We extend our sincere gratitude to the scientists and subject-matter experts contributing to Chimica Techno Acta for their valuable time and expertise in reviewing submitted manuscripts. Their dedicated efforts are essential in upholding the journal's rigorous peer-review standards, which are fundamental to the quality and integrity of our published research. The Editorial Board acknowledges the following reviewers...

Solid oxide electrochemical cells (SOCs) operating at low and intermediate temperatures represent a promising technology for efficient and environmentally friendly energy conversion. The performance of these cells is predominantly governed by their total area specific resistance, which comprises two principal components: the ohmic resistance (associated with ionic transport within the electrolyte) and the polarization resistance (originating from electrode reaction kinetics). Consequently, the rational design of high-performance SOCs necessitates the independent optimization of these resistive contributions. It is generally accepted that ohmic and polarization resistances are intrinsic properties of the electrolyte and electrodes, respectively, and can thus be controlled separately through material doping or microstructural engineering of the corresponding components. However, the electrolyte and electrode materials form a common area (interface), indicating their close relation to each other. In the present study, a simple experiment was conducted to confirm the relationship between ohmic and polarization resistances. In detail, several symmetrical cells were prepared using the same electrode material and various electrolytes. It was shown that the polarization resistance of the electrode was as low as higher ionic conductivity of the electrolytes under identical experimental conditions. The obtained results are further discussed within the broader context of literature data for protonic ceramic fuel and electrolysis cells, revealing a commonality: the performance of the electrode is not an isolated property but is intrinsically linked to the characteristics of the electrolyte with which it interfaces.

The design of intermediate-temperature protonic ceramic cells requires novel proton-conducting electrolytes. Although hexagonal perovskites with structural oxygen vacancies show promise, they remain insufficiently studied. This work investigates Ba5Ho2Al2SnO13 as a tin-based analog of well-established zirconium-based systems. Single-phase ceramics were synthesized and analyzed using structural and thermogravimetric methods, which confirmed the hexagonal perovskite structure and its significant hydration capacity. Electrical conductivity was found to be higher in wet environments, showing the appearance of protonic conductivity. According to conductivity measurements depending on the oxygen partial pressure, ionic conduction predominated under reducing conditions, whereas p-type electronic conductivity originated under oxidizing conditions. While the total conductivity is lower than that of widely studied zirconate-cerates, it is competitive with other emerging proton conductors and surpasses most existing hexagonal perovskite analogs. As a result, Ba5Ho2Al2SnO13 is a promising proton-conducting model oxide for further computational and applied studies.

The development of intermediate-temperature protonic ceramic electrochemical devices requires novel electrolyte materials with enhanced transport properties. Among the emerging candidates, hexagonal perovskite-related oxides with structurally defined oxygen-deficient layered structures have attracted considerable attention because of their ability to incorporate high concentrations of protonic defects without acceptor doping. However, the number of systematically investigated representatives of this structural family remains limited, and the relationships between their crystal chemistry, hydration behavior, and transport properties have not yet been fully established. In this work, we report findings for a tin-containing hexagonal Ba5Y2Al2SnO13 (BYAS) perovskite. The crystal structure was refined using the Rietveld method in the framework of a layered intergrowth architecture with intrinsically oxygen-deficient layers. The hydration behavior was investigated by thermogravimetric analysis, which demonstrated the exceptionally high water uptake capacity of BYAS. Electrical conductivity measurements performed under various atmospheres confirmed the occurrence of proton transport, with significantly increased conductivity in wet environments. The thermal expansion behavior was found to be remarkably linear despite substantial hydration, providing a unique example of anisotropic chemical expansion compensation. The practical viability of BYAS was successfully demonstrated by fabricating and testing a reversible protonic ceramic cell. These findings contribute to the fundamental understanding of hexagonal perovskite-related proton conductors and establish a foundation for further compositional optimization strategies in this promising class of electrolyte materials.

