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  • 201.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Besharat, Zahra
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ghadami Yazdi, Milad
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Önsten, Anneli
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Leygraf, Christofer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    The Surface Structure of Cu2O(100)2016Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 8, s. 4373-4381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.

  • 202.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Lundgren, E.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation of Fe(110) in oxygen gas at 400 °c2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, s. 172-179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial oxidation of Fe(110) in oxygen gas at 400 °C beyond initial adsorbate structures has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM). Formation of several ordered phases of surface oxides is observed at oxygen coverages between approximately 2.3 and 3.5 oxygen atoms/Fe(110) surface atom. Initially, a FeO(111)-like film is formed with a parallelogram-shaped moiré pattern. It has two mirror domains that are formed symmetrically around the growth direction of a zigzag-shaped adsorbate structure. With increased local oxygen coverage, the moiré structure transforms into a ball-shaped form. Both these moiré structures have equal atomic stacking at the surface and equal apparent height in STM, suggesting oxygen ions diffusing into the film upon oxidation and that the oxide growth takes place at the iron-iron oxide interface. The FeO(111)-like film turns into a Fe3O4(111)-like film with a triangular bistable surface termination as the oxidation proceeds further. The FeO(111)-like film growth proceeds according to the Frank-van der Merwe mechanism while the Fe3O4(111)-like film grows according to the Stranski-Krastanov mechanism.

  • 203.
    Soroka, Inna
    et al.
    KTH, Skolan för kemivetenskap (CHE).
    Tarakina, Nadezda V.
    Hermansson, Anton
    KTH, Skolan för kemivetenskap (CHE).
    Bigum, Lukas
    KTH, Skolan för kemivetenskap (CHE).
    Widerberg, Rickard
    KTH, Skolan för kemivetenskap (CHE).
    Andersson, Mikael S.
    Mathieu, Roland
    Paulraj, Alagar R.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Kiros, Yohannes
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Radiation-induced synthesis of nanoscale Co- and Ni-based electro-catalysts on carbon for the oxygen reduction reaction2017Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, nr 30, s. 9995-10002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A facile synthesis of 3d-metal based electro-catalysts directly incorporated into a carbon support was carried out by.-radiation. Transition metals of period 4, i.e. Ni and Co, were precipitated and reduced from their respective salt solutions. The obtained materials were characterized by XRD, SEM, SQUID and the BET methods. Thereafter, the electrodes for fuel cells were fabricated out of synthesized material and their electrochemical performance for the oxygen reduction reaction in 6 M KOH was measured. Although the concentrations of Co and Ni in the electrode material were low (3.4% Co and 0.4% Ni) after reduction by irradiation, both the Ni and Co-based gas diffusion electrodes showed high catalytic activity for oxygen reduction both at room temperature and at 60 degrees C.

  • 204. Spets, J. -P
    et al.
    Lampinen, M. J.
    Kiros, Yohannes
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Anttila, T.
    Rantanen, J.
    Granström, T.
    The Simultaneous Uses of the Direct-Mode Bioorganic Fuel Cell and the Function Generator for the Enhancement of the Glucose Electro-chemical Oxidation2010Inngår i: International Journal of Electrochemical Science, ISSN 1452-3981, Vol. 5, nr 4, s. 547-555Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study a test of the direct-mode bioorganic fuel cell (DMBFC) in which the fuel and the alkaline electrolyte are mixed with each other at two temperatures of 20 and 35 degrees C are carried out. The direct-mode bioorganic fuel cell is exposed to an externally generated electromagnetic field with simultaneous discharging in order to split the fuel molecule before the electrochemical oxidation at the two operation temperatures. The current-voltage characteristics are measured and analyzed. The liquid phase of the fuel-electrolyte concentration of the glucose was analysed both before and after the electrochemical tests at the operation temperature 20 degrees C. The aim is to continue with the development of the direct-mode glucose fuel cell by increasing the power density range by several mWcm(-2). This type of the fuel cell with glucose as a fuel has increased to the specific capacity levels of 120.8 and 132.7 Ah / kg glucose at the temperatures of 20 degrees C and 35 degrees C, respectively.

  • 205. Spets, J-P
    et al.
    Kiros, Yohannes
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Kuosa, M. A.
    Rantanen, J.
    Lampinen, M. J.
    Saari, K.
    Bioorganic materials as a fuel source for low-temperature direct-mode fuel cells2010Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 55, nr 26, s. 7706-7709Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study a direct-mode fuel cell in which the fuel and electrolyte are mixed with each other is tested. An alkaline electrolyte is used. The aim was to develop a fuel cell which operates directly by mixing the fuel with the electrolyte. The target is to create a fuel cell with a capacity of a few mW cm(-2) with starch as a fuel source. Starch, glucose, and sorbitol were tested as fuels for the fuel cell. With the selected fuel cell type and with glucose as the fuel, a maximum current density of 8 mA cm(-2) with a voltage of 0.5 V was obtained.

  • 206. Spijksma, Gerald I.
    et al.
    Seisenbaeva, Gulaim A.
    Fischer, Andreas
    Bouwmeester, Henny J. M.
    Blank, Dave H. A.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Kessler, Vadim G.
    The molecular composition of non-modified and acac-modified propoxide and butoxide precursors of zirconium and hafnium dioxides2009Inngår i: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 51, nr 1, s. 10-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Long-term storage at 0 A degrees C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr(4)O(O(n)Pr)(14)((n)PrOH)(2) in over 20% yield. The structure of this molecule can be described as a triangular Zr(3)(mu(3)-O)(OR)(10)(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)(4)(ROH) unit attached through a pair of (mu-OR) bridges. Mass spectrometric and (1)H NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be similar to 20% for n-propoxide and similar to 35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr(O(n)Pr)(O(i)Pr)(3)((i)PrOH)](2), from zirconium n-propoxide. A high yield has been observed (similar to 90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)(3)(acac)](2) in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)(4) through very unstable M(acac)(3)(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by (1)H NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction.

  • 207.
    Staehle, Robert
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Tong, Lianpeng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Wang, Lei
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Duan, Lele
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Fischer, Andreas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Ahlquist, Mårten S. G.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Rau, Sven
    Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2′-bipyridine-6,6′-dicarboxylate (bda) ligand: How ligand environment influences the catalytic behavior2014Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, nr 3, s. 1307-1319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new water oxidation catalyst [RuIII(bda)(mmi)(OH 2)](CF3SO3) (2, H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid; mmi = 1,3- dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.

  • 208.
    Svens, Pontus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindström, Johan
    Scania CV AB, Södertälje, Sweden.
    Gelin, Olle
    Scania CV AB, Södertälje, Sweden.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Novel Field Test Equipment for Lithium-Ion Batteries in Hybrid Electrical Vehicle Applications2011Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 4, nr 5, s. 741-757Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lifetime testing of batteries for hybrid-electrical vehicles (HEV) is usually performed in the lab, either at the cell, module or battery pack level. Complementary field tests of battery packs in vehicles are also often performed. There are, however, difficulties related to field testing of battery-packs. Some examples are cost issues and the complexity of continuously collecting battery performance data, such as capacity fade and impedance increase. In this paper, a novel field test equipment designed primarily for lithium-ion battery cell testing is presented. This equipment is intended to be used on conventional vehicles, not hybrid vehicles, as a cheaper and faster field testing method for batteries, compared to full scale HEV testing. The equipment emulates an HEV environment for the tested battery cell by using real time vehicle sensor information and the existing starter battery as load and source. In addition to the emulated battery cycling, periodical capacity and pulse testing capability are implemented as well. This paper begins with presenting some background information about hybrid electrical vehicles and describing the limitations with today's HEV battery testing. Furthermore, the functionality of the test equipment is described in detail and, finally, results from verification of the equipment are presented and discussed.

