Activation Energy For Ion Transport Research Articles

Synthesis and electrochemical characterization of sulfur-doped Li3PO4 for all-solid-state battery applications

Isovalent and aliovalent cation-doping have been widely investigated to enhance ion transport in γ‑Li3PO4-type lithium superionic conductors (LISICONs). Anion doping, however, has been restricted to a full replacement of oxide ions by sulfide ions in some compounds (the so-called thio-LISICONs). The replacement of oxide ions by sulfide ions enhances both ion conductivity and deformability of the materials. Similar to other sulfide-type solid-electrolytes, thio-LISICONs, however, showed limited electrochemical stability against oxidation. In this report, a sonication-assisted liquid-phase synthesis approach was employed to achieve substantial sulfur‑oxygen mixing in γ-type Li3PO4. Sulfur-doped Li3PO4 possessed an ion conductivity four orders of magnitude higher than that of γ-Li3PO4, and a notably low activation energy of ion transport of 0.40(8) eV. Sulfur-oxygen mixing in sulfur-doped Li3PO4 enhanced electrochemical stability against oxidation (up to 4 V vs. Li+/Li) compared with sulfur-based Li3PS4. This study paves the way for developing mixed-anion phases in the γ-type Li3PO4 structure with enhanced electrochemical properties for all-solid-state battery applications.

Directed Dehydration of Na4Sn2S6 ⋅ 5H2O Generates the New Compound Na4Sn2S6: Crystal Structure and Selected Properties

AbstractThe new thiostannate Na4Sn2S6 was prepared by directed crystal water removal from the hydrate Na4Sn2S6 ⋅ 5H2O at moderate temperatures. While the structure of the hydrate comprises isolated [Sn2S6]4− anions, that of the anhydrate contains linear chains composed of corner‐sharing SnS4 tetrahedra, a structural motif not known in thiostannate chemistry. This structural rearrangement requires bond‐breakage in the [Sn2S6]4− anion, movements of the fragments of the opened [Sn2S6]4− anion and Sn−S−Sn bond formation. Simultaneously, the coordination environment of the Na+ cations is significantly altered and the in situ formed NaS5 polyhedra are joined by corner‐ and edge‐sharing to form a six‐membered ring. Time‐dependent in situ X‐ray powder diffraction evidences very fast rehydration into Na4Sn2S6 ⋅ 5H2O during storage in air atmosphere, but recovery of the initial crystallinity requires several days. Impedance spectroscopy demonstrates a mediocre room‐temperature Na+ ion conductivity of 0.31 μS cm−1 and an activation energy for ionic transport of Ea=0.75 eV.

Vertically Oriented Porous PET as Template to Integrated Metal Halide for High-Performance Large-Area and Ultra-Flexible X-Ray Detector.

High-performance X-ray detectors have immense potential in medical and security inspections. However, the current X-ray detectors are limited in flexible, high-spatial-resolution large-scale detection, and integration for imaging. Here, nuclear track-etched porous polyethylene terephthalate (PET) is developed as the template for preparing uniform, large-area (≥105 cm2 ), and flexible metal halide (MH)-based X-ray detectors. Adjustable high-density vertically oriented porous PET with adjustable thickness can provide proper physical support for flexible thick absorption film, thus improving X-ray absorption ability with excellent bending stability. Moreover, vertical channels can block the ion migration, lateral charge diffusion, and water/oxygen attacks, increasing activation energy for ionic transport, charge collection rate of electrodes, and environmental stability. Hence, the related detectors eventually obtain large sensitivity (6722 µC Gyair -1 cm-2 ), low detection limit (1.87 nGyair s-1 ), and high spatial resolution (5.17 lp mm-1 ) compared to the detectors without porous PET template. Meanwhile, the device shows no degradation after storage or working under various thermal attacks. MH-filled-PET is also monolithically integrated on the bottom circuit with different MHs and it is applied to single-pixel mode and fast linear-array imaging in a broad range of X-rays photon energy (20 to 160keV).

