Solid-state Electrochemical Cells Research Articles

Oxygen potentials and phase equilibria in the system Ca–Co–O and thermodynamic properties of Ca3Co2O6 and Ca3Co4O9.163

Oxygen potentials established by the equilibrium between three condensed phases, CaOss+CoOss+Ca3Co2O6 and CoOss+Ca3Co2O6+Ca3Co3.93+αO9.36−δ, are measured as a function of temperature using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte and pure oxygen as the reference electrode. Cation non-stoichiometry and oxygen non-stoichiometry in Ca3Co3.93+αO9.36−δ are determined using different techniques under defined conditions. Decomposition temperatures and thermodynamic properties of Ca3Co2O6 and Ca3Co4O9.163 are calculated from the results. The standard entropy and enthalpy of formation of Ca3Co2O6 at 298.15K are evaluated. Using thermodynamic data from this study and auxiliary information from the literature, phase diagram for the ternary system Ca–Co–O is computed. Isothermal sections at representative temperatures are displayed to demonstrate the evolution of phase relations with temperature.

Characteristics of Light Emitting Electrochemical Cells Using Cationic Iridium(III) Complexes with Imidazole Based Ancillary Ligand

Two cationic heteroleptic iridium(III) complexes with imidazole based ancillary ligands, namely, [Ir(ppz)2(Hpyim)]PF6 and [Ir(dfppy)2(Hpyim)]PF6 (where ppz is 1-phenylpyrazole, dfppy is 2-(2,4-difluorophenyl)pyridine, Hpyim is 2-(1H-Imidazol-2yl)pyridine and PF6− is hexafluorophosphate) have been synthesized and characterized by various spectroscopic methods and studied their photophysical and electrochemical properties. Solid-state light-emitting electrochemical cells (LECs) were fabricated using the synthesized complexes and resulted in green electroluminescence through the particular selection of cyclometalated ligands.

Effect of ceramic fillers on polyethylene glycol-based solid polymer electrolytes for solid-state magnesium batteries

Composite polymer electrolyte (CPE) materials are very attractive for components of batteries and optoelectronic devices. Polyethylene glycol–magnesium nitrate polymer electrolytes and their composites were prepared by using addition of different weight percentage of titanium dioxide (TiO2) and cerium oxide ceramic fillers. Several experimental techniques, such as composition-dependence conductivity, temperature-dependence conductivity, and transport number measurements, have been employed to characterize these CPEs. The magnitude of conductivity increased with increase in the concentration of the ceramic fillers and temperature. The highest ionic conductivity achieved was 1.06 × 10−4 S/cm for the sample prepared with 10 wt% of TiO2 at room temperature. The charge transport in the present CPEs was obtained using Wagner’s polarization technique, which demonstrated that the charge transport was mainly due to ions. Using these polymer electrolytes, solid-state electrochemical cells were fabricated and their discharge profiles were studied under a constant load of 100 kΩ.

Effects of incorporating salts with various alkyl chain lengths on carrier balance of light-emitting electrochemical cells

Recently, solid-state light-emitting electrochemical cells (LECs) have attracted much attention since they have advantages such as low operation voltages, simple device structure and balanced carrier injection. Salts are commonly added in the emissive layer of LECs to provide additional mobile ions and thus to accelerate device response. However, in addition to modified ionic property, carrier balance of LECs would also be tailored by salt additives. In this work, we improve device efficiency of LECs by incorporating imidazole-based salts bearing various alkyl chain lengths. As the alkyl chain length of the added salt increases, the device current decreases and the recombination zone approaches the anode. These results reveal that hole transport in the emissive layer of LEC containing a salt with a larger size would be impeded more significantly than electron transport. When doped with a salt possessing a proper size, nearly doubled device efficiency as compared to that of the neat-film device can be obtained due to improved carrier balance. This work demonstrates a feasible strategy to improve device performance of LECs and clarifies the physical insights of the effect of salt size on carrier balance of LECs.

