In this paper we present the electrochemical performance of YSr2Cu2FeO7+δ (YSCF). YSCF was prepared by the combustion method and showed YBaCuO-type structure. Symmetrical cells with YSCF-Ce0.9Gd0.1O2-δ (CGO) electrodes showed a polarization resistance of 0.3 Ω·cm2 at 600 °C. Then, YSCF was incorporated in fuel electrode supported solid oxide cells (SOCs). SOCs were composed by the Ni-8% mol stabilized ZrO2 (YSZ) cermet as fuel electrode, YSZ as electrolyte, CGO as barrier layer and the composite YSCF-CGO as oxygen electrode. A SOC with (La₀.₆Sr₀.₄)₀.₉₅Fe₀.₈Co₀.₂O₃−δ (LSCF)-CGO oxygen electrode was also fabricated as reference cell. At 800 °C under 50:50% H2O:H2 in the fuel electrode and air in the oxygen electrode, YSCF-based cell reached a maximum power output of 0.74 W·cm-2 at 0.5 V in SOFC mode and -1.1 A·cm-2 at thermoneutral voltage (1.3 V) in SOEC mode. In the same conditions, EIS measurements revealed a polarization resistance of 0.17 Ω·cm2.

Introduction The society is undergoing a transition from carbon-based polluting non-renewable energy sources to greener ones based on electricity. While important advancements have been made, some issues related with intermittent supply must be solved [1]. Hydrogen serves as possible solution for this problem as energy carrier, although its production costs must be reduced. Solid Oxide Cell (SOC) technology offers an efficient method for hydrogen generation from water electrolysis if it is operating in Solid Oxide Electrolysis Cell (SOEC) mode, and for its transformation to electricity afterwards, when working as Solid Oxide Fuel Cell (SOFC) [2]. SOC technology presents several advantages, including the absence of precious materials, lower electricity consumption for hydrogen production and lower hydrogen consumption for electricity production or higher efficiency in both modes. SOCs can be classified as function or their architectures, with the most significant types being planar and tubular [3]. Additionally, they can be classified by their support type, being the most important configurations fuel electrode-supported and electrolyte-supported [4]. Since some of the objectives of SOC technology are reducing operating temperatures and manufacturing cost without compromising performance, planar fuel electrode-supported configurations are particularly attractive thanks to thinner electrolytes [5] compared to electrolyte-supported and more economic cost production than tubular [6]. Objectives Planar fuel electrode-supported SOCs of 5x5 cm 2 were manufactured and characterized at Instituto de Nanociencia y