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For reliable long-term operation of solid oxide electrochemical devices for the hydrogen energy system, an electrolyte with high ionic conductivity and excellent chemical stability is required. SrHfO 3 -based perovskites are known for their high chemical resistance; however, their ionic conductivity must be increased. In the present research, the effect of doping with yttrium and ytterbium on the electrical properties of strontium hafnate was studied for the first time. The crystal structure, solubility limit of the dopants, morphology and electrical properties of SrHf 1-x M x O 3-δ (M = Y, Yb) materials were investigated by the X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, direct current four-probe technique, and impedance spectroscopy. The solubility limits of Y and Yb in SrHfO 3 were found to lie slightly below x = 0.10. It was revealed that yttrium doping is more favorable for the grain growth and densification of ceramics. A comparative analysis of the influence of dopant type (Y, Yb and Sc) and concentration on the electrical properties of SrHfO 3 is provided. [Display omitted] • Homogeneity range of SrHf 1-x Y x O 3-δ and SrHf 1-x Yb x O 3-δ solid solutions extends to x ≈< 0.10. • Y-doping is more favorable for the grain growth and densification of ceramics. • Y and Yb-doping enhance proton conductivity of SrHfO 3. • Y-doped SrHfO 3 has higher ionic transference numbers in wet oxidizing atmospheres. [ABSTRACT FROM AUTHOR]

Ruddlesden-Popper La 2- x Gd x NiO 4+δ (x = 0–0.4) nickelates were synthesized by glycerol-nitrate combustion technique and explored as potential oxygen electrode materials for solid oxide fuel/electrolysis cells. Similar to the parent La 2 NiO 4+δ , the metastability of RP-type n = 1 structure limits the applicability of La 2- x Gd x NiO 4+δ to temperatures below 900 °C. These solid solutions are mixed conductors with predominantly p -type electronic conductivity that exceeds 50 S/cm at 500–800 °C in air. Substitution by gadolinium does not change the overstoichiometric oxygen content in air but has a negative impact on the mobility of interstitial oxygen, most likely, due to steric effects associated with the lattice shrinkage on doping. The electrochemical activity of bilayer electrodes comprising functional La 2- x Gd x NiO 4+δ and current collecting LaNi 0.6 Fe 0.4 O 3-δ + 3 wt% CuO layers in contact with Ce 0.8 Gd 0.2 O 1.9 electrolyte was studied in air at 550–850 °C. Analysis of electrochemical impedance spectroscopy data employing the ALS (Adler-Lane-Steele) model revealed the limiting role of oxygen-ionic conductivity of functional La 2- x Gd x NiO 4+δ materials in overall electrode performance. • La 2- x Gd x NiO 4+δ (x = 0–0.4) were synthesized by the glycerol-nitrate combustion method. • Gd substitutions do not change oxygen nonstoichiometry in air. • p -type electronic conductivity is above 50 S/cm in air at 500–800 °C. • Crystal lattice shrinkage on substitution has a negative effect on oxygen-ion mobility. • Electrochemical activity of La 2- x Gd x NiO 4+δ electrodes correlates with ionic conductivity. [ABSTRACT FROM AUTHOR]

In order to develop economically competitive solid oxide fuel cell (SOFC) systems it is necessary to design new functional materials with the purpose of enhancing their performance, extending operational lifetime and reducing the cost. The present work focuses on the study of Pr 2-x Ca x NiO 4+δ cathode materials prepared by a simple and cheap conventional solid state reaction method. The structure, oxygen nonstoichiometry, electrical properties and chemical compatibility of the materials with a number of well-known oxygen ion and proton conducting electrolytes were systematically investigated. Chemical composition (Ca content) and technological factors (powders pre-history, electrodes' sintering temperature), as well as external parameters (temperature, air humidity) were correlated with the electrochemical performance of the electrodes to determine the optimal compositions and conditions. Based on this study and testing results of the single anode-supported cell with BaCe 0.89 Gd 0.1 Cu 0.01 O 3-δ electrolyte, the Pr 1.7 Ca 0.3 NiO 4+δ -based electrode compositions are proposed for preferred usage in SOFCs in place of Pr 2 NiO 4+δ electrode. Image 1 • Pr 2-x Ca x NiO 4+ δ was prepared by a solid state reaction method. • Materials with Ca are more compatible with solid state electrolytes. • Introducing SDC into the PCNO electrodes improves their performance. • Polarization resistance of PCNO3-BCGCu was 0.26 Ω cm2 at 700 C. • Test in SOFC mode revealed stability of the composite electrode. [ABSTRACT FROM AUTHOR]

