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Cao R.,Renmin University of China | Lai W.,Renmin University of China | Du P.,CAS Hefei Key Laboratory of Materials for Energy Conversion
Energy and Environmental Science | Year: 2012

Nature utilizes solar energy to extract electrons and release protons from water, a process called photosynthetic water oxidation or oxygen evolution. This sunlight-driven reaction is vital to the planet because it directly produces dioxygen and couples with photosystem I to generate the reducing equivalents for the reduction of carbon dioxide to carbohydrates (also known as CO2 fixation). Inspired by this natural process, people are intensely interested in water splitting using sunlight to convert and store solar energy into chemical energy, which is believed to be able to ultimately solve the energy problem that we are facing. Water splitting can be separated into two half reactions, namely water oxidation and water reduction, and they can be studied individually. Catalysts are very helpful in both reactions. Recent progress in finding new highly efficient water oxidation catalysts (WOCs) has shed light on this complicated four-electron/four-proton reaction and made it possible to catalyze water oxidation using mononuclear metal complexes. This article focuses on molecular catalysts that are able to perform catalytic water oxidation at single metal sites. Different series of catalysts (or precatalysts) made of ruthenium, iridium and earth abundant elements (iron, cobalt, and manganese) that can be applied in chemical, electrochemical and photochemical (light-driven) water oxidation are summarized, and their catalytic mechanisms are discussed in detail. Finally, the future outlook and perspective to design and develop catalysts that are efficient, cheap and stable are presented. This journal is © The Royal Society of Chemistry 2012.


Sun W.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Liu M.,Georgia Institute of Technology | Liu W.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Liu W.,CAS Hefei Institutes of Physical Science
Advanced Energy Materials | Year: 2013

BaZr0.7Sn0.1Y0.2O3-δ (BZSY) is developed as a novel chemically stable proton conductor for solid oxide fuel cells (SOFCs). BZSY possesses the same cubic symmetry of space group Pm-3m with BaZr0.8Y0.2O3-δ (BZY). Thermogravimetric analysis (TGA) and X-ray photoelectron spectra (XPS) results reveal that BZSY exhibits remarkably enhanced hydration ability compared to BZY. Correspondingly, BZSY shows significantly improved electrical conductivity. The chemical stability test shows that BZSY is quite stable under atmospheres containing CO2 or H2O. Fully dense BZSY electrolyte films are successfully fabricated on NiO-BZSY anode substrates followed by co-firing at 1400 °C for 5 h and the film exhibits excellent electrical conductivity under fuel cell conditions. The single cell with a 12-μm-thick BZSY electrolyte film outputs by far the best performance for acceptor-doped BaZrO3-based SOFCs. With wet hydrogen (3% H2O) as the fuel and static air as the oxidant, the peak power density of the cell achieves as high as 360 mWcm-2 at 700 °C, an increase of 42% compared to the reported highest performance of BaZrO3-based cells. The encouraging results demonstrate that BZSY is a good candidate as the electrolyte material for next generation high performance proton-conducting SOFCs. A novel chemically stable proton conductor BaZr0.7Sn0.1Y0.2O 3-δ (BZSY) with sufficiently high conductivity is developed for solid oxide fuel cells (SOFCs). The single cell with a 12-μm-thick BZSY electrolyte film outputs by far the best performance for BaZrO3-based proton-conducting SOFCs, achieving 360 mW cm-2 at 700 °C. The result is significant progress for proton-conducting SOFCs, demonstrating that BZSY is a promising electrolyte material for low-temperature SOFCs. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhu C.,Max Planck Institute for Solid State Research | Song K.,Max Planck Institute for Intelligent Systems (Stuttgart) | Van Aken P.A.,Max Planck Institute for Intelligent Systems (Stuttgart) | Maier J.,Max Planck Institute for Solid State Research | And 2 more authors.
Nano Letters | Year: 2014

Sodium ion batteries are one of the realistic promising alternatives to the lithium analogues. However, neither theoretical energy/power density nor the practical values reach the values of Li cathodes. Poorer performance is expected owing to larger size, larger mass, and lower cell voltage. Nonetheless, sodium ion batteries are considered to be practically relevant in view of the abundance of the element Na. The arguments in favor of Li and to the disadvantage of Na would be completely obsolete if the specific performance data of the latter would match the first. Here we present a cathode consisting of carbon-coated nanosized Na3V2(PO4)3 embedded in a porous carbon matrix, which not only matches but even outshines lithium cathodes under high rate conditions. It can be (dis)charged in 6 s with a current density as high as 22 A/g (200 C), still delivering a specific capacity of 44 mAh/g, while up to 20 C, the polarization is completely negligible. © 2014 American Chemical Society.


