The Experts below are selected from a list of 211842 Experts worldwide ranked by ideXlab platform
Jens K Norskov - One of the best experts on this subject based on the ideXlab platform.
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high efficiency Oxygen Reduction to hydrogen peroxide catalysed by oxidized carbon materials
Nature Catalysis, 2018Co-Authors: Guangxu Chen, Thomas F. Jaramillo, Samira Siahrostami, Zhihua Chen, Kai Liu, Jin Xie, Lei Liao, Dingchang Lin, Yayuan Liu, Jens K NorskovAbstract:Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from Oxygen Reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical Oxygen Reduction. We find that both the activity and selectivity are positively correlated with the Oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several Oxygen functional groups (–COOH and C–O–C) are the active sites for Oxygen Reduction reaction via the two-electron pathway, which are further supported by a series of control experiments.
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universality in Oxygen Reduction electrocatalysis on metal surfaces
ACS Catalysis, 2012Co-Authors: Venkatasubramanian Viswanathan, Jan Rossmeisl, Heine Anton Hansen, Jens K NorskovAbstract:In this work, we extend the activity volcano for Oxygen Reduction from the face-centered cubic (fcc) metal (111) facet to the (100) facet. Using density functional theory calculations, we show that the recent findings of constant scaling between OOH* and OH* holds on the fcc metal (100) facet, as well. Using this fact, we show the existence of a universal activity volcano to describe Oxygen Reduction electrocatalysis with a minimum overpotential, ηmin = 0.37 ± 0.1 V. Specifically, we find that the (100) facet of Pt is found to bind Oxygen intermediates too strongly and is not active for Oxygen Reduction reaction (ORR). In contrast, Au(100) is predicted to be more active than Au(111) and comparable in activity to Pt alloys. Using this activity volcano, we further predict that Au alloys that bind OH more strongly could display improved ORR activity on the (100) facet. We carry out a computational search over candidate alloys and suggest that alloying Au with early transition metals could lead to materials t...
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trends in Oxygen Reduction and methanol activation on transition metal chalcogenides
Electrochimica Acta, 2011Co-Authors: Georgios A Tritsaris, Jens K Norskov, Jan RossmeislAbstract:Abstract We use density functional theory calculations to study the Oxygen Reduction reaction and methanol activation on selenium and sulfur-containing transition metal surfaces. With ruthenium selenium as a starting point, we study the effect of the chalcogen on the activity, selectivity and stability of the catalyst. Ruthenium surfaces with moderate content of selenium are calculated active for the Oxygen Reduction reaction, and insensitive to methanol. A significant upper limit for the activity of transition metal chalcogenides is estimated.
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steady state Oxygen Reduction and cyclic voltammetry
Faraday Discussions, 2009Co-Authors: Jan Rossmeisl, Thomas F. Jaramillo, Gustav Karlberg, Jens K NorskovAbstract:The catalytic activity of Pt and Pt3Ni for the Oxygen Reduction reaction is investigated by applying a Sabatier model based on density functional calculations. We investigate the role of adsorbed OH on the activity, by comparing cyclic voltammetry obtained from theory with previously published experimental results with and without molecular Oxygen present. We find that the simple Sabatier model predicts both the potential dependence of the OH coverage and the measured current densities seen in experiments, and that it offers an understanding of the Oxygen Reduction reaction (ORR) at the atomic level. To investigate kinetic effects we develop a simple kinetic model for ORR. Whereas kinetic corrections only matter close to the volcano top, an interesting outcome of the kinetic model is a first order dependence on the Oxygen pressure. Importantly, the conclusion obtained from the simple Sabatier model still persists: an intermediate binding of OH corresponds to the highest catalytic activity, i.e. Pt is limited by a too strong OH binding and Pt3Ni is limited by a too weak OH binding.
Liming Dai - One of the best experts on this subject based on the ideXlab platform.
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polyelectrolyte functionalized graphene as metal free electrocatalysts for Oxygen Reduction
ACS Nano, 2011Co-Authors: Shuangyin Wang, Liming Dai, Dong Wook Chang, Jongbeom BaekAbstract:Poly(diallyldimethylammonium chloride), PDDA, was used as an electron acceptor for functionalizing graphene to impart electrocatalytic activity for the Oxygen Reduction reaction (ORR) in fuel cells. Raman and X-ray photoelectron spectroscopic measurements indicate the charge transfer from graphene to PDDA. The resultant graphene positively charged via intermolecular charge-transfer with PDDA was demonstrated to show remarkable electrocatalytic activity toward ORR with better fuel selectivity, tolerance to CO posing, and long-term stability than that of the commercially available Pt/C electrode. The observed ORR electrocatalytic activity induced by the intermolecular charge-transfer provides a general approach to various carbon-based metal-free ORR catalysts for Oxygen Reduction.