BACKGROUND:Precise monitoring of water vapor and hydrogen in industrial gas streams is critical for the efficiency, safety, and control of processes in chemical synthesis, energy conversion, and fuel cell technologies. Current solid-state electrochemical sensors are often limited by insufficient sensitivity at lower operating temperatures, cross-sensitivity in complex gas mixtures, and material degradation under humid conditions. This work addresses these gaps by introducing a new sensor material that overcomes the stability-selectivity trade-off common to existing devices. RESULTS:To overcome these challenges, a novel amperometric solid-state sensor was developed. This sensor employs a newly engineered proton-conducting electrolyte, Ba1.15La1.85In2O7-δ. This complex oxide material was selected for its high proton conductivity at temperatures below 500 °C and its exceptional chemical stability. The fabricated sensor demonstrated a distinct quantitative limiting current response to both H2 and H2O, with minimal cross-interference between these species. The sensor exhibited a consistent ability to analyze water vapor across a concentration range of 1.3 to 10.0 vol% in nitrogen and hydrogen from 0.8 to 6.0 vol% in N2-H2 mixtures. The key performance metrics included high signal stability, a linear response to target gas concentrations, and relatively fast response and recovery times, confirming its operational robustness for continuous monitoring. SIGNIFICANCE AND NOVELTY:The novelty of this work lies in the first application of a Ba1.15La1.85In2O7-δ -based electrochemical cell as a dual-function (H2/H2O) amperometric sensor validated under industrially relevant conditions (350-450 °C). This finding is significant as it provides a direct pathway for reliable in-situ analysis in complex streams. More broadly, this finding validates the potential shift from conventional single-perovskite electrolytes to new tailored material classes for electrochemical sensing. The results demonstrate that this material class enables a stable, linear, and selective responses, allowing the fabrication of high-performance amperometric-type sensors.

Layered nickelate phases represent a convenient matrix for designing complex oxides intended for high-temperature applications. This study examines the structural, electrical, and electrochemical properties of the novel Pr1.8-xLaxBa0.2NiO4+s (x = 0.0-0.8) materials as potential air electrodes for reversible solid oxide cells (rSOCs). Additionally, we attempted to study the hydration ability of these materials. These materials are based on the Ruddlesden-Popper phase, Pr2NiO4+s, which is known for its mixed ionic-electronic transport behavior and favorable oxygen-diffusion characteristics. Substituting praseodymium with lanthanum and barium partially enhances the phase stability and optimizes the defect chemistry, improving the electrochemical performance of the designed electrodes. Compared with traditional perovskite and Ruddlesden-Popper cathode materials, the proposed electrode materials demonstrate superior surface oxygen exchange kinetics and thermal stability, positioning them as promising candidates for long-term rSOC applications.

BaSnO3 is one of the materials prospective for high-temperature proton-conducting membranes. For that purpose, it is subjected to acceptor doping-BaSn1-xMxO3-delta (M = M3+ metal). This provides appearance of oxygen vacancies in the crystal structure allowing for further hydration and, consequently, proton conductivity. Such doping, oxygen vacancies formation, and hydration influence materials electronic properties in the vicinity of the band gap. However, for BaSnO3, as a proton conducting oxide, such effects have not been considered before. This work aims to experimentally and theoretically reveal changes in the band gap parameters of BaSn1-xScxO3-delta depending on the dopant concentration x and hydration. The results obtained indicate on strong concentration dependence of the band gap parameters, showing three distinct ranges: x <= 0.10, 0.15 <= x <= 0.20, and x >= 0.25. This effect arises mainly from redistribution of the Sn 5s-and Sc 3d-states in the conduction band. In general, Sc doping gradually increases the band gap of the BaSnO3 from 3.04 eV at x = 0 to 3.63 eV at x = 0.37. Effect of hydration is even more complex, with no changes of the band gap at x <= 0.10, and with transformation of the absorption edge shape and the band gap increase at x >= 0.15. Besides, absorption spectra of BaSnO3 show no typical for acceptor-doped oxides oxygen vacancy peak near the absorption edge. Thus, such behavior of BaSnO3 differs significantly from that for other similar proton-conducting perovskites, making it intriguing material for further deeper studies.