  • 209. Svensson, Per H.
    et al.
    Rosdahl, Jan
    Kloo, Lars
    Metal Iodides in Polyiodide Networks -The Structural Chemistry of Complex Gold Iodides with Excess of Iodine1999Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 5, nr 1, s. 305-311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theoretical calculations that compare the Ij ion and the [AuI4](-) ion show that they are closely related and have potential energy surface (PES) minima corresponding to an L-shaped structure. These calculations also indicate that the I-3(-) and [AuI2](-) ions should be exchangeable. These results were confirmed by the synthesis of the compounds (Et3S)[AuI4]. 2I(2) (1) and (Me3S)(2)[AuI4][I-3] (4), which have been characterised by X-ray diffraction, Raman and far-IR spectroscopy. The structure of 1 is made up of [AuI4](-) units coordinated by infinite zig-zag chains of I, molecules, and can be regarded as [AuI4](-) ions incorporated into a polyiodide network. The structure of 4 is closely related to those of the compounds of the M2Au2X6 family (M = Cs+, Rb+, NH4+, K+; X = Cl-, Br-, I-) which consist of square-planar [AuX4](-) and linear [AuX2](-) ions. However, in the structure of 4, the [AuX2](-) ions are replaced by IS ions.

  • 210.
    Swerin, Agne
    et al.
    YKI, Institute for Surface Chemistry, Sweden.
    Brandner, Birgitt
    Wallqvist, Vivica
    Wåhlander, Martin
    YKI, Institute for Surface Chemistry, Sweden.
    Probing molecular, nanoscale and adhesive forces related to fiber-fiber bonding and optimized surface interactions2009Inngår i: International Conference on Nanotechnology for the Forest Products Industry 2009, Edmonton Canada, 2009, Vol. 1, s. 229-283Konferansepaper (Fagfellevurdert)
  • 211.
    Swerin, Agne
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Sundin, Mikael
    Wåhlander, Martin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Ytbehandlingsteknik.
    Formulation of superhydrophobic pigment coatings2015Inngår i: Formulation of superhydrophobic pigment coatings, TAPPI Press, 2015, Vol. 2, s. 1410-1424Konferansepaper (Fagfellevurdert)
  • 212. Tenn, William J., III
    et al.
    Conley, Brian L.
    Hoevelmann, Claas H.
    Ahlquist, Mårten
    Division of Chemistry and Chemical Engineering, California Institute of Technology.
    Nielsen, Robert J.
    Ess, Daniel H.
    Oxgaard, Jonas
    Bischof, Steven M.
    Goddard, William A.
    Periana, Roy A.
    Oxy-Functionalization of Nucleophilic Rhenium(I) Metal Carbon Bonds Catalyzed by Selenium(IV)2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 7, s. 2466-2468Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report that SeO(2) catalyzes the facile oxy-functionalization of (CO)(5)Re(I)-Me(delta-) with IO(4)(-) to generate methanol. Mechanistic studies and DFT calculations reveal that catalysis involves methyl group transfer from Re to the electrophilic Se center followed by oxidation and subsequent reductive functionalization of the resulting CH(3)Se(VI) species. Furthermore, (CO)(3)Re(I)(Bpy)-R (R = ethyl, n-propyl, and aryl) complexes show analogous transfer to SeO(2) to generate the primary alcohols. This represents a new strategy for the oxy-functionalization of M-R(delta-) polarized bonds.

  • 213.
    Tiberg, Charlotta
    et al.
    SLU.
    Sjöstedt, Carin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Persson, Ingmar
    SLU.
    Gustafsson, Jon Petter
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Phosphate effects on copper(II) and lead(II) sorption to ferrihydriteManuskript (preprint) (Annet vitenskapelig)
  • 214.
    Tong, Lianpeng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Mononuclear Ruthenium Complexes that Catalyze Water to Dioxgen Oxidation2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The theme of this thesis is the development of mononuclear Ru-based complexes that are capable of catalyzing the water oxidation (or O2-evolving) reaction, e.g. 2 H2O → O2 + 4 H+ + 4 e. Several families of mononuclear Ru water oxidation catalysts were designed and prepared. They feature with anionic ancillary ligands that contain carboxylate or phenolate donors. The properties of the catalysts were investigated in various aspects including coordination geometry, electrochemical behavior, and ligand exchange. All catalysts showed outstanding catalytic activity towards water oxidation in the presence of cerium(IV) ammonium nitrate as a sacrificial oxidant. High-valent Ru intermediates involved in the reactions were characterized both experimentally and theoretically. The kinetics of catalytic water oxidation was examined based on one catalyst and a prevailing catalytic pathway was proposed. The catalytic cycle involved a sequence of oxidation steps from RuII−OH2 to RuV=O species and O−O bond formation via water-nucleophilic-attack to the RuV=O intermediate. By comparing properties and catalytic performance of Ru catalysts herein with that of previously reported examples, the effect of anionic ancillary ligands was clearly elucidated in the context of catalytic water oxidation. Aiming to further application in an envisaged artificial photosynthesis device, visible light-driven water oxidation was conducted and achieved primarily in a homogeneous three-component system containing catalyst, photosensitizer, and sacrificial electron acceptor. Moreover, one model Ru catalyst was successfully immobilized on ordinary glass carbon surface through a facile and widely applicable method.

  • 215.
    Tong, Lianpeng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Inge, A. Ken
    Stockholm University.
    Duan, Lele
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Wang, Lei
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Zou, Xiaodong
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Catalytic Water Oxidation by Mononuclear Ru Complexes with an Anionic Ancillary Ligand2013Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, nr 5, s. 2505-2518Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mononuclear Ru-based water oxidation catalysts containing anionic ancillary ligands have shown promising catalytic efficiency and intriguing properties. However, their insolubility in water restricts a detailed mechanism investigation. In order to overcome this disadvantage, complexes [Ru-II(bpc)(bpy)OH2](+) (1(+), bpc = 2,2'-bipyridine-6-carboxylate, bpy = 2,2'-bipyridine) and [Ru-II(bpc)(pic)(3)](+) (2(+), pic = 4-picoline) were prepared and fully characterized, which features an anionic tridentate ligand and has enough solubility for spectroscopic study in water. Using Ce-IV as an electron acceptor, both complexes are able to catalyze O-2-evolving reaction with an impressive rate constant. On the basis of the electrochemical and kinetic studies, a water nucleophilic attack pathway was proposed as the dominant catalytic cycle of the catalytic water oxidation by 1(+), within which several intermediates were detected by MS. Meanwhile, an auxiliary pathway that is related to the concentration of Ce-IV was also revealed. The effect of anionic ligand regarding catalytic water oxidation was discussed explicitly in comparison with previously reported mononuclear Ru catalysts carrying neutral tridentate ligands, for example, 2,2':6',2 ''-terpyridine (tpy). When 2(+) was oxidized to the trivalent state, one of its picoline ligands dissociated from the Ru center. The rate constant of picoline dissociation was evaluated from time-resolved UV-vis spectra.

  • 216. Tong, Lianpeng
    et al.
    Kopecky, Andrew
    Zong, Ruifa
    Gagnon, Kevin J.
    Ahlquist, Mårten S. G.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Thummel, Randolph P.
    Light-Driven Proton Reduction in Aqueous Medium Catalyzed by a Family of Cobalt Complexes with Tetradentate Polypyridine-Type Ligands2015Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, nr 16, s. 7873-7884Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of tetradentate 2,2':6',2":6",2"-quaterpyridine-type ligands related to ppq (ppq = 8-(1",10"phenanthrol-2"-y1)-2-(pyrid-2'-yOquinoline) have been synthesized. One ligand replaces the 1,10-phenanthroline (phen) moiety of ppq with 2,2'-bipyridine and the other two ligands have a 3,3'-polymethylene subunit bridging the quinoline and pyridine. The structural result is that both the planarity and flexibility of the ligand are modified. Co (II) complexes are prepared and characterized by ultraviolet-visible light (UVvis) and mass spectroscopy, cyclic voltammetry, and X-ray analysis. The light-driven H-2-evolving activity of these Co complexes was evaluated under homogeneous aqueous conditions using [Ru(bpy)(3)](2) as the photosensitizer, ascorbic acid as a sacrificial electron donor, and a blue light-emitting diode (LED) as the light source. At pH 4.5, all three complexes plus [Co(ppq)Cl-2] showed the fastest rate, with the dimethylene-bridged system giving the highest turnover frequency (2125 h(-1)). Cyclic voltammograms showed a significant catalytic current for H2 production in both aqueous buffer and H2O/DMF medium. Combined experimental and theoretical study suggest a formal Co(L)-hydride species as a key intermediate that triggers H-2 generation. Spin density analysis shows involvement of the tetradentate ligand in the redox sequence from the initial Co(II) state to the Co(II)-hydride intermediate. How the ligand scaffold influences the catalytic activity and stability of catalysts is discussed, in terms of the rigidity and differences in conjugation for this series of ligands.

