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Jonathan Rivnay - One of the best experts on this subject based on the ideXlab platform.

  • time resolved structural kinetics of an organic Mixed ionic electronic Conductor
    Advanced Materials, 2020
    Co-Authors: Bryan D Paulsen, Christopher J Takacs, Hansgeorg Steinruck, Joseph Strzalka, Qingteng Zhang, Michael F Toney, Jonathan Rivnay
    Abstract:

    The structure and packing of organic Mixed ionic-electronic Conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady-state and transient structure of the model organic Mixed Conductor, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time-resolved operando techniques. Steady-state operando X-ray scattering reveals a doping-induced lamellar expansion of 1.6 A followed by 0.4 A relaxation at high doping levels. Time-resolved operando X-ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time-resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron-bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic Mixed-Conductor-based devices, and present the first real-time observation of the structural changes during doping and dedoping of a conjugated polymer system via X-ray scattering.

  • structural control of Mixed ionic and electronic transport in conducting polymers
    Nature Communications, 2016
    Co-Authors: Jonathan Rivnay, Sahika Inal, Brian Collins, Michele Sessolo, Eleni Stavrinidou, Xenofon Strakosas, Christopher J Tassone, Dean M Delongchamp
    Abstract:

    UNLABELLED: Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT: PSS, has been utilized for over two decades as a stable, solution-processable hole Conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT: PSS as a Mixed ionic/electronic Conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on Mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT: PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical Mixed Conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on Mixed conduction.

  • structural control of Mixed ionic and electronic transport in conducting polymers
    Nature Communications, 2016
    Co-Authors: Jonathan Rivnay, Sahika Inal, Brian Collins, Michele Sessolo, Eleni Stavrinidou, Xenofon Strakosas, Christopher J Tassone, Dean M Delongchamp
    Abstract:

    Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole Conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a Mixed ionic/electronic Conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on Mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical Mixed Conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on Mixed conduction. Conducting polymers are promising materials for applications including bioelectronics and soft robotics, but little is known about how morphology affects Mixed conduction. Here, the authors show how bulk ionic/electronic transport is affected by changes in nano- and meso-scale structure in PEDOT:PSS films.

Joachim Maier - One of the best experts on this subject based on the ideXlab platform.

  • cu22bi12s21cl16 a Mixed Conductor with fast one dimensional copper i ion transport
    ChemInform, 2011
    Co-Authors: Andreas Heerwig, Rotraut Merkle, Joachim Maier, Michael Ruck
    Abstract:

    Black, shiny needles of the title compound are prepared by melting a mixture of Cu, CuCl, S, and Bi2S3 (1120 K, tempering at 570 K for 14 d).

  • cu22bi12s21cl16 a Mixed Conductor with fast one dimensional copper i ion transport
    Journal of Solid State Chemistry, 2011
    Co-Authors: Andreas Heerwig, Rotraut Merkle, Joachim Maier, Michael Ruck
    Abstract:

    Abstract Melting reactions of Cu, CuCl, S, and Bi 2 S 3 yield black, shiny needles of Cu 22(1) Bi 12 S 21(1) Cl 16(1) . The compound decomposes peritectically at 649(5) K. Oxidation state +I of the copper atoms is supported by Cu– K -XANES. The compound crystallizes in the hexagonal space group P 6/ m with a= 2116.7(7) pm and c =395.17(5) pm. Seven anions coordinate each of the two independent bismuth cations in the shape of mono-capped trigonal prisms. These polyhedra share edges and faces to form trigonal and hexagonal tubes running along [0 0 1]. The hexagonal tubes are centered by chloride ions, which are surrounded by disordered copper cations. The majority of copper cations are distributed over numerous sites between the tubes. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [0 0 1]. The high mobility of the copper cations along [0 0 1] was demonstrated by impedance spectroscopy and DC polarization measurements on single crystals. The ionic conductivity at 450 K is about σ ion =0.06 S cm −1 , and the activation energy for Cu + ion conduction is E a =0.44 eV. The chemical diffusion coefficient of copper is in the order of D cu δ =10 19  cm −3 at 420 K. The electronic band gap (p-type Conductor) was determined as E g =0.06 eV. At room temperature the thermal conductivity of a pressed pellet is about κ =0.3 W K −1  m −1 and the Seebeck coefficient is S =43 μV K −1 .

  • mechanistic understanding and electrochemical modeling of Mixed conducting sofc electrodes
    Handbook of Fuel Cells, 2010
    Co-Authors: R Merkle, Joachim Maier, Jurgen Fleig
    Abstract:

    In this article it is shown how the phenomenological transport parameters measured on a Mixed conducting solid oxide fuel cell (SOFC) cathode are related to the underlying fundamental quantities, such as bulk defect concentrations and mobilites, and surface reaction mechanism and corresponding equilibrium exchange rate. Complications due to charged oxygen adsorbates and arising under an applied dc bias are discussed. Dense thin-film microelectrodes are shown to serve as valuable model systems for achieving a mechanistic understanding and obtaining reliable experimental data. Keywords: solid oxide fuel cell; cathode; Mixed Conductor; equivalent circuit; microelectrodes; oxygen incorporation mechanism; adsorbate coverage; current-voltage-curves; modeling

