Showing papers on "Noble metal published in 2014"
TL;DR: Dry (CO2) reforming of methane literature for catalysts based on Rh, Ru, Pt, and Pd metals is reviewed, including the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
Abstract: Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
1,472 citations
TL;DR: This work reports the synthesis and assessment of a new non-precious-metal oxygen reduction reaction (ORR) catalyst from pyrolysis of an iron-coordinated complex which manifests superior activity in both alkaline and acidic media and proposes that the optimal Fe-N/C-800 catalyst displays much greater durability and tolerance of methanol than Pt/C.
Abstract: In this work, we report the synthesis and assessment of a new non-precious-metal oxygen reduction reaction (ORR) catalyst from pyrolysis of an iron-coordinated complex which manifests superior activity in both alkaline and acidic media. 11,11′-bis(dipyrido[3,2-a:2′,3′-c]phenazinyl) (bidppz) was selected as a ligand for the formation of a nitrogen-rich iron-coordinated coordination polymer (Fe–bidppz) which forms a self-supporting catalyst containing high densities of nitrogen and iron doping by pyrolysis. The catalyst pyrolyzed at 800 °C (Fe–N/C-800) shows the highest ORR activity with onset and half-wave potentials of 923 and 809 mV in 0.1 M KOH, respectively, which are comparable to those of Pt/C (half-wave potential 818 mV vs RHE) at the same catalyst loading. Besides, the Fe–N/C-800 catalyst has an excellent ORR activity with onset and half-wave potentials only 38 and 59 mV less than those of the Pt/C catalyst in 0.1 M HClO4. The optimal Fe–N/C-800 catalyst displays much greater durability and toleran...
888 citations
TL;DR: In this paper, reduced graphene oxide (RGO)-CdS nanorod composites were successfully prepared by a one-step microwave-hydrothermal method in an ethanolamine-water solution.
Abstract: Solar-fuel production has attracted considerable attention because of the current demand to find alternative transportation fuels with particular emphasis on those fuels obtained photocatalytically from water and CO2. In this work, reduced graphene oxide (RGO)–CdS nanorod composites were successfully prepared by a one-step microwave-hydrothermal method in an ethanolamine–water solution. These composite samples exhibited a high activity for the photocatalytic reduction of CO2 to CH4, even without a noble metal Pt co-catalyst. The optimized RGO–CdS nanorod composite photocatalyst exhibited a high CH4-production rate of 2.51 μmol h−1 g−1 at an RGO content of 0.5 wt%. This rate exceeded that observed for the pure CdS nanorods by more than 10 times and was better than that observed for an optimized Pt–CdS nanorod composite photocatalyst under the same reaction conditions. This high photocatalytic activity was ascribed to the deposition of CdS nanorods onto the RGO sheets, which act as an electron acceptor and transporter, thus efficiently separating the photogenerated charge carriers. Furthermore, the introduction of RGO can enhance the adsorption and activation of CO2 molecules, which speeds up the photocatalytic reduction of CO2 to CH4. The proposed mechanism for the observed photocatalytic reaction with the RGO–CdS nanorod composite was further confirmed using transient photocurrent response and electrochemical impedance spectra. This work not only demonstrates a facile microwave-assisted hydrothermal method for fabricating highly active RGO–CdS nanorod composite photocatalysts, but also demonstrates the possibility of utilizing of an inexpensive carbon material as a substitute for noble metals in the photocatalytic reduction of CO2.
472 citations
TL;DR: In this article, an overview of the application of Ir and Ir-containing catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane water electrolyzer anodes, for both OER and ORR in unit regenerative fuel cell oxygen electrodes is presented.
Abstract: Among noble metal electrocatalysts, only iridium presents high activity for both the oxygen reduction reaction (ORR) in acid medium, in the oxide form, and the oxygen evolution reaction (OER) in acid medium, alloyed with first row transition metals. Indeed, platinum, the best catalyst for the ORR, has poor activity for the OER in any form, and ruthenium, the best catalyst for the OER, in the oxide form, possess poor activity for the ORR in any form. In this work, an overview of the application of Ir and Ir-containing catalysts for the OER in proton-exchange membrane water electrolyzer anodes, for the ORR in proton exchange membrane fuel cell cathodes, and for both OER and ORR in unit regenerative fuel cell oxygen electrodes is presented.
