Solid-state Electrochemical Cells Research Articles

Extracting evolution of recombination zone position in sandwiched solid-state light-emitting electrochemical cells by employing microcavity effect

Techniques of probing for time-dependent evolution of recombination zone position in sandwiched light-emitting electrochemical cells (LECs) would be highly desired since they can provide direct experimental evidence to confirm altered carrier balance when device parameters are adjusted. However, direct imaging of recombination zones in thin emissive layers of sandwiched LECs could not be obtained easily. In this work, we propose an alternative way to extract evolution of recombination zone position in sandwiched LECs by utilizing microcavity effect. Recombination zone positions can be estimated by fitting the measured electroluminescence spectra to simulated output spectra based on microcavity effect and properly adjusted emissive zone positions. With this tool, effects of modified carrier transport and carrier injection on performance of LECs are studied and significantly altered carrier balance can be measured, revealing that microcavity effect is useful in tracing evolution of recombination zone position in sandwiched LECs.

Phase chemistry of the system Nb–Rh–O

Abstract Phase relations in the system Nb–Rh–O at 1223 K were investigated by isothermal equilibration of eleven compositions and analysis of quenched samples using OM, XRD, SEM and EDS. The oxide phase in equilibrium with the alloy changes progressively from NbO to NbO2, NbO2.422 and Nb2O5−x with increasing Rh. Only one ternary oxide NbRhO4 with tetragonal structure (a=0.4708 nm and c=0.3017 nm) was detected. It coexists with Rh and Nb2O5. The standard Gibbs energy of formation of NbRhO4 from its component binary oxides measured using a solid-state electrochemical cell can be represented by the equation; Δ G f , ox o ( J / mol ) = − 38 , 350 + 5.818 × T ( ± 96 ) Constructed on the basis of thermodynamic information of the various alloy and oxide phases are oxygen potential diagram for the system Nb–Rh–O at 1223 K and temperature–composition diagrams at constant partial pressures of oxygen.

Gibbs energy of formation of Ca7V4O17

Thermodynamic properties of Ca7V4O17 are measured for the first time using a solid-state electrochemical cell incorporating single crystal of CaF2 as the electrolyte over the temperature range from (900 to 1175)K. An equimolar mixture of CaO and CaF2 is used as the reference electrode and a mixture of Ca3V2O8, Ca7V4O17 and CaF2 as the measuring electrode. Both the electrodes are placed under flowing oxygen gas at ambient pressure. The standard Gibbs energy change for the reaction:2Ca3V2O8+CaO→Ca7V4O17,which is related to the chemical potential of CaO in the two-phase region (Ca3V2O8+Ca7V4O17) of the pseudo-binary system CaO+V2O5, is obtained from the electromotive force of the cell as:ΔrGo±127/(J·mol-1)=ΔμCaO=-11453+8.273(T/K).The derived standard enthalpy of formation of Ca7V4O17 from elements in their normal standard states is – (8208.97±8)kJ⋅mol−1and its standard entropy is (560.05±7.5)J⋅K−1⋅mol−1, both at T=298.15K. The results indicate that Ca7V4O17 decomposes into Ca3V2O8 and CaO at T=(1384±3)K.

Potentiometric CO2 sensor with Au,Li2CO3/Li+-electrolyte/LiMn2O4 structure

A new solid-state electrochemical cell for CO2 sensing has been set up using Li3PO4 and Li4SiO4 (LiSiPO) solid electrolyte and Li1-δMn2O4/MnO2 as reference electrode. The electromotive force (EMF), the reproducibility, and the long-term stability of the sensor signals have been examined at temperature between 400 and 500 °C exposure on dry atmosphere. The EMF is dependent on the partial pressure of CO2 and can be expressed by the Nernst equation. The cell is long-term stable at temperature as low as 450 °C and the sensor signals are reproducible with high accuracy.

