Proton-conducting Electrolyte Research Articles

Novel co-doped protonic conductors BaLa1.9Sr0.1In1.95M0.05O6.925 with layered perovskite structure

Active development of electrochemical devices such as proton-conducting fuel cells and electrolyzers should ensure sustainable environmental development. An electrolyte material of a hydrogen-powered electrochemical device must satisfy a number of requirements, including high proton conductivity. Layered perovskites are a promising class of proton-conducting electrolytes. The cationic co-doping method has been successfully applied to well-known proton conductors with the classical perovskite structure ABO3. However, the data on the application of this method to layered perovskites are limited. In this work, the bilayer perovskites BaLa1.9Sr0.1In1.95M0.05O6.925 (M = Mg2+, Ca2+) were obtained and investigated for the first time. Cationic co-doping increases oxygen-ion and proton conductivity values.

Thermal and chemical expansion behavior of hydrated barium stannate materials

BaSnO3 is a relatively new family of proton-conducting materials, which are attractive for high-temperature applications, including protonic ceramic fuel cells and protonic ceramic electrolysis cells. In this work, we synthesized the BaSn1–xYxO3–δ (0 ≤ x ≤ 0.4) phases and provided their in-depth characterization utilizing high-temperature X-ray diffraction and dilatometry techniques to reveal the fundamental regularities in the variations of chemical and thermal strains depending on composition. It is found that chemical expansion/contraction effects become to be more important with increasing the Y-content. In particular, the weakly doped stannates exhibit predominantly thermal expansion, while the heavily doped stannates (especially, x = 0.4) display a notable chemical contribution. The mentioned effects are discussed in terms of the BaSn1–xYxO3–δ defect structure and its ability towards hydration and dehydration. This work therefore provides valuable data for the real application of the studied materials (in both powder and ceramic forms) as well as other pronounced proton-conducting electrolytes.

Improvement of the Structural and Electrical Properties of the Proton-Conducting PVA-NH4NO3 Solid Polymer Electrolyte System by Incorporating Nanosized Anatase TiO2 Single-Crystal

Improvement of the Structural and Electrical Properties of the Proton-Conducting PVA-NH4NO3 Solid Polymer Electrolyte System by Incorporating Nanosized Anatase TiO2 Single-Crystal

Особенности протонного транспорта в допированных перовскитах BaLa0.9M0.1InO4 (M = Nd, Gd, Pr) и BaLaIn0.9M0.1O4 (M = Sc, Y) на основе индата бария-лантана

The paper discusses the features of proton transport in isovalently doped layered perovskites based on barium-lanthanum indate BaLaInO4. The effect of the nature and concentration of the dopant on the unit cell size, water absorption, and proton conductivity was estimated. It is shown that the doping of the cationic sublattices of the layered perovskite BaLaInO4 with Nd3+, Gd3+, Pr3+, In3+, Y3+ ions makes it possible to increase the proton conductivity up to ~ 2 orders of magnitude, and the complex oxides obtained by this method are promising from the point of view of their further study as a material for a proton-conducting solid oxide electrolyte fuel cell.

Implications of Cation Interdiffusion between Double Perovskite Cathode and Proton-Conducting Electrolyte for Performance of Solid Oxide Fuel Cells

Chemical compatibility and cation interdiffusion between the double perovskite cobaltites RBaCo2O6−δ (R = Gd, Pr) and proton-conducting electrolyte BaZr0.8Y0.2O3−δ were studied. Chemical interaction was found to occur already at 1100 °C as a result of the partial dissolution of RBaCo2O6−δ (R = Gd, Pr) in BaZr0.8Y0.2O3−δ. Analysis of the element distribution along the cross sections of diffusion couples RBaCo2O6−δ(R = Gd, Pr)|BaZr0.8Y0.2O3−δ showed strong interdiffusion of cations, with cobalt being the most mobile one. Its diffusion depth in the electrolyte reaches up to several hundreds of micrometers. The addition of NiO as a sintering aid to BaZr0.8Y0.2O3−δ promotes cation diffusion especially through the grain boundary mechanism, increasing the diffusion depth of Co. The possible implications of cation interdiffusion on the performance of proton-conducting SOFCs are discussed based on the results obtained.