452 citations
TL;DR: In this article, metal organic frameworks (MOFs) are used as precursors to synthesize ORR catalysts via pyrolysis in an inert atmosphere, and the ORR performance is closely associated with the metal/ligand combination in MOFs.
Abstract: Developing noble metal free catalysts for the oxygen reduction reaction (ORR) is of critical importance for the production of low cost polymer electrolyte membrane fuel cells. In this paper, metal organic frameworks (MOFs) are used as precursors to synthesize ORR catalysts via pyrolysis in an inert atmosphere. The ORR performance is found to be closely associated with the metal/ligand combination in MOFs. The Co-imidazole based MOF (ZIF-67) derived catalyst exhibits the best ORR activity in both alkaline and acidic electrolytes. The Co cations coordinated by the aromatic nitrogen ligands in ZIF-67 may assist the formation of ORR active sites in the derived catalyst. The best ORR performance is obtained when the porosity of the derived catalyst is maximized, by optimizing the pyrolysis temperature and the acid leaching process. The performance of the best MOF derived catalyst is comparable to that of Pt/C in both alkaline and acidic electrolytes.
377 citations
TL;DR: The strategy of using functionalized cavities of MOFs as hosts for different metal NPs looks promising for the development of high-performance heterogeneous catalysts.
Abstract: The encapsulation of noble-metal nanoparticles (NPs) in metal-organic frameworks (MOFs) with carboxylic acid ligands, the most extensive branch of the MOF family, gives NP/MOF composites that exhibit excellent shape-selective catalytic performance in olefin hydrogenation, aqueous reaction in the reduction of 4-nitrophenol, and faster molecular diffusion in CO oxidation. The strategy of using functionalized cavities of MOFs as hosts for different metal NPs looks promising for the development of high-performance heterogeneous catalysts.
369 citations
TL;DR: The results suggest that chemically exfoliated 1T-MoS2/Si heterostructures are promising earth-abundant alternatives to photocathodes based on noble metal catalysts for solar-driven hydrogen production.
Abstract: We report the preparation and characterization of highly efficient and robust photocathodes based on heterostructures of chemically exfoliated metallic 1T-MoS2 and planar p-type Si for solar-driven hydrogen production. Photocurrents up to 17.6 mA/cm(2) at 0 V vs reversible hydrogen electrode were achieved under simulated 1 sun irradiation, and excellent stability was demonstrated over long-term operation. Electrochemical impedance spectroscopy revealed low charge-transfer resistances at the semiconductor/catalyst and catalyst/electrolyte interfaces, and surface photoresponse measurements also demonstrated slow carrier recombination dynamics and consequently efficient charge carrier separation, providing further evidence for the superior performance. Our results suggest that chemically exfoliated 1T-MoS2/Si heterostructures are promising earth-abundant alternatives to photocathodes based on noble metal catalysts for solar-driven hydrogen production.
367 citations
TL;DR: Using DFT calculations, a specific structural element is identified, a ceria "nanopocket", which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion and is therefore identified as an anchoring site for Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis.
Abstract: Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria "nanopocket", which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.
354 citations
TL;DR: The hierarchical nanostructured 1D-spinel NiCo2O4 materials showed a remarkable electrocatalytic activity towards oxygen reduction and evolution in an aqueous alkaline medium, making them promising cathode materials for metal-air batteries.
Abstract: A nickel-doped cobalt oxide spinel structure is a promising non-precious metal electrocatalyst for oxygen evolution and oxygen reduction in rechargeable metal–air batteries and water electrolyzers operating with alkaline electrolytes. One dimensional NiCo2O4 (NCO) nanostructures were prepared by using a simple electrospinning technique with two different metal precursors (metal nitrate/PAN and metal acetylacetonate/PAN). The effect of precursor concentration on the morphologies was investigated. Single-phase, NCO with an average diameter of 100 nm, porous interconnected fibrous morphology was revealed by FESEM and FETEM analysis. The hierarchical nanostructured 1D-spinel NiCo2O4 materials showed a remarkable electrocatalytic activity towards oxygen reduction and evolution in an aqueous alkaline medium. The extraordinary bi-functional catalytic activity towards both ORR and OER was observed by the low over potential (0.84 V), which is better than that of noble metal catalysts [Pt/C (1.16 V), Ru/C (1.01 V) and Ir/C (0.92 V)], making them promising cathode materials for metal–air batteries. Furthermore, the rechargeable zinc–air battery with NCO-A1 as a bifunctional electrocatalyst displays high activity and stability during battery discharge, charge, and cycling processes.
347 citations
TL;DR: In this paper, the role of halide ions in shape control of anisotropic metal nanocrystals has been investigated, including modulating the redox potentials of the metal ions, acting as face-specific capping agents, and controlling the extent of silver underpotential depositi...
Abstract: Anisotropic (nonspherical) metal nanoparticles are of widespread research interest because changing the shape of metals at the nanoscale can provide access to materials with unique optical, electronic, and catalytic properties. The development of seeded growth syntheses has provided researchers unprecedented access to anisotropic metal nanocrystals (particularly, gold, silver, platinum, and palladium nanocrystals) with precisely controlled dimensions and crystallographic features. The mechanisms by which the various reagents present in seeded growth syntheses accomplish shape control, however, have yet to be fully elucidated. Recently, the role halide ions play in controlling metal nanocrystal shape has become a subject of particular interest. There are many ways in which the halide ions may direct the anisotropic growth of metal nanocrystals, including modulating the redox potentials of the metal ions, acting as face-specific capping agents, and/or controlling the extent of silver underpotential depositi...
340 citations
TL;DR: This review article summarizes the state-of-the art progress in synthesis and catalytic application of noble metal nanoparticle@metal oxide core/yolk-shell nanostructures and hopes that this review will help the readers to obtain better insight into the design and application of well-defined nanocomposites in both the energy and environmental fields.
Abstract: Controllable integration of noble metals (e.g., Au, Ag, Pt, and Pd) and metal oxides (e.g., TiO2, CeO2, and ZrO2) into single nanostructures has attracted immense research interest in heterogeneous catalysis, because they not only combine the properties of both noble metals and metal oxides, but also bring unique collective and synergetic functions in comparison with single-component materials. Among many strategies recently developed, one of the most efficient ways is to encapsulate and protect individual noble metal nanoparticles by a metal oxide shell of a certain thickness to generate the core–shell or yolk–shell structure, which exhibits enhanced catalytic performance compared with conventional supported catalysts. In this review article, we summarize the state-of-the art progress in synthesis and catalytic application of noble metal nanoparticle@metal oxide core/yolk–shell nanostructures. We hope that this review will help the readers to obtain better insight into the design and application of well-defined nanocomposites in both the energy and environmental fields.
TL;DR: In this article, the preparation of single-layer TiS2 and TaS2 nanosheets is realized by optimizing the electrochemical lithium interaction and exfoliation method.
Abstract: The preparation of single-layer TiS2 and TaS2 nanosheets is realized by optimizing the electrochemical lithium interaction and exfoliation method. As a proof of concept, Pt and Au nanoparticles are grown on the aforementioned ultra-thin nanosheets to form functional composites. Notably, the Pt–TiS2 hybrid presents good electrocatalytic activity in the hydrogen evolution reaction.
TL;DR: Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).
Abstract: A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM–MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM–MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM–MoS2 NSs a potential electrochemical catalyst. For the first time, Pd–MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd–MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).
TL;DR: The principles and examples of three major classes of conversion chemical reactions are reviewed: the Kirkendall effect for metal NPs, galvanic exchange, and anion exchange, each of which can result in void formation in NPs.
Abstract: Conversion chemistry is a rapidly maturing field, where chemical conversion of template nanoparticles (NPs) into new compositions is often accompanied by morphological changes, such as void formation. The principles and examples of three major classes of conversion chemical reactions are reviewed: the Kirkendall effect for metal NPs, galvanic exchange, and anion exchange, each of which can result in void formation in NPs. These reactions can be used to obtain complex structures that may not be attainable by other methods. During each kind of conversion chemical reaction, NPs undergo distinct chemical and morphological changes, and insights into the mechanisms of these reactions will allow for improved fine control and prediction of the structures of intermediates and products. Conversion of metal NPs into oxides, phosphides, sulphides, and selenides often occurs through the Kirkendall effect, where outward diffusion of metal atoms from the core is faster than inward diffusion of reactive species, resulting in void formation. In galvanic exchange reactions, metal NPs react with noble metal salts, where a redox reaction favours reduction and deposition of the noble metal (alloying) and oxidation and dissolution of the template metal (dealloying). In anion exchange reactions, addition of certain kinds of anions to solutions containing metal compound NPs drives anion exchange, which often results in significant morphological changes due to the large size of anions compared to cations. Conversion chemistry thus allows for the formation of NPs with complex compositions and structures, for which numerous applications are anticipated arising from their novel catalytic, electronic, optical, magnetic, and electrochemical properties.
TL;DR: In this paper, a review of thermal ALD of noble metals and their oxides is presented, where reaction mechanisms in various types of processes are discussed and issues in nucleation are addressed.
Abstract: Atomic layer deposition (ALD) is an attractive method to deposit thin films for advanced technological applications such as microelectronics and nanotechnology. One material group in ALD that has matured in 10 years and proven to be of wide technological importance is noble metals. In this paper, thermal ALD of noble metals and their oxides is reviewed. Noble metal films are mostly grown using O2 as the nonmetal precursor in a combustion-type chemistry. Alternatively, lower growth temperatures can be reached via noble metal oxide growth with consecutive reactions with ozone and H2. The use of true reducing chemistry (i.e., H2) is typical only for ALD of palladium at low temperatures. On the other hand, ALD of noble metal oxides has been limited with reactants such as ozone and O2 gas. In this review, reaction mechanisms in various types of processes are discussed and issues in nucleation are addressed. Deposition temperatures, film growth rates, and purities as well as evaporation temperatures used for no...
TL;DR: In this article, a family of dealloyed metal-oxide hybrid core-shell catalysts is demonstrated to provide substantial advances toward more efficient and less expensive electrolytic water splitting.
Abstract: A family of dealloyed metal–oxide hybrid (M1M2@M1Ox) core@shell nanoparticle catalysts is demonstrated to provide substantial advances toward more efficient and less expensive electrolytic water splitting. IrNi@IrOx nanoparticles were synthesized from IrNix precursor alloys through selective surface Ni dealloying and controlled surface oxidation of Ir. Detailed depth-resolved insight into chemical structure, composition, morphology, and oxidation state was obtained using spectroscopic, diffraction, and scanning microscopic techniques (XANES, XRD, STEM-EDX, XPS), which confirmed our structural hypotheses at the outset. A 3-fold catalytic activity enhancement for the electrochemical oxygen evolution reaction (OER) over IrO2 and RuO2 benchmark catalysts was observed for the core-shell catalysts on a noble metal mass basis. Also, the active site-based intrinsic turnover frequency (TOF) was greatly enhanced for the most active IrNi@IrOx catalyst. This study documents the successful use of synthetic dealloying for the preparation of metal-oxide hybrid core-shell catalysts. The concept is quite general, can be applied to other noble metal nanoparticles, and points out a path forward to nanostructured proton-exchange-electrolyzer electrodes with dramatically reduced noble metal content.
TL;DR: The elucidation of the mechanism on the photocatalysis over M/NH2-MIL-125(Ti) can provide some guidance in the development of new photocatalysts based on MOF materials and demonstrates the potential of using noble metal-doped MOFs in photoc atalytic reactions involving hydrogen as a reactant, like hydrogenation reactions.
Abstract: M-doped NH2-MIL-125(Ti) (M=Pt and Au) were prepared by using the wetness impregnation method followed by a treatment with H2 flow. The resultant samples were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analyses, N2-sorption BET surface area, and UV/Vis diffuse reflectance spectroscopy (DRS). The photocatalytic reaction carried out in saturated CO2 with triethanolamine (TEOA) as sacrificial agent under visible-light irradiations showed that the noble metal-doping on NH2-MIL-125(Ti) promoted the photocatalytic hydrogen evolution. Unlike that over pure NH2-MIL-125(Ti), in which only formate was produced, both hydrogen and formate were formed over Pt- and Au-loaded NH2-MIL-125(Ti). However, Pt and Au have different effects on the photocatalytic performance for formate production. Compared with pure NH2-MIL-125(Ti), Pt/NH2-MIL-125(Ti) showed an enhanced activity for photocatalytic formate formation, whereas Au has a negative effect on this reaction. To elucidate the origin of the different photocatalytic performance, electron spin resonance (ESR) analyses and density functional theory (DFT) calculations were carried out over M/NH2-MIL-125(Ti).The photocatalytic mechanisms over M/NH2-MIL-125(Ti) (M=Pt and Au) were proposed. For the first time, the hydrogen spillover from the noble metal Pt to the framework of NH2-MIL-125(Ti) and its promoting effect on the photocatalytic CO2 reduction is revealed. The elucidation of the mechanism on the photocatalysis over M/NH2-MIL-125(Ti) can provide some guidance in the development of new photocatalysts based on MOF materials. This study also demonstrates the potential of using noble metal-doped MOFs in photocatalytic reactions involving hydrogen as a reactant, like hydrogenation reactions.
TL;DR: In this article, the authors provide an overview of the main catalytic studies of H2 production by ethanol steam reforming (ESR) in terms of selectivity and selectivity to H2.
TL;DR: The X-ray photoelectron spectroscopy investigation revealed a distinctive atomic structure in nitrogen-sulfur codoped material in comparison to other codoped catalysts, most likely explaining its superior electrocatalytic activity.
Abstract: The synthesis and characterization of functionalized carbon using variable doping profiles are presented. The hybrids were obtained from nitrile-functionalized ionic precursors and a ferric chloride mediator. This way, novel nitrogen doped and nitrogen–sulfur, nitrogen–phosphorus, and nitrogen–boron codoped carbon hybrids with a morphology containing microporous nanometer-sized particles were obtained. As-prepared heteroatom doped carbons exhibited superior electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline and acid electrolytes. In particular, both the heteroatom type and iron were found to play crucial roles in improving the catalytic activity of functionalized carbon. It is worth noting that sulfur–nitrogen codoped functionalized materials synthesized in the presence of ferric chloride showed higher activity and stability in comparison to those of the commercial state-of-the-art Pt catalyst in alkaline electrolyte. Moreover, in acid electrolyte, sulfur–nitrogen codoped cat...
TL;DR: In this paper, the magnetic porous carbon (MPC) composite synthesized from metal organic framework (MOF) was used as a catalyst support to fabricate gold and palladium (Pd) nanoparticle (NP) based nanocatalysts.
Abstract: The development of low cost noble metal nanocatalysts with high activity and selectivity, high catalytic performance, convenient separation, and reusability is a significant challenge. Herein, the magnetic porous carbon (MPC) composite synthesized from metal organic framework (MOF) was used as a catalyst support to fabricate gold (Au) and palladium (Pd) nanoparticle (NP) based nanocatalysts. The MPC not only provided a large surface area and mesopores on which the active centers (Au and Pd NPs) were finely dispersed, but also exhibited superparamagnetic behaviour that enabled the magnetic separation and convenient recovery of the nanocatalysts from the reaction mixture. Thus, the nanocatalysts were repeatedly used without loss of catalytic efficiency. Both the Au/MPC and Pd/MPC nanocatalysts showed excellent catalytic activity for the reduction of 4-nitrophenol. Moreover, the Pd/MPC nanocatalyst exhibited higher efficiency toward hydrodechlorination of 4-chlorophenol compared to the other reported catalysts. This study indicated that the noble metal NPs (NMNPs) supported on MOF-derived MPC materials could act as promising catalysts exhibiting potential applications in numerous NMNP based catalytic reactions.
TL;DR: It is conclusively demonstrated that adding Au to MnOx significantly enhances OER activity relative to Mn Ox in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnOx catalysts reported to date.
Abstract: To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnOx, a promising OER catalyst. We conclusively demonstrate that adding Au to MnOx significantly enhances OER activity relative to MnOx in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnOx catalysts reported to date. We also provide evidence that it i...
TL;DR: The facile synthesis of hollow Co3O4 microspheres composed of porous, ultrathin (<5 nm), single-crystal-like nanosheets via a novel "self-template" route is reported, suggesting that delicate nanostructuring can offer unique advantages for developing efficient water oxidation catalysts.