High‐Quality 0D Cs4PbBr6‐Based Dense Wafer for High‐Sensitivity X‐Ray Detection and High‐Resolution Imaging in Harsh Environment

AbstractThe use of metal halides promotes the development of X‐ray detectors (XDs) owing to their excellent X‐ray absorbance, electrically benign defects, and large mobility−lifetime (µτ) product. Yet the severe baseline drift, size limitation, large dark current, and mediocre stability are still waiting to be solved. Herein, high density size‐scalable Cs4PbBr6 wafer‐based XD is constructed by the hot isostatic‐pressed method for the first time. Meanwhile, different Br− vacancy (VBr) concentration‐based Cs4PbBr6 is realized. The role of VBr in electrical structure and charge transport is highlighted by density functional theory and experimental measurement. Moreover, the further study points the 0D structure endows Cs4PbBr6 with high activation energy for ionic transport (1044 meV) and bandgap (3.88 eV), which finally results in an ultra‐stable baseline and thermal stability. On the basis of efficient response (7068 µC Gyair−1 cm−2), reliable current output, ultra‐low detection limit (1.75 nGyair s−1), high spatial resolution (5.2 lp mm−1 at modulation transfer function = 0.2), fast response speed and radiation stabilities (>1000 Gyair), the high‐resolution X‐ray images under broad energy range (20–160 keV) are realized on both single‐pixel and linear scanning mode, thus holding huge potential for medical diagnosis, safety inspection, and outer space detection.

Parameters Affecting Lithium Ion Conductivity of Carboxymethyl Cellulose Binders

In an effort to minimize green house gas emissions, the development of renewable energy storage has become important, especially for the transportation industry.(I) Currently, the most effective energy storage solution is Li-ion batteries due to their long cycle life and high energy density.(I) However, this current technology uses highly reactive and flammable liquid electrolytes which are both limited by their limited charging speed through a liquid medium and their unsafe nature.(II) For this reason, many large companies such as Hyundai and Samsung have heavily invested in the development of all-solid-state batteries (ASSB), seen as the next step in safe fast-charging energy storage.(III)However, problems remain that need to be solved before ASSBs can become commercially viable. One of these problems is cycling stability, where battery performance significantly drops after a few charge/discharge cycles, notably through mechanical degradation and interfacial contact issues caused by volume changes of the active material against a rigid solid electrolyte.(I) For this reason, there is growing interest in increasing the system’s mechanical flexibility thus preventing degradation by the use of ionically conductive polymers as soft binders and volume buffers.(IV) One potential choice for such materials are environmentally friendly natural biopolymers such as cellulose derivatives like carboxymethyl cellulose (CMC), whose functional groups coordinate cations during transport. CMC has already been shown to act as a binder that increases mechanical stability for electrodes of current Li-ion technology and exhibits proton conductivity in fuel cell applications. It is also being investigated for its potential in ASSBs, Na-ion, and Zn batteries where it has been shown to have high durability and that it combines well with a variety of other polymers when used as binders or as a solid electrolyte in these batteries.(IV-VII)To further our understanding of incorporating this biopolymer in batteries, we are studying the effects of various aspects of CMC film preparation on their ionic conductivity such as salt concentration and film homogeneity. In addition, to the preparation parameters, we investigated the activation energy of ion transport for CMC films of differing concentrations through temperature dependence measurements. Furthermore, we investigated the structure of these materials with infrared spectroscopy and differential scanning calorimetry to see the effects of salt concentration on the microstructure. This data is of importance in assessing the impact of CMC binders and will lay a foundation for optimizing binder choice for cheap and biodegradable components in both current and next-generation battery technology. References (I) Li, L.; Deng, Y.; Chen, G. Status And Prospect Of Garnet/Polymer Solid Composite Electrolytes For All-Solid-State Lithium Batteries. Journal of Energy Chemistry 2020, 50, 154-177.(II) Zheng, Y.; Li, X.; Li, C. A Novel De-Coupling Solid Polymer Electrolyte Via Semi-Interpenetrating Network For Lithium Metal Battery. Energy Storage Materials 2020, 29, 42-51.(III) Eckhouse, B. Samsung Venture, Hyundai Investing in Battery Producer. https://www.bloomberg.com/news/articles/2018-09-10/samsung-and-hyundai-investing-in-solid-state-battery-producer.(IV) Shetty, S.; Ismayil; Shetty, G. Enhancement Of Electrical And Optical Properties Of Sodium Bromide Doped Carboxymethyl Cellulose Biopolymer Electrolyte Films. Journal of Macromolecular Science, Part B 2020, 59 (4), 235-247.(V) Darjazi, H.; Staffolani, A.; Sbrascini, L.; Bottoni, L.; Tossici, R.; Nobili, F. Sustainable Anodes For Lithium- And Sodium-Ion Batteries Based On Coffee Ground-Derived Hard Carbon And Green Binders. Energies 2020, 13 (23), 6216.(VI) Dueramae, I.; Okhawilai, M.; Kasemsiri, P.; Uyama, H.; Kita, R. Properties Enhancement Of Carboxymethyl Cellulose With Thermo-Responsive Polymer As Solid Polymer Electrolyte For Zinc Ion Battery. Scientific Reports 2020, 10 (1).(VII) Sasso, C.; Beneventi, D.; Zeno, E.; Petit-Conil, M.; Chaussy, D.; Belgacem, M. Carboxymethylcellulose: A Conductivity Enhancer And Film-Forming Agent For Processable Polypyrrole From Aqueous Medium. Synthetic Metals 2011, 161 (5-6), 397-403.