Highly efficient exciplex emission in solid-state light-emitting electrochemical cells based on mixed ionic hole-transport triarylamine and ionic electron-transport 1,3,5-triazine derivatives

Highly efficient exciplex emission in solid-state light-emitting electrochemical cells (LECs) was achieved by mixing two ionic fluorescent emitters with opposite bipolarity. A triarylamine derivative as a hole-transport material (HTM) and a 1,3,5-triazine derivative as an electron-transport material (ETM) were selected due to their superior carrier mobilities. The ionic character of HTM and ETM was achieved by chemically attaching three pendant methylimidazolium groups as peripheries, rendering them amenable to LEC applications. Strong exciplex green emission can be observed either from photoluminescence in solid states or electroluminescence in LEC devices when HTM and ETM are mixed. By optimizing the mixing ratio, the external quantum efficiency and power efficiency can be achieved up to 3.04% and 10.29 lm W−1, respectively. These results are among the highest reported for fluorescent LECs.

Solid-state Forensic Finger sensor for integrated sampling and detection of gunshot residue and explosives: towards ‘Lab-on-a-finger’

Increasing security needs require field-deployable, on-the-spot detection tools for the rapid and reliable identification of gunshot residue (GSR) and nitroaromatic explosive compounds. This manuscript presents a simple, all-solid-state, wearable fingertip sensor for the rapid on-site voltammetric screening of GSR and explosive surface residues. To fabricate the new Forensic Fingers, we screen-print a three-electrode setup onto a nitrile finger cot, and coat another finger cot with an ionogel electrolyte layer. The new integrated sampling/detection methodology relies on 'voltammetry of microparticles' (VMP) and involves an initial mechanical transfer of trace amounts of surface-confined analytes directly onto the fingertip-based electrode contingent. Voltammetric measurements of the sample residues are carried out upon bringing the working electrode (printed on the index finger cot) in direct contact with a second finger cot coated with an ionogel electrolyte (worn on the thumb), thus completing the solid-state electrochemical cell. Sampling and screening are performed in less than four minutes and generate distinct voltammetric fingerprints which are specific to both GSR and explosives. The use of the solid, flexible ionogel electrolyte eliminates any liquid handling which can resolve problems associated with leakage, portability and contamination. A detailed study reveals that the fingertip detection system can rapidly identify residues of GSR and nitroaromatic compounds with high specificity, without compromising its attractive behavior even after undergoing repeated mechanical stress. This new integrated sampling/detection fingertip strategy holds considerable promise as a rapid, effective and low-cost approach for on-site crime scene investigations in various forensic scenarios.

Thermodynamics of TmRhO3, Phase Equilibria, and Chemical Potentials in the System Tm–Rh–O

Phase equilibria in the system Tm–Rh–O at 1200 K is established by isothermal equilibration of selected compositions and phase identification after quenching to room temperature. Six intermetallic phases (Tm3Rh, Tm7Rh3, Tm5Rh3, Tm3Rh2, TmRh, TmRh2±δ) and a ternary oxide TmRhO3 are identified. Based on experimentally determined phase relations, a solid-state electrochemical cell is devised to measure the standard free energy of formation of orthorhombic perovskite TmRhO3 from cubic Tm2O3 and β-Rh2O3 in the temperature range from (900 to 1300) K. The results can be summarized as: ΔGf,ox° ± 104/J·mol–1 = −46474 + 3.925(T/K). Invoking the Neumann-Kopp rule, the standard enthalpy of formation of TmRhO3 from its constituent elements at 298.15 K is estimated as −1193.89 (± 2.86) kJ·mol–1. The standard entropy of TmRhO3 at 298.15 K is evaluated as 103.8 (± 1.6) J·mol–1·K–1. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1200 K and temperature–composition diagrams at c...

Cationic Iridium Complexes with Intramolecular π–π Interaction and Enhanced Steric Hindrance for Solid-State Light-Emitting Electrochemical Cells

Cationic iridium complexes incorporated 4,5-diaza-9,9'-spirobifluorene as N(∧)N ancillary ligands, in which one (2) or two (3) phenyl groups were introduced onto 4,5-diazafluorene to afford intraligand π-π interactions. The X-ray crystal structures of complexes 2 and 3 show that the pendant phenyl ring forms strong intramolecular face-to-face π-stacking with the difluorophenyl ring of the cyclometalated ligand with distances of 3.38 Å for complex 2 and 3.40 and 3.46 Å for complex 3. This π-π stacking interaction minimizes the expansion of the metal-ligand bonds in the excited state, resulting in a longer device lifetime in the light-emitting electrochemical cell (LEC) devices.

