analogous Mo2C catalysts. The enhanced electrochemical activity is facilitated by unique effects of the anchored structure coupled with the electronic modification.
TL;DR: Atomically precise Aun(SR)m nanoclusters are expected to become a promising class of model catalysts that will provide new opportunities for achieving fundamental understanding of metal nanocatalysis, such as insight into size dependence and deep understanding of molecular activation, active centers, and catalytic mechanisms through correlation of behavior with the structures of nanocluster structures.
Abstract: Many industrial catalysts involve nanoscale metal particles (typically 1–100 nm), and understanding their behavior at the molecular level is a major goal in heterogeneous catalyst research. However, conventional nanocatalysts have a nonuniform particle size distribution, while catalytic activity of nanoparticles is size dependent. This makes it difficult to relate the observed catalytic performance, which represents the average of all particle sizes, to the structure and intrinsic properties of individual catalyst particles. To overcome this obstacle, catalysts with well-defined particle size are highly desirable.In recent years, researchers have made remarkable advances in solution-phase synthesis of atomically precise nanoclusters, notably thiolate-protected gold nanoclusters. Such nanoclusters are composed of a precise number of metal atoms (n) and of ligands (m), denoted as Aun(SR)m, with n ranging up to a few hundred atoms (equivalent size up to 2–3 nm). These protected nanoclusters are well-defined ...
TL;DR: A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density.
Abstract: A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density of 10 mA cm–2 at −0.20 V vs RHE at low catalyst loadings of 0.24 mg/cm2 in rotating disk experiments under a H2 atmosphere. Neutron powder diffraction and pair distribution function (PDF) studies have been used to overcome the insensitivity of X-ray diffraction data to different transition-metal nitride structural polytypes and show that this cobalt molybdenum nitride crystallizes in space group P63/mmc with lattice parameters of a = 2.85176(2) A and c = 10.9862(3) A and a formula of Co0.6Mo1.4N2. This space group results from the four-layered stacking sequence of a mixed close-packed structure with alternating layers of transition metals in octahedral and trigonal prismatic coordination and is a structure type for which HER activ...
TL;DR: A composite made from the assembly of graphene oxide (GO) and copper-centered metal organic framework (MOF) shows good performance as a tri-functional catalyst in three important electrocatalysis reactions, namely: the hydrogen evolution reaction (HER), oxygen evolution reaction, and oxygen reduction reaction (ORR) as discussed by the authors.
Abstract: A composite made from the assembly of graphene oxide (GO) and copper-centered metal organic framework (MOF) shows good performance as a tri-functional catalyst in three important electrocatalysis reactions, namely: the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). One of the challenges in the area of electrocatalysis is to find an effective catalyst that will reduce, as well as generate, oxygen at moderate temperatures. The enhanced electrocatalytic properties and stability in acid of the GO-MOF composite is due to the unqiue porous scaffold structure, improved charge transport and synergistic interactions between the GO and MOF. In polymer electrolyte membrane fuel cell testing, the GO-incorporated Cu-MOF composite delivers a power density that is 76% that of the commercial Pt catalyst.
TL;DR: The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach, resulting in a more open framework with a large number of open sites and is a highly active catalyst for several Lewis acid catalyzed reactions.
Abstract: The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions.