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Peter C Stair - One of the best experts on this subject based on the ideXlab platform.
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atomic layer deposition sequential self limiting surface reactions for advanced Catalyst bottom up Synthesis
Surface Science Reports, 2016Co-Authors: Jeffrey W Elam, Peter C StairAbstract:Abstract Catalyst Synthesis with precise control over the structure of catalytic active sites at the atomic level is of essential importance for the scientific understanding of reaction mechanisms and for rational design of advanced Catalysts with high performance. Such precise control is achievable using atomic layer deposition (ALD). ALD is similar to chemical vapor deposition (CVD), except that the deposition is split into a sequence of two self-limiting surface reactions between gaseous precursor molecules and a substrate. The unique self-limiting feature of ALD allows conformal deposition of catalytic materials on a high surface area Catalyst support at the atomic level. The deposited catalytic materials can be precisely constructed on the support by varying the number and type of ALD cycles. As an alternative to the wet-chemistry based conventional methods, ALD provides a cycle-by-cycle “bottom-up” approach for nanostructuring supported Catalysts with near atomic precision. In this review, we summarize recent attempts to synthesize supported Catalysts with ALD. Nucleation and growth of metals by ALD on oxides and carbon materials for precise Synthesis of supported monometallic Catalyst are reviewed. The capability of achieving precise control over the particle size of monometallic nanoparticles by ALD is emphasized. The resulting metal Catalysts with high dispersions and uniformity often show comparable or remarkably higher activity than those prepared by conventional methods. For supported bimetallic Catalyst Synthesis, we summarize the strategies for controlling the deposition of the secondary metal selectively on the primary metal nanoparticle but not on the support to exclude monometallic formation. As a review of the surface chemistry and growth behavior of metal ALD on metal surfaces, we demonstrate the ways to precisely tune size, composition and structure of bimetallic metal nanoparticles. The cycle-by-cycle “bottom up” construction of bimetallic (or multiple components) nanoparticles with near atomic precision on supports by ALD is illustrated. Applying metal oxide ALD over metal nanoparticles can be used to precisely synthesize nanostructured metal Catalysts. In this part, the surface chemistry of Al2O3 ALD on metals is specifically reviewed. Next, we discuss the methods of tailoring the catalytic performance of metal Catalysts including activity, selectivity and stability, through selective blocking of the low-coordination sites of metal nanoparticles, the confinement effect, and the formation of new metal-oxide interfaces. Synthesis of supported metal oxide Catalysts with high dispersions and “bottom up” nanostructured photocatalytic architectures are also included. Therein, the surface chemistry and morphology of oxide ALD on oxides and carbon materials as well as their catalytic performance are summarized.
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Synthesis and stabilization of supported metal Catalysts by atomic layer deposition
Accounts of Chemical Research, 2013Co-Authors: Jeffrey W Elam, Peter C StairAbstract:Supported metal nanoparticles are among the most important cata-lysts for many practical reactions, including petroleum refining, automobile exhaust treatment, and Fischer–Tropsch Synthesis. The catalytic performance strongly depends on the size, composition, and structure of the metal nanoparticles, as well as the underlying support. Scientists have used conventional Synthesis methods including impregnation, ion exchange, and deposition–precipitation to control and tune these factors, to establish structure–performance relationships, and to develop better Catalysts. Meanwhile, chemists have improved the stability of metal nanoparticles against sintering by the application of protective layers, such as polymers and oxides that encapsulate the metal particle. This often leads to decreased catalytic activity due to a lack of precise control over the thickness of the protective layer.A promising method of Catalyst Synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition in ...
Georges Hadziioannou - One of the best experts on this subject based on the ideXlab platform.
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Core-Shell Double Gyroid Structure Formed by Linear ABC Terpolymer Thin Films
Macromolecular Rapid Communications, 2018Co-Authors: Ségolène Antoine, Karim Aissou, Muhammad Mumtaz, Siham Telitel, Gilles Pecastaings, Anne-laure Wirotius, Cyril Brochon, Eric Cloutet, Guillaume Fleury, Georges HadziioannouAbstract:The Synthesis and self-assembly in thin-film configuration of linear ABC triblock terpolymer chains consisting of polystyrene (PS), poly(2-vinylpyridine) (P2VP), and polyisoprene (PI) are described. For that purpose, a hydroxylterminated PS-b-P2VP (45 kg mol−1) building block and a carboxyl-terminated PI (9 kg mol−1) are first separately prepared by anionic polymerization, and then are coupled via a Steglich esterification reaction. This quantitative and metal-free Catalyst Synthesis route reveals to be very interesting since functionalization and purification steps are straightforward, and well-defined terpolymers are produced. A solvent vapor annealing (SVA) process is used to promote the self-assembly of frustrated PS-b-P2VP-b-PI chains into a thinfilm core–shell double gyroid (Q230, space group: Ia3d) structure. As terraces are formed within PS-b-P2VP-b-PI thin films during the SVA process under a CHCl3 vapor, different plane orientations of the Q230 structure ((211), (110), (111), and (100)) are observed at the polymer–air interface depending on the film thickness.