Electrochemical determination of thermodynamic properties of DyRhO3 and phase relations in the system Dy-Rh-O

Thermodynamic properties of Dysprosium rhodite (DyRhO3) are measured in the temperature range from 900 to 1,300 K using a solid-state electrochemical cell incorporating yttria-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of DyRhO3 with O-type perovskite structure from its components binary oxides, Dysprosia with C-rare earth structure and β-Rh2O3 with orthorhombic structure, can be represented by the equation: $$ {{{\varDelta G_{{f\left( {ox} \right)}}^o\left( {\pm 182} \right)}} \left/ {{{\mathrm{J} ~ \mathrm{mo}}{{\mathrm{l}}^{{ - 1}}}}} \right.} = - 52710 + 3.821\left( {{{T} \left/ {\mathrm{K}} \right.}} \right). $$

ChemInform Abstract: A New Family of Mo‐Doped SrCoO3‐δ Perovskites for Application in Reversible Solid State Electrochemical Cells.

AbstractThe introduction of Mo in SrCoO3‐δ to form SrCo0.95Mo0.05O3‐δ and SrCo0.9Mo0.1O3‐δ leads to a change from a hexagonal to a tetragonal (space group P4/mmm) perovskite structure at room temperature.

System Ho-Rh-O: Phase Equilibria, Chemical Potentials and Gibbs Energy of Formation of HoRhO3

The thermodynamic properties of the HoRhO3 were determined in the temperature range from 900 to 1300 K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of orthorhombic perovskite HoRhO3, from Ho2O3 with C-rare earth structure and Rh2O3 with orthorhombic structure, can be expressed by the equation; $$ \Updelta G_{{{\text{f}}({\text{ox}})}}^{ \circ } \left( { \pm 78} \right)/({\text{J}}/{\text{mol}}) = - 50535 + 3.85\left( {T/{\text{K}}} \right) $$ Using the thermodynamic data of HoRhO3 and auxiliary data for binary oxides from the literature, the phase relations in the Ho-Rh-O system were computed at 1273 K. Thermodynamic data for intermetallic phases in the binary Ho-Rh were estimated from experimental enthalpy of formation for three compositions from the literature and Miedema’s model, consistent with the phase diagram. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1273 K, and temperature-composition diagrams at constant oxygen partial pressures were computed for the system Ho-Rh-O. The decomposition temperature of HoRhO3 is 1717(±2) K in pure O2 and 1610(±2) K in air at a total pressure p o = 0.1 MPa.

System Gd–Rh–O: Thermodynamics and phase relations

Thermodynamic properties of GdRhO3 are investigated in the temperature range from 900 to 1300K by employing a solid-state electrochemical cell, incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of GdRhO3 from component binary oxide Gd2O3 with C-rare earth structure and Rh2O3 with orthorhombic structure can be expressed as;ΔGf(ox)o(±60)/Jmol-1=-56603+3.78(T/K)Based on the thermodynamic information on GdRhO3 from experiment and auxiliary data for binary oxides from the literature and estimated properties of Gd–Rh alloys, phase relations are computed for the system Gd–Rh–O at 1273K. Gibbs free energies for intermetallic phases in the binary Gd–Rh are evaluated using calorimetric data available in the literature for two compositions and Miedema’s model, consistent with the binary phase diagram. Isothermal section of the ternary phase diagram, oxygen potential-composition diagram and a 3-D chemical potential diagram for the system Gd–Rh–O at 1273K are developed. Phase relations in the ternary Gd–Rh–O are also computed as a function of temperature at constant oxygen partial pressures. The ternary oxide, GdRhO3 decomposes to Gd2O3 with B-rare earth structure, metallic Rh and O2 at 1759(±2)K in pure O2 and 1649(±2)K in air at a total pressure P0=0.1MPa.