Barium stannate BaSnO3 is a semiconducting oxide with cubic perovskite structure. It is capable for different types of doping, both in Ba and Sn sites, both by acceptor and donor dopants, allowing efficiently tuning its properties. Thus, BaSnO3 finds numerous applications, and its usage as a proton conducting ceramic electrolytes is one of them. Recently, it was reported that In-doped BaSn1-xInxO3-delta shows outstanding properties, like ability to form wide range of solid solutions up to x = 0.65, good chemical stability and high proton conductivity. However, this material lacks data on its band gap parameters, but given the semiconducting nature of barium stannate these data is crucial for comprehensive understanding of its functional properties. Therefore, this work is aimed at elucidating changes in the band gap parameters of BaSn1-xInxO3-delta promoted by doping and proton incorporation by hydration and hydrogenation. The results obtained indicate on systematic decrease of the band gap E-g with In concentration, from 3.04 eV at x = 0 to 2.76 eV at x = 0.6, which is suggested to be due to replacement of the Sn 5s states by In 5s. Besides, there is transformation of the absorption edge shape at x > 0.4 arising from substantial oxygen non-stoichiometry. Hydration leads to increase of E-g, and the higher the x, the greater the E-g change. However, that nature of this effect is not yet clear. Simultaneously, as oxygen sublattice becomes complete, the absorption edge shape restores to initial state. Effect of hydrogenation is more complex, leading to strong local tetragonal/orthorhombic distortions at x <= 0.2 and even phase decomposition at x >= 0.4. All this behavior of In-doped BaSnO3 diverges from typical trends observed in classical wide-gap proton conductors, such as doped LaScO3, BaZrO3, SrTiO3, and SrZrO3, thus, requiring a special attention.

The rational orientation toward sustainable energy systems has led to an ever-growing focus on the development of efficient energy conversion and storage technologies. Protonic ceramic electrochemical cells (PCCs) have emerged as promising solutions for highly efficient power generation and green hydrogen production. The performance and operating temperatures of PCCs with thin-film electrolytes are predominantly influenced by the oxygen electrode, which affects the kinetics of the oxygen reduction and oxygen evolution reactions. In recent years, this specific research domain is represented by a large amount of review articles, each of which aims to systematize the rapidly growing body of literature. However, this has created a significant gap: a large number of reviews complicate the formation of a data-driven perspective on the discussed scientific field. To address these limitations, the present work employs a unique dual methodology. A specialized Python code has been developed to perform a comprehensive scientometric analysis of 19 recent reviews as well as their referenced and citing sources. This analysis utilizes metadata from the open-source Crossref and OpenAlex databases. This data-driven approach meticulously maps the publication landscape, leading contributors, international collaborations, and thematic trends. This quantitative foundation subsequently provides a brief summary of these reviews, allowing the main strategies for designing oxygen (steam) PCC electrodes to be determined. This review offers a perspective on the current state and future directions of oxygen electrode design for PCCs by integrating big data analysis with traditional scholarly assessment.

Proton-conducting oxides constitute a wide class of materials that exhibit pronounced proton transport in humid atmospheres. Owing to their high proton mobility, these oxides are regarded as promising electrolytes for low- and intermediate-temperature protonic ceramic fuel cells and electrolysis cells, which offer efficient and clean energy conversion. Protons appear in complex oxides through a dissociative water adsorption process, which consists of the interaction between existing oxygen vacancies and water molecules in the gas phase. This process is also known as hydration or water uptake. Within the present work, we analyze the hydration features of BaSn1–xInxO3–δ perovskite materials (BSIx), which include a wide range of solid solutions (0 ≤ x < 0.7) and a nearly theoretical hydration limit for almost all studied compounds at the same time. The latter is a unique property of In-doped stannates, which is untypical for most other proton-conducting oxides. Along with the experimental data on the water uptake of BSIx, we provide an in-depth investigation of proton concentrations depending on external factors, involving a further comparison with literature data on materials hydration, as well as the discovery of hidden relationships between proton concentration and various functional properties. Therefore, this work contributes to theoretical and applied investigations of proton-conducting oxides, especially in the context of their hydration behavior.