Jiujun Zhang - One of the best experts on this subject based on the ideXlab platform.
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a review of fe n c and co n c Catalysts for the oxygen reduction reaction
Electrochimica Acta, 2008Co-Authors: Cicero W B Bezerra, Haijiang Wang, Lei Zhang, Aldaldea L B Marques, Edmar P Marques, Jiujun ZhangAbstract:Abstract This paper reviews over 100 articles related to heat-treated Fe– and Co–N/C Catalysts for the oxygen reduction reaction. The literature shows that through several decades’ effort in the development of non-noble Catalysts such as heat-treated Fe– and Co–N/C Catalysts, tremendous progress has been made in Catalyst Synthesis methodologies and the understanding of the mechanism. A heat-treatment step has been identified as necessary for Catalyst activity and stability improvement. The enhanced performance of the Catalysts is strongly dependent on the carbon support, the source of metal and nitrogen, and the thermal treatment conditions. The metal content in these Catalysts also plays an important role in their activity and stability. A saturated metal content has been identified as a major limiting factor for further improvement of Catalyst activity. The nitrogen content and the presence of a disordered or heterogeneous phase on the carbon-support surface seem to be the main requirements for an effective Catalyst. The mechanisms by which activity and stability are enhanced after the heat treatment of these Fe– and Co–N/C Catalysts are not fully understood yet. It is necessary to answer the question of whether or not the metal is part of the active catalytic site, as well as to identify the nature of the catalytic site. A more fundamental understanding will be of great help in designing alternative and innovative routes for Catalyst Synthesis. In general, the catalytic activity and stability of Fe– and Co–N/C Catalysts are still below those of a Pt-based Catalyst. However, under the strong driving force of fuel cell commercialization, Pt-free cathode Catalysts with methanol tolerance, such as Fe– and Co–N/C, are attractive candidates for solving the problem of the cost of fuel cell Catalysts.
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pem fuel cell electroCatalysts and Catalyst layers fundamentals and applications
2008Co-Authors: Jiujun ZhangAbstract:PEM Fuel Cell Fundamentals Electrocatalytic Oxygen Reduction Reaction Electrocatalytic H2 Oxidation Reaction Electrocatalytic Oxidation of Methanol, Ethanol and Formic Acid Application of First Principles Methods in the Study of Fuel Cell Air-Cathode Electrocatalysis Catalyst Contamination in PEM Fuel Cells PEM Fuel Cell Catalyst Layers and MEAs Catalyst Layer Modeling: Structure, Properties and Performance Catalyst Synthesis Techniques Physical Characterization of ElectroCatalysts Electrochemical Methods for Catalyst Activity Evaluation Combinatorial Methods for PEM Fuel Cell ElectroCatalysts Platinum-based Alloy Catalysts for PEM Fuel Cells Nanotubes, Nanofibers and Nanowires as Supports for Catalysts Non-noble ElectroCatalysts for the PEM Fuel Cell Oxygen Reduction Reaction CO-tolerant Catalysts Reversal-tolerant Catalyst Layers High-temperature PEM Fuel Cell Catalysts and Catalyst Layers Conventional Catalyst Ink, Catalyst Layer and MEA Preparation Spray-based and CVD Processes for Synthesis of Fuel Cell Catalysts and Thin Catalyst Layers Catalyst Layer/MEA Performance Evaluation Catalyst Layer Composition Optimization Catalyst Layer Degradation, Diagnosis and Failure Mitigation
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Progress in the Synthesis of carbon nanotube- and nanofiber-supported Pt electroCatalysts for PEM fuel cell catalysis
Journal of Applied Electrochemistry, 2006Co-Authors: Kunchan Lee, Jiujun Zhang, Haijiang Wang, David P. WilkinsonAbstract:This paper reviews the literature on the Synthesis of carbon nanotube- and nanofiber-supported Pt electroCatalysts for proton exchange membrane (PEM) fuel cell Catalyst loading reduction through the improvement of Catalyst utilization and activity, especially focusing on cathode nano-electroCatalyst preparation methods. The features of each synthetic method were also discussed based on the morphology of the synthesized Catalysts. It is clear that Synthesis methods play an important role in Catalyst morphology, Pt utilization and catalytic activity. Though some remarkable progress has been made in nanotube- and nanofiber-supported Pt Catalyst preparation techniques, the real breakthroughs have not yet been made in terms of cost-effectiveness, catalytic activity, durability and chemical/electrochemical stability. In order to make such electroCatalysts commercially feasible, cost-effective and innovative, Catalyst Synthesis methods are needed for Pt loading reduction and performance optimization.
Jeffrey W Elam - One of the best experts on this subject based on the ideXlab platform.