Low‐Temperature Melt Processing Monolithic Integration of Organic Manganese (II) Bromide Wafers with Pixelated Substrate for High Sensitivity X‐Ray Imaging

AbstractEnvironmentally‐friendly metal halides have become emerging candidates for X‐ray imaging applications. However, it remains challenging to obtain noise and ion migration suppressed crystal structures. More seriously, integration with mature circuits in an easy‐to‐implement manner is a huge obstacle to commercialization. Here, a 0D structure‐based benzyltrimethylammonium manganese bromide (BTA2MnBr4, BTA: C10H16N) is reported. Further studies point out that such structure exhibits obvious quantum confinement effects, providing large bandgap (3.20 eV) and exciton activation energy (≈115 meV) with decreasing thermal noise, and large activation energy for ionic transport (≈0.37 eV) with limited ion migration. Then, the BTA2MnBr4 wafer is fabricated via solvent‐free, scalable, and low‐temperature (175 °C) melt processing technology. The obtained wafer shows highly crystalline and good densification that can effectively collect the generated charges, which avoids the compound losses and further limits the ion migration. As a result, the related X‐ray detector demonstrates high sensitivity of 5.56 × 103 µC Gyair−1 cm−2, a low detection limit of 8.7 nGyair s−1, fast response (≈10 ms), high‐spatial resolution (≈4.1 lp mm−1), good stability, and imaging capability. Moreover, the integration of the wafer with pixelated electrode substrate is also successfully achieved, applied, and validated with strong mechanical connection and reliable contact.

Two-Dimensional Perovskite-Gated AlGaN/GaN High-Electron-Mobility-Transistor for Neuromorphic Vision Sensor.

The extraordinary optoelectronic properties and continued commercialization of GaN enable it a promising component for neuromorphic visual system (NVS). However, typical GaN‐based optoelectronic devices demonstrated to data only show temporary and unidirectional photoresponse in ultraviolet region, which is an insurmountable obstacle for construction of NVS in practical applications. Herein, an ultrasensitive visual sensor with phototransistor architecture consisting of AlGaN/GaN high‐electron‐mobility‐transistor (HEMT) and two‐dimensional Ruddlesden–Popper organic–inorganic halide perovskite (2D OIHP) is reported. Utilizing the significant variation in activation energy for ion transport in 2D OIHP (from 1.3 eV under dark to 0.4 eV under illumination), the sensor can efficiently perceive and storage optical information in ultraviolet–visible region. Meanwhile, the photo‐enhanced field‐effect mechanism in the depletion‐mode HEMT enables gate‐tunable negative and positive photoresponse, where some typical optoelectronic synaptic functions including inhibitory and excitatory postsynaptic current as well as paired‐pulse facilitation are demonstrated. More importantly, a NVS based on the proposed visual sensor array is constructed for achieving neuromorphic visual preprocessing with an improved color image recognition rate of 100%.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Thermodynamic and Kinetic Analyses of Ion Intercalation/Deintercalation Using Different Temperatures on NiHCF Electrodes for Battery Electrode Deionization.