Progress in hydrogen energy and promising directions for its modern development are closely related to design of fuel cells, including solid oxide fuel cells, and solid state membranes for hydrogen, oxygen and synthesis gas production. A necessary condition for fabrication of economically competitive devices in this area is the use of cheap electrode materials combining high electrochemical activity and long-term stability. Ln 2 NiO 4+δ oxides with the Ruddlesden–Popper layered structure possessing a high mixed ion-electron conductivity and moderate values of the coefficients of thermal expansion are promising materials for development of oxygen-conducting membranes and cathodes of intermediate-temperature solid oxide fuel cells. In this paper structural characteristics, electrical conductivity, oxygen mobility and electrochemical properties of Ln 2-x Ca x NiO 4+δ (Ln = La, Pr, Nd; x = 0; 0.3) samples were studied to determine factors, which have the most significant effect on the electrochemical activity of electrodes and their stability. It was found that doping with calcium lead to stabilization of the structure and increased the electrical conductivity of materials. However, addition of calcium decreased the electrochemical activity of electrodes in varying degrees depending on the nature of lanthanide. There is no direct interrelation of such a decrease of activity with either the electrical properties or the interstitial oxygen content. We have revealed correlation of the polarization resistance of electrodes with characteristics of oxygen transfer in the electrode material (self-diffusion coefficient, surface exchange constant). Using the C 18 O 2 SSITKA method, the total oxygen mobility in the doped materials was shown to fall with doping due to a decrease in the content of highly mobile interstitial oxygen and hampering of the cooperative oxygen transport mechanism. In the case of La 1.7 Ca 0.3 NiO 4+δ , this leads to the appearance of a slow diffusion channel and a substantial decrease in the total diffusion coefficient value which results in a sharp increase in the polarization resistance of the electrodes. This phenomenon is not observed in materials with praseodymium and neodymium. The electrodes based on Pr 1.7 Ca 0.3 NiO 4+δ and Nd 1.7 Ca 0.3 NiO 4+δ , developed in this work, have an acceptable level of the electrochemical activity along with a high electrical conductivity and increased stability in comparison with undoped compositions and can be recommended for use as cathodes for intermediate temperature fuel cells. [ABSTRACT FROM AUTHOR]

Oil-water transition zones in carbonate reservoirs represent important but rarely studied diagenetic environments that are now increasingly re-evaluated because of their potentially large effects on reservoir economics. Here, data from cathodoluminescence and fluorescence microscopy, isotope geochemistry, microthermometry, and X-ray tomography are combined to decipher the diagenetic history of a 5-m-long core interval comprising the oil-water transition zone in a Lower Pennsylvanian carbonate reservoir. The aim is to document the cementation dynamics prior, during, and after oil emplacement in its context of changing fluid parameters. Intergrain porosity mean values of 7% are present in the upper two sub-zones of the oil-water transitions zone but values sharply increase to a mean of 14% in the lower sub-zone grading into the water-saturated portions of the reservoir and a very similar pattern is observed for permeability values. In the top of the water-filled zone, cavernous porosity with mean values of about 24% is found. Carbonate cements formed from the earliest marine to the late burial stage. Five calcite (Ca-1 through 5) and one dolomite (Dol) phase are recognized with phase Ca-4b recording the onset of hydrocarbon migration. Carbon and oxygen cross-plots clearly delineate different paragenetic phases with Ca-4 representing the most depleted δ 13 C ratios with mean values of about −21‰. During the main phase of oil emplacement, arguably triggered by far-field Alpine tectonics, carbonate cementation was slowed down and eventually ceased in the presence of hydrocarbons and corrosive fluids with temperatures of 110–140 °C and a micro-hiatal surface formed in the paragenetic sequence. These observations support the “oil-inhibits-diagenesis” model. The presence an earlier corrosion surface between phase Ca-3 and 4 is best assigned to initial pulses of ascending corrosive fluids in advance of hydrocarbons. The short-lived nature of the oil migration event found here is rather uncommon when compared to other carbonate reservoirs. The study is relevant as it clearly documents the strengths of a combined petrographic and geochemical study in order to document the timing of oil migration in carbonate reservoirs and its related cementation dynamics. [ABSTRACT FROM AUTHOR]