The design of novel proton-conducting materials is important for clarifying the fundamentals of proton transport in complex oxides. Strontium stannate (SrSnO3) is an emerging and insufficiently studied class, and prior research has only provided fragmented insights into its doping chemistry. This study systematically explores the Sc-doping strategy in SrSn1-xScxO3-delta (where 0 <= x <= 0.2) to address the mentioned gap. A series of phase-pure ceramics was prepared via solid-state reaction. Their charge transport properties were characterized using comprehensive (DC/AC) conductivity measurements under controlled atmospheres (with various water vapor and oxygen partial pressures). Water uptake was analyzed using thermogravimetric analysis, which determined the temperature limits of proton conductivity. This methodology established direct correlations between the Scconcentration, defect chemistry, and ionic conduction. The optimal composition, SrSn0.8Sc0.2O3-delta, was integrated into a reversible protonic ceramic cell, demonstrating a peak power density of 13.7 mW cm(-2) at 700 degrees C in fuel cell operation and a hydrogen evolution rate of 0.24 mL cm(-2) min(-1) at 725 degrees C in electrolysis mode. These findings confirm the viability of SrSnO3-based systems as a proton-conducting platform and provide foundational structure-property-performance relationships, although further optimization of electrode microstructure and ohmic resistance is critical to achieve the acceptable output cell performances.

The development of low-temperature solid oxide fuel cells (LT-SOFCs) is of significant importance for realizing the widespread application of SOFCs. This has stimulated a substantial materials research effort in developing high oxide-ion conductivity in the electrolyte layer of SOFCs. In this context, for the first time, a dielectric material, CaCu3Ti4O12 (CCTO) is designed for LT-SOFCs electrolyte application in this study. Both individual CCTO and its heterostructure materials with a p-type Ni0.8Co0.15Al0.05LiO2−δ (NCAL) semiconductor are evaluated as alternative electrolytes in LT-SOFC at 450–550 °C. The single cell with the individual CCTO electrolyte exhibits a power output of approximately 263 mW cm−2 and an open-circuit voltage (OCV) of 0.95 V at 550 °C, while the cell with the CCTO–NCAL heterostructure electrolyte capably delivers an improved power output of approximately 605 mW cm−2 along with a higher OCV over 1.0 V, which indicates the introduction of high hole-conducting NCAL into the CCTO could enhance the cell performance rather than inducing any potential short-circuiting risk. It is found that these promising outcomes are due to the interplay of the dielectric material, its structure, and overall properties that led to improve electrochemical mechanism in CCTO–NCAL. Furthermore, density functional theory calculations provide the detailed information about the electronic and structural properties of the CCTO and NCAL and their heterostructure CCTO–NCAL. Our study thus provides a new approach for developing new advanced electrolytes for LT-SOFCs.

Proton-conducting ceramics constitute an important class for intermediate-temperature solid oxide cells, but their chemo-mechanical behavior (particularly, hydration-induced chemical expansion) remains poorly understood for heavily doped systems. Conventional studies on materials with low acceptor concentrations (<20 mol.%) yield a subtle dimensional response, complicating analysis in dense ceramic forms relevant to device integration. This cause difficulties in revealing the relationship between defect concentration, hydration thermodynamics, and resultant macroscopic strain. This work addresses this gap by investigating the model highly doped perovskite, BaSn0 & centerdot;5In0 & centerdot;5O3-delta, where the high oxygen vacancy concentration enables a pronounced chemical expansion effect. We employed a methodology combining thermogravimetric analysis for quantifying water uptake with dilatometry under controlled humidity levels to separate thermal and chemical expansion contributions during dynamic cooling cycles. The results demonstrate a clearly measurable chemical strain, which enables the precise determination of the chemical expansion coefficient and the deconvolution of the total dimensional change. Importantly, the analysis reveals that trace amounts of water vapor in apparently dry environments can induce significant chemical expansion, resulting in apparent negative thermal expansion coefficients within certain temperature ranges. The analytical framework developed in this study provides essential insights to predict dimensional stability and to mitigate interfacial stresses in multilayer protonic ceramic electrochemical cells.