  • 217.
    Trummer, Martin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    The effect of solid state inclusions on the reactivity of UO2: A kinetic and mechanistic study2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The release of radionuclides is a key process in the safety assessment of a deep geological repository for spent nuclear fuel. A large fraction of the release is assumed to be a consequence of dissolution of the fuel matrix, UO2. In this doctoral thesis, the kinetics and the mechanisms behind oxidative U(IV) dissolution were studied. The eects of solid phase inclusions mimicking the presence of fission products, and solutes mimicking expected groundwater components were also evaluated.

    Palladium, as a model substance for noble metal particle (fission products) inclusions, was shown to catalyze surface oxidation of U(IV), as well as reduction of U(VI). The second order rate constant for the surface reduction of U(VI) by H2was found to be on the order of 10-6 m s-1 (diusion controlled). Under 40 bar H2, 1 wt.% Pd was sufficient to suppress oxidative U(IV) dissolution in 2mM H2O2 aqueous solution. During g γirradiation under 1 bar H2, 0.1 wt.% Pd were sufficient to completely suppress oxidative dissolution. Under inert conditions, where H2 is only produced radiolytically, complete inhibition is observed for 3 wt.% Pd.

    The presence of Y2O3 as a model substance for trivalent fission products was found to decrease U(VI) dissolution significantly under inert, as well as reducing conditions. Based on kinetic data, it was shown that pure competition kinetics cannot explain the observed decrease. From experiments using pure oxidants it was shown that Y2O3 doping of UO2 decreases the redox reactivity. In addition, from experiments where hydroxyl radical formation from the catalytic decomposition of H2O2 was monitored, it could be concluded that doping has a minor influence on this process.

    On the basis of numerical simulations, the H2 concentration necessary to suppressradiolytic H2O2 production was found to increase with an increase in dose rate or HCO-3 concentration. Furthermore, the steady state concentration of H2O2 was found to be inversely proportional to the H2 pressure, and proportional to the square root of the dose rate. Fe2 diers strongly from the total reaction volume, the actual dose rate should not be converted into a homogeneous dose rate in numerical simulations.

  • 218.
    Trummer, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Dahlgren, Björn
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    The effect of Y2O3 on the dynamics of oxidative dissolution of UO22010Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 407, nr 3, s. 195-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we have studied the impact of Y2O3 on the kinetics of oxidative dissolution of UO2 and the consumption of H2O2. The second order kinetics of catalytic consumption of H2O2 on Y2O3 was investigated in aqueous Y2O3 powder suspensions by varying the solid surface area to solution volume ratio. The resulting second order rate constant is 10(-8) m s(-1), which is of the same magnitude as for the reaction between H2O2 and UO2. Powder experiments with mixtures of UO2 and Y2O3 show that Y2O3 has no effect on the oxidative dissolution of UO2, whereas the consumption of H2O2 seems to be slightly slower in the presence of Y2O3 and H-2 respectively. UO2 pellets with solid inclusions of Y2O3 show a decrease in oxidative dissolution by a factor of 3.3 and 5.3 under inert and hydrogen atmosphere, respectively. The rate of H2O2 consumption is similar for all cases and is well in line with kinetic data from powder experiments. The effects of H-2 and Y2O3 on the oxidative dissolution of UO2 under gamma irradiation are similar to those found in experiments with H2O2. No significant difference in dissolution between inert and reducing atmosphere can be observed for pure UO2.

  • 219.
    Trummer, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Nilsson, Sara
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    On the effects of fission product noble metal inclusions on the kinetics of radiation induced dissolution of spent nuclear fuel2008Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 378, nr 1, s. 55-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiation induced oxidative dissolution of UO2 is a key process for the safety assessment of future geological repositories for spent nuclear fuel. This process is expected to govern the rate of radionuclide release to the biosphere. In this work, we have studied the catalytic effects of fission product noble metal inclusions on the kinetics of radiation induced dissolution of spent nuclear fuel. The experimental studies were performed using UO2 pellets containing 0%, 0.1%, 1% and 3% Pd as a model for spent nuclear fuel. H2O2 was used as a model for radiolytical oxidants (previous studies have shown that H2O2 is the most important oxidant in such systems). The pellets were immersed in aqueous solution containing H2O2 and HCO3- and the consumption of H2O2 and the dissolution of uranium were analyzed as a function of H2 pressure (0-40 bar). The noble metal inclusions were found to catalyze oxidation of UO2 as well as reduction of surface bound oxidized UO2 by H2. In both cases the rate of the process increases with increasing Pd content. The reduction process was found to be close to diffusion controlled. This process can fully account for the inhibiting effect of H2 observed in several studies on spent nuclear fuel dissolution.

  • 220.
    Trummer, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Razdan, Mayuri
    Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada N6A 5B7.
    Zagidulin, Dimitri
    Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada N6A 5B7.
    Shoesmith, David W.
    Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada N6A 5B7.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    An electrochemical and kinetic study of oxidative dissolution of Y2O3-doped UO2Manuskript (preprint) (Annet vitenskapelig)
  • 221.
    Trummer, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Roth, Olivia
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Hinhibition of radiation induced dissolution of spent nuclear fuel2009Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 383, nr 3, s. 226-230Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to elucidate the effect of noble metal clusters in spent nuclear fuel on the kinetics of radiation induced spent fuel dissolution we have used I'd particle doped UO2 pellets. The catalytic effect of Pd particles on the kinetics of radiation induced dissolution Of UO2 during gamma-irradiation in HCO3- containing solutions purged with N-2 and H-2 was studied in this work. Four pellets with Pd concentrations of 0%, 0.1%, 1% and 3% were produced to mimic spent nuclear fuel. The pellets were placed in 10 mM HCO3- aqueous solutions and gamma-irradiated, and the dissolution of UO22+ was measured spectrophotometrically as a function of time. Under N-2 atmosphere, 3% I'd prevent the dissolution of uranium by reduction with the radiolytically produced H-2, while the other pellets show a rate of dissolution of around 1.6 x 10(-9) mol m(-2) s(-1). Under H-2 atmosphere already 0.1% Pd effectively prevents the dissolution of uranium, while the rate of dissolution for the pellet without Pd is 1.4 x 10(-9) mol m(-2) s(-1). It is also shown in experiments without radiation in aqueous solutions containing H2O2 and O-2 that epsilon-particles catalyze the oxidation of the UO2 matrix by these molecular oxidants, and that the kinetics of the catalyzed reactions is close to diffusion controlled.

  • 222.
    Trybula, Marcela E.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Polish Academy of Sciences, Krakow, 30-059, Poland.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Atomistic Simulations of Al(100) and Al(111) Surface Oxidation: Chemical and Topological Aspects of the Oxide Structure2019Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 1, s. 334-346Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The chemical and topological aspects of short- and medium-range atomic ordering on oxidized Al(100) and Al(111) surfaces have been studied by employing reactive force field-based molecular dynamics (ReaxFF-MD) simulations as a function of O-2 gas density at 300 K. We found two oxide film growth regimes, compatible with experimental and recent modeling data. Trend of changes in oxide film thickness with increasing oxygen gas density agrees with available literature data, while slightly thicker oxide film forms on the Al(100) substrate. Chemical descriptors of short- and medium-range correlation manifest difference in atom environment between two ultrathin oxide films as Al-[3,Al-4] and O-[2,O-3]-coordinated species dominate. In turn, a highly liquid-like structure of ultrathin oxide film develops on the Al(100) surface compared to an amorphous nature of the Al(111) oxide film with slightly lower thickness. Three-dimensional analysis of oxide structures reveals a medium-range atomic order formed by the arrangement of dominating corner-sharing configurations over edge-sharing ones with some deviation from the ideal polyhedral units. Three-fold ring is in majority over 2-, 4-, and 5-fold ones, in conjunction with a 2-fold ring forming the most frequent ring linkage. The high-n ring structure can be treated as a measure of a certain degree of "free volume", incorporated in the oxide film during its growth on the Al(100) or Al(111) surfaces and can initiate nanostructure formation in anodic oxide film. Such diversity in ring abundance also explains the lower mass density of the oxide films compared to crystalline alumina compounds.