Oxygen Diffusion and Dissolution Rates in Sulfonated Polyetheretherketone Copolymer Thin Film Electrolyte Formed on Pt Microelectrode

Introduction Proton exchange membrane fuel cells (PEMFCs) are promising alternative devices for electrochemical energy transformers. In the PEMFCs, electrolyte materials are one of the key components. So far, perfluorinated sulfonic acid (PFSA) membranes, such as Nafion®(DuPont), have been used as the electrolyte membrane in the PEMFCs. Recently, sulfonated polyetheretherketone copolymers (SPEEK, Fig. 1) have been synthesized as low-cost and high-temperature-resistant alternative polymer electrolyte membranes [1], and the SPEEK copolymers exhibited high proton conductivity and excellent thermal stability.Oxygen gas permeability is an important property for the electrolyte. For example, it is widely recognized that oxygen gas crossover from the cathode to the anode through the electrolyte membrane leads to membrane degradation [2, 3]. In contrast, high oxygen gas permeability is required for ionomer which is added in the catalyst layer and cover Pt NP catalysts, influencing the PEMFCs performance. In this study, oxygen transport across the SPEEK thin film electrolyte was investigated. We used a Pt microelectrode (ME) covered with recast SPEEK thin film electrolyte. Oxygen diffusion and oxygen dissolution rates were determined from the limiting currents across the films of different thicknesses. The rate dependence on temperature was investigated to understand the mechanism for the gas transport across the SPEEK thin film electrolyte. Experimental Pt ME (100 μmφ) working electrode (W.E.) and Pt ME (250 μmφ) counter electrode (C.E.) were sealed in a glass rod (8 mmφ). A dynamic hydrogen electrode (DHE) consisting of two Pt MEs (250 μmφ) was used as a reference electrode (Fig. 2). SPEEK was dissolved in N,N-dimethyl-formamide (DMF) and casted onto the glass rod surface, followed by heat treatment at 120°C for 3 h in air. The resultant rod was soaked in 0.5 M H2SO4at room temperature for 24 h and repeatedly washed by DI water. The thickness of the SPEEK thin film electrolyte formed on the Pt ME W.E. was measured by contacting surface profile meter.The rod was set up in a solid-state electrochemical cell placed in temperature-humidity-controllable chamber. Cyclic voltammograms (CVs) were measured in the chamber under atmospheric pressure. Oxygen transport parameters, DCeq/d and kCeq , were determined from the limiting current (I lim) for oxygen reduction reaction (ORR) on the Pt ME W.E. using eq. (1) [3], where F is the Faraday constant (96485 C/mol), kCeq is the oxygen dissolution rate (mol/cm2/s), d is the thickness (cm) and DCeq is the oxygen permeability (mol/cm/s), respectively. Results and discussion Figure 3 shows CVs of Pt ME W.E. covered with SPEEK thin film electrolyte of 1.13 μm in thickness at different temperatures (R.H. 80 %). Characteristic Pt redox waves were clearly observed, indicating a sufficient interface contact between the W.E. and the SPEEK thin film electrolyte. The I limfor the ORR increased with an increase in temperature.The oxygen diffusion rate (DCeq/d) and the oxygen dissolution rate (kCeq ) were determined from I lim at various SPEEK thicknesses using eq. (1). Figure 4 summarizes DCeq/d and kC eq at different temperatures (80 %R.H). Here, the ionomer thickness d of 1.13 μm, which was the thinnest film in this work, was used for adjusting unit of DCeq in mol/cm2/s (y axis in Fig. 4). Both the oxygen diffusion and the oxygen dissolution rates increased with increase in temperature, however, the oxygen dissolution rates (kCeq ) were lower than the oxygen diffusion rates (DCeq/d) in the temperature range tested (40-80°C). Similar results on recast Nafion®thin film electrolyte have been reported by us [4]. Therefore, it could be concluded that the oxygen dissolution rate at the air/ionomer interface is the rate-determining step for the oxygen transport across the ionomer thin film formed the Pt catalyst. It is considered that increase in the oxygen dissolution rate is crucial for the enhancement of the cathode performance at high current densities in PEMFCs.

Magnesium ion conducting solid polymer blend electrolyte based on biodegradable polymers and application in solid-state batteries

Magnesium ion conducting solid polymer blend electrolyte based on biodegradable polymers polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) mixed with different molecular weight percentages (wt.%) of magnesium nitrate (Mg(NO3)2) was prepared by using solution casting technique. X-ray diffraction studies lead the reduction of crystalline nature by the addition of magnesium nitrate to the polymeric matrix. The complex formation between polymer and salt confirmed by Fourier transform infrared spectroscopy studies. Differential scanning calorimetry shows that the glass transition temperature decreases with increase in magnesium salt concentration and the thermal stability of PVA–PVP–Mg(NO3)2 complexes. The maximum ionic conductivity σ ~ 3.78 × 10−5 S cm−1 was obtained for 50PVA–50PVP–30 wt.% of Mg(NO3)2 polymer blend electrolyte at room temperature (303 K). The conductivity–temperature plot is found to follow the Arrhenius behavior, which showed the decrease in activation energy with the increasing salt concentration. The transference number data indicated the dominance of ion-type charge transport in these polymer blend electrolytes. The solid-state electrochemical cells were fabricated, and their discharge profiles were studied for this polymer blend electrolyte system under a constant load of 100 kΩ.