Fe-containing perovskite materials have attracted considerable attention in the field of high temperature electrochemistry as potential electrode materials for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). Belonging to the cobalt-free family of materials, they exhibit high redox stability, acceptable thermal expansion behavior, and good electronic conductivity. However, in order to design electrochemically active electrodes towards oxygen reduction and evolution reactions, the oxygen-ionic conductivity of the iron-based materials must also be high. In the present work, the oxygen-ion transport behavior of Pr0.6Ba04FeO3-delta (PBF) was comprehensively investigated by oxygen permeation experiments as a function of doping effects (Pr0.6Ba0.4Fe0.9M0.1O3-delta, M = Ni, Cu, and Co) and external parameters. In detail, three-layer porous|dense|porous membranes with a dense layer thickness of similar to 100 mu m were successfully prepared by the tape calendaring method followed by their electrochemical characterization. It was found that the highest oxygen permeation fluxes were obtained for the basic PBF composition, while the Co-containing membrane showed the inferior permeation properties. The Ni- and Cu-doped PBF materials were intermediate in permeation properties and derived oxygen-ionic conductivity. These data, together with other functional properties tailored by doping, make Ni- and Cu-containing materials one of the most promising derivatives from (Pr,Ba)FeO3-delta for electrochemical applications.

Sintering additives have been widely employed to achieve good sinterability of barium-based proton-conducting perovskites (based on BaZrO3, BaCeO3, BaTiO3, BaHfO3, BaThO3, and BaSnO3). This is of particular importance for the fabrication of multilayered ceramic cells, in which the thin-film electrolyte layer can be primarily densified at relatively low sintering temperatures (1350–1500 °C). The introduction of sintering additives facilitates the fabrication of gas-tight ceramics; however, the precise nature of their localization and their effects on the functional properties remain uncertain and even questionable. In this study, we present a comprehensive characterization of ceramic materials based on Y-doped BaSnO3 prepared with the addition of three sintering additives (copper, cobalt, and nickel oxides) at 1 wt%. Although these introduced oxides belong to a group of compounds with similar physicochemical properties, each additive exerts a distinct influence on the microstructural and electrochemical properties of the ceramics owing to their own chemical localization features. These features are discussed in detail in the present work, providing useful information in the field of using sintering additives for the preparation of oxide ceramics for high-temperature applications.

Ln2Zr2O7 (Ln = Sm, Gd) zirconate solid solutions doped with Mg on the Ln and Zr sites have been prepared via mechanical activation of oxide mixtures, followed by heat treatment of green compacts at 1500 and 1600 degrees C for 4 h. The ceramics prepared at 1600 degrees C have been characterized by X-ray diffraction and scanning electron microscopy. Their electrical conductivity has been determined in dry and wet air using impedance spectroscopy, and the total conductivity of the best samples has been measured from 700 to 1000 degrees C in a wide range of oxygen partial pressures. The conductivity data obtained in dry and wet air for the samarium zirconate-based solid solutions doped with Mg on the Zr site demonstrate that raising the Mg content on the Zr site in the Sm2Zr2-xMgxO7-delta (x = 0, 0.05, 0.1, 0.2) pyrochlore series leads to a decrease in the total conductivity of the materials. However, the Sm2Zr2-xMgxO7-delta (x = 0.05, 0.1) materials have a proton component of conductivity in the range of 300-600 degrees C, which also decreases with increasing Mg content. Among the samarium zirconates studied here, high proton conductivity (1 x 10-4 S/cm at 500 degrees C) is offered by the Sm2Zr1.95Mg0.05O7-delta solid solution. Sm1.9Mg0.1Zr2O7-delta, containing Mg on the Sm site, has the highest oxygen ion conductivity: 5 x 10-3 S/ cm at 750 degrees C. The total conductivity of the Gd2Zr2-xMgxO7-delta (x = 0, 0.05, 0.1, 0.2) series also decreases with increasing Mg content, and no proton conduction has been detected in these zirconates. Mg doping of Gd2Zr2O7 on the Zr site reduces the total conductivity of the material, whereas Mg doping on the Gd site (Gd1.9Mg0.1Zr2O7-delta) raises it to 7.5 x 10-3 S/cm at 750 degrees C.

