Search Results (26)

Oxygen transport membranes (OTMs) have gained a lot of attention for their application in different innovative fields, but the development of new materials able to combine high oxygen permeability and good chemical stability is crucial to boost the exploitation of such membrane-based technologies. Perovskite oxides are widely studied as mixed ionic-electronic conductors for the realization of OTMs. In this article, we focus on _Sr1-xCa_xTi_0.8Fe_0.2O_3-ẟ (SCTF) perovskites and investigate the effect of Ca content on the A-site of the permeation properties, both in single-phase SCTF membranes and in dual-phase membranes obtained by combining SCTF and the ionic conductor Ce_0.8Gd_0.2O₂ (CGO). In single-phase samples, we observed that the substitution of 40% Ca preserves the permeation performances of the non-substituted SrTi_0.8Fe_0.2O_3−ẟ membrane while allowing for a substantial decrease in the sintering temperature, thus facilitating membrane manufacturing. In dual-phase membranes, the increase in the Ca content in the perovskite causes an increase in grain size. The permeation is, at least partially, controlled by the kinetics of the surface exchange reactions. This limitation can be overcome by the addition of an activation layer; however, the permeance of activated CGO-SCTF membranes still remains lower compared to the single-phase parent perovskitic membranes. Full article

The structural and electrical properties of double perovskite compounds SrLaFe_1−xMn_xTiO_6−δ (x = 0, 0.33, 0.67, and 1.0) were studied using X-ray diffraction (XRD) and dielectric impedance measurements. The reparation of perovskite compounds was successfully achieved through the precursor solid-state reaction in air at 1250 °C. The purity phase and crystal structures of perovskite compounds were determined by means of the standard Rietveld refinement method using the FullProf suite. The best fitting results showed that SrLaFeTiO_6−δ was orthorhombic with space group Pnma, and both SrLaFe_0.67Mn_0.33TiO_6−δ and SrLaFe_0.33Mn_0.67TiO_6−δ were cubic structures with space group Fm3m, while SrLaMnTiO_6−δ was tetragonal with a I/4m space group. The charge density maps obtained for these structures indicated that the compounds show an ionic and mixed ionic–electronic conduction. The dielectric impedance measurements were carried out in the range of 20 Hz to 1 MHz, and the analysis showed that there is more than one relaxation mechanism of Debye type. Doping with Mn was found to reduce the dielectric impedance of the samples, and the major contribution to the dielectric impedance was established to change from a capacitive for SrLaFeTiO_6−δ to a resistive for SrLaMnTiO_6−δ. The fall in values of electrical resistance may be related to the possible occurrence of the double exchange (DEX) mechanism among the Mn ions, provided there is oxygen deficiency in the samples. DC-resistivity measurements revealed that SrLaFeTiO_6−δ was an insulator while SrLaMnTiO_6−δ was showing a semiconductor–metallic transition at ~250 K, which is in support of the DEX interaction. The dielectric impedance of SrLaFe_0.67Mn_0.33TiO_6−δ was found to be similar to that of (La,Sr)(Co,Fe)O_3-δ, the mixed ionic–electronic conductor (MIEC) model. The occurrence of a mixed ionic–electronic state in these compounds may qualify them to be used in free lead solar cells and energy storage technology. Full article

Double perovskite oxides with mixed ionic and electronic conductors (MIECs) have been widely investigated as cathode materials for solid oxide fuel cells (SOFCs). Classical Fe-based double perovskites, due to their inherent low electronic and oxygen ionic conductivity, usually exhibit poor electrocatalytic activity. The existence of various valence states of B-site ions modifies the material’s catalytic activity, indicating the possibility of the partial substitution of Fe by higher-valence ions. LaBaFe_2−xMo_xO_5+δ (x = 0, 0.03, 0.05, 0.07, 0.1, LBFM_x) is used as intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode materials. At a doping concentration above 0.1, the Mo substitution enhanced the cell volume, and the lattice expansion caused the formation of the impurity phase, BaMoO₄. Compared with the parent material, Mo doping can regulate the oxygen vacancy concentration and accelerate the oxygen reduction reaction process to improve the electrochemical performance, as well as having a suitable coefficient of thermal expansion and excellent electrode stability. LaBaFe_1.9Mo_0.1O_5+δ is a promising cathode material for IT-SOFC, which shows an excellent electrochemical performance, with this being demonstrated by having the lowest polarization resistance value of 0.017 Ω·cm² at 800 °C, and the peak power density (PPD) of anode-supported single-cell LBFM_0.1|CGO|NiO+CGO reaching 599 mW·cm⁻². Full article