Prussian blue analogues are used in electrochemical deionization due to their cation sorption capabilities and ion selectivity properties. Elucidating the fundamental mechanisms underlying intercalation/deintercalation is important for the development of ion-selective electrodes. We examined the thermodynamic and kinetic properties of nickel hexacyanoferrate electrodes by studying different temperatures effects on intercalation/deintercalation with monovalent ions (Li+, Na+, K+, and NH4+) relevant to battery electrode deionization applications. Higher temperatures reduced the interfacial charge transfer resistance and increased the diffusion coefficient of cations in the solid material. Ion transport in the solid material, rather than interfacial charge transfer, was found to be the rate-controlling step, as shown by higher activation energies for ion transport (e.g., 31 ± 3 kJ/mol for K+) than for interfacial charge transfer (5 ± 1 kJ/mol for K+). The largest increase in cation adsorption capacity with temperature was observed for NH4+ (28.1% from 15 to 75 °C) due to its smallest activation energy. These results indicate that ion hydration energy determines the intercalation potential and activation energies of ion transport in solid material control intercalation/deintercalation rate. Together with the endothermic behavior of deintercalation and exothermic behavior of intercalation, the higher operating temperature results in improvement of ion adsorption capacity depending on specific cations.

Ferrocene based ionic liquid: synthesis, structure, transport properties and mechanism of thermal degradation

Doping with transition metals is a promising way to expand the industrial applications of ionic liquids (ILs). This study reports the synthesis, structure and physicochemical properties of a novel butyl-dimethyl-(ferrocenylmethyl)ammonium bis(trifluoromethanesulfonyl)imide ([BDFA][NTf2]) IL. The thermo-gravimetric analysis combined with mass spectrometry of evolved gases demonstrated the high thermal stability of [BDFA][NTf2] up to 500 K. The thermal degradation of [BDFA][NTf2] at higher temperatures is a multi-step process accompanied by the cation destruction through the Hofmann elimination reaction and the subsequent transformations, such as fragmentation of the products of thermal degradation of the [NTf2]-anion and the direct interaction between these products. The glass transition and melting temperatures of [BDFA][NTf2] measured by the differential scanning calorimetry are 229 and 320 K, respectively. The electrical conductivities and densities of binary mixtures of [BDFA][NTf2] with acetonitrile (AN) were measured in the temperature range of 293 – 348 K at atmospheric pressure. The isobaric thermal expansion coefficients were calculated from the experimental data. The conductivity – temperature dependences were analyzed using the Arrhenius and Vogel-Fulcher-Tammann equations. The activation energy of ion transport and limiting conductivity increased with the IL mole fraction in AN.

Ionic transport in K2Ti6O13

Abstract The increasing demand for batteries forced the development of energy storage systems that rely on materials consisting of abundant elements in the Earth’s crust. Switching from Li+ to K+ as the main ionic charge carrier needs highly conducting potassium-bearing electrolytes to realize K+ ion batteries (PIBs). The knowledge gained from the design of Li-ion batteries (LIBs) and Na-ion batteries (NIBs) may conceptually inspire also the establishment of PIBs. Considering, for instance, the hexatitanates Na2Ti6O13, Li2Ti6O13, and H2Ti6O13, which were previously investigated as components for LIBs and NIBs, here we investigated ion dynamics in the K-analog K2Ti6O13. Ionic transport in polycrystalline samples of K2Ti6O13 was studied in a moisture-free atmosphere by broadband impedance spectroscopy in a temperature range from 20 °C to 450 °C. The current study aims at establishing a correlation between structural features of K2Ti6O13 and long-range ionic transport. As expected for K+ transport in K2Ti6O13 with its geometrically obstructed structure, the overall activation energy of ion transport in the ternary oxide takes a rather high value of 0.97(2) eV. Almost the same result (0.95(3) eV) is obtained for the migration activation energy, which we extracted from the analysis of crossover frequencies of the corresponding conductivity isotherms. By comparing our results with those of Na2Ti6O13 (0.82 eV), Li2Ti6O13 (0.65 eV), and H2Ti6O13, we clearly see how the size of the mobile cation correlates with both specific conductivities and activation energies. This comparison points to K+ being the main charge carrier in K2Ti6O13. It also helps in laying the foundations to derive the relevant structure-property relationships in this class of materials.