The current work focuses on the investigation of the structural and electrical properties of La 2 NiO 4±δ , La 1.7 Sr 0.3 NiO 4±δ and La 1.7 Ca 0.3 NiO 4±δ layered perovskites and electrochemical performance of the cathodes on their base in contact with the Ce 0.8 Sm 0.2 O 1.9 electrolyte with special attention given to the influence of the introduction of the sintering additives (CuO, Bi 0.75 Y 0.25 O 1.5 ) into cathode layers on their in-plane and polarization resistances. Studies by the dc four-probe technique and impedance spectroscopy were performed on the samples with/without the collector layer on a base of LaNi 0.6 Fe 0.4 O 3 with different sintering temperatures of the electrode layers. [ABSTRACT FROM AUTHOR]

• 3D phase diagram of invasion patterns presented. • Maximum effect of disorder on sweep efficiency increases with capillary forces. • Maximum effect of disorder is maximum at neutral wettability. Pore space heterogeneity, numerically described by the disorder parameter, is a factor that strongly influences the displacement mechanics in porous media. This paper presents a systematic study of the simultaneous effects of capillary number, wetting angle, and pore space disorder on the invasion patterns of immiscible displacement: viscous and capillary fingering, compact displacement, and various crossover regimes. The results are based on lattice Boltzmann simulations performed on synthetic micromodels and natural X-ray computed tomography models of natural sandstones. This paper addresses two objectives. The first is to present for the first time a three-dimensional phase diagram in «capillary number, wetting angle, disorder» coordinates, which accurately indicates the regions of invasion patterns. The identification is based on a number of displacement characteristics, such as sweep efficiency map, fractal dimension, and the dynamics of the leading front movement. Based on the phase diagram, the critical wetting angles, which define the boundary of the viscous fingering, capillary fingering, and compact displacement regimes, shift towards imbibition with increasing disorder. A decrease in capillary number shifts the critical wetting angles for the viscous fingering and compact displacement modes towards drainage, and for the capillary fingering mode towards imbibition. The second goal is to identify the maximum effect of pore space disorder on sweep efficiency as a function of capillary number and wetting angle. It has been found that at high capillary numbers the disorder effect is independent of the wetting angle. A decrease in capillary number enhances the maximum disorder effect on sweep efficiency and it becomes strongly dependent on the wetting angle. With increased capillary forces the transition from deep imbibition and drainage regimes to the mode with neutral wettability greatly enhances the effect of disorder. The extremum point of wetting angle, at which the effect of disorder is maximum, shifts towards drainage with decreasing capillary number. [ABSTRACT FROM AUTHOR]