  • generalised equivalent circuits for mass and charge transport chemical capacitance and its implications
    Physical Chemistry Chemical Physics, 2001
    Co-Authors: J Jamnik, Joachim Maier
    Abstract:

    An exact equivalent circuit including terminal parts, which takes account of electrical and chemical control parameters in a unified way, is derived for a cell with a Mixed Conductor (or electrolyte) without internal sources or sinks. In one-dimensional problems electrochemical kinetics can be mapped by two-dimensional circuits exhibiting the spatial and the thermodynamic displacement as two independent coordinates. One main advantage of the exact circuits with respect to the underlying differential equations is the ability to simplify the description according to specific situations. As we show in several examples in the second part of the paper, it is straightforward to select the elements relevant for the particular experimental conditions and so to make appropriate approximations. This is most helpful for the description of electrochemical systems, such as fuel cells, membranes, pumps and batteries.

  • treatment of the impedance of Mixed Conductors equivalent circuit model and explicit approximate solutions
    Journal of The Electrochemical Society, 1999
    Co-Authors: J Jamnik, Joachim Maier
    Abstract:

    The electrochemical impedance of a Mixed Conductor with two charge carriers sandwiched between two equal electrodes is modeled phenomenologically. A simple analytical approximation is found which applies in a very broad materials parameter window (arbitrary carrier mobilities and concentrations) as long as linear response is guaranteed and the sample thickness is great compared to the Debye length. The approximation is applicable to reversible, selectively blocking as well as to partially blocking electrodes. The validity of the approximation is justified by comparison with the exact solution of Nernst‐Planck‐Poisson set of equations as given, e.g., by Macdonald. The analytical approximation describes the typical Warburg response as well as the single‐carrier behavior as limiting cases. Finite interfacial resistances (not perfectly blocking or not perfectly reversible electrodes) lead to additional semicircles and/or to distorted Warburg responses. © 1999 The Electrochemical Society. All rights reserved.

Masakazu Aono - One of the best experts on this subject based on the ideXlab platform.

  • material dependence of switching speed of atomic switches made from silver sulfide and from copper sulfide
    Journal of Physics: Conference Series, 2007
    Co-Authors: K Terabe, Tomonobu Nakayama, Tsuyoshi Hasegawa, Takuro Tamura, T Sakamoto, Hiroshi Sunamura, Hisao Kawaura, Sumio Hosaka, Masakazu Aono
    Abstract:

    We developed an atomic switch consisting of an ionic and electronic Mixed Conductor electrode and a counter metal electrode, having a space of about 1 nm between them. Formation and annihilation of a conductive atomic bridge is controlled using a solid electrochemical reaction, which is caused by applying a certain bias voltage between the electrodes. In this study, we measured the switching time of atomic switches made of silver sulfide and copper sulfide. The switching times were different, and this difference can be attributed to the different activation energies and chemical potentials of the materials.

  • formation and disappearance of a nanoscale silver cluster realized by solid electrochemical reaction
    Journal of Applied Physics, 2002
    Co-Authors: K Terabe, Tomonobu Nakayama, Tsuyoshi Hasegawa, Masakazu Aono
    Abstract:

    We have developed a nanostructuring method using the solid electrochemical reaction induced by a scanning tunneling microscope (STM). This method has some distinctive features that have not previously been obtained by conventional nanostructuring STM methods. The formation and disappearance of the nanostructure are reversible, and the rates can be controlled using STM. These features are realized via a local oxidation/reduction reaction of mobile metal ions in an ionic/electronic Mixed Conductor. In this study, a crystal of silver sulfide (Ag2S), a Mixed Conductor, was used as the material for the STM tip. A nanoscale Ag cluster was formed at the apex of the Ag2S tip when a negative bias voltage was applied to the sample. The Ag ions in the Ag2S tip are reduced to Ag atoms by the tunneling electrons from the sample, and the Ag cluster is formed by the precipitation of the Ag atoms at the apex of the tip. The Ag cluster shrank gradually and disappeared when the polarity of the sample bias voltage was switc...

  • ionic electronic Mixed Conductor tip of a scanning tunneling microscope as a metal atom source for nanostructuring
    Applied Physics Letters, 2002
    Co-Authors: K Terabe, Tomonobu Nakayama, Tsuyoshi Hasegawa, Masakazu Aono
    Abstract:

    Silver sulfide (Ag2S) which has Ag-ionic/electronic Mixed conductivity is used for fabricating a tip used for a scanning tunneling microscope. The Mixed Conductor tip is capable of nanostructuring by depositing Ag atoms continuously on a sample as well as imaging the surface structure. To obtain the surface image, a nanoscale Ag protrusion is formed at an apex of the tip using a local solid electrochemical reaction, working as “a mini-tip.” We fabricate a nanoscale line structure on the sample by scanning the Ag2S tip with the protrusion under appropriate bias voltages and tunneling currents. The structuring is thought to be made up of two layers of Ag atoms deposited from the protrusion.

Zongping Shao - One of the best experts on this subject based on the ideXlab platform.