Assessment of the Y-doped Ca3Co4O9+δ as cathode material for proton-conducting fuel cells

This work presents the investigation of functional properties of the yttrium-doped Ca3Co4O9+δ complex oxides as the prospective cathode materials for the proton-conducting fuel cells. The phase equilibria in the ½Y2O3–CaO–⅓Co3O4 system at 900 °C in air is experimentally observed, and the phase diagram is constructed. The misfit-layered structure of the Ca3-kYkCo4O9+δ solid solutions, and their chemical compatibility in air with proton-conducting electrolytes BaCe0.7 Ba3Ca1.18Nb1.82O8.73 are established. Functional properties of the obtained Ca3-kYkCo4O9+δ materials have been studied. The oxygen non-stoichiometry values of δ at room temperature are equal to 0.48 and 0.62 for Ca2.5Y0.5Co4O9+δ and Ca2YCo4O9+δ, respectively. The electrical conductivity in air reaches maximum value of 32 S cm−1 at 800 °C for Ca2.5Y0.5Co4O9+δ. The values of linear thermal expansion coefficient for Ca2.5Y0.5Co4O9+δ and Ca2YCo4O9+δ are equal to 13.5 × 10−6 and 14 × 10−6 K−1 in the temperature range of 25–800 °C in air. Minimum value of the polarization resistance Rp of 0.86 Ω cm2 at 600 °C is observed for the Ca2YCo4O9+δ electrode on the BaCe0.7Zr0.1Y0.1Yb0.1O3-δ substrate. Results of the work demonstrate that Y-doping of Ca3Co4O9+δ can be recommended as the successful strategy for the enhancement of the electrochemical performance of the cathodes, based on Ca3Co4O9+δ, in the solid oxide fuel cells with the proton-conducting electrolytes.

High Performance and Stability Enabled by Tuning the Component Thermal Expansion Coefficients of a Proton-Conducting Solid Oxide Cell Operating at High Steam Concentration

The solid oxide cell (SOC) based on a proton-conducting electrolyte is promising to play an important role in large-scale energy storage and hydrogen production. However, its development is hindered by performance degradation caused by the mismatch in thermal expansion coefficients (TECs) between the electrolyte and the oxygen electrode. Although there is work on reducing TECs of the oxygen electrode, it is difficult to find proper materials having a low TEC while maintaining a high performance. In this paper, we propose a new path to solve this problem: increasing the TEC of the electrolyte. We demonstrate that doping Fe into BaZr0.3Ce0.5Y0.1Yb0.1O3−δ (BZCYYb) can increase the TEC from 10.3 × 10–6 K–1 of BZCYYb to 13.4 × 10–6 K–1 of BaZr0.3Ce0.48Fe0.02Y0.1Yb0.1O3−δ (BZCYYbF). Fe doping also enhances the sinterability, electrochemical performance, and stability of the electrolyte. Meanwhile, we find that doping Fe into the oxygen electrode material PrNi0.5Co0.5O3−δ (PNC) decreases the TEC from 19.2 × 10–6 K–1 of PNC to 17.4 × 10–6 K–1 of PrNi0.4Co0.4Fe0.2O3−δ (PNCF). The improved stability of the SOC with the BZCYYbF electrolyte and the PNCF oxygen electrode is verified for steam electrolysis under a high steam partial pressure, 50%. Such a cell operates stably at a current density of 1.76 A cm–2 under 1.30 V and 700 °C for 150 h.

Ba-doped Pr2NiO4+δ electrodes for proton-conducting electrochemical cells. Part 2: Transport and electrochemical properties

Materials based on barium-containing Pr2NiO4+δ are considered as promising air electrodes for protonic ceramic electrochemical cells owing to a wide range of attractive properties. In the present work, we thoroughly analyze the transport properties of Pr2NiO4+δ upon its chemical modification by Ba-doping. In detail, electrical conductivity and thermo-EMF measurements of Pr2–xBaxNiO4+δ (where x = 0, 0.1, 0.2, and 0.3) allow the effects of charge carrier concentration and mobility on overall transport to be determined depending on the chemical composition and defect structure. Lower polarization resistances of the Ba-containing electrodes when used in symmetrical cells with a BaCe0.5Zr0.3Y0.1Yb0.1O3–δ proton-conducting electrolyte confirm the functional benefits of barium as a dopant. However, the obtained experimental results can be explained not only by the better transport properties of barium-containing Pr2NiO4+δ (shown in the second part of our research), but also by the improved chemical and thermal compatibilities resulting in a good interface quality in an electrolyte/electrode couple (shown in the first part).