• Double–layer electrode based on Sr 2 Fe 1.5 Mo 0.5 O 6-δ investigated for the first time. • Solid oxide fuel cell with symmetrical electrodes was tested during 400 hours. • After eight redox cycles, a decrease in the fuel cell power by 20% was detected. The development of solid oxide electrochemical devices with symmetrical electrodes, is a promising direction in the field of resource saving and green energy. A feature of symmetrical electrodes is their stability to reduction–oxidation (redox) cycling, which can be useful in the case of carbon or sulphur deposition on a fuel electrode. The results of studies of a double-layer symmetrical electrode, where the functional layer consist of 50 wt.% Sr 2 Fe 1.5 Mo 0.5 O 6-δ + 50 wt.% Ce 0.8 Sm 0.2 O 1.9-δ and the collector is Sr 2 Fe 1.5 Mo 0.5 O 6-δ are presented for the first time. It was shown that the introduction of Ce 0.8 Sm 0.2 O 1.9-δ into the electrode functional layer, as well as the use of the current layer, does not lead to a change in the mechanism of oxygen reduction and hydrogen oxidation reactions. An analysis of the fuel cell impedance spectra by the distribution of relaxation times (DRT) method and comparison of the DRT functions with the results of the analysis of symmetric cells made it possible to conclude that during redox cycling the resistance of the oxygen exchange stage increases. It has been suggested that the cause of this is the formation of iron under reducing conditions, followed by its oxidation to oxide in an oxidizing atmosphere. [ABSTRACT FROM AUTHOR]

• 6.5 μm thick Hf 0.8 Yb 0.2 O 2-δ films were obtained by chemical solution deposition • The films had a nanogranular morphology with a grain size of ~130 nm • Across-plane film conductivity was studied using impedance and DRT • The film conductivity is hindered by grain-boundaries Films of HfO 2 – 10 mol% Yb 2 O 3 (HY) electrolyte were prepared on yttria–stabilized zirconia (YSZ) substrates by chemical solution deposition. 10-fold dip-coating followed by synthesis at 1100 °C, 1h resulted in formation of 6.5 μm thick films with nanogranular morphology. The across-plane electrical conductivity of the films was studied by electrochemical impedance spectroscopy using a Pt|YSZ|HY-film|Pt cell in the temperature range from 400 to 800°C. For correct separation of the film conductivity, the impedance measurements were also carried out on a reference Pt|YSZ|Pt cell with a blank YSZ sample. Methods of equivalent circuits and distribution of relaxation times were used for deconvolution of the impedance spectra of the cells. It was found that charge transport across the film is hindered by low grain boundary conductivity. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Contrast-comparison of dolostones located on flanks and crests of anticlinal hydrocarbon reservoirs. • Petrographic, isotopic and fluid inclusion data set provides evidence of coeval formation of burial dolostone. • Replacive and porosity-destructive dolomitization has deteriorated reservoir properties. • The temperature range, as based on fluid-inclusion data, points to an abnormally high-temperature background thermal regime in the Volga-Ural basin. A significant proportion of the remaining oil reserves worldwide is concentrated in dolostone rock bodies. The present paper focuses on Tournaisian and Visean limestones and geologically younger diagenetic dolomite units in two mature oil fields of the Volga-Ural Basin, Russia. In contrast to many dolostone-hosted hydrocarbon reservoirs worldwide, the Tournaisian and Visean dolostones in the Demkinskoye and the Onbiyskoye oil fields plot near the low end of the porosity–permeability range. Replacive and porosity-destructive burial dolomitization has deteriorated the reservoir properties of these units. Dolomitization is related to the ascent of hot (170–215 °C) and saline (22–24 wt%) fluids as based on fluid inclusion data. This temperature range points to an abnormally high temperature background thermal regime of the Volga-Ural basin. The onset of burial dolomitization predates oil charge as documented by the fact that oil-bearing inclusions are only present in the outermost zones of porosity-occluding dolomite cements. Isotope geochemical data, dolomite petrography and fluid inclusion data reveal important similarities between hydrothermal dolostone units in the Demkinskoye and the Onbiyskoye oil fields. Based on these data and the detailed cement stratigraphy presented here, it is argued that dolomite bodies in both oil fields formed as the result of one main, Alpine tectonic event pushing hot and saline dolomitizing brines ahead of ascending hydrocarbons. [ABSTRACT FROM AUTHOR]