  • 223. Ulvenlund, Stefan
    et al.
    Rosdahl, Jan
    KTH, Tidigare Institutioner                               , Kemi.
    Fischer, Andreas
    KTH, Tidigare Institutioner                               , Kemi.
    Schwerdtfeger, Peter
    Kloo, Lars
    KTH, Tidigare Institutioner                               , Kemi.
    Hard Acid and Soft Base Stabilisation of Di- and Trimercury Cations in Benzene Solution - A Spectroscopic, X-ray Scattering, and Quantum Chemical Study1999Inngår i: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, nr 4, s. 633-642Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hg2Cl2 dissolves in GaCl3/benzene solution to yield Hg-2(2+) and chlorogallate(III) ions, GanCl3n+1-. In such solutions, Hg-2(2+) can be reduced to Hg-3(2+) by metallic mercury. Solubility measurements show that one mol of Hg is oxidised per mol of Hg-2(2+). The Hg-3(2+) ion gives a strong band at 110 cm(-1) in the Raman spectrum and Hg-Hg correlations at about 2.60 and 5.15 Angstrom in the radial distribution function obtained by Liquid X-ray scattering. - Hg-3(2+) can also be synthesised in high yield by direct oxidation of metallic mercury by Ga-III in GaCl3/benzene solution. In contrast, mercury is insoluble in neat Liquid GaCl3 and only sparingly soluble in GaCl3/KCl melts. It therefore seems likely that the thermodynamic stabilisation of subvalent mercury species in benzene solution not only relies on the traditional acid stabilisation provided by the hard Lewis acid GaCl3, but also on a "soft-base stabilisation" provided by interactions between the aromatic molecules and the cations. Evidence for such specific interactions between Hg-m(2+) cations and C6H6 are observed in the Raman spectra: The totally symmetric C6H6 band at 991 cm(-1) is found to split in the presence of Hg-m(2+) ions and to give new peaks at 978 (m = 2) and 982 (m = 3) cm(-1). - In order to further elucidate the cluster-arene interactions, ab initio and density functional calculations were performed for the model compounds Hg-m(C6H6)(2)(2+) and HgmCl2(C6H6)(2), m = 2 and 3. The calculations show that both models represent coordinations modes which are feasible for Hg-m(2+) ions. However, the calculated vibrational frequencies for the Hg-m(C6H6)(2)(2+) models with eta(1)/quasi-eta(3) coordination of the benzene molecules along the Hg-Hg vector are most consistent with the body of experimental and literature data. The counterions are thus suggested to occupy secondary coordination sites.

  • 224. Vallet, Valerie
    et al.
    Fischer, Andreas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Szabo, Zoltan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Grenthe, Ingmar
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    The structure and bonding of Y, Eu, U, Am and Cm complexes as studied by quantum chemical methods and X-ray crystallography2010Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, nr 33, s. 7666-7672Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two isomers of Y/Eu(TTA)(3)(OH2) complexes and their structures were identified by single crystal X-ray diffraction, and their geometry and bond distances were also determined using quantum chemical (QM) methods. The data from the two methods agree very well, suggesting that QM is appropriate for calculating structures for which no experimental data are available. This method was therefore used to determine the structures of U/Am/Cm(TTA)(3)(OH2)(2) both in gas phase and in CPCM models of CCl4, CHCl3, and H2O. In these calculations the metal sites were described using the f-in-core approximation, comparing small- and large-core pseudopotentials (SPP and LPP) with their corresponding segmented basis sets. The difference between the Y/Eu-O bond distances between the LPP and SPP is less than 0.02 angstrom. However, in the actinide complexes the LPP results in larger An-O distances and the difference between the LPP and SPP results decreases from about 0.20 angstrom in the U-complex to 0.05 angstrom in the Am-and 0.04 angstrom in the Cm-complex. The chemical bonding studied by population analysis indicates that there is a significant back bonding in U(TTA)(3)(OH2)(2) from filled orbitals centered on uranium into empty pi* orbitals on coordinated oxygen; there is some evidence of back-bonding also in the americium complex, but a significantly smaller effect in the europium and curium species. The relative energy of the two isomers indicates they may be present in solution in comparable amounts, suggesting the possibility of exchange between them. The X-ray structures suggest two exchange pathways, a topological "twist" mechanism and a site exchange involving the opening of a TTA chelate ring.

  • 225. Vallet, Valerie
    et al.
    Szabo, Zoltan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Grenthe, Ingmar
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Structure and dynamics of binary and ternary lanthanide(III) and actinide(III) tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione] (TTA) - tributylphosphate (TBP) complexes.: Part 3, the structure, thermodynamics and reaction mechanisms of 8-and 9-coordinated binary and ternary Y-TTA-TBP complexes studied by quantum chemical methods2011Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, nr 13, s. 3154-3165Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Possible mechanisms for intermolecular exchange between coordinated and solvent water in the complexes Y(TTA)(3)(OH2)(2) and Y(TTA)(3)(TBP)(OH2) and intermolecular exchange between free and coordinated HTTA in Y(TTA)(3)(OH2)(HTTA) and Y(TTA)(3)(TBP)(HTTA) have been investigated using ab initio quantum chemical methods. The calculations comprise both structures and energies of isomers, intermediates and transition states. Based on these data and experimental NMR data (Part 2) we have suggested intimate reaction mechanisms for water exchange, intramolecular exchange between structure isomers and intermolecular exchange between free HTTA and coordinated TTA. A large number of isomers are possible for the complexes investigated, but only some of them have been investigated, in all of them the most stable geometry is a more or less distorted square anti-prism or bicapped trigonal prism; the energy differences between the various isomers are in general small, less than 10 kJ mol(-1). 9-coordinated intermediates play an important role in all reactions. Y(TTA)(3)(OH2)(3) has three non-equivalent water ligands that can participate in ligand exchange reactions. The fastest of these exchanging sites has a QM activation energy of 18.1 kJ mol(-1), in good agreement with the experimental activation enthalpy of 19.6 kJ mol(-1). The mechanism for the intramolecular exchange between structure isomers in Y(TTA)(3)(OH2)(2) involves the opening of a TTA-ring as the rate determining step as suggested by the good agreement between the QM activation energy and the experimental activation enthalpy 47.8 and 58.3 J mol(-1), respectively. The mechanism for the intermolecular exchange between free and coordinated HTTA in Y(TTA)(3)(HTTA) and Y(TTA)(3)(TBP)(HTTA) involves the opening of the intramolecular hydrogen bond in coordinated HTTA followed by proton transfer to coordinated TTA. This mechanism is supported by the good agreement between experimental activation enthalpies (within parenthesis) and calculated activation energies 68.7 (71.8) and 35.3 (38.8) kJ mol(-1). The main reason for the difference between the two systems is the much lower energy required to open the intramolecular hydrogen bond in the latter. The accuracy of the QM methods and chemical models used is discussed.

  • 226.
    Vegunta, Vijaya Lakshmi
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    A study on the thermal stability of sodium dithionite using ATR-FTIR spectroscopy2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Sodium dithionite (Na2S2O4) is a powerful reducing agent. It has therefore been suggested to be used as an additive in kraft pulping to improve the yield. However, sodium dithionite easily decomposes and it is thus important to determine the effect of different conditions. The aim of this thesis has been to investigate the thermal stability of sodium dithionite under anaerobic conditions using ATR-FTIR spectroscopy under different conditions, such as heating temperature, concentration of the solution, heating time and pH.

    The stability of sodium dithionite was found to decrease with increasing heating temperature, concentration of sodium dithionite, heating time and pH. Sodium dithionite was found to be relatively stable at moderate alkaline pH:s 11.5 and 12.5, while a rapid decrease in stability with time was noted at higher heating temperatures and concentrations of sodium dithionite.

    Based on this study on the thermal stability of sodium dithionite, the following conditions are suggested as the most promising, when adding sodium dithionite to the kraft cooking as an additive; pH 12.5, with 0.4 M concentration of the solution, at a heating temperature of 100 °C.