The Impact of Ammonium Fluoride on Structural, Absorbance Edge, and the Dielectric Properties of Polyvinyl Alcohol Films: Towards a Novel Analysis of the Optical Refractive Index, and CUT-OFF Laser Filters

The new proton-conducting composite electrolyte films (PCCEFs) consisting of polyvinyl alcohol (PVA) with varying ammonium fluoride salt concentrations were created using an expanded liquid casting process. The X-ray diffraction (XRD) study confirms the composite electrolyte films (CEFs) formation. The improvement in AMF02 salt doping compared to the PVA matrix film approach resulted in decreased variation in the crystalline size values, thus explaining how [NH4+] and polymer PVA matrix films interact. The band gaps decrease when the AMF02 salt filler concentration increases due to increased crystallite size. The suggested composites evaluated successful CUT-OFF laser filters and attenuation, as well as limiting laser power systems. For the 11.11 wt% AMF02 doping salt, the highest DC conductivity was 73.205 × 10−9 (siemens/m) at ambient temperature. Our dielectric results demonstrate that the CEFs are usually suitable for optoelectronic systems. There is a huge need to develop low dielectric permittivity composite electrolyte films (CEFs) for microelectronic devices and the high-frequency region.

Effects of ZnO addition and microwave sintering on the properties of BaCe0.2Zr0.7Y0.1O3-δ proton conductor electrolyte

The reduction of sintering time and temperature using an unconventional route and sintering aid for the densification of BaCe0.2Zr0.7Y0.1O3-δ were investigated. The effects of ZnO addition and microwave sintering were explored on the structure, sinterability, microstructure, and electrical conductivity. BaCe0.2Zr0.7Y0.1O3-δ powders were synthesized by solid-state reaction. The addition of 2 and 4 mol% ZnO was beneficial to obtain a single perovskite structure and improved sinterability producing dense samples. Relative densities of 99% at 1300 °C by conventional sintering and 98% at 1400 °C by microwave sintering were reached. A total conductivity of 1.20 mS cm−1 for the sample with 2 mol% ZnO by conventional sintering (relative density 99%) was obtained at 550 °C in a wet nitrogen atmosphere. Additionally, a high conductivity was also obtained for this compound produced by microwave sintering (relative density 98%) even with its microstructure exhibiting the smallest average grain size. In conventional sintering, the presence of the eutectic liquid phase responsible for the densification, was prejudicial to the total conductivity, being more evident in the samples with 4 mol% ZnO addition. The results indicate that microwave sintering was a rapid alternative for sintering, capable of reducing or inhibiting the appearance of the liquid phase producing dense, uniform samples, and with high conductivity.

Influence of transition or lanthanide metal doping on the properties of Sr0.6Ba0.4Ce0.9M0.1O3-δ (M = In, Pr or Ga) electrolytes for proton-conducting solid oxide fuel cells