Abstract: Developing noble metal-free water oxidation catalysts is essential for many energy conversion/storage processes (e.g., water splitting). Herein, we report the facile synthesis of hollow Co3O4 microspheres composed of porous, ultrathin (<5 nm), single-crystal-like nanosheets via a novel “self-template” route. The successful preparation of these hollow Co3O4 nanomaterials includes three main steps: (1) the synthesis of solid cobalt alkoxide microspheres, (2) their subsequent self-template conversion into hollow cobalt hydroxide microspheres composed of ultrathin nanosheets, and finally (3) thermal treatment of hollow cobalt hydroxide microspheres into the hollow Co3O4 material. The as-obtained hollow Co3O4 nanomaterial possesses a high BET surface area (∼180 m2 g−1), and can serve as an active and stable water oxidation catalyst under both electrochemical and photochemical reaction conditions, owing to its unique structural features. In the electrochemical water oxidation, this catalyst affords a current density of 10 mA cm−2 (a value related to practical relevance) at an overpotential of ∼0.40 V. Moreover, with the assistance of a sensitizer [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine), this nanomaterial can catalyze water oxidation reactions under visible light irradiation with an O2 evolution rate of ∼12 218 μmol g−1 h−1. Our results suggest that delicate nanostructuring can offer unique advantages for developing efficient water oxidation catalysts.
TL;DR: In this article, a roll-like carbon nitride (C3N4) photocatalyst was synthesized using a supramolecular complex composed of cyanuric acid, melamine, and barbituric acids as the starting monomers.
Abstract: Herein, we report the facile synthesis of an efficient roll-like carbon nitride (C3N4) photocatalyst for hydrogen production using a supramolecular complex composed of cyanuric acid, melamine, and barbituric acid as the starting monomers. Optical and photocatalytic investigations show, along with the known red shift of absorption into the visible region, that the insertion of barbituric acid results in the in situ formation of in-plane heterojuctions, which enhance the charge separation process under illumination. Moreover, platinum as the standard cocatalyst in photocatalysis could be successfully replaced with first row transition metal salts and complexes under retention of 50% of the catalytic activity. Their mode of deposition and interaction with the semiconductor was studied in detail. Utilization of the supramolecular approach opens new opportunities to manipulate the charge transfer process within carbon nitride with respect to the design of a more efficient carbon nitride photocatalyst with cont...
TL;DR: Ru@SiO2 core shell structured nanospheres have been prepared via a one-pot synthetic route in a NP-5/cyclohexane reverse micelle system and characterized by XRD, SEM, TEM, N-2 adsorption-desorption, and H-2 temperature programmed desorption as discussed by the authors.
TL;DR: A simple, industrially viable iron catalyst is described that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts.
Abstract: Chiral molecules, such as alcohols, are vital for the manufacturing of fine chemicals, pharmaceuticals, agrochemicals, fragrances, and novel materials. These molecules need to be produced in high yield and high optical purity and preferentially catalytically. Among all the asymmetric catalytic reactions, asymmetric hydrogenation with H2 (AH) is the most widely used in the industry. With few exceptions, these AH processes use catalysts based on the three critical metals, rhodium, ruthenium, and iridium. Herein we describe a simple, industrially viable iron catalyst that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts. By combining a chiral, 22-membered macrocyclic ligand with the cheap, readily available Fe3(CO)12, a wide variety of ketones have been hydrogenated under 50 bar H2 at 45–65 °C, affording highly valuable chiral alcohols with enantioselectivities approaching or surpassing those obtained with the noble metal catalysts. In contrast to AH by most nobl...
TL;DR: In this paper, an economic photocatalytic H 2 generation system consisting of earth-abundant elements was proposed by coupling graphitic carbon nitride (g-C 3 N 4 ) with Ni(dmgH) 2 sub-microwires that serve as effective co-catalysts for H 2 evolution.
TL;DR: In this paper, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end-opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing.
Abstract: Although Li-oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end-opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT-encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li2O2 nanocrystals on CNT surfaces instead of localized distribution of Li2O2 aggregation, thus providing efficient charge transfer for the decomposition of Li2O2.