Evaporation-assisted phase separation preparation and electrorheological effect of poly(ionic liquid) microspheres with dual and mixed counterions

We prepare poly(ionic liquid) (PIL) microspheres containing dual counterion and single counterion in a unitary unit via an evaporation-assisted phase separation method, and study the influence of the number and type of counterions on the electrorheological (ER) effect and dielectric properties of the PIL microspheres. The morphology and structure of PIL microspheres are characterized and the ER effect of PIL microspheres in insulating carrier liquid is measured under electric fields. It shows that when the type of counterions is identical, the dual-ion PIL (D-PIL) microspheres have a stronger ER effect than that of the single-ion PIL (S-PIL) microspheres. Dielectric spectra analysis indicates that D-PIL microspheres have higher interfacial polarization rate compared to S-PIL microspheres due to enhanced charge density and ion transport dynamics according to Raman spectra and activation energy analysis. This should be responsible for the stronger ER effect of D-PIL microspheres. However, when the type of counterions is different, the ER effect of D-PIL microspheres is largely reduced. This is because the mixed alkali effect of mixed counterions significantly increases the activation energy of ion transport and decreases conductivity and interfacial polarization rate of PIL microspheres containing mixed counterions. The result can provide a new understanding of structure-property relationship for PIL-based ER material design and preparation.

Measuring Activation Energies for Ion Transport Using Tethered Bilayer Lipid Membranes (tBLMs).

Model lipid bilayers tethered to a gold substrate with molecular tethers are constructed. The conductance versus temperature dependence curve is then obtained. Here, a method to measure the activation energy for translocation of an ion through existing transmembrane pores in a sparsely tethered bilayer lipid membranes is presented.

The ionic conductivity of alkali aluminum germanium phosphate glasses – comparison of Plasma CAIT with two electrode DC measurements

Abstract The ionic conductivity of alkali aluminum germanium phosphates (MAGP) has been investigated by two different techniques, i.) a fs-Plasma-Charge Attachment Induced Transport (CAIT) approach and ii.) a classical two electrode DC approach. Amorphous MAGP samples of the composition M1.5Al0.5Ge1.5(PO4)3 M=(Li–Cs) have been synthesized by the melt-quenching technique. Comparison of fs-Plasma-CAIT and DC data reveal that the ionic conductivities as well as the activation energies for ion transport agree within the error margins of the experiment. While conventional expectation suggests that a DC approach should fail because of spontaneous charge carrier blocking, this work demonstrates that DC measurements are a simple tool for quantifying ionic conductivities provided that only a small amount of charge has been transported in total.

A large enhancement of ionic conductivity in SrCoO2.5 controlled by isostructural phase transition and negative linear compressibility

The exploration of next-generation materials and the underlying mechanisms for high ionic conductivity have been the mainstay of the study in the solid state ionic field, but with limited success. Here, we performed closely integrated in situ high-pressure structural and electronic characterizations on SrCoO2.5, a typical material for solid fuel cell application. We discovered that the activation energy for ionic transport decreased by approximately 47% at 13.6 GPa upon compression, demonstrating a large enhancement of conductivity. Such a desired functional behavior is strongly interlinked with the pressure-driven isostructural phase transition at which negative linear compressibility occurs along c-lattice, weakening the interaction between Co and O atoms and then enhancing the ionic diffusion. Our results provide fundamental insight of the solid ionic mechanism and materials-by-design for future high-performance oxides.

High-throughput characterization of Lu-doped zirconia

Lu-doped zirconia (LuDZ) was reported in the 1960s to be a poor oxygen ion conductor. However, we identified this system as worthy of reexamination based on the results of a machine learning-based screen for promising oxygen ion conductors, further supported by a physical argument: because Lu is the heaviest and smallest of the lanthanides, it should offer the possibility of high conductivity due to its high polarizability and size compatibility with the zirconia structure. The relationship between dopant concentration and conductivity in the LuDZ system was determined using a high throughput experimental methodology in which spatially resolved conductivity was measured across a compositionally graded film, spanning from Zr0.93Lu0.07O1.965 to Zr0.82Lu0.18O1.91. The conductivity broadly peaks with composition at 15 cation % Lu, coinciding with the approximate phase boundary of the fully stabilized cubic phase. The composition-dependent conductivity measurements reveal a surprising increase in activation energy for ion transport with increasing Lu content with no change in this trend at the composition of the conductivity maximum. The pre-exponential factor increases sharply with Lu content, but displays a distinct plateau once the conductivity maximum composition is attained. At 500 °C, the conductivity of Zr0.85Lu0.15O1.925 is 2 × 10−3 S cm−1, approaching that of optimally doped Sc-stabilized zirconia, which has the highest reported conductivity among zirconia compounds. In comparison to other oxide ion conductors, Lu-stabilized zirconia offers the advantage over ceria of negligible electronic conductivity and is easier to process than (La,Sr)(Ga,Mg)O3-δ.