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atomic layer deposition sequential self limiting surface reactions for advanced Catalyst bottom up Synthesis
Surface Science Reports, 2016Co-Authors: Jeffrey W Elam, Peter C StairAbstract:Abstract Catalyst Synthesis with precise control over the structure of catalytic active sites at the atomic level is of essential importance for the scientific understanding of reaction mechanisms and for rational design of advanced Catalysts with high performance. Such precise control is achievable using atomic layer deposition (ALD). ALD is similar to chemical vapor deposition (CVD), except that the deposition is split into a sequence of two self-limiting surface reactions between gaseous precursor molecules and a substrate. The unique self-limiting feature of ALD allows conformal deposition of catalytic materials on a high surface area Catalyst support at the atomic level. The deposited catalytic materials can be precisely constructed on the support by varying the number and type of ALD cycles. As an alternative to the wet-chemistry based conventional methods, ALD provides a cycle-by-cycle “bottom-up” approach for nanostructuring supported Catalysts with near atomic precision. In this review, we summarize recent attempts to synthesize supported Catalysts with ALD. Nucleation and growth of metals by ALD on oxides and carbon materials for precise Synthesis of supported monometallic Catalyst are reviewed. The capability of achieving precise control over the particle size of monometallic nanoparticles by ALD is emphasized. The resulting metal Catalysts with high dispersions and uniformity often show comparable or remarkably higher activity than those prepared by conventional methods. For supported bimetallic Catalyst Synthesis, we summarize the strategies for controlling the deposition of the secondary metal selectively on the primary metal nanoparticle but not on the support to exclude monometallic formation. As a review of the surface chemistry and growth behavior of metal ALD on metal surfaces, we demonstrate the ways to precisely tune size, composition and structure of bimetallic metal nanoparticles. The cycle-by-cycle “bottom up” construction of bimetallic (or multiple components) nanoparticles with near atomic precision on supports by ALD is illustrated. Applying metal oxide ALD over metal nanoparticles can be used to precisely synthesize nanostructured metal Catalysts. In this part, the surface chemistry of Al2O3 ALD on metals is specifically reviewed. Next, we discuss the methods of tailoring the catalytic performance of metal Catalysts including activity, selectivity and stability, through selective blocking of the low-coordination sites of metal nanoparticles, the confinement effect, and the formation of new metal-oxide interfaces. Synthesis of supported metal oxide Catalysts with high dispersions and “bottom up” nanostructured photocatalytic architectures are also included. Therein, the surface chemistry and morphology of oxide ALD on oxides and carbon materials as well as their catalytic performance are summarized.
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Synthesis and stabilization of supported metal Catalysts by atomic layer deposition
Accounts of Chemical Research, 2013Co-Authors: Jeffrey W Elam, Peter C StairAbstract:Supported metal nanoparticles are among the most important cata-lysts for many practical reactions, including petroleum refining, automobile exhaust treatment, and Fischer–Tropsch Synthesis. The catalytic performance strongly depends on the size, composition, and structure of the metal nanoparticles, as well as the underlying support. Scientists have used conventional Synthesis methods including impregnation, ion exchange, and deposition–precipitation to control and tune these factors, to establish structure–performance relationships, and to develop better Catalysts. Meanwhile, chemists have improved the stability of metal nanoparticles against sintering by the application of protective layers, such as polymers and oxides that encapsulate the metal particle. This often leads to decreased catalytic activity due to a lack of precise control over the thickness of the protective layer.A promising method of Catalyst Synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition in ...
Ségolène Antoine - One of the best experts on this subject based on the ideXlab platform.
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Core-Shell Double Gyroid Structure Formed by Linear ABC Terpolymer Thin Films
Macromolecular Rapid Communications, 2018Co-Authors: Ségolène Antoine, Karim Aissou, Muhammad Mumtaz, Siham Telitel, Gilles Pecastaings, Anne-laure Wirotius, Cyril Brochon, Eric Cloutet, Guillaume Fleury, Georges HadziioannouAbstract:The Synthesis and self-assembly in thin-film configuration of linear ABC triblock terpolymer chains consisting of polystyrene (PS), poly(2-vinylpyridine) (P2VP), and polyisoprene (PI) are described. For that purpose, a hydroxylterminated PS-b-P2VP (45 kg mol−1) building block and a carboxyl-terminated PI (9 kg mol−1) are first separately prepared by anionic polymerization, and then are coupled via a Steglich esterification reaction. This quantitative and metal-free Catalyst Synthesis route reveals to be very interesting since functionalization and purification steps are straightforward, and well-defined terpolymers are produced. A solvent vapor annealing (SVA) process is used to promote the self-assembly of frustrated PS-b-P2VP-b-PI chains into a thinfilm core–shell double gyroid (Q230, space group: Ia3d) structure. As terraces are formed within PS-b-P2VP-b-PI thin films during the SVA process under a CHCl3 vapor, different plane orientations of the Q230 structure ((211), (110), (111), and (100)) are observed at the polymer–air interface depending on the film thickness.