Electrical Properties of Pure and Doped (KNO3 & MgCl2) Polyvinyl Alcohol Polymer Thin Films

Polymer thin films find wide range of technological applications such as coatings, adhesives, lithography, sensors and as solid state electrochemical cells they can be directly deposited on to chips in any shape or size. In the present work pure and doped (KNO3 & MgCl2) polyvinyl alcohol thin films were synthesized using solution-casting method. The optical absorption spectra of synthesized thin films were recorded at room temperature over a wavelength range of 200-800 nm using JASCO spectrophotometer Model V-570. From the spectral data the optical constants such as band edge, optical band gap (both direct and indirect) were determined. The variation of optical band gap on doping is explained on the basis of incorporation of charge transfer complexes (CTCs) by the dopants. The absorption studies have led to a variety of interesting thin film optical phenomenon, which have thrown considerable light on the band structure of solids and phonic states.

Thermochemistry of the Cu2Se–In2Se3 system

Solid state electrochemical cells were employed to obtain standard Gibbs energy of formation of CuInSe2 as well as the temperature and enthalpy of the α to δ-CuInSe2 transformation in the Cu2Se–In2Se3 pseudo-binary system. The reversible EMF data of the following solid-state electrochemical cell were measured:Pt,In(l),In2O3(s)‖YSZ‖In2O3(s),Cu2Se(s),Cu(s),CuInSe2(αorδ),C,PtCell IThe calculated standard molar Gibbs energy of formation of α and δ-CuInSe2 from measured data are given byΔGf∘CuInSe2(α)±0.0003=0.0051T(K)-220.92kJ/mol(949–1044K)ΔGf∘CuInSe2(δ)±0.0004=-0.0043T(K)-210.92kJ/mol(1055–1150K)The α to δ phase transition temperature Ttrans and the enthalpy of transition ΔHtrans∘ for CuInSe2 were determined to be 1064K and 10.0kJ/mol respectively. ΔStrans∘ was calculated as 9.4J/molK.The thermodynamic and phase diagram data in the Cu2Se–In2Se3 pseudo-binary system were critically assessed. A self consistent set of thermochemistry and phase diagram data was obtained with the help of measured data. The liquid phase along the Cu2Se–In2Se3 pseudo-binary was calculated with the Redlich–Kister model. The β-Cu1In3Se5 and γ-Cu1In5Se8 phases were represented by the sub-regular model. The ordered non-stoichiometric α-CuInSe2 and δ-CuInSe2 phases were modeled by using a three-sublattice formalism. The calculated phase diagram and thermochemical data show reasonable agreement.

Preparation and characterization of PEG–Mg(CH3COO)2–CeO2 composite polymer electrolytes for battery application

Composite polymer electrolytes based on poly(ethylene glycol) (PEG), magnesium acetate [Mg(CH3COO)2], and x wt% of cerium oxide (CeO2) ceramic fillers (where x = 0, 5, 10, 15 and 20, respectively) have been prepared using solution casting technique. X-ray diffraction patterns of PEG–Mg(CH3COO)2 with CeO 2 ceramic filler indicated the decrease in the degree of crystallinity with increasing concentration of the filler. DSC measurements of PEG–Mg(CH3COO)2–CeO2 composite polymer electrolyte system showed that the melting temperature is shifted towards the lower temperature with increase of the filler concentration. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (i.e. 15 wt%) increases the ionic conductivity and upon further addition the conductivity decreases. The transference number data indicated the dominance of ion-type charge transport in these specimens. Using this (PEG–Mg(CH3COO)2–CeO2) (85-15-15) electrolyte, solid-state electrochemical cell was fabricated and their discharge profiles were studied under a constant load of 100 kΩ.

Redox-Gated Molecular Memory Devices Based on Dynamic Doping of Polythiophene

A solid state electrochemical cell resembling a field effect transistor will be described which can act as a nonvolatile memory element. “Write” and “Erase” pulses cause oxidation of a polythiophene to its conducting form, while the conductance is monitored by a “read” circuit. Raman and UV-Vis spectroelectrochemistry were used during device operation to investigate redox reactions which underlie memory operation. Important electrochemical concepts which control device operation include activated electron transfer, ion motion, and extended conjugation. In particular, internal ion transport creates ohmic potential losses which slow W/E operation, but can be significantly improved with higher mobility solid electrolytes. Applications seeking to augment existing silicon electronics with molecular components will be described.Recent references:(1) Yan, H.; Bergren, A. J.; McCreery, R.; Della Rocca, M. L.; Martin, P.; Lafarge, P.; Lacroix, J. C.; Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions; Proceedings of the National Academy of Sciences 2013, 110, 5326.(2) McCreery, R.; Yan, H.; Bergren, A. J.; A Critical Perspective on Molecular Electronic Junctions: There is Plenty of Room in the Middle; Phys. Chem. Chem. Phys. 2013, 15, 1065.(3) Sayed, S. Y.; Fereiro, J. A.; Yan, H.; McCreery, R. L.; Bergren, A. J.; Charge transport in molecular electronic junctions: Compression of the molecular tunnel barrier in the strong coupling regime; Proceedings of the National Academy of Sciences 2012, 109, 11498.(4) Kumar, R.; Pillai, R. G.; Pekas, N.; Wu, Y.; McCreery, R. L.; Spatially Resolved Raman Spectroelectrochemistry of Solid-State Polythiophene/Viologen Memory Devices; Journal of the American Chemical Society 2012, 134, 14869.

Electrochemical study of the thermodynamic properties of matildite (β-AgBiS2) in different temperature and compositional ranges

Thermodynamic properties of matildite (β-AgBiS2) in equilibrium with sulfur and bismuth have been studied by an EMF method, using the fast Ag+ ion-conducting solid electrolytes AgI and RbAg4I5. The ternary phases were synthesized from the pure binary compounds. Properties of the electrolytes used have been reviewed, and their usage as pure conductors of Ag+ ions in the temperature ranges of the electrochemical cells employed was well defined. The EMF measurements were carried out using the solid-state electrochemical cells Pt(−)|Ag|RbAg4I5|β‐AgBiS2 + AgBi3S5 + S|Pt(+) and Pt(−)|Ag|AgI|β‐AgBiS2 + AgBi3S5 + Bi|C|Pt(+), in the temperature range 325–464 K. Based on the obtained results, thermodynamic functions for the formation of matildite (β-AgBiS2) at sulfur and bismuth saturation have been determined. The obtained experimental values have been compared with the available literature values. New experimentally determined thermodynamic properties of the bismuth-saturated matildite (β-AgBi1 + x S2) and sulfur-saturated matildite (β-AgBiS2 + y ) were generated and analyzed in detail.

Enhancing device efficiencies of solid-state near-infrared light-emitting electrochemical cells by employing a tandem device structure

Compared to near-infrared (NIR) organic light-emitting devices, solid-state NIR light-emitting electrochemical cells (LECs) could possess several superior advantages such as simple device structure, low operating voltages and balanced carrier injection. However, intrinsically lower luminescent efficiencies of NIR dyes and self-quenching of excitons in neat-film emissive layers limit device efficiencies of NIR LECs. In this work, we demonstrate a tandem device structure to enhance device efficiencies of phosphorescent sensitized fluorescent NIR LECs. The emissive layers, which are composed of a phosphorescent host and a fluorescent guest to harvest both singlet and triplet excitons of host, are connected vertically via a thin transporting layer, rendering multiplied light outputs. Output electroluminescence (EL) spectra of the tandem NIR LECs are shown to change as the thickness of emissive layer varies due to altered microcavity effect. By fitting the output EL spectra to the simulated model concerning microcavity effect, the stabilized recombination zones of the thicker tandem devices are estimated to be located away from the doped layers. Therefore, exciton quenching near doped layers mitigates and longer device lifetimes can be achieved in the thicker tandem devices. The peak external quantum efficiencies obtained in these tandem NIR LECs were up to 2.75%, which is over tripled enhancement as compare to previously reported NIR LECs based on the same NIR dye. These efficiencies are among the highest reported for NIR LECs and confirm that phosphorescent sensitized fluoresce combined with a tandem device structure would be useful for realizing highly efficient NIR LECs.