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polyelectrolyte functionalized carbon nanotubes as efficient metal free electrocatalysts for Oxygen Reduction
Journal of the American Chemical Society, 2011Co-Authors: Shuangyin Wang, Liming DaiAbstract:Having a strong electron-withdrawing ability, poly(diallyldimethylammonium chloride) (PDDA) was used to create net positive charge for carbon atoms in the nanotube carbon plane via intermolecular charge transfer. The resultant PDDA functionalized/adsorbed carbon nanotubes (CNTs), either in an aligned or nonaligned form, were demonstrated to act as metal-free catalysts for Oxygen Reduction reaction (ORR) in fuel cells with similar performance as Pt catalysts. The adsorption-induced intermolecular charge-transfer should provide a general approach to various carbon-based efficient metal-free ORR catalysts for Oxygen Reduction in fuel cells, and even new catalytic materials for applications beyond fuel cells.
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nitrogen doped graphene as efficient metal free electrocatalyst for Oxygen Reduction in fuel cells
ACS Nano, 2010Co-Authors: Yong Liu, Jongbeom Baek, Liming DaiAbstract:Nitrogen-doped graphene (N-graphene) was synthesized by chemical vapor deposition of methane in the presence of ammonia. The resultant N-graphene was demonstrated to act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for Oxygen Reduction via a four-electron pathway in alkaline fuel cells. To the best of our knowledge, this is the first report on the use of graphene and its derivatives as metal-free catalysts for Oxygen Reduction. The important role of N-doping to Oxygen Reduction reaction (ORR) can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, even new catalytic materials for applications beyond fuel cells.
Nicolas Alonsovante - One of the best experts on this subject based on the ideXlab platform.
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transition metal chalcogenides for Oxygen Reduction
2013Co-Authors: Nicolas AlonsovanteAbstract:Transition metal chalcogenide materials represent nowadays a new family of alternative materials for the cathode Oxygen Reduction reaction (ORR). During the last decade, the efforts have been concentrated in developing this kind of materials due to their capacity to remain selective and tolerant in the presence of small organics in acid as well as in alkaline media. This is a good advantage regarding their potential use in low power systems working in mixed reactant conditions. Recent efforts have focused on the discovery and/or modification of sensitive catalytic centers. This chapter adds new challenges for the development of such “sophisticated” materials that become popular in recent years, giving a panorama of the state of the art particularly of nanodivided materials.
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chalcogenide metal centers for Oxygen Reduction reaction activity and tolerance
Electrochimica Acta, 2011Co-Authors: Yongjun Feng, Aldo Gago, Laure Timperman, Nicolas AlonsovanteAbstract:Abstract This mini-review summarizes materials design methods, Oxygen Reduction kinetics, tolerance to small organic molecules and fuel cell performance of chalcogenide metal catalysts, particularly, ruthenium (RuxSey) and non-precious transition metals (MxXy: M = Co, Fe and Ni; X = Se and S). These non-platinum catalysts are potential alternatives to Pt-based catalysts because of their comparable catalytic activity (RuxSey), low cost, high abundance and, in particular, a high tolerance to small organic molecules. Developing trends of synthesis methods, mechanism of Oxygen Reduction reaction and applications in direct alcohol fuel cells as well as the substrate effect are highlighted.
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methanol tolerant Oxygen Reduction on carbon supported pt ni alloy nanoparticles
Journal of Electroanalytical Chemistry, 2005Co-Authors: Hui Yang, Jeanmichel Leger, Christophe Coutanceau, Nicolas AlonsovanteAbstract:Abstract The preparation of carbon-supported Pt–Ni alloy catalysts at a 40 wt% total metal loading and with high Ni content within the alloys and their electrocatalysis for the Oxygen Reduction reaction has been studied. Emphasis is placed on the methanol-tolerant Oxygen Reduction on as-prepared alloy catalysts and their application in direct methanol fuel cells. It was found that as-prepared alloy catalysts have single-phase disordered structures and small particle sizes with a relatively narrow size distribution even at 40 wt% loading. As compared to pure Pt/C catalyst for Oxygen Reduction, such alloy catalysts exhibited enhanced electrocatalytic activities in pure acidic electrolyte and significantly enhanced electrocatalytic activities in methanol-containing electrolyte. The high methanol tolerance of Pt–Ni alloy catalysts during Oxygen Reduction could be ascribed to a lowered activity of methanol oxidation, which may originate from the composition effect and the disordered structure of the alloy catalysts. Fuel cell tests confirmed that as-prepared Pt–Ni alloy catalysts for Oxygen Reduction are more active than a commercial Pt/C catalyst with the same metal loading and that the maximum activity was found with a Pt/Ni atomic ratio of 2:1, which is similar to results in half-cell tests.
Jan Rossmeisl - One of the best experts on this subject based on the ideXlab platform.
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universality in Oxygen Reduction electrocatalysis on metal surfaces
ACS Catalysis, 2012Co-Authors: Venkatasubramanian Viswanathan, Jan Rossmeisl, Heine Anton Hansen, Jens K NorskovAbstract:In this work, we extend the activity volcano for Oxygen Reduction from the face-centered cubic (fcc) metal (111) facet to the (100) facet. Using density functional theory calculations, we show that the recent findings of constant scaling between OOH* and OH* holds on the fcc metal (100) facet, as well. Using this fact, we show the existence of a universal activity volcano to describe Oxygen Reduction electrocatalysis with a minimum overpotential, ηmin = 0.37 ± 0.1 V. Specifically, we find that the (100) facet of Pt is found to bind Oxygen intermediates too strongly and is not active for Oxygen Reduction reaction (ORR). In contrast, Au(100) is predicted to be more active than Au(111) and comparable in activity to Pt alloys. Using this activity volcano, we further predict that Au alloys that bind OH more strongly could display improved ORR activity on the (100) facet. We carry out a computational search over candidate alloys and suggest that alloying Au with early transition metals could lead to materials t...