In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce_0.8Gd_0.2O_1.9, Sc_0.1Ce_0.01Zr_0.89O_1.95, and Sc_0.09Yb_0.01Zr_0.9O_1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH₃ in argon, 10% H₂ in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce_0.8Gd_0.2O_1.9 material is a mixed ionic–electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH₃ gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc_0.09Yb_0.01Zr_0.9O_1.95, showing a high, reversible reaction with hydrogen. Full article

Silver iodide is a prototype compound of superionic conductors that allows ions to flow through its structure. It exhibits a first-order phase transition at 420 K, characterized by an abrupt change in its ionic conductivity behavior, and above this temperature, its ionic conductivity increases by more than three orders of magnitude. Introducing small concentrations of carbon into the silver iodide structure produces a new material with a mixed conductivity (ionic and electronic) that increases with increasing temperature. In this work, we report the experimental results of the ionic conductivity as a function of the reciprocal temperature for the (AgI)_x − C_(1−x) mixture at low carbon concentrations (x = 0.99, 0.98, and 0.97). The ionic conductivity behavior as a function of reciprocal temperature was well fitted using a phenomenological model based on a random variable theory with a probability distribution function for the carriers. The experimental data show a proximity effect between the C and AgI phases. As a consequence of this proximity behavior, carbon concentration or temperature can control the conductivity of the (AgI)_x − C_(1−x) mixture. Full article

Here, we report the preparation and evaluation of PVA/PEDOT:PSS-conducting hydrogels working as channel materials for OECT applications, focusing on the understanding of their charge transport and transfer properties. Our conducting hydrogels are based on crosslinked PVA with PEDOT:PSS interacting via hydrogen bonding and exhibit an excellent swelling ratio of ~180–200% w/w. Our electrochemical impedance studies indicate that the charge transport and transfer processes at the channel material based on conducting hydrogels are not trivial compared to conducting polymeric films. The most relevant feature is that the ionic transport through the swollen hydrogel is clearly different from the transport through the solution, and the charge transfer and diffusion processes govern the low-frequency regime. In addition, we have performed in operando Raman spectroscopy analyses in the OECT devices supported by first-principle computational simulations corroborating the doping/de-doping processes under different applied gate voltages. The maximum transconductance (g_m~1.05 μS) and maximum volumetric capacitance (C*~2.3 F.cm⁻³) values indicate that these conducting hydrogels can be promising candidates as channel materials for OECT devices. Full article

Simultaneous syngas and pure hydrogen production through partial oxidation of methane and water splitting, respectively, were demonstrated by using mixed ionic–electronic conductors. Tubular ceramic membranes prepared from La_0.5Sr_0.5FeO₃ perovskite were successfully utilized in a 10 M lab scale reactor by applying a radial arrangement. The supply of methane to the middle area of the reaction zone was shown to provide a uniform distribution of the chemical load along the tubes’ length. A steady flow of steam feeding the inner part of the membranes was used as oxidative media. A described configuration was found to be favorable to maintaining oxygen permeability values exceeding 1.1 mL∙cm^–2∙min^–1 and long-term stability of related functional characteristics. Methane’s partial oxidation reaction assisted by 10%Ni@Al₂O₃ catalyst proceeded with selectivity values above 90% and conversion of almost 100%. The transition from a laboratory model of a reactor operating on one tubular membrane to a ten-tube one resulted in no losses in the specific performance. The optimized supply of gaseous fuel opens up the possibility of scaling up the reaction zone and creating a promising prototype of a multitubular reaction zone with a simplified sealing procedure. Full article

The ability to bridge ionic and electronic transport coupled with large volumetric capacitance renders organic electrochemical transistors (OECTs) ideal candidates for bioelectronic applications. Adopting ionic-liquid-based solid electrolytes extends their applicability and facilitates large-area printable productions. However, OETCs employing solid electrolytes tend to show a pronounced hysteresis in the transfer curve. A detailed understanding of the hysteresis is crucial for their accurate characterizations and reliable applications. Here, we demonstrated fully photopatternable poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos)- based OECTs incorporating the ionic liquid [EMIM][EtSO₄] in a solid electrolyte (SE). The PEDOT:Tos films deposited through vapor phase polymerization (VPP) were annealed for different durations after the polymerization step. Upon rinsing with ethanol and the deposition of the SE, the OECTs made of these films showed impressive bias stress stability under prolonged operation cycles, a high switching ratio, a low threshold voltage, and a high transconductance. Furthermore, by taking transfer measurements with different sweep rates, we revealed two distinct regimes of hysteresis: kinetic hysteresis and non-kinetic hysteresis. We observed pronounced changes in these regimes after annealing. Finally, impedance spectroscopy exhibited that the PEDOT:Tos turned from a Faradaic to a non-Faradaic response through annealing, explaining the observed hysteresis changes in both regimes. Full article