  • 227. Viklund, Peter
    et al.
    Juma, Susann
    Eriksson, Cecilia
    Engvall, Klas
    Swerea KIMAB AB, Stockholm, Sweden.
    Corrosion resistance of 304L, 310S and APMT in simulated biomass gasification environments2011Inngår i: European Corrosion Congress 2011, EUROCORR 2011, Curran Associates, Inc., 2011, Vol. 2, s. 1035-1043Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Gasification of biomass and waste is one feasible solution for the production of environmentally-friendly substitutes for motor fuels and chemicals. In the present study the austenitic stainless steels 304L and 310S, together with the ferritic APMT were exposed to conditions expected during biomass gasification. Isothermal experiments were performed for 200h at 500°C and 600°C in a bulk gas composition of 40%H 2-30%CO-20%CO 2-10%H 2O. Different exposures were conducted with HCl-concentrations of 0,500 and 1000 ppm. The corrosion behaviour was analysed using SEM-EDS, GDOES, XRD and CLSM. In the syngas atmosphere without HCl no signs of pitting attack or carbon ingress could be observed. In the presence of HCl, pitting attack and graphite formation became evident for both the 304L and 310S alloys. The attack became more severe at higher temperature and HCl-concentration. While the austenitic stainless steels suffered from accelerated corrosion in the presence of chlorine, the ferritic steel APMT displayed a smooth and thin oxide scale under all conditions. The general materials performance observed were of the order APMT > 310S > 304L. The results are discussed in terms of a detrimental effect of chlorine on the ability to form protective oxide scales.

  • 228. Viotti, Olle
    et al.
    Fischer, Andreas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Seisenbaeva, Gulaim A.
    Kessler, Vadim G.
    Straightforward synthesis and structural characterization of the first alkoxy-zircono-silsesquioxanes - Potential models for zirconia-silica epoxidation catalysts Molecular hybrid materials mimicking solution exchange in MOFs2010Inngår i: Inorganic Chemistry Communications, ISSN 1387-7003, E-ISSN 1879-0259, Vol. 13, nr 6, s. 774-777Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first representatives of alkoxy-zircono-silsesquioxane compounds, dinuclear [Cy7Si7O12]Zr(ROH)(mu-OR)(2)Zr(ROH)[O12Si7Cy7], where R = Pr-n, Bu-n, Bu-t: Cy = c-C6H11, and [Cy*7Si7O12]Zr(mu-ROH)(mu-OR)(2)Zr [O12Si7Cy*(7)], R = Bu-t; Cy* = c-C5H9, have been prepared with quantitative yield by interaction of the corresponding zirconium alkoxides with the cycloalkyl-substituted cage silsesquioxanes in hexane. The Xray single crystal study of the n-butoxide derivative revealed that zirconium atoms are hexacoordinated with the 3 oxygen atoms of the cage ligand, 2 from the bridging alkoxide groups and one from the solvating alcohol molecule in the coordination sphere. The molecule is additionally supported by a hydrogen bond between the solvating alcohol and an oxygen atom belonging to the cage ligand coordinated by the other zirconium atom. The structures of produced silsesquioxanes display behavior typical for metal-organic frameworks as they crystallize initially as hexane clathrates, but lose the solvent on storage in inert atmosphere. This results in formation of empty channels situated along the c-axis. (C) 2010 Elsevier B.V. All rights reserved.

  • 229. Wahlin, Pernilla
    et al.
    Vallet, Valerie
    Wahlgren, Ulf
    Grenthe, Ingmar
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Water Exchange Mechanism in the First Excited State of Hydrated Uranyl(VI)2009Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, nr 23, s. 11310-11313Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The water exchange mechanism of the uranyl(VI) aquo ion in the luminescent state, (3)Delta(g) in the spin-orbit free nomenclature, has been investigated using quantum chemical methods and compared to the corresponding reaction in the electronic ground state. The reaction mechanism was studied by calculation of the enthalpy of reaction of the A- and D-intermediates relative to the reactant, using a penta-aquo ion model with one additional water molecule in the second hydration sphere. The reaction barriers around the intermediates are low, and they are therefore a good approximation for the activation enthalpy. The energy of the D-intermediate is significantly larger than that of the A-intermediate both in the luminescent and in the ground states, suggesting that the water exchange is the same in both states. This suggestion is supported by the experimental rate constants for luminescence decay and water exchange in the electronic ground state that are 0.5 x 10(6) s(-1) and 1.3 x 10(6) s(-1), respectively.

  • 230.
    Wang, Ke
    et al.
    China Univ Petr, Beijing Key Lab Proc Fluid Filtrat & Separat, Beijing, Peoples R China.;KTH, Dept Phys, Stockholm, Sweden..
    Gong, Shengjie
    Shanghai Jiao Tong Univ, Sch Nucl Sci & Engn, Shanghai, Peoples R China..
    Bai, Bofeng
    Xi An Jiao Tong Univ, State Key Lab Multiphase Flow Power Engn, Xian, Shaanxi, Peoples R China..
    Ma, Weimin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnkraftssäkerhet.
    On the Relation between Nucleation Site Density and Critical Heat Flux of Pool Boiling2018Inngår i: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 39, nr 17-18, s. 1498-1506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is traditionally accepted that the critical heat flux (CHF) decreases with increasing nucleation site density (NSD). However, such a CHF-NSD relation was no longer observed in the BETA-B experiment performed on nano-film heaters; instead the increase of NSD resulted in a gain in CHF. To address this seeming contradiction in the relation between critical heat flux and nucleation site density, the present work employed probabilistic analysis to reveal the different tendencies. A concept of effective NSD was proposed, which concerns the active nucleation sites appear within a bubble lifetime, and the resulting bubbles have the chance of direct interaction. We assumed that the boiling crisis on a heater surface is mainly induced by two mechanisms: dry spot expanding in isolated bubble regime for low-NSD surface, coalescence of dry spots under multiple bubbles in fully developed nucleate boiling regime for high-NSD surface, or a combination of the two in the transition regime for medium-NSD surface. Accordingly, we estimated the critical heat flux of each boiling regime at which the boiling crisis occurs. The result indicated that there is a threshold of nucleation site density below which the increase of NSD is contributing to CHF enhancement, while the trend is inverted beyond the threshold.

  • 231.
    Wang, Xiaodi
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Ma, Ying
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Li, Shanghua
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Kashyout, Abdel-Hady
    Zhu, Bin
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Ceria-based nanocomposite with simultaneous proton and oxygen ion conductivity for low-temperature solid oxide fuel cells2011Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, nr 5, s. 2754-2758Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The samarium doped ceria-carbonate (SDC/Na2CO3) nanocomposite systems have shown to be excellent electrolyte materials for low-temperature SOFCs, yet, the conduction mechanism is not well understood. In this study, a four-probe d.c. technique has been successfully employed to study the conduction behavior of proton and oxygen ion in SDC/Na2CO3 nanocomposite electrolyte. The results demonstrated that the SDC/Na2CO3 nanocomposite electrolyte possesses unique simultaneous proton and oxygen ion conduction property, with the proton conductivity 1-2 orders of magnitude higher than the oxygen ion conductivity in the temperature range of 200-600 degrees C, indicating the proton conduction in the nanocomposite mainly accounts for the enhanced total ionic conductivity. It is suggested that the interface in composite electrolyte supplies high conductive path for proton, while oxygen ions are probably transported by the SDC grain interiors. An empirical "Swing Model" has been proposed as a possible mechanism of superior proton conduction. (C) 2010 Elsevier B.V. All rights reserved.

  • 232.
    Wesselmark, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Methanol and formic acid oxidation in zinc electrowinning under process conditions2008Inngår i: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 38, nr 1, s. 17-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility of using methanol or formic acid oxidation as the anode process in zinc electrowinning was examined. The activity for methanol and formic acid oxidation on Pt coated high surface area electrodes was investigated over 36 h, at a current density used in industry. The activity could be maintained at a constant potential level in a synthetic electrowinning electrolyte if the current was reversed for short periods. During the tests, the anode potential was, more than 1.2 V below the potential for the oxygen evolving lead anodes used in modern zinc electrowinning. The lowered anode potential would lead to a significant energy reduction. However, tests in industrial electrolyte resulted in a very low activity for both methanol and formic acid oxidation. The low activity was shown to be caused mainly by chloride impurities. A reduction of the chloride content below 10(-5) M is needed in order to obtain sufficient activity for methanol oxidation on Pt for use in zinc electrowinning. Pt and PtRu electrodes were compared regarding their activity for methanol oxidation and the latter was shown to be more affected by chloride impurities. However, at a potential of 0.7 V vs NHE, with a chloride content of 10(-4) M, formic acid oxidation on PtRu gives the highest current density.