Reversible solid oxide cells (rSOCs) based on proton-conducting electrolytes represent an advanced electrochemical technology aimed at reversible energy conversion. Their high levels of efficiency, minimal impact on the environment and economic viability point to a positive future for rSOCs. In this study we present the results of electrochemical characterization of the Ca 3 Co 4 O 9+δ -based oxygen (or steam) electrodes for rSOCs with the BaCe 0.5 Zr 0.3 Y 0.2 O 3–δ electrolyte. The electrodes developed display excellent electrochemical activity both in the symmetrical and reversible cells. In detail, the electrode polarization resistance at 700 °C amounts to less than 0.25 Ω cm2 after long-term measurements (1500 h, symmetrical cell mode of operation) and lower than 0.13 Ω cm2 (open circuit voltage mode of operation), exceeding the electrode performances of other Co-based materials of "112" (LnBaCo 2 O 5+δ , Ln is the lanthanide) and "114" (YBaCo 4 O 7+δ) families. Analysis of these data shows that Ca 3 Co 4 O 9+δ can be considered to be a promising alternative to the state-of-the-art electrodes utilized in protonic ceramic fuel and electrolysis cells. Image 1 • Ca 3 Co 4 O 9+δ (CC) material was successfully synthesized. • CC was comprehensively studied as an oxygen electrode of H+-SOFC/H+-SOEC. • CC electrodes demonstrate superior long-term (1500 h) stability in humid conditions. • CC shows a higher activity than Co-based electrodes of "112" and "114" families. [ABSTRACT FROM AUTHOR]

In this study the methods to increase electrochemical activity and stability of air electrodes based on LaNi 0·6 Fe 0·4 O 3-δ (LNF) and Сe 0.8 Sm 0.2 O 1.9 (SDC) with different collector layers has been developed. The influence of the electrode layers' composition and sintering conditions on the electrode performance in contact with the SDC electrolyte is considered. The polarization resistance of the electrodes with the LNF collector containing a combined Bi–Cu additive is in a range of 0.60–0.67 Ωcm2 at 600 °C. Appearance of low-melting liquid phases during the collector formation gives rise to both additional sintering and electrochemical activation of the functional layers. The optimized electrodes exhibit a low degradation (13–15%) preserving a polarization resistance level of 0.15–0.21 Ω cm2 at 700 °C after long-term testing for 600 h. To elucidate reasons of the electrode ageing, changes in the electrode performance and microstructure are analyzed using DRT technique and autocorrelation function analysis of SEM images. [Display omitted] • Methods to increase performance of LaNi 0·6 Fe 0·4 O 3 -based electrodes are considered. • Introduction of a Bi 1·75 Y 0·25 O 3 –CuO additive into collectors is most effective. • Polarization resistance Rη for the optimized electrodes are 0.6–0.7 Ω cm2 at 600 °C. • 600 h long-term tests at 700 °C reveal degradation ~15% and Rη to remain ~0.2 Ω cm2. • Electrode performance evolution is analyzed using DRT and SEM images' processing. [ABSTRACT FROM AUTHOR]

In this study the bilayer composite electrodes based on LaNi 0. 6 Fe 0. 4 O 3-δ (LNF) electronic conductor and Bi 2 O 3 -based electrolytes doped with Er (Bi 1. 6 Er 0. 4 O 3 , EDB) and Y (Bi 1. 5 Y 0. 5 O 3 , YDB) have been developed and their performance has been investigated in the dependence on the electrolyte content and sintering conditions. The polarization resistance of the optimized electrodes with electrolyte content of 50 wt % in the functional layer and with the LNF-EDB-CuO collector is in a range of 0.65–1.09 Ω cm2 at 600 °C and 0.10–0.12 Ω cm2 at 700 °C. The polarization characteristics of the Bi-based electrodes are compared with those for the composite electrodes based on LNF and Ce 0.8 Sm 0.2 O 1.9 (SDC). The developed electrodes have been tested in a SOFC mode in the anode-supported cells with a thin film electrolyte of YSZ/YDC (Y-doped zirconia/ceria). The single cells with such cathodes are shown to have performance characteristics that are several times higher than that for the cell with a standard platinum cathode. This is due to the optimized content and dispersity of the components; high conductivity of ionic and electronic constituents of the composite electrodes; greatly extended triple phase boundary (TPB) of the electrochemical reaction and advanced electrode design with collector providing uniform current distribution. [Display omitted] • LaNi 0·6 Fe 0·4 O 3 -based composite electrodes comprising doped Bi 2 O 3 or CeO 2 are studied. • Optimal electrolyte content and sintering conditions of electrode layers are defined. • Polarization resistance of developed electrodes is as low as 0.10–0.12 Ω cm2 at 700 °C. • SOFC with YSZ/YDC electrolyte and optimized electrode performs 745 mW/cm2 at 700 °C. • Electrode characteristics under various atmospheres are analyzed using DRT method. [ABSTRACT FROM AUTHOR]