Network former mixing effects in alkali germanotellurite glasses: A vibrational spectroscopic study

Alkali germanotellurite glasses of composition 0.3M2O–0.7[(1-x)GeO2–xTeO2], M=Li, Na and 0 ≤ x ≤ 1, were investigated by Raman and infrared vibrational spectroscopic techniques to search for the origins of the alkali ion-dependent network former mixing (NFM) effect in these ion-conducting glasses. The vibrational spectra measured on mixed network-former glasses, and the spectral comparison between equimolar-mixed glasses (x = 0.5) and pellet-mixtures of the endmember glasses, 0.3M2O–0.7GeO2 and 0.3M2O–0.7TeO2, provided evidence for the formation of hetero-atomic Ge–O–Te linkages and structural rearrangements in the germanate and tellurite components of the glass. The mixing-induced structural rearrangements were expressed in terms of chemical equilibria between the network-building units and were used to make qualitative predictions for changes in the network cross-linking density and the related network-strain energy, as well as in the binding energy part of the activation energy for ion conduction. Thus, it is proposed that the mixing-induced structural modifications in the germanate and tellurite parts of glass cause the cancelation of changes in the binding energy and the network-strain energy contributions to the activation energy for ion transport. These qualitative predictions were discussed in the context of the previously found absence of an NFM effect in ionic conductivity for M=Na and the presence of a weak positive NFM effect for M=Li.

Influence of Yttria Segregation and Platinum Nanoparticles on the Ionic Conductivity of Yttria-Stabilized Zirconia (YSZ) Films Under Hydrogen Exposure

Yttria-stabilized zirconia (YSZ) films have high ionic conductivities over the range 400-800oC which make them useful for solid oxide fuels cells, oxygen sensors, and other sensing applications. Adding catalytic particles to the YSZ surface can induce reactivities and associated conductivity changes for gases other than oxygen. In this work, the surface reactivity towards hydrogen was investigated on thin films with a 8-YSZ composition (8at.% Y2O3 - 92at.% ZrO2) that were deposited onto Langasite (La3Ga5SiO14) substrates using RF-magnetron sputtering in a 5% O2 - 95% Ar gas mixture. Films were grown to thicknesses up to 200 nm using different growth temperatures (30 - 7000C), deposition rates (0.03 - 0.07 nm/s), and substrate bias (-300 - +300 V). To create Pt nanoparticles on the YSZ film surface, Pt was deposited in-situ via e-beam evaporation to equivalent Pt thicknesses of 1 - 10 nm with the YSZ film held at either 25oC or 400oC and then subsequently annealed in an air furnace up to 1000oC to cause Pt agglomeration and nanoparticle formation. To assess steady-state surface reactivity to hydrogen in the range 400 - 600oC after the 1000oC treatments, film ionic conductivities were measured with electrochemical impedance spectroscopy (EIS) using an impedance/gain-phase analyzer after long annealing times in air, in pure N2, or in a 4% H2 - 96% N2 mixture within the furnace tube. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also used to analyze the characteristics of the as-deposited and annealed YSZ and Pt/YSZ films.YSZ films were synthesized with a variety of crystallographic textures, nanomorphology, and composition using the deposition parameters discussed above. Films deposited at 25, 400, or 700oC all have (111) cubic YSZ preferred texture with random in-plane orientation on the Langasite substrate. The smoothest films were produced using a rate of 0.07 nm/s at 400oC. However, films deposited using the other growth conditions contain significant nano-roughness and hillocks generated by film stress as evidenced by Williamson Hall XRD measurements. In films deposited at 25oC there is also a minor (200) grain population in addition to (111). To create Pt nanoparticles on these various film surfaces, Pt was evaporated with the YSZ film surface being held at either 25oC or 400oC. Pt layers (1 - 10 nm) were uniform at 25oC whereas the Pt started to agglomerate during deposition at 4000C.Following deposition, all the YSZ and Pt/YSZ films were annealed in air up to 1000oC and held for 1 hour prior to measuring conductivity and hydrogen reactivity over the range 400-600oC. This 1000oC annealing treatment was performed to (i) promote Pt agglomeration at high temperature to form individual Pt islands, (ii) stabilize the YSZ nanostructure in terms of film stress and grain size, and (iii) obtain high temperature ionic conductivity measurements over a range of temperatures. XPS indicates that post-deposition air annealing causes significant yttria segregation to the YSZ surface region as evidenced by increases in the Y3d/Zr3d photoelectron peak area ratio upon annealing up to 1000oC. This yttria enrichment decreases the film ionic conductivity and decreases the activation energy for ion transport compared to the as-deposited films. EIS experiments performed in air, N2 or 4%H2-N2 between 400-600oC indicate that the YSZ films without Pt that are most sensitive to hydrogen are those deposited at 400-700oC using a rate of 0.03 nm/s which contain rough surfaces, a population of (200) grains, and minimal yttria surface enrichment. The EIS results also show that YSZ films decorated with Pt nanoparticles all exhibit varying baseline conductivities and sensitivities to hydrogen with a magnitude dependent on the Pt nanoparticle distribution as well as film nanostructure. These YSZ and Pt/YSZ films hold promise as hydrogen sensing films that can be incorporated onto a variety of sensing platforms for H2 gas detection and management. Figure 1