  • 233.
    Wesselmark, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Methanol oxidation as anode reaction in zinc electrowinning2005Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, nr 11, s. D201-D207Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, different types of Pt- and PtRu-based electrodes were compared regarding their activity and stability for methanol oxidation in an acid zinc sulfate solution. The lead anodes used in zinc electrowinning today are not dimensionally stable and have a high overvoltage for oxygen evolution. By replacing the oxygen evolution in sulfate-based electrolytes with methanol oxidation, the anode potential could be significantly lowered. This would reduce the energy consumption and also enable the use of new and more stable types of electrodes. The activities of the electrodes studied were found sufficient for electrowinning. The highest activity was obtained with porous PtRu, while platinized titanium was the most stable electrode. All electrodes were deactivated with time, and the deactivation rate of PtRu was influenced by mass transport. The dominating reaction mechanism seemed to be different on Pt and on PtRu. Due to deactivation of the electrodes with time, a reactivation method was needed. The best method tested in this study was to periodically reverse the current. After assessing the electrodes with respect to important properties, the platinized titanium electrode was considered to be most suitable for use in electrowinning processes.

  • 234.
    Wesselmark, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Wickman, B.
    Chalmers University of Technology.
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Electrochemical performance and stability of thin film electrodes with metal oxides in polymer electrolyte fuel cells2010Inngår i: Electrochimica Acta, ISSN 0013-4686, Vol. 55, nr 26, s. 7590-7596Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thin film electrodes are prepared by thermal evaporation of nanometer thick layers of metal oxide and platinum on a gas diffusion layer (GDL), in order to evaluate different metal oxides' impact on the activity and stability of the platinum cathode catalyst in the polymer electrolyte fuel cell. Platinum deposited on tin, tantalum, titanium, tungsten and zirconium oxide is investigated and the morphology and chemistry of the catalysts are examined with scanning electron microscopy and X-ray photoelectron spectroscopy. Cyclic sweeps in oxygen and nitrogen are performed prior and after potential cycling degradation tests. Platinum seems to disperse better on the metal oxides than on the GDL and increased electrochemically active surface area (ECSA) of platinum is observed on tin, titanium and tungsten oxide. A thicker layer metal oxide results in a higher ECSA. Platinum deposited on tungsten performs better than sole platinum in the polarisation curves and displays higher Tafel slopes at higher current densities than all other samples. The stability does also seem to be improved by the addition of tungsten oxide, electrodes with 3 nm platinum on 3, 10 and 20 nm tungsten oxide, performs better than all other electrodes after the accelerated degradation tests.

  • 235.
    Wesselmark, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Wickman, B.
    Chalmers University of Technology.
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Hydrogen oxidation reaction on thin platinum electrodes in the polymer electrolyte fuel cell2010Inngår i: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 12, nr 11, s. 1585-1588Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method for measuring the kinetics of the hydrogen oxidation reaction (HOR) in a fuel cell under enhanced mass transport conditions is presented. The measured limiting current density was roughly 1600 mA cmPt− 2, corresponding to a rate constant of the forward reaction in the Tafel step of 0.14 mol m− 2 s− 1 at 80 °C and 90% RH. The exchange current density for the HOR was determined using the slope at low overvoltages and was found to be 770 mA cmPt− 2. The high values for the limiting and exchange current densities suggest that the Pt loading in the anode catalyst can be reduced further without imposing measurable voltage loss.

  • 236.
    Wiezell, Katarina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Modelling and Experimental Investigation of the Dynamics in Polymer Electrolyte Fuel Cells2009Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In polymer electrolyte fuel cells (PEFC) chemical energy, in for example hydrogen, is converted by an electrochemical process into electrical energy. The PEFC has a working temperature generally below 100 °C. Under these conditions water management and transport of oxygen to the cathode are the parameters limiting the performance of the PEFC.

    The purpose of this thesis was to better understand the complex processes in different parts of the PEFC. The rate-limiting processes in the cathode were studied using pure oxygen while varying oxygen pressure and humidity. Mass-transport limitations in the gas diffusion layer using oxygen diluted in nitrogen or helium was also studied. A large capacitive loop was seen at 1-10 Hz with 5-20 % oxygen. When nitrogen was changed to helium, which has a higher binary diffusion coefficient, the loop decreased and shifted to a higher frequency.

    Steady-state and electrochemical impedance spectroscopy (EIS) models have been developed that accounts for water transport in the membrane and the influence of water on the anode. Due to water drag, the membrane resistance changes with current density. This gives rise to a low frequency loop in the complex plane plot. The loop appeared at a frequency of around 0.1 Hz and varied with D/Lm2, where D is the water diffusion coefficient and Lm is the membrane thickness. The EIS model for the hydrogen electrode gave three to four semicircles in the complex plane plot when taking the influence of water concentration on the anode conductivity and kinetics into account. The high-frequency semicircle is attributed to the Volmer reaction, the medium-frequency semicircle to the pseudocapacitance resulting from the adsorbed hydrogen, and the low-frequency semicircles to variations in electrode performance with water concentration. These low-frequency semicircles appear in a frequency range overlapping with the low-frequency semicircles from the water transport in the membrane. The effects of current density and membrane thickness were studied experimentally. An expected shift in frequency, when varying the membrane thickness was seen. This shift confirms the theory that the low-frequency loop is connected to the water transport in the membrane.

  • 237.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Gode, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Steady-State and EIS Investigations of Hydrogen Electrodes and Membranes in Polymer Electrolyte Fuel Cells: I. Modeling2006Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. A749-A758Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrochemical impedance spectroscopy (EIS) and steady-state models have been developed for the porous hydrogen electrode with water concentration dependence and water transport in a polymer electrolyte fuel cell membrane. Because the hydrogen electrode performance is influenced by its water content, the hydrogen electrode model was coupled to the membrane model. The EIS model for the hydrogen electrode gave three to four loops in the complex plane plots. The high-frequency semicircle was attributed to the Volmer reaction and the medium-frequency semicircle to the hydrogen adsorption. The additional low-frequency loops were connected to changes in the hydrogen electrode performance with water concentration, due to changes in kinetics or proton conductivity. Those loops appear in a frequency range depending on the water transport in the membrane, changing with D/L-m(2), where D is the water diffusivity and L-m is the membrane thickness. Modeling of the membrane alone showed that the membrane gives rise to a loop in EIS. The difference between the high- and low-frequency intercepts of the loop is idR/di, where the high-frequency intercept is equal to the membrane resistance. The loop appears in the same frequency range as the hydrogen electrode low-frequency loops and thus overlaps.

  • 238.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Gode, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Steady-state and EIS investigations of hydrogen electrodes and membranes in polymer electrolyte fuel cells: II. Experimental2006Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. A759-A764Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Influence of water on membrane and anode performance was studied with steady-state and electrochemical impedance spectroscopy (EIS) measurements using a symmetrical cell with hydrogen on both sides. Both full-cell and half-cell measurements were performed. To obtain half-cell data a new reference electrode approach was demonstrated based on porous references in a four-electrode setup. A varying membrane resistance with current density was obtained using current interrupt and EIS measurements. The EIS measurements showed two semicircles at 10(4) Hz and 0.01-0.1 Hz, respectively. The first corresponds to hydrogen adsorption and the second to the water dependence of the electrode performance and membrane resistance. The low-frequency semicircle appears in a frequency range depending on the membrane thickness. The loop corresponding to the discharge of the double-layer capacitance through the Volmer reaction appears at frequencies too high to be experimentally measurable. The experimental data were in good agreement with the model developed in Part I of this paper. The model was also successfully fitted to experimental full cell data at different current densities and membrane thicknesses. The experiments confirmed that the low-frequency semicircle is attributed to the water dependence of both anode and membrane performance.