  • surface exchange and bulk diffusion properties of ba0 5sr0 5co0 8fe0 2o3 δ Mixed Conductor
    International Journal of Hydrogen Energy, 2011
    Co-Authors: Dengjie Chen, Zongping Shao
    Abstract:

    Abstract Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is a Mixed conducting oxide that shows high oxygen permeability to perform as a ceramic membrane and high electrochemical activity for oxygen reduction to perform as a cathode of solid oxide fuel cells. Both performances are closely related to the bulk and surface properties of the BSCF oxide. In this study, the chemical bulk diffusion coefficient (Dchem) and chemical surface exchange coefficient (kchem) of BSCF at various temperatures and oxygen partial pressures are determined by an electrical conductivity relaxation (ECR) method. Both Dchem and kchem are found to be dependent on p O 2 with positive effect. Ea of Dchem and kchem are respectively 111 ± 5 and 110 ± 6 kJ mol−1 between 600 and 800 °C. Oxygen-ion diffusion and tracer diffusion coefficients are estimated from Dchem and compared with the literature results. Ionic conductivities are further derived according to the Nernst–Einstein relation. The poisoning effect of CO2 on the performances of BSCF is further investigated by the ECR method in combination with oxygen temperature-programmed desorption technique. The presence of CO2 causes a substantial decrease in kchem, however, the surface kinetics can be recovered by performing re-calcination in an oxidative atmosphere at 900 °C, agreeing well with literature reports.

  • evaluation of ba0 6sr0 4co0 9nb0 1o3 δ Mixed Conductor as a cathode for intermediate temperature oxygen ionic solid oxide fuel cells
    Journal of Power Sources, 2010
    Co-Authors: Cheng Huang, Dengjie Chen, Ye Lin, Ran Ran, Zongping Shao
    Abstract:

    Abstract A perovskite-type Ba 0.6 Sr 0.4 Co 0.9 Nb 0.1 O 3− δ (BSCN) oxide is investigated as the cathode material of oxygen-ionic solid-oxide fuel cells (SOFCs) with Sm 0.2 Ce 0.8 O 3− δ (SDC) electrolyte. Powder X-ray diffraction and SEM characterization demonstrate that solid phase reactions between BSCN and SDC are negligible at temperatures up to 1100 °C. The results of thermal-expansion and electrical conductivity measurements indicate the introduction of Ba 2+ into the A-site of SrCo 0.9 N 0.1 O 3− δ (SCN) led to a decrease in the thermal-expansion coefficient (TEC) and electrical conductivity of the compound. A TEC of 14.4 × 10 −6  K −1 is observed for BSCN within a temperature range of 200–500 °C. The chemical diffusion coefficient ( D chem ) and surface exchange constant ( k ex ) of BSCN and SCN are obtained using an electrical conductivity relaxation technique and BSCN prove to have higher D chem and k ex than SCN. An area-specific resistance of 0.1 Ω cm −2 is achieved for BSCN cathodes at 600 °C based on symmetric cells test. Peak power density of ∼1150 mW cm −2 is reached for a thin-film electrolyte cell with BSCN cathode at 600 °C, which is higher than a similar cell with SCN cathode (∼1008 mW cm −2 ). BSCN is a promising cathode material for oxygen-ionic IT-SOFCs.

Tom Nilges - One of the best experts on this subject based on the ideXlab platform.

  • polymorphism structural frustration and electrical properties of the Mixed Conductor ag10te4br3
    Chemistry of Materials, 2007
    Co-Authors: Stefan Lange, Melanie Bawohl, D Wilmer, Hinrichwilhelm Meyer, Hansdieter Wiemhofer, Tom Nilges
    Abstract:

    Ag10Te4Br3 is polymorphic with four polymorphs in the temperature range from 3 to 450 K. It represents the first member of a formerly unseen class of materials featuring covalently and ionically bonded tellurium substructures. Thermal analyses (DSC and Cp) prove the reversibility of the α−β, β−γ, and γ−δ phase transitions at 355, 317, and 290 K, respectively. The existence of the low-temperature δ-phase is substantiated by Cp measurements down to 3 K. Temperature-dependent single-crystal structure analysis and nonharmonic refinements of the silver distribution for all polymorphs reveal a high silver mobility over the whole temperature range. A significant change in the dimensionality of the silver distribution, from an exclusively 2D (δ, γ) to a 3D (β, α) arrangement, can be observed for Ag10Te4Br3 with the increase in temperature. The enhanced silver mobility causes a structural frustration and disorder phenomena of the predominantly covalently bonded tellurium substructure for the high-temperature α- an...

  • polymorphism structural frustration and electrical properties of the Mixed Conductor ag10te4br3
    Chemistry of Materials, 2007
    Co-Authors: Stefan Lange, Melanie Bawohl, D Wilmer, Hinrichwilhelm Meyer, Hansdieter Wiemhofer, Tom Nilges
    Abstract:

    Ag10Te4Br3 is polymorphic with four polymorphs in the temperature range from 3 to 450 K. It represents the first member of a formerly unseen class of materials featuring covalently and ionically bo...