Novel methods were applied in this work to elucidate the structure evolution of Ln 2-x Ca x NiO 4+δ oxides (Ln = La, Pr, Nd; x = 0, 0.3) and study their oxygen mobility. Relationship between cations state, structural, electrical, electrochemical and kinetic properties was revealed. In all doped materials the overall oxygen mobility characterized by Do declined by more than an order of magnitude due to decreasing the interstitial oxygen content and hampering cooperative mechanism of oxygen migration. For La nikelate additional slow diffusion channel appears with D O 5.4·10−14 cm2/s at 700 K. Correlation of electrochemical and oxygen transport properties was demonstrated. A high electrical conductivity (up to 120 S/cm at 700 K) in Ln 1.7 Ca 0.3 NiO 4+ δ (Ln = Pr, Nd) along with satisfactory oxygen mobility and electrochemical properties makes these materials promising for a wide row of electrochemical applications. • Ln 2-x Ca x NiO 4+δ (Ln = La, Pr, Nd; x = 0, 0.3) structure evolution was studied. • The samples behave differently during heating/cooling in O 2 rich/inert atmosphere. • Doping with Ca was shown to decrease δ and increase the electrical conductivity. • Extra slow O migration channel forms due to cooperative migration violation. • Electrochemical properties are determined by O mobility and surface reactivity. [ABSTRACT FROM AUTHOR]

This work presents the investigation of functional properties of the yttrium-doped Ca 3 Co 4 O 9+δ complex oxides as the prospective cathode materials for the proton-conducting fuel cells. The phase equilibria in the ½Y 2 O 3 –CaO–⅓Co 3 O 4 system at 900 °C in air is experimentally observed, and the phase diagram is constructed. The misfit-layered structure of the Ca 3-k Y k Co 4 O 9+δ solid solutions, and their chemical compatibility in air with proton-conducting electrolytes BaCe 0.7 Ba 3 Ca 1.18 Nb 1.82 O 8.73 are established. Functional properties of the obtained Ca 3-k Y k Co 4 O 9+δ materials have been studied. The oxygen non-stoichiometry values of δ at room temperature are equal to 0.48 and 0.62 for Ca 2.5 Y 0.5 Co 4 O 9+δ and Ca 2 YCo 4 O 9+δ , respectively. The electrical conductivity in air reaches maximum value of 32 S cm−1 at 800 °C for Ca 2.5 Y 0.5 Co 4 O 9+δ. The values of linear thermal expansion coefficient for Ca 2.5 Y 0.5 Co 4 O 9+δ and Ca 2 YCo 4 O 9+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 R p of 0.86 Ω cm2 at 600 °C is observed for the Ca 2 YCo 4 O 9+δ electrode on the BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ substrate. Results of the work demonstrate that Y-doping of Ca 3 Co 4 O 9+δ can be recommended as the successful strategy for the enhancement of the electrochemical performance of the cathodes, based on Ca 3 Co 4 O 9+δ , in the solid oxide fuel cells with the proton-conducting electrolytes. [Display omitted] • Phase diagram for the ½Y 2 O 3 –CaO–⅓Co 3 O 4 system at 900 °С in air is constructed. • Ca 3-k Y k Co 4 O 9+δ is chemically compatible with proton-conducting electrolytes. • The minimum R p at 600 °C is measured for Ca 2 YCo 4 O 9+δ on BaCe 0 · 7 Zr 0·1 Y 0.1 Yb 0.1 O 3-δ. [ABSTRACT FROM AUTHOR]