  • 239.
    Wikander, Kjell
    et al.
    Chalmers tekniska högskola, Göteborg.
    Ekström, Henrik
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Palmqvist, Anders
    Chalmers tekniska högskola, Göteborg.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    On the influence of Pt particle size on PEMFC cathode performance2007Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 52, nr 24, s. 6848-6855Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Colloidal suspensions of almost spherical and crystalline Pt nanoparticles between 1.6 and 2.6 nm in diameter and with narrow size distribution were synthesized using the phase transfer method (PTM) with alkylamines, CnNH2, as stabilizing agents. Batches of such homogenous Pt-CnNH2 (n =8, 12) nanocrystals were deposited onto Vulcan XC-72 carbon powder, and the activity for the oxygen reduction reaction (ORR) of this series of Pt/C materials was evaluated under PEMFC conditions. The aim was to elucidate whether this type of stabilized Pt nanoparticles were as active for the ORR as a corresponding commercial Pt/C material, and if any difference in mass activity could be observed between catalysts with different Pt particle size. In the PEMFC experiments, i.e. voltammetry in oxygen and nitrogen, it was found that, after an initial electrode activation, the ORR activity of the catalysts prepared from the alkylamine-stabilized Pt nanoparticles deposited on carbon was as high as that of the employed commercial reference catalyst. In fact, all samples in the Pt/C series showed high and very similar ORR activity normalized to Pt-loading, without significant dependence on the initial Pt particle size. However, pre- and post-electrochemical characterization of the Pt/C material series with TEM showed that structural changes of the Pt nanoparticles occurred during electrochemical evaluation. In all samples studied the mean Pt particle size increased during the electrochemical evaluation resulting in decreased differences between the samples explaining the observed similar ORR performance of the different materials. These results emphasize the necessity of post-operation characterization of fuel cell catalysts when discussing electrocatalytic activity. In addition, employing complex preparation efforts for lowering the Pt particle size below 3 ran may have limited practical value unless the particles are stabilized from electrochemical sintering.

  • 240.
    Wikander, Kjell
    et al.
    Chalmers tekniska högskola, Göteborg.
    Ekström, Henrik
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Palmqvist, Anders
    Chalmers tekniska högskola, Göteborg.
    Lundblad, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Holmberg, Krister
    Chalmers tekniska högskola, Göteborg.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Alternative catalysts and carbon support material for PEMFC2006Inngår i: Fuel Cells, ISSN 1615-6846, E-ISSN 1615-6854, Vol. 6, nr 1, s. 21-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to investigate the possibility of increasing the reactivity for oxygen reduction reaction (ORR) of the cathode in a PEMFC a series of Pt/C catalysts was prepared using water-in-oil microemulsions for synthesizing Pt nanoparticles. The Pt nanoparticles were deposited on porous carbon support (Vulcan XC-72 or a mesoporous carbon) and the catalysts were processed into MEAs. The MEA samples were evaluated and compared with a commercial sample and with Pt/C catalyst samples prepared using a conventional direct impregnation method. The mesoporous carbon support investigated as a potential alternative to Vulcan XC72 has a very high specific surface area and a narrow pore size distribution. The materials were characterized with XRD, TEM, SEM-EDX, N-2 sorption and steady state polarization. It was found that it is possible to increase the ORR reactivity using the microemulsion route for formation of Pt nanoparticles. It was concluded that the MEA processing conditions for the mesoporous carbon support have to be modified to reach improved ORR reactivity, likely due to the large differences in specific surface area, porosity and conductivity compared to the Vulcan carbon.

  • 241.
    Wreland Lindström, Rakel
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Kortsdottir, Katrin
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Wesselmark, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Oyarce, Alejandro
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects2010Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 157, nr 12, s. B1795-B1801Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper discusses the proper measure of the electrochemically active area (ECA)of carbon supported Pt catalyst in PEM fuel cells employing in situ cyclic voltammetry. The charges of the hydrogen underpotential deposition (Hupd) and CO stripping peak obtained in situ are compared, and the influence of operation temperature (25–80°C) and relative humidity (40%–90%) is discussed. The results show that the charges of the Hupd decrease with rising temperature, while the corresponding charges of the CO stripping peak are essentially independent of temperature, at least at high relative humidity. The unexpectedly small Hupd charges are explained by the significant overlap with the hydrogen evolution reaction in a fuel cell at elevated temperatures. According to our results, it is proposed that a more reliable value of Pt ECA is estimated from the CO stripping charge. However, with decreasing humidity the charges of both Hupd and CO stripping peaks decrease, which is probably an effect of increasing blockage of Pt active sites by hydrophobic domains in the electrode ionomer. Some implications of varying cell conditions on the estimated Pt ECA and its correlation with fuel cell activity are discussed in an example from a fuel cell degradation test.

  • 242. Wu, Xiujuan
    et al.
    Wu, Xingqiang
    Lee, Husileng
    Ye, Qilun
    Wang, Xiaoxiao
    Zhao, Yimeng
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Hollow Carbon@NiCo2O4 Core-Shell Microspheres for Efficient Electrocatalytic Oxygen Evolution2019Inngår i: ENERGY TECHNOLOGY, ISSN 2194-4288, Vol. 7, nr 4, artikkel-id 1800919Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earth-abundant transition metal oxides are considered one of the most promising oxygen evolution reaction (OER) catalysts. However, their intrinsically low electrical conductivity inhibits the fast kinetics for OER. To overcome this drawback, hollow carbon@NiCo2O4 core-shell microspheres (C@NiCo2O4 HSs) are synthesized with enhanced electrocatalytic activity and stability toward OER. The prepared C@NiCo2O4/Ni foam delivers a current density of 10 mA cm(-2) at a small overpotential of 268 mV and exhibits a low Tafel slope of 54 mV dec(-1). The enhanced OER performance is attributed to the enlarged specific surface area induced by the combination effect between the 1D nanosheet structure and the 3D hollow microsphere structure, and the improved electrical conductivity is ascribed to the carbon core support.

  • 243. Xiong, P.
    et al.
    Ma, R.
    Sakai, N.
    Bai, X.
    Li, Shen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sasaki, T.
    Redox Active Cation Intercalation/Deintercalation in Two-Dimensional Layered MnO2 Nanostructures for High-Rate Electrochemical Energy Storage2017Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, nr 7, s. 6282-6291Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two-dimensional (2D) layered materials with a high intercalation pseudocapacitance have long been investigated for Li+-ion-based electrochemical energy storage. By contrast, the exploration of guest ions other than Li+ has been limited, although promising. The present study investigates intercalation/deintercalation behaviors of various metal ions in 2D layered MnO2 with various interlayer distances, K-birnessite nanobelt (K-MnO2), its protonated form (H-MnO2), and a freeze-dried sample of exfoliated nanosheets. Series of metal ions, such as monovalent Li+, Na+, and K+ and divalent Mg2+, exhibit reversible intercalation during charge/discharge cycling, delivering high-rate pseudocapacitances. In particular, the freeze-dried MnO2 of exfoliated nanosheets restacked with the largest interlayer spacing and a less compact 3D network exhibits the best rate capability and a stable cyclability over 5000 cycles. Both theoretical calculation and kinetic analysis reveal that the increased interlayer distance facilitates the fast diffusion of cations in layered MnO2 hosts. The results presented herein provide a basis for the controllable synthesis of layered nanostructures for high-rate electrochemical energy storage using various single- and multivalent ions.

  • 244. Yang, X.
    et al.
    Li, H.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Kang, T.
    Luo, W.
    Formation and electronic properties of palladium hydrides and palladium-rhodium dihydride alloys under pressure2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, nr 1, artikkel-id 3520Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the formation possibility for Pd-hydrides and Pd-Rh hydrides system by density functional theory (DFT) in high pressure upto 50 GPa. Calculation confirmed that PdH2 in face-centered cubic (fcc) structure is not stable under compression that will decomposition to fcc-PdH and H2. But it can be formed under high pressure while the palladium is involved in the reaction. We also indicate a probably reason why PdH2 can not be synthesised in experiment due to PdH is most favourite to be formed in Pd and H2 environment from ambient to higher pressure. With Rh doped, the Pd-Rh dihydrides are stabilized in fcc structure for 25% and 75% doping and in tetragonal structure for 50% doping, and can be formed from Pd, Rh and H2 at high pressure. The electronic structural study on fcc type Pd x Rh1-xH2 indicates the electronic and structural transition from metallic to semi-metallic as Pd increased from x = 0 to 1.

  • 245. Yu, Xinhai
    et al.
    Li, Hongliang
    Tu, Shan-Tung
    Yan, Jinyue
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Energiprocesser.
    Wang, Zhengdong
    Pt-Co catalyst-coated channel plate reactor for preferential CO oxidation2011Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 36, nr 5, s. 3778-3788Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To achieve preferential CO oxidation, a Pt-Co catalyst-coated channel plate reactor (CCPR) was produced via conventional mechanical milling and catalyst coating. The proposed reactor performed well under a wide range of operating temperatures and provided satisfactory results at low temperatures (CO concentrations of 1-10 ppm at 413-443 K and 1-50 ppm at 413-453 K). In the proposed CCPR, significant deactivation was not observed during continuous operation for 100 h. In addition, the reactor exhibited excellent tolerance to undesirable conditions, including reaction temperature runaway and feeding stream failure. Characterisation results indicated that the catalytic activity of the proposed CCPR was high due to the formation of Pt3Co intermetallic compounds and nanoscale metal particles. The capacity per channel of the proposed CCPR was approximately 50-100 times greater than those of conventional microchannel reactors; thus, problems associated with excessive reactors were significantly reduced. In general, the results indicated that CCPR has great potential in the small-scale production of hydrogen for fuel cells.