Dual-phase membranes are increasingly attracting attention as a solution for developing stable oxygen permeation membranes. Ce_0.8Gd_0.2O_2−δ–Fe_3−xCo_xO₄ (CGO-F(3−x)CxO) composites are one group of promising candidates. This study aims to understand the effect of the Fe/Co-ratio, i.e., x = 0, 1, 2, and 3 in Fe_3−xCo_xO₄, on microstructure evolution and performance of the composite. The samples were prepared using the solid-state reactive sintering method (SSRS) to induce phase interactions, which determines the final composite microstructure. The Fe/Co ratio in the spinel structure was found to be a crucial factor in determining phase evolution, microstructure, and permeation of the material. Microstructure analysis showed that all iron-free composites had a dual-phase structure after sintering. In contrast, iron-containing composites formed additional phases with a spinel or garnet structure which likely contributed to electronic conductivity. The presence of both cations resulted in better performance than that of pure iron or cobalt oxides. This demonstrated that both types of cations were necessary to form a composite structure, which then allowed sufficient percolation of robust electronic and ionic conducting pathways. The maximum oxygen flux is j_O2 = 0.16 and 0.11 mL/cm²·s at 1000 °C and 850 °C, respectively, of the 85CGO-FC2O composite, which is comparable oxygen permeation flux reported previously. Full article

The mixture of H₂ and CO, the so-called syngas, is the value-added product of H₂O and CO₂ co-electrolysis and the feedstock for the production of value-added chemicals (mainly through Fischer-Tropsch). The H₂/CO ratio determines the process in which syngas will be utilized and the type of chemicals it will produce. In the present work, we investigate the effect of H₂O/CO₂ (steam/carbon dioxide, S/C) ratio of 0.5, 1 and 2 in the feed, on the electrochemical performance of an 8YSZ electrolyte-supported solid oxide cell and the H₂/CO ratio in the outlet, under co-electrolysis at 900 °C. The B-site iron doped lanthanum strontium chromite La₀.₇₅Sr₀.₂₅Cr₀.₉Fe₀.₁O_3-δ (LSCF) is used as fuel electrode material while as oxygen electrode the state-of-the art LSM perovskite is employed. LSCF is a mixed ionic-electronic conductor (MIEC) operating both under a reducing and oxidizing atmosphere. The cell is electrochemically characterized under co-electrolysis conditions both in the presence and absence of hydrogen in the feed of the steam and carbon dioxide mixtures. The results indicate that under the same concentration of hydrogen and different S/C ratios, the same electrochemical performance with a maximum current density of approximately 400 mA cm⁻² is observed. However, increasing p(H₂) in the feed results in higher OCV, smaller iV slope and R_p values. Furthermore, the maximum current density obtained from the cell does not seem to be affected by whether H₂ is present or absent from the fuel electrode feed but has a significant effect on the H₂/CO ratio in the analyzed outlet stream. Moreover, the H₂/CO ratio seems to be identical under polarization at different current density values. Remarkably, the performance of the LSCF perovskite fuel electrode is not compromised by the exposure to oxidizing conditions, showcasing that this class of electrocatalysts retains their reactivity in oxidizing, reducing, and humid environments. Full article

Mixed ionic-electronic conducting materials are not used as a single-layer electrolyte of solid oxide fuel cells (SOFCs) at relatively high operating temperatures of ~800 °C. This is because of a significant decrease in the open-circuit voltage (OCV) and, consequently, the SOFC power density. The paper presents a comparative analysis of the anode-supported SOFC properties obtained within the temperature range of 600 to 800 °C with yttria-stabilized zirconia (YSZ) electrolyte and gadolinium-doped ceria (GDC) electrolyte thin films. Electrolyte layers that are 3 µm thick are obtained by magnetron sputtering. It is shown that at 800 °C, the SOFC with the GDC electrolyte thin film provides an OCV over 0.9 V and power density of 2 W/cm². The latter is comparable to the power density of SOFCs with the YSZ electrolyte, which is a purely ionic conductor. The GDC electrolyte manifests the high performance, despite the SOFC power density loss induced by electronic conductivity of the former, which, in turn, is compensated by its other positive properties. Full article