Liu J.,Max Planck Institute for Solid State Research | Song K.,Max Planck Institute for Intelligent Systems (Stuttgart) | Van Aken P.A.,Max Planck Institute for Intelligent Systems (Stuttgart) | Maier J.,Max Planck Institute for Solid State Research | And 2 more authors.
Nano Letters | Year: 2014

Self-supported Li4Ti5O12-C nanotube arrays with high conductivity architectures are designed and fabricated for application in Li-ion batteries. The Li4Ti5O12 nanotube arrays grow directly on stainless steel foil by a facile template-based solution route, further enhancing electronic conductivity by uniform carbon-coating on the inner and outer surfaces of Li4Ti 5O12 nanotubes. Owing to the shortened Li+ diffusion distance, high contact surface area, sufficient conductivity, and very good structure stability of the nanotube arrays, the self-supported Li 4Ti5O12-C nanotube arrays exhibit remarkable rate capability (a reversible capability of 135 mA h g-1, 105 mA h g-1, and 80 mA h g-1 at 30C, 60C, and 100C, respectively) and cycling performance (approximate 7% capacity loss after 500 cycles at 10C with a capacity retention of 144 mA h g-1). © 2014 American Chemical Society.


Zhu C.,Max Planck Institute for Solid State Research | Mu X.,Max Planck Institute for Intelligent Systems (Stuttgart) | Vanaken P.A.,Max Planck Institute for Intelligent Systems (Stuttgart) | Yu Y.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Maier J.,Max Planck Institute for Solid State Research
Angewandte Chemie - International Edition | Year: 2014

The preparation and electrochemical storage behavior of MoS2 nanodots - more precisely single-layered ultrasmall nanoplates - embedded in carbon nanowires has been studied. The preparation is achieved by an electrospinning process that can be easily scaled up. The rate performance and cycling stability of both lithium and sodium storage were found to be outstanding. The storage behavior is, moreover, highly exciting from a fundamental point of view, as the differences between the usual storage modes - insertion, conversion, interfacial storage - are beneficially blurred. The restriction to ultrasmall reaction domains allows for an almost diffusion-less and nucleation-free "conversion", thereby resulting in a high capacity and a remarkable cycling performance. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Chen W.,Hefei University of Technology | Li S.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Chen C.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Yan L.,Hefei University of Technology
Advanced Materials | Year: 2011

A 3D graphene architecture can be prepared via an in situ self-assembly of graphene prepared by a mild chemical reduction. Fe 3O 4 nanoparticles are homogeneously dispersed into graphene oxide (GO) aqueous suspension and a 3D magnetic graphene/Fe 3O 4 aerogel is prepared during the reduction of GO to graphene. This provides a general method to prepare 3D graphene/nanoparticle composites for a wide range of applications including catalysis and energy conversion. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cui Y.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Wen Z.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Liu Y.,CAS Hefei Key Laboratory of Materials for Energy Conversion
Energy and Environmental Science | Year: 2011

A novel free-standing type cathode of rechargeable Li-O 2 battery composed of only Co 3O 4 catalyst and Ni foam current collector was designed and realized by a simple chemical deposition reaction. The carbon and binder are no longer necessary for the air electrode. The new air electrode was found to yield obviously higher specific capacity and improved cycle efficiency than the conventional carbon-supported one with almost the highest discharge voltage (2.95 V), the lowest charge voltage (3.44 V), the highest specific capacity (4000 mAh g-1cathode) and the minimum capacity fading among the Li-O 2 batteries reported to date. During its discharge process, the discharge products would deposit at the surface and in the pores of the free-standing catalysts. The improved performance was attributed to the abundant available catalytic sites of the particularly structured air electrode, the intimate contact of the discharge product with the catalyst, the effective suppression of the volume expansion in the electrode during subsequent deposition/decomposition of the discharge products, the good adhesion of the catalyst to the current collector, and the open pore system for unrestricted access of the reactant molecules to and from active sites of the catalysts. Furthermore, EIS study pointed out the intrinsic distinction resulting in the different performance between the new electrode and the conventional carbon-supported electrode. The new free-standing type electrode represents a critical step toward developing high-performance Li-O 2 batteries. © 2011 The Royal Society of Chemistry.