Proton-conducting electrolytes offer an alternative electrolyte to replace the oxygen-ion conducting conventional electrolyte for solid oxide fuel cells (SOFCs). In this study, proton-conducting Sr0.6Ba0.4Ce0.9M0.1O3-δ (M = In, Pr, Ga) electrolytes without Zr were synthesized by the glycine-nitrate process for intermediate-temperature SOFC applications. The thermal decomposition and crystalline structure of the electrolyte powders were analysed by thermogravimetry (TG) analyses and X-ray diffraction (XRD), respectively. The morphological structure and chemical stability of the electrolyte pellets were examined by field-emission scanning electron microscopy (FESEM) and XRD. Electrochemical impedance spectroscopy (EIS) analysis was used to evaluate the proton conductivity of each electrolyte pellet at different operating temperatures (500–800 °C) in a gas mixture composed of hydrogen (10%) and nitrogen (90%) humidified at room temperature (wet H2/N2), air humidified at room temperature (wet air) and dry air. The ideal calcination temperature for the electrolyte is determined to be 1000 °C based on TGA and XRD analyses, which indicate a high degree of crystallization without any formation of secondary phases. Furthermore, the relative density of all sintered electrolyte pellets is found to lie within an acceptable range (>90%) for good ion conduction. The Sr0.6Ba0.4Ce0.9Ga0.1O3-δ electrolyte displays the highest relative density (99%). However, the chemical stability analysis shows that Sr0.6Ba0.4Ce0.9Pr0.1O3-δ is the most stable electrolyte with a small additional secondary phase. The EIS results indicate that the Sr0.6Ba0.4Ce0.9In0.1O3-δ electrolyte shows the highest ionic conductivities of 1.80 × 10-3, 2.26 × 10-3 and 1.28 × 10-3 S/cm at 700 °C in wet H2/N2, wet air and dry air, respectively. Overall, Sr0.6Ba0.4Ce0.9M0.1O3-δ doped with transition elements (In and Ga) are considered potential electrolytes for proton-conducting SOFCs. In terms of sinterability, chemical stability and proton conductivity, the Sr0.6Ba0.4Ce0.9In0.1O3-δ electrolyte doped with indium (In) is considered the best electrolyte in this work.

Mo-doped BaCe0·9Y0·1O3-δ proton-conducting electrolyte at intermediate temperature SOFCs. Part I: Microstructure and electrochemical properties

Researchers' interest in proton-conducting reversible solid oxide cells (RSOCs) is growing due to their distinct benefits. In the present work, single-phase BaCe0.9–xMoxY0.1O3–δ (x = 0, 0.025, 0.05, 0.1, 0.2) electrolyte is prepared via sol-gel method and sintered at 1400 °C for 10 h. Optimal density, structure, composition, electrochemical performance, and thermal stability are confirmed via SEM, XRD, EDS, XPS, FTIR, EIS, and TGA/DSC. The conductivity of the grain interior and boundaries between 127 and 727 °C is reported for the first time in SOFC studies. The BaCe0·875Mo0·025Y0·1O3–δ sample shows a grain interior conductivity of 1.3 × 10−3 S cm−1 at 707 °C with grain interior activation energy of 0.75 eV (127–727 °C), and a grain boundary activation energy of 0.85 eV (380–727 °C), 0.43 eV (167–357 °C) in air atmosphere, respectively. BaCe0.875Mo0.025Y0.1O3–δ showed extreme stability for 300 h, and thus can be considered suitable for an efficient protonic conductor at intermediate temperatures.

A New Class of Proton Conductors with Dramatically Enhanced Stability and High Conductivity for Reversible Solid Oxide Cells.

Reversible solid oxide cells based on proton conductors (P-ReSOCs) have potential to be the most efficient and low-cost option for large-scale energy storage and power generation, holding promise as an enabler for the implementation of intermittent renewable energy technologies and the widespread utilization of hydrogen. Here, the rational design of a new class of hexavalent Mo/W-doped proton-conducting electrolytes with excellent durability while maintaining high conductivity is reported. Specifically, BaMo(W)0.03 Ce0.71 Yb0.26 O3-δ exhibits dramatically enhanced chemical stability against high concentrations of steam and carbon dioxide than the state-of-the-art electrolyte materials while retaining similar ionic conductivity. In addition, P-ReSOCs based on BaW0.03 Ce0.71 Yb0.26 O3-δ demonstrate high peak power densities of 1.54, 1.03, 0.72, and 0.48W cm-2 at 650, 600, 550, and 500°C, respectively, in the fuel cell mode. During steam electrolysis, a high current density of 2.28 A cm-2 is achieved at a cell voltage of 1.3V at 600°C, and the electrolysis cell can operate stably with no noticeable degradation when exposed to high humidity of 30% H2 O at -0.5 A cm-2 and 600°C for over 300h. Overall, this work demonstrates the promise of donor doping for obtaining proton conductors with both high conductivity and chemical stability for P-ReSOCs.