Nonstoichiometry, defects and thermodynamic properties of YFeO3, YFe2O4 and Y3Fe5O12

Oxygen nonstoichiometry of three ternary oxides, YFeO3−δ, YFe2O4−α and Y3Fe5O12−θ, in the system Y–Fe–O was investigated as a function of oxygen partial pressure by thermogravimetry at high temperature. The defects responsible for nonstoichiometry were identified as oxygen vacancies for YFeO3−δ and YFe2O4−α, although the manner of variation of nonstoichiometric parameter with oxygen partial pressure for these two oxides is quite different. Cation interstitials are the predominant defects in Y3Fe5O12−θ. Gibbs energies of formation of the three nonstoichiometric oxides were determined using solid-state electrochemical cells in the temperature range from 975 to 1475K. YFe2O4−α was found to be stable only above 1391K. Gibbs energies of formation of the three stoichiometric compounds from their component binary oxides were obtained by combining information from solid state cells with results of thermogravimetric analysis using the Gibbs–Duhem relation. The results can be summarized as:(1/2)Y2O3+(1/2)Fe2O3→YFeO3;ΔGf(ox)O(±250)(J/mol)=−17,126−8.263T(1/2)Y2O3+FeO+(1/2)Fe2O3→YFe2O4;ΔGf(ox)O(±260)(J/mol)=−10,352−13.24T(3/2)Y2O3+(5/2)Fe2O3→Y3Fe5O12;ΔGf(ox)O(±780)(J/mol)=−56,647−31.091T.

Microelectrode Analysis of Oxygen Permeation through Nafion® Thin Films

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Gibbs Energy of Formation of Ca3Ti8Al12O37 and Phase Relations and Chemical Potentials in the System Al2O3-TiO2-CaO

The quaternary oxide in the system Al2O3-CaO-TiO2 is found to have the composition Ca3Ti8Al12O37 rather than CaTi3Al8O19 as reported in the literature. The standard Gibbs energy of formation of Ca3Ti8Al12O37 from component binary oxides is measured in the temperature range from 900 to 1250 K using a solid-state electrochemical cell incorporating single crystal CaF2 as the solid electrolyte. The results can be represented by the equation: $$ \Updelta G_{\text{f(ox)}}^{\text{o}} ( \pm 70)/{\text{J}}\,{\text{mol}}^{ - 1} = - 248474 - 15.706(T/{\text{K}}). $$ Combining this information with thermodynamic data on calcium aluminates and titanates available in the literature, subsolidus phase relations in the pseudo-ternary system Al2O3-CaO-TiO2 are computed and presented as isothermal sections. The evolution of phase relations with temperature is highlighted. Chemical potential diagrams are computed at 1200 K, showing the stability domains of the various phases in the chemical potential-composition space. In each chemical potential diagram, chemical potential of one component is plotted against the cationic fraction of the other two components. The diagrams are valid at relatively high oxygen potentials where Ti is present in its four-valent state in all the oxide phases.

ChemInform Abstract: Solid‐State Light‐Emitting Electrochemical Cells Based on Ionic Iridium(III) Complexes

AbstractReview: 87 refs.

Materials development for intermediate-temperature solid oxide electrochemical devices

One of the major challenges in developing electrochemical devices for energy generation has been the identification and development of materials with outstanding performance at reduced (intermediate) temperatures (500–700 °C), increasing the durability and lowering the cost of the device. A solid-state electrochemical cell is in outline a simple device consisting of three components: anode, electrolyte and cathode. The function of each component is critical to cell performance, and as interest in fuel cells and electrolysers has gathered pace, many materials have been evaluated as functional components of these cells. Typically, the requirement for new materials development has been the drive to lower operation temperature, overcoming sluggish reaction kinetics in existing materials. Novel materials for the functional components of both electrolysers and fuel cells are introduced, with emphasis placed on the air electrode and electrolyte, with the potential of new classes of materials discussed, including layered materials, defect fluorites and tetrahedrally coordinated phases. Furthermore, the opportunity presented by thin film deposition to characterize anisotropic transport in materials and develop devices based on thin films is discussed.