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trends in Oxygen Reduction and methanol activation on transition metal chalcogenides
Electrochimica Acta, 2011Co-Authors: Georgios A Tritsaris, Jens K Norskov, Jan RossmeislAbstract:Abstract We use density functional theory calculations to study the Oxygen Reduction reaction and methanol activation on selenium and sulfur-containing transition metal surfaces. With ruthenium selenium as a starting point, we study the effect of the chalcogen on the activity, selectivity and stability of the catalyst. Ruthenium surfaces with moderate content of selenium are calculated active for the Oxygen Reduction reaction, and insensitive to methanol. A significant upper limit for the activity of transition metal chalcogenides is estimated.
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steady state Oxygen Reduction and cyclic voltammetry
Faraday Discussions, 2009Co-Authors: Jan Rossmeisl, Thomas F. Jaramillo, Gustav Karlberg, Jens K NorskovAbstract:The catalytic activity of Pt and Pt3Ni for the Oxygen Reduction reaction is investigated by applying a Sabatier model based on density functional calculations. We investigate the role of adsorbed OH on the activity, by comparing cyclic voltammetry obtained from theory with previously published experimental results with and without molecular Oxygen present. We find that the simple Sabatier model predicts both the potential dependence of the OH coverage and the measured current densities seen in experiments, and that it offers an understanding of the Oxygen Reduction reaction (ORR) at the atomic level. To investigate kinetic effects we develop a simple kinetic model for ORR. Whereas kinetic corrections only matter close to the volcano top, an interesting outcome of the kinetic model is a first order dependence on the Oxygen pressure. Importantly, the conclusion obtained from the simple Sabatier model still persists: an intermediate binding of OH corresponds to the highest catalytic activity, i.e. Pt is limited by a too strong OH binding and Pt3Ni is limited by a too weak OH binding.
Jun Chen - One of the best experts on this subject based on the ideXlab platform.
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Chemical etching of manganese oxides for electrocatalytic Oxygen Reduction reaction
Chemical Communications, 2015Co-Authors: Yuxiang Hu, Liang Cong, Fangyi Cheng, Jun ChenAbstract:Mixed-valent MnOx (1 < x < 2) was selectively synthesized by chemically etching MnO and Mn2O3 with ceric ammonium nitrate. The obtained MnOx exhibited greatly enhanced electrocatalytic activity toward the Oxygen Reduction reaction (ORR) as compared to the corresponding pristine oxides.
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enhancing electrocatalytic Oxygen Reduction on mno2 with vacancies
Angewandte Chemie, 2013Co-Authors: Fangyi Cheng, Tianran Zhang, Yi Zhang, Xiaopeng Han, Jun ChenAbstract:Oxygen-vacant nanocrystalline MnO(2) has been prepared by the simple process of annealing pristine oxide in Ar or O(2) . Both experimental and computational studies indicate that the catalytic activity of MnO(2) towards Oxygen Reduction is enhanced by introducing a modest concentration of Oxygen vacancies.
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porous calcium manganese oxide microspheres for electrocatalytic Oxygen Reduction with high activity
Chemical Science, 2013Co-Authors: Xiaopeng Han, Fangyi Cheng, Tianran Zhang, Jun ChenAbstract:A series of calcium–manganese oxides (Ca–Mn–O) were prepared through thermal decomposition of carbonate solid–solution precursors and investigated as electrocatalysts for Oxygen Reduction reaction (ORR). The synthesized crystalline Ca–Mn–O compounds, including perovskite-type CaMnO3, layered structured Ca2Mn3O8, post-spinel CaMn2O4 and CaMn3O6, presented similar morphologies of porous microspheres with agglomerated nanoparticles. Electrochemical results, surface analysis, and computational studies revealed that the catalytic activities of Ca–Mn–O oxides, in terms of onset potential, Reduction current, and transferred electron number, depended strongly on both the surface Mn oxidation state and the crystallographic structures. Remarkably, the as-synthesized CaMnO3 and CaMn3O6 exhibited considerable activity and enabled an apparent quasi 4-electron Oxygen Reduction with low yield of peroxide species in alkaline solutions, suggesting their potential applications as cheap and abundant ORR catalysts.
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mno2 based nanostructures as catalysts for electrochemical Oxygen Reduction in alkaline media
Chemistry of Materials, 2010Co-Authors: Fangyi Cheng, Jing Liang, Zhanliang Tao, Jun ChenAbstract:This paper reports a systematical study on the electrochemical properties of MnO2-based nanostructures as low-cost catalysts for Oxygen Reduction reaction (ORR) in alkaline media. The results show ...