BaCe0.6Zr0.3Y0.1O3-α electrochemical hydrogen sensor for fusion applications

Potentiometric sensors are broadening their application scope because they are affordable and scalable devices capable of being used in-field and online. In that frame, the use of proton-conducting solid-state electrolytes in these sensors architecture offers the possibility to operate at high temperatures, with high physical and chemical stabilities. A potential application for this kind of sensor is tritium monitoring in future fusion reactors. The first steps toward the development of this analytical tool will be devices capable of measuring hydrogen in high temperature applicationsIn the present work, a potentiometric sensor based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) solid-state proton-conductor was tested for hydrogen monitoring at 325 °C, 350 °C and 375 °C. BCZY was synthesized by the solid-state method and characterized using XRD. The sensor's linear range, accuracy and limit of detection were evaluated at the selected temperatures (325 °C, 350 °C and 375 °C). Moreover, sensors presented a very short response and recovery times (<100 s).

Operando monitoring of the evolution of triple-phase boundaries in proton exchange membrane fuel cells

The electrochemical reactions in proton exchange membrane fuel cells take place at the interface between the proton conductive electrolyte, gases, and catalyst active site, or the so-called triple-phase boundary. The triple-phase boundary area can increase through catalyst layer designs and hydrogen fuel cell operations. While catalyst layers are commonly characterized using physical methods, the impact of hydrogen fuel cell operations on triple-phase boundaries is significantly more challenging to analyze, with operando electrochemical characterizations currently lacking the necessary accuracy and sensitivity to capture these evolutions. Herein, we introduce an innovative approach to monitoring triple-phase boundary evolutions by simultaneously capturing the ohmic resistance and double-layer capacitance in transient operations using high-frequency zero-phase impedance spectroscopy. The operando catalyst layer utilization quickly reduces through-out dehydration, flooding, excessive load increase, and cell degradations. This approach precisely pinpoints how proton transport, electron transport and oxygen diffusion can altogether reduce the triple-phase boundary area. This new analysis, conducted using commercial materials, unravels the evolutions of the active site and electrolyte interactions throughout the hydrogen fuel cell operations and lifecycle, evidencing a rapid evolution in the triple-phase boundary area throughout the hydrogen fuel cell operations.

Orientation-dependent electrochemical reduction and proton evolution in the oxygen-deficient perovskite SrFeO2.5+y

Electrochemical reactions with insertions of ions in solids depend on crystallographic orientations. We investigated electrochemical responses of (100), (110) and (111)-oriented oxygen-deficient perovskite SrFeO2.5+y epitaxial films in electric-field-effect transistor structures with the proton-conducting electrolyte Nafion as a gate insulator. We found that only (100)-oriented SrFeO2.5+y films exhibit changes associated with gate-voltage-induced electrochemical reductions. Furthermore, elastic recoil detection analysis shows that electrochemically reduced (100) films can accommodate protons, forming the proton-containing oxide H0.11SrFeO2.5+y . Our results show that oxygen vacancies form preferentially along the {100} axes and ion diffusion in electrochemical reactions occurs dominantly along the {100} directions in SrFeO2.5+y .

Synthesis and Studies on Polymer Electrolyte Membrane using Polyvinyl Alcohol, Polyvinylidene Fluoride and Ammonium Bromide as Dopants for Proton-conducting Electrolyte

Different compositions of Polyvinyl alcohol (PVA), Polyvinylidene fluoride (PVDF) and Ammonium bromide (NH4Br) were employed to synthesize the proton-conducting polymer electrolyte membranes by Solution casting method, which have potential applications in proton (H+) ion batteries and fuel cells. Structural, vibrational and electrical properties of the synthesized polymer electrolyte membrane were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy and Electrical Impedance Spectroscopy (EIS) analysis and results were reported. The semi-crystalline nature of the prepared polymer was confirmed by XRD analysis. FTIR spectroscopy revealed the vibrational spectra of the prepared polymer membrane. The Nyquist plot drawn from the AC Impedance analysis was a straight line, confirming the dielectric nature of the prepared membrane.