TL;DR: In this paper, the authors synthesized Co3V2O8 nanoparticles by a simple and cost-effective technique, which have low crystallinity and large specific surface area (122.8 m2 g−1).
Abstract: Water splitting, to produce hydrogen and oxygen, has long been considered to be a desirable option for the storage of electrical energy. The catalysts for oxygen evolution reactions (OER) are very important in this process. Herein, we have synthesized Co3V2O8 nanoparticles by a simple and cost-effective technique, which have low crystallinity and large specific surface area (122.8 m2 g−1). Because of the low crystallinity, large specific surface area and suitable pore size, Co3V2O8 nanoparticles yielded an electrocatalytic OER current density of up to 429.7 mA cm−2 at 2.05 V vs. RHE and low OER over potentials of 359 mV (at 10 mA cm−2) and 497 mV (at 100 mA cm−2). In addition, the OER stability of the Co3V2O8 catalyst was very excellent, and the current density at 2.05 V was reduced by just 7.3% after galvanostatic OER measurement at 10 mA cm−2 for 3 h. This work demonstrates that binary metal oxides Co3V2O8 is a highly active and stable oxygen evolution electrocatalyst that can potentially replace expensive noble metal-based anode catalysts for electrochemical water splitting to generate hydrogen fuels.
TL;DR: In this paper, non-noble metal copper (Cu) nanoparticles (NPs) with controlled size and surface coverage are decorated on silicon nanowire arrays (SiNWAs) by a simple galvanic displacement reaction.
Abstract: Non-noble metal copper (Cu) nanoparticles (NPs) with controlled size and surface coverage are decorated on silicon nanowire arrays (SiNWAs) by a simple galvanic displacement reaction. Using the combined efforts of all these approaches, SiNWAs-supported Cu NPs (SiNWAs–Cu) exhibit excellent and stable activity for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH4) in an aqueous solution, which can be recycled for five successive cycles of the reaction with a conversion efficiency of more than 95%. This novel catalyst also shows excellent catalytic performance for the degradation of other organic dyes, such as methylene blue (MB) and rhodamine B (RhB). Additionally, we demonstrate that the catalytic activity of SiNWAs–Cu is comparable to other SiNWAs-supported noble metal NPs (i.e., Ag and Au). Furthermore, SiNWAs as powerful substrates can be reused for decorating with Cu NPs after dilute HNO3 treatment. SiNWAs–Cu is particularly attractive as a catalyst, although Cu is orders of magnitude cheaper than any noble metals, its catalytic performance is comparable to other noble metals. So SiNWAs–Cu is thus expected to have the potential as a highly efficient, cost-effective and eco-friendly reusable catalyst to replace noble metals for certain catalytic applications.
TL;DR: The authors' Ag(Au)/CuPd nanoparticles are promising non-Pt catalysts for oxygen reduction reactions, with their mass activity reaching 0.20 A/mg of noble metal at -0.1 V vs Ag/AgCl (4 M KCl).
Abstract: Controlling the electronic structure and surface strain of a nanoparticle catalyst has become an important strategy to tune and to optimize its catalytic efficiency for a chemical reaction. Using density functional theory (DFT) calculations, we predicted that core/shell M/CuPd (M = Ag, Au) NPs with a 0.8 or 1.2 nm CuPd2 shell have similar but optimal surface strain and composition and may surpass Pt in catalyzing oxygen reduction reactions. We synthesized monodisperse M/CuPd NPs by the coreduction of palladium acetylacetonate and copper acetylacetonate in the presence of Ag (or Au) nanoparticles with controlled shell thicknesses of 0.4, 0.75, and 1.1 nm and CuPd compositions and evaluated their catalysis for the oxygen reduction reaction in 0.1 M KOH solution. As predicted, our Ag/Cu37Pd63 and Au/Cu40Pd60 catalysts with 0.75 and 1.1 nm shells were more efficient catalysts than the commercial Pt catalyst (Fuel Cells Store), with their mass activity reaching 0.20 A/mg of noble metal at -0.1 V vs Ag/AgCl (4 M KCl); this was over 3 times higher than that (0.06 A/mg Pt) from the commercial Pt. These Ag(Au)/CuPd nanoparticles are promising non-Pt catalysts for oxygen reduction reactions.