Solid-state light-emitting electrochemical cells based on ionic iridium(iii) complexes

Solid-state light-emitting electrochemical cells (LECs) have aroused great interest in recent years as novel organic light-emitting devices and a promising lighting solution. LECs have many advantages over multilayered organic lighting-emitting diodes (OLEDs), such as single layer, solution process and air-stable cathodes. In recent years, ionic iridium complexes are widely used in LECs for their high efficiencies and tunable emission colours. In this feature article, we will review the proposed operation mechanisms of LECs, the development of ionic iridium complexes and the progress in improving colour, efficiency, stability and response time of the LECs. Finally, the prospects and remaining problems will be discussed.

Improving the balance of carrier mobilities of host–guest solid-state light-emitting electrochemical cells

We report efficient host-guest solid-state light-emitting electrochemical cells (LECs) utilizing a cationic terfluorene derivative as the host and a red-emitting cationic transition metal complex as the guest. Carrier trapping induced by the energy offset in the lowest unoccupied molecular orbital (LUMO) levels between the host and the guest impedes electron transport in the host-guest films and thus improves the balance of carrier mobilities of the host films intrinsically exhibiting electron preferred transporting characteristics. Photoluminescence measurements show efficient energy transfer in this host-guest system and thus ensure predominant guest emission at low guest concentrations, rendering significantly reduced self-quenching of guest molecules. EL measurements show that the peak EQE (power efficiency) of the host-guest LECs reaches 3.62% (7.36 lm W(-1)), which approaches the upper limit that one would expect from the photoluminescence quantum yield of the emissive layer (∼0.2) and an optical out-coupling efficiency of ∼20% and consequently indicates superior balance of carrier mobilities in such a host-guest emissive layer. These results are among the highest reported for red-emitting LECs and thus confirm that in addition to reducing self-quenching of guest molecules, the strategy of utilizing a carrier transporting host doped with a proper carrier trapping guest would improve balance of carrier mobilities in the host-guest emissive layer, offering an effective approach for optimizing device efficiencies of LECs.

Tailoring carrier injection efficiency to improve the carrier balance of solid-state light-emitting electrochemical cells

We study the influence of the carrier injection efficiency on the performance of light-emitting electrochemical cells (LECs) based on a hole-preferred transporting cationic transition metal complex (CTMC) [Ir(dfppz)(2)(dtb-bpy)](+)(PF(6)(-)) (complex 1) and an electron-preferred transporting CTMC [Ir(ppy)(2)(dasb)](+)(PF(6)(-)) (complex 2) (where dfppz is 1-(2,4-difluorophenyl) pyrazole, dtb-bpy is 4,4'-di(tert-butyl)-2,2'-bipyridine, ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9'-spirobifluorene). Experimental results show that even with electrochemically doped layers, the ohmic contacts for carrier injection could be formed only when the carrier injection barriers were relatively low. Thus, adding carrier injection layers in LECs with relatively high carrier injection barriers would affect carrier balance and thus would result in altered device efficiency. Comparison of the device characteristics of LECs based on complex 1 and 2 in various device structures suggests that the carrier injection efficiency of CTMC-based LECs should be modified according to the carrier transporting characteristics of CTMCs to optimize device efficiency. Hole-preferred transporting CTMCs should be combined with an LEC structure with a relatively high electron injection efficiency, while a relatively high hole injection efficiency would be required for LECs based on electron-preferred transporting CTMCs. Since the tailored carrier injection efficiency compensates for the unbalanced carrier transporting properties of the emissive layer, the carrier recombination zone would be located near the center of the emissive layer and exciton quenching near the electrodes would be significantly mitigated, rendering an improved device efficiency approaching the upper limit expected from the photoluminescence quantum yield of the emissive layer and the optical outcoupling efficiency from a typical layered light-emitting device structure.