A protonic ceramic fuel cell (PCFC) has great potential for medium temperature power generation. Its working process, however, is complicated and quite different from the traditional oxygen ionic solid oxide fuel cell (O²⁻-SOFC) and proton exchange membrane fuel cell (PEMFC). In this paper, a multi-physical model for the PCFC with H⁺/e⁻/O²⁻ mixed conducting cathode is established, in which the fuel- and oxidant-diffusing processes; electron-, oxygen ion-, and proton-conducting processes; three electrochemical reactions; and their coupling working details are carefully considered. Taking Ni-BZCY/BZCY/BZCY-LSCF PCFC as an example, the validation of the model is well verified by good agreements with the experiment i_op-V_op curves at different temperatures. The result shows that the cathodic electrochemical reactions will be concentrated to a small thickness near the electrolyte because of the greatly decreased ionic conductivity compared with the high electronic conductivity at an intermediate temperature. O²⁻ within the PCFC cathode is only an intermediate transform substance between the electrons and protons. Thus, there is a peak oxygen ion current distribution within the composite cathode of PCFC. The cathodic oxygen reduction half reaction is found to be a key factor to dominate the total PCFC voltage loss at the intermediate temperature zone. The concentration polarization of anode-supported PCFC is small, due to the vapors that are generated in the cathode side instead of anode side. Full article

In this study, the technology of electrophoretic deposition (EPD) micrometer barrier layers based on a BaCe_0.8Sm_0.19Cu_0.1O₃ (BCSCuO) protonic conductor on dense carrying Ce_0.8Sm_0.2O_1.9 (SDC) solid-state electrolyte substrates is developed. Methods for creating conductive sublayers on non-conductive SDC substrates under EPD conditions, such as the synthesis of a conductive polypyrrole (PPy) layer and deposition of a layer of finely dispersed platinum from a suspension of its powder in isopropanol, are proposed. The kinetics of disaggregation, disperse composition, electrokinetic potential, and the effect of adding iodine to the BCSCuO suspension on these parameters as factors determining the preparation of stable suspensions and successful EPD processes are explored. Button cells based on a carrying SDC electrolyte of 550 μm in thickness with BCSCuO layers (8–35 μm) on the anode, cathode, and anode/cathode side, and Pt electrodes are electrochemically tested. It was found that the effect of blocking the electronic current in the SDC substrate under OCV conditions was maximal for the cells with barrier layers deposited on the anode side. The technology developed in this study can be used to fabricate solid oxide fuel cells with doped CeO₂ electrolyte membranes characterized by mixed ionic–electronic conductivity (MIEC) under reducing atmospheres. Full article

A double-channel transmission line impedance model was applied to the study of supercapacitors to investigate the charge transport characteristics in the ionic and electronic conductors forming the electrode/solution interface. The macro homogeneous description of two closely mixed phases (Paasch–Micka–Gersdorf model) was applied to study the influence of disordered materials on the charge transport anomalies during the interfacial charge–discharge process. Different ex situ techniques were used to characterize the electrode materials used in electrical double-layer (EDLC) and pseudocapacitor (PC) devices. Two time constants in the impedance model were adequate to represent the charge transport in the different phases. The interfacial impedance considering frequency dispersion and blocked charge transfer conditions adequately described the charge storage at the interface. Deviations from the normal (Fickian) transport involving the ionic and electronic charge carriers were identified by the dispersive parameters (e.g., n and s exponents) used in the impedance model. The ionic and electronic transports were affected when the carbon-based electrical double-layer capacitor was converted into a composite with strong pseudocapacitive characteristics after the decoration process using NiO. The overall capacitance increased from 2.62 F g⁻¹ to 536 F g⁻¹ after the decoration. For the first time, the charge transport anomalies were unequivocally identified in porous materials used in supercapacitors with the impedance technique. Full article

This review presents thermoelectric phenomena in copper chalcogenides substituted with sodium and lithium alkali metals. The results for other modern thermoelectric materials are presented for comparison. The results of the study of the crystal structure and phase transitions in the ternary systems Na-Cu-S and Li-Cu-S are presented. The main synthesis methods of nanocrystalline copper chalcogenides and its alloys are presented, as well as electrical, thermodynamic, thermal, and thermoelectric properties and practical application. The features of mixed electron–ionic conductors are discussed. In particular, in semiconductor superionic copper chalcogenides, the presence of a “liquid-like phase” inside a “solid” lattice interferes with the normal propagation of phonons; therefore, superionic copper chalcogenides have low lattice thermal conductivity, and this is a favorable factor for the formation of high thermoelectric efficiency in them. Full article