Yang S.,CAS Hefei Key Laboratory of Materials for Energy Conversion
Current Organic Chemistry | Year: 2012

Endohedral fullerenes represent a novel type of nanostructures, which are characterized by a robust fullerene cage with atoms, ions, or clusters trapped in its hollow. Since the first separation of the endohedral metallofullerene La@C 82, a large variety of endohedral structures have been isolated and their endohedral nature has been proved by experimental studies. The world of endohedral fullerenes was significantly enlarged within the past decade by the clusterfullerenes including nitride clusterfullerenes and the new carbon cages including non-IPR (IPR=isolated pentagon rule) structures. With the classification of endohedral fullerenes presented first, we review the synthesis methods of endohedral fullerenes focusing on the new synthetic routes of nitride clusterfullerenes, the extraction and separation of endohedral fullerenes. Finally the intriguing molecular structures of endohedral fullerenes are addressed as well. © 2012 Bentham Science Publishers.


Huang W.,CAS Hefei Key Laboratory of Materials for Energy Conversion
Accounts of Chemical Research | Year: 2016

Model catalysts with uniform and well-defined surface structures have been extensively employed to explore structure-property relationships of powder catalysts. Traditional oxide model catalysts are based on oxide single crystals and single crystal thin films, and the surface chemistry and catalysis are studied under ultrahigh-vacuum conditions. However, the acquired fundamental understandings often suffer from the "materials gap" and "pressure gap" when they are extended to the real world of powder catalysts working at atmospheric or higher pressures. Recent advances in colloidal synthesis have realized controlled synthesis of catalytic oxide nanocrystals with uniform and well-defined morphologies. These oxide nanocrystals consist of a novel type of oxide model catalyst whose surface chemistry and catalysis can be studied under the same conditions as working oxide catalysts.In this Account, the emerging concept of oxide nanocrystal model catalysts is demonstrated using our investigations of surface chemistry and catalysis of uniform and well-defined cuprous oxide nanocrystals and ceria nanocrystals. Cu2O cubes enclosed with the {100} crystal planes, Cu2O octahedra enclosed with the {111} crystal planes, and Cu2O rhombic dodecahedra enclosed with the {110} crystal planes exhibit distinct morphology-dependent surface reactivities and catalytic properties that can be well correlated with the surface compositions and structures of exposed crystal planes. Among these types of Cu2O nanocrystals, the octahedra are most reactive and catalytically active due to the presence of coordination-unsaturated (1-fold-coordinated) Cu on the exposed {111} crystal planes. The crystal-plane-controlled surface restructuring and catalytic activity of Cu2O nanocrystals were observed in CO oxidation with excess oxygen. In the propylene oxidation reaction with O2, 1-fold-coordinated Cu on Cu2O(111), 3-fold-coordinated O on Cu2O(110), and 2-fold-coordinated O on Cu2O(100) were identified as the active sites, respectively, to produce acrolein, propylene oxide, and CO2. Ceria rods enclosed with the {110} and {100} crystal planes, ceria cubes enclosed with the {100} crystal planes, and ceria octahedra enclosed with the {111} crystal planes exhibit distinct morphology-dependent oxygen vacancy concentrations and structures that can be well correlated with the surface compositions and structures of exposed crystal planes. Consequently, the metal-ceria interactions, structures, and catalytic performances of ceria-supported catalysts depend on the CeO2 morphology.Our results comprehensively reveal the morphology-dependent surface chemistry and catalysis of oxide nanocrystals that not only greatly deepen the fundamental understanding of oxide catalysis but also demonstrate a morphology-engineering strategy to optimize the catalytic performance of oxide catalysts. These results adequately exemplify the concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the "materials gap" and "pressure gap". With the structure-catalytic property relationships learned from oxide nanocrystal model catalyst studies and the advancement of controlled-synthesis methods, it is promising to realize the structural design and controlled synthesis of novel efficient oxide catalysts in the future. (Chemical Equation Presented). © 2016 American Chemical Society.


Zhan Z.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Zhao L.,CAS Hefei Key Laboratory of Materials for Energy Conversion
Journal of Power Sources | Year: 2010

This paper describes results on the electrochemical reduction of carbon dioxide using the same device as the typical planar nickel-YSZ cermet electrode supported solid oxide fuel cells (H2-CO2, Ni-YSZYSZLSCF-GDC, LSCF, air). Operation in both the fuel cell and the electrolysis mode indicates that the electrodes could work reversibly for the charge transfer processes. An electrolysis current density of ≈1 A cm -2 is observed at 800 °C and 1.3 V for an inlet mixtures of 25% H2-75% CO2. Mass spectra measurement suggests that the nickel-YSZ cermet electrode is highly effective for reduction of CO2 to CO. Analysis of the gas transport in the porous electrode and the adsorption/desorption process over the nickel surface indicates that the cathodic reactions are probably dominated by the reduction of steam to hydrogen, whereas carbon monoxide is mainly produced via the reverse water gas shift reaction. © 2010 Elsevier B.V.

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