Tuning Ion Exchange Capacity in Hydroxide-Stable Poly(arylimidazolium) Ionenes: Increasing the Ionic Content Decreases the Dependence of Conductivity and Hydration on Temperature and Humidity

Increasing the ion exchange capacity (IEC, mmol·g–¹) of anion exchange membranes (AEMs) decreases the dependence of ionic conductivity (σ) and ion pair hydration on limiting conditions of temperature and humidity. We present novel, hydroxide-stable polycationic ionenes having penta-substituted imidazolium repeating units. Variation of N,N′-dialkyl substituents having 1–4 carbons yields a range in IEC₍Cₗ₎ (1.56–2.32 mmol·g–¹). The trend of σ₍Cₗ₎ ∼ IEC is in agreement with comparable poly(arylimidazolium)s. This is the first report cross-correlating water uptake (WU) and ionic conductivity of a homologous series of poly(arylimidazolium) ionenes. The AEMs of higher IEC have a lower range in σ and hydration number (λ = WU / IEC) within limits of temperature and humidity. Decreasing IEC correlates to increasing effective activation energy of ion transport (Eₐ₍ₑff.₎), at constant hydration. The AEM of N,N′-dimethyl-2,4,5-arylimidazolium repeating units and the highest IEC provides σ₍Cₗ₎ = 12 mS·cm–¹ (80 °C, 95 RH%) and σ₍OH₎ = 120 mS·cm–¹ (40 °C, 90 RH%).

Role of Fast Dynamics in Conductivity of Polymerized Ionic Liquids.

Polymerized ionic liquids (PolyILs) are promising candidates for a broad range of technologies. However, the relatively low conductivity of PolyILs at room temperature has strongly limited their applications. In this work, we provide new insights into the roles of various microscopic parameters controlling ion transport in these polymers, which are crucial for their rational design and practical applications. Using broadband dielectric spectroscopy and neutron and light scattering techniques, we found a clear connection between the activation energy for conductivity, fast dynamics, and high-frequency shear modulus in PolyILs at their glass transition temperature (Tg). In particular, our analysis reveals a correlation between conductivity and the amplitude of fast picosecond fluctuations at Tg, suggesting the possible involvement of fast dynamics in lowering the energy barrier for ion conductivity. We also demonstrate that both the activation energy for ion transport and the amplitude of the fast fluctuations depend on the high-frequency shear moduli of PolyILs, thus identifying a practically important parameter for tuning conductivity. The parameters recognized in this work and their connection to the ionic conductivity of PolyILs set the stage for a deeper understanding of the mechanism of ion transport in PolyILs in the glassy state.