  • 246.
    Yu, Ze
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Liquid Redox Electrolytes for Dye-Sensitized Solar Cells2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis focuses on liquid redox electrolytes in dye-sensitized solar cells (DSCs). A liquid redox electrolyte, as one of the key constituents in DSCs, typically consists of a redox mediator, additives and a solvent. This thesis work concerns all these three aspects of liquid electrolytes, aiming through fundamental insights to enhance the photovoltaic performances of liquid DSCs.

    Initial attention has been paid to the iodine concentration effects in ionic liquid (IL)-based electrolytes. It has been revealed that the higher iodine concentration required in IL-based electrolytes can be attributed to both triiodide mobility associated with the high viscosity of the IL, and chemical availability of triiodide. The concept of incompletely solvated ionic liquids (ISILs) has been introduced as a new type of electrolyte solvent for DSCs. It has been found that the photovoltaic performance of ISIL-based electrolytes can even rival that of organic solvent-based electrolytes. And most strikingly, ISIL-based electrolytes provide highly stable DSC devices under light-soaking conditions, as a result of the substantially lower vapor pressure of the ISIL system. A significant synergistic effect has been observed when both guanidinium thiocyanate and N-methylbenzimidazole are employed together in an IL-based electrolyte, exhibiting an optimal overall conversion efficiency.

    Tetrathiafulvalene (TTF) has been investigated as an organic iodine-free redox couple in electrolytes for DSCs. An unexpected worse performance has been observed for the TTF system, albeit it possesses a particularly attractive positive redox potential. An organic, iodine-free thiolate/disulfide system has also been adopted as a redox couple in electrolytes for organic DSCs. An impressive efficiency of 6.0% has successfully been achieved by using this thiolate/disulfide redox couple in combination with a poly (3, 4-ethylenedioxythiophene) (PEDOT) counter electrode material under full sunlight illumination (AM 1.5G, 100 mW/cm2). Such high efficiency can even rival that of its counterpart DSC using a state-of-the-art iodine-based electrolyte in the systems studied.The cation effects of lithium, sodium and guanidinium ions in liquid electrolytes for DSCs have been scrutinized. The selection of the type of cations has been found to exert quite different impacts on the conduction band edge (CB) of the TiO2 and also on the electron recombination kinetics, therefore resulting in different photovoltaic behavior.

  • 247.
    Yu, Ze
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Investigation of Cation Effects in the Electrolytes for Dye-Sensitized Solar CellsArtikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    A comparison of the effects of the cations of lithium, sodium and guanidinium in electrolytes for dye-sensitized solar cells have been investigated. Upon addition of cations to the reference electrolyte, short-circuit currents are generally found to be significantly enhanced, largely due to the positive shift of the conduction band edge (CB) in the TiO2. This probably results in an increase of the electron injection yield from the excited state of the sensitizing dye to the CB of TiO2. The open-circuit voltages for electrolytes incorporating lithium and sodium cations, however, are found to be slightly lower in comparison to the reference electrolyte. This may be attributed to the more positive shift of the conduction band edge in the TiO2. On the contrary, a slight improvement of the open-circuit voltage for electrolytes containing higher concentrations of guanidinium cations is observed relative to the reference electrolyte. This can most likely be ascribed to the collective effect of a much longer electron lifetime in the TiO2 and less positive shift of the CB. The electrolyte higher concentrations of guanidinium cations exhibits the optimal overall conversion efficiency among all the electrolytes investigated. the optimal performance can be attributed to the dual gain in both short-circuit current and open-circuit voltage with respect to the reference electrolyte.

  • 248.
    Yu, Ze
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Vlachopoulos, Nick
    Uppsala University, Sweden.
    Gorlov, Mikhail
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Liquid electrolytes for dye-sensitized solar cells2011Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, nr 40, s. 10289-10303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present review offers a survey of liquid electrolytes used in dye-sensitized solar cells from the beginning of photoelectrochemical cell research. It handles both the solvents employed, and the prerequisites identified for an ideal liquid solvent, as well as the various effects of electrolyte solutes in terms of redox systems and additives. The conclusions of the present review call for more detailed molecular insight into the electrolyte-electrode interface reactions and structures.

  • 249.
    Yu, Zu
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Vlachopoulos, Nick
    Physical Chemistry, Uppsala University.
    Hagfeldt, Anders
    Physical Chemistry, Uppsala University.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Incompletely Solvated Ionic Liquids as Electrolyte Solvents for Highly Stable Dye-Sensitized Solar CellsArtikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Ionic liquids have been intensively investigated as alternative stable electrolyte solvents for dye-sensitized solar cells (DSCs). A highest overall conversion efficiency of over 8% has been achieved using ionic-liquid-based electrolyte in combination with an iodide/triiodide redox couple. However, the relatively high viscosities of ionic liquids require higher iodine concentration in the electrolyte due to mass-transport limitations of the triiodide ions. The higher iodine concentration significantly reduces the photovoltaic performance, which normally are lower than those using organic solvent-based electrolytes. Here, the concept of incompletely solvated ionic liquids (ISILs) is introduced and represents a conceptually new type of electrolyte solvents for DSCs. It is found that the photovoltaic performance of ISIL-based electrolytes can rival that of organic solvent-based electrolytes. Furthermore, the vapor pressures of ISILs are found be considerably lower than that for pure organic solvent. Stability tests show that ISIL-based electrolytes provide highly stable DSCs under light-soaking conditions. Thus, ISIL-based electrolytes offer a new platform to develop more efficient and stable DSC devices of relevance to future large-scale applications.

  • 250. Zanonato, Pier Luigi
    et al.
    Di Bernardo, Plinio
    Grenthe, Ingmar
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Chemical equilibria in the binary and ternary uranyl(VI)-hydroxide-peroxide systems2012Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, nr 12, s. 3380-3386Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The composition and equilibrium constants of the complexes formed in the binary U(VI)-hydroxide and the ternary U(VI)-hydroxide-peroxide systems have been studied using potentiometric and spectrophotometric data at 25 degrees C in a 0.100 M tetramethylammonium nitrate medium. The data for the binary U(VI) hydroxide complexes were in good agreement with previous studies. In the ternary system two complexes were identified, [UO2(OH)(O-2)](-) and [(UO2)(2)(OH)(O-2)(2)](-). Under our experimental conditions the former is predominant over a broad p[H+] region from 9.5 to 11.5, while the second is found in significant amounts at p[H+] < 10.5. The formation of the ternary peroxide complexes results in a strong increase in the molar absorptivity of the test solutions. The absorption spectrum for [(UO2)(2)(OH) (O-2)(2)](-) was resolved into two components with peaks at 353 and 308 nm with molar absorptivity of 16200 and 20300 M-1 cm(-1), respectively, suggesting that the electronic transitions are dipole allowed. The molar absorptivity of [(UO2)(OH)(O-2)](-) at the same wave lengths are significantly lower, but still about one to two orders of magnitude larger than the values for UO22+(aq) and the binary uranyl(VI) hydroxide complexes. It is of interest to note that [(UO2)(OH)(O-2)](-) might be the building block in cluster compounds such as [UO2(OH)(O-2)](60)(60-) studied by Burns et al. (P. C. Burns, K. A. Kubatko, G. Sigmon, B. J. Fryer, J. E. Gagnon, M. R. Antonio and L. Soderholm, Angew. Chem. 2005, 117, 2173-2177). Speciation calculations using the known equilibrium constants for the U(VI) hydroxide and peroxide complexes show that the latter are important in alkaline solutions even at very low total concentrations of peroxide, suggesting that they may be involved when the uranium minerals Studtite and meta-Studtite are formed by alpha-radiolysis of water. Radiolysis will be much larger in repositories for spent nuclear fuel where hydrogen peroxide might contribute both to the corrosion of the fuel and to transport of uranium in a ground water system.

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