Phase equilibria in the system Sm–Rh–O and thermodynamic and thermal studies on SmRhO3

Using isothermal equilibration, phase relations are established in the system Sm-Rh-O at 1273 K. SmRhO3 with GdFeO3-type perovskite structure is found to be the only ternary phase. Solid-state electrochemical cells, containing calcia-stabilized zirconia as an electrolyte, are used to measure the thermodynamic properties of SmRhO3 formed from their binary component oxides Rh2O3 (ortho) and Sm2O3 (C-type and B-type) in two different temperature ranges. Results suggest that C-type Sm2O3 with cubic structure transforms to B-type Sm2O3 with monoclinic structure at 1110 K. The standard Gibbs energy of transformation is . Standard Gibbs energy of formation of SmRhO3 from binary component oxides Rh2O3 and Sm2O3 with B-type rare earth oxide structure can be expressed as . The decomposition temperature of SmRhO3 estimated from the extrapolation of electrochemical data is 1665 (+/- 2) K in air and 1773 (+/- 3) K in pure oxygen. Temperature-composition diagrams at constant oxygen pressures are constructed for the system Sm-Rh-O. Employing the thermodynamic data for SmRhO3 from emf measurement and auxiliary data for other phases from the literature, oxygen potential-composition phase diagram and 3-D chemical potential diagram for the system Sm-Rh-O at 1273 K are developed.

Effect of zinc salt on transport, structural, and thermal properties of PEG-based polymer electrolytes for battery application

Solid polymer polyethylene glycol (PEG)-based electrolytes composed with zinc acetate Zn(CH3COO)2 have been prepared by using solution blending. We proposed a scheme of PEG–zinc acetate for battery application. The structure confirmation was done by using X-ray diffraction studies detecting the phase variation. The thermal properties demonstrate the optimization of melting point (T m) as a function of loading zinc acetate. The impedance analysis reveals that the role of ionic conductivity depends on the controlled concentration of Zn(CH3COO)2. Optimum ionic conductivity σ ~ 1.55 × 10−6 S cm−1 at room temperature (303 K) was observed for 70:30 composition. The linear variation in log σ vs 1000/T plot is based on the Arrhenius-type thermally activated process. The simultaneous discharge profile was confirmed by the solid-state electrochemical cell. Hence, the PEG–zinc acetate composition was suggested for polymer electrolyte battery application.

Solution-processable tandem solid-state light-emitting electrochemical cells

Compared to organic light-emitting diodes (OLEDs), solid-state light-emitting electrochemical cells (LECs) exhibit simple single-layered structure and low operating voltages due to in situ electrochemical doped layers. However, device efficiencies of LECs are usually lower than those of sophisticatedly designed OLEDs. Furthermore, device efficiencies and lifetimes of LECs degrade significantly as brightness increases. In this work, we demonstrate tandem LECs to obtain nearly doubled light outputs (μWcm−2) in comparison with single-layered LECs under similar current densities. Since the output EL emission is modified by microcavity effect of the device structure, the EL spectra of tandem LECs exhibit EL emission peak at ca. 625nm while the EL spectra of single-layered LECs center at ca. 660nm. Better spectral overlap between the EL spectrum of tandem LECs and the luminosity function results in further enhanced candela values, rendering a tripled brightness (cdm−2). The device efficiencies can be optimized by adjusting the thickness of the connecting layer between the two emitting units of the tandem devices. The peak external quantum efficiency achieved in tandem LECs is up to 5.83%, which is higher than twice of that obtained in single-layered LECs due to improved carrier balance. When single-layered and tandem LECs are biased under higher voltages to reach similarly higher brightness, tandem LECs show higher device efficiencies and longer lifetimes simultaneously. These results indicate that device efficiencies and lifetimes of LECs can be improved by employing a tandem device structure.

Thermodynamics of NdRhO3 and phase relations in the system Nd–Rh–O

Phase equilibrium experiments indicate that NdRhO3 is the only ternary oxide in the system Nd-Rh-O at 1273 K; it has orthorhombically-distorted perovskite structure. By employing a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte, thermodynamic properties of NdRhO3 are determined. The standard Gibbs energy of formation of NdRhO3 from its component binary oxides in the temperature ranges from 900 to 1300 K can be expressed as: 1/2Rh(2)O(3) (ortho)+1/2Nd(2)O(3)(hex)=NdRhO3(ortho), Delta(f(o,x))G(0)/J mol(-1)( +/- 197) = - 66256+5.64 (T/K). The decomposition temperature of NdRhO3 computed from extrapolated thermodynamic data is 1803 (+/- 4) K in pure oxygen and 1692 (+/- 4) K in air at standard pressure. Oxygen partial pressure-composition diagram and three-dimensional chemical potential diagram at 1273 K are developed from thermodynamic data obtained in this study and auxiliary information from the literature. Equilibrium temperature-composition phase diagrams at constant oxygen partial pressures are also constructed. (C) 2013 Elsevier Ltd. All rights reserved.