Solid-state electrochemical sensors based on yttria-stabilized zirconia (YSZ) are commonly used in various industrial applications to analyze gaseous media. One of the important industrial tasks is the determination of carbon monoxide content in various gas environments at elevated temperatures. This work describes the preparation and characterization of an amperometric solid electrolyte sensor, which is used to measure the carbon monoxide content in inert gases (nitrogen, argon, and helium) at temperatures ranging from 600 to 700 °C. The sensor exhibited a linear relationship between the limiting current as a sensor reading and carbon monoxide concentration in the gas mixtures analyzed within the range of 1 to 10 vol.

The addition of sintering additives is frequently regarded as an effective approach for increasing the density of proton-conducting oxide materials for their subsequent application as thin-film electrolytes for high-efficiency and high-performance protonic ceramic fuel cells (PCFCs) and electrolysis cells (PCECs). Although the positive effects of sintering additives on the sinterability of materials have been repeatedly confirmed, the nature of their localization in produced ceramics remains unclear. In particular, an analysis of approximately 20 studies related to the use of CuO for the densification of Ba-based ceramics does not allow solid conclusions about the real role of CuO to be drawn. Some researchers believe that CuO acts as a dopant, whereas others detect no significant solubility but instead observe the formation of Cu-containing impurities. To overcome the ambiguity of the different experimental results, we selected a reference system of BaSn0.8Y0.2O3-delta + x wt% CuO (BSYx, 0 <= x <= 2) and performed complex structural, microstructural, and electrochemical characterization using as-prepared (oxidized) and H2-treated (reduced) ceramics. Our results indicate that CuO facilitates liquid-phase sintering and therefore cannot act as a dopant, as CuO segregates at the grain boundaries or surface ceramic sites upon cooling. Furthermore, the high-temperature sintering of the studied materials at 1500 degrees C allows for the evaporation of the majority of the CuO (similar to 90%), thereby reducing the potential negative effects of CuO on proton transport. Electrochemical impedance spectroscopy analysis demonstrated that the BSYx ceramics exhibit high grain boundary proton transport, which is beneficial for the prospective application of such or similar electrolyte systems in PCFCs and PCECs.

Proton-conducting perovskite materials have attracted considerable attention from experts in materials science, solid-state ionics, and high-temperature electrochemistry. These materials are unique because the original complex oxide structure is free of protons; however, proton defects (charge carriers) may appear in the structure when it is in contact with a humid atmosphere at high temperatures. These newly formed protons result in high ionic conductivity values, which are greatly beneficial for designing low- and intermediate-temperature electrochemical devices. Many breakthrough results have been recently achieved in the application of proton-conducting perovskite materials and related electrochemical cells. Most of these results were obtained using state-of-the-art electrolytes based on Y/Yb-doped cerate-zirconates. However, the class of proton-conducting perovskite oxides is much broader than just cerates and zirconates. Each type of oxides has its own advantages and limitations. This review briefly outlines potential proton-conducting perovskite materials and focuses on strategies for their chemical modification (doping). In this regard, not only classical A(2+)B(4+)O(3) perovskites, but also A(1+)B(5+)O(3) and A(3+)B(3+)O(3) counterparts were considered in detail. In conclusion, this work is a valuable resource for identifying interesting objects among the wide variety of proton-conducting oxide perovskites, considering their historical milestones and recent progress.