Pressure-induced negative capacitance and enhanced grain boundary conductivity in nanocrystalline solid electrolyte BaZrO3

Proton-conducting BaZrO3-doped electrolytes are considered as potential high temperature proton conductors due to their high ionic conductivity and electrical efficiency in the operating temperature range of solid oxide fuel cells. However, doping leads to a decrease in grain boundary conductivity and greatly limits its applications. Here, the charge transport properties of sub-micro and nano-BaZrO3 electrolytes were studied by in situ high-pressure impedance measurements and first-principles calculations. Mixed ionic-electronic conduction was found in both samples in the whole pressure range. Pressure-induced negative capacitance in the tetragonal phase of nano-BaZrO3 was observed, which was related to the space charge layer of grain boundaries as well as the electrostrictive strain of grains. The enhanced electrostrictive effect was attributed to the existence of polar nano-domains in nano-BaZrO3. Furthermore, the coincident imaginary part of impedance and modulus peaks on the frequency scale indicated a non-localized carrier conduction in the tetragonal phase of nano-BaZrO3. The grain boundary conductivity of nano-BaZrO3 was enhanced by four orders of magnitude, and the impedance response changed from a constant phase element to an ideal capacitance, which was accompanied by the cubic to tetragonal phase transition. At a switching frequency of 0.1 Hz, the real part of the dielectric function of nano-BaZrO3 increases sharply with frequencies from negative to positive values, exhibiting a plasma-like Drude behavior. Our results provide insight into the optimization and application of BaZrO3-based proton conductors in solid oxide fuel cells.

Potentiometric Hydrogen Sensor with 3D-Printed BaCe0.6Zr0.3Y0.1O3-α Electrolyte for High-Temperature Applications.

Hydrogen is expected to play an important role in the near future in the transition to a net-zero economy. Therefore, the development of new in situ and real-time analytical tools able to quantify hydrogen at high temperatures is required for future applications. Potentiometric sensors based on perovskite-structured solid-state electrolytes can be a good option for H2 monitoring. Nevertheless, the geometry of the sensor should be designed according to the specific necessities of each technological field. Conventional shaping processes need several iterations of green shaping and machining to achieve a good result. In contrast, 3D printing methods stand out from conventional ones since they simplify the creation of prototypes, reducing the cost and the number of iterations needed for the obtainment of the final design. In the present work, BaCe0.6Zr0.3Y0.1O3-α (BCZY) was used as a proton-conducting electrolyte for potentiometric sensors construction. Two different shapes were tested for the sensors' electrolyte: pellets (BCZY-Pellet) and crucibles (BCZY-Crucible). Ceramics were shaped using extrusion-based 3D printing. Finally, parameters, such as sensitivity, response time, recovery time and the limit of detection and accuracy, were evaluated for both types of sensors (BCZY-Pellet and BCZY-Crucible) at 500 °C.

Transport properties of LaYbO3-based electrolytes doped with alkaline earth elements

The rapid development of efficient high-temperature electrochemical devices stimulates the search for new electrolytic materials with high conductivity and excellent chemical stability. From this point of view, lanthanum-containing perovskites can be considered as suitable materials for solid oxide fuel cell applications. In this work, the successfully synthesis and comprehensive study of acceptor-doped lanthanum ytterbates, La1–xMxYbO3–δ (M = Ca, Sr, Ba; x = 0, 0.05, 0.1) is described. X-ray diffraction analysis showed all samples to possess an orthorhombic structure with the space group Pna21, whose stability was confirmed at temperatures up to 1000 °C. The high chemical stability of the materials with respect to carbon dioxide and water vapor was confirmed by SEM and XRD methods. The dilatometry data allowed the determination of thermal expansion coefficient values of ceramic samples, which are close to those for conventionally used YSZ electrolytes. The transport properties of the ceramic were studied in a wide range of temperatures (300–900°C) and oxygen partial pressures. It was found that ytterbates doped with 5 and 10 wt.% of strontium and 5 wt.% of barium exhibited the high electrical conductivity among other considered materials. Thus, these materials can be considered as promising proton-conducting electrolytes for various electrochemical devices.