System Er–Ru–O: High temperature study of the heavy rare earth pyrochlore Er2Ru2O7(s) by electrochemical cell and differential scanning calorimeter

Abstract The Gibbs free energy of formation of Er 2 Ru 2 O 7 (s) has been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cell has been measured: (−)Pt/{Er 2 O 3 (s) + Er 2 Ru 2 O 7 (s) + Ru(s)}//CSZ//O 2 (p(O 2 ) = 21.21 kPa)/Pt(+). The Gibbs free energy of formation of Er 2 Ru 2 O 7 (s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be given by: {Δ f G°(Er 2 Ru 2 O 7 ,s) / (kJ∙mol −1 ) ± 2.2} = − 2517.3 + 0.6099 ∙ (T/K); (934.6 ≤ T/K ≤ 1236.3). Standard molar heat capacity C° p,m (T) of Er 2 Ru 2 O 7 (s) was measured using a heat flux type differential scanning calorimeter (DSC) in two different temperature ranges, from 129 K to 296 K and 307 K to 845 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: C° p,m (Er 2 Ru 2 O 7 ,s,T)(J∙K −1 ∙mol −1 ) = 293.88 + 2.397 10 −2 T(K) − 54.74717 10 5 /T 2 (K); (307 ≤ T(K) ≤ 845). The heat capacity of Er 2 Ru 2 O 7 (s), was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.

Increase in adsorptivity of sulfonate anions on Pt (111) surface with drying of ionomer

The interface between Nafion and Pt (111) was analyzed in a solid-state electrochemical cell to clarify the catalyst poisoning property of the ionomer in various hydration states. With dehydration of the ionomer, peaks for adsorption and desorption of the sulfonate anions in the cyclic voltammogram showed significant shifts to lower potentials, which indicate increase in the anion adsorptivity.

The system Yb–Ru–O: High temperature studies on the oxides Yb2Ru2O7(s) and Yb3RuO7(s)

The standard molar Gibbs free energy of formation of Yb2Ru2O7(s) and Yb3RuO7(s) was determined using an oxide solid-state electrochemical cell wherein calcia-stabilized-zirconia (CSZ) was used as an electrolyte. The standard molar Gibbs free energy of formation of Yb2Ru2O7(s) and Yb3RuO7(s) from elements in their standard state was calculated by the least squares regression analysis of the data obtained in the present study and can be given respectively by:{ΔfG°(Yb2Ru2O7, s)/(kJ mol−1) ± 1.88} = −2450.4 + 0.6025·(T/K) and{ΔfG°(Yb3RuO7, s)/(kJ mol−1) ± 2.36} = −3109.6 + 0.6202·(T/K).Standard molar heat capacity C°p,m(T) of Yb2Ru2O7(s), was measured using a heat flux type differential scanning calorimeter (DSC) in the temperature range from 307 K to 845 K. The heat capacity of Yb2Ru2O7(s) was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy of formation of the compound Yb2Ru2O7(s), from elements at 298.15 K.

Improving device efficiencies of solid-state white light-emitting electrochemical cells by adjusting the emissive-layer thickness

Exciton quenching in the recombination zone close to electrochemically doped regions would be one of the bottlenecks for improving device efficiencies of solid-state white light-emitting electrochemical cells (LECs). To further enhance device efficiencies of white LECs for practical applications, we adjust the emissive-layer thickness to reduce exciton quenching. In white LECs with properly thickened emissive-layer thickness, the recombination zone can be situated near the center of the emissive layer, rendering mitigated exciton quenching and thus enhanced device efficiencies. High external quantum efficiencies and power efficiencies of optimized devices reach ca. 11% and 20lm/W, respectively, which are among the highest reported for white LECs. These results confirm that tailoring the thickness of the emissive layer to avoid exciton quenching would be a feasible approach to improve device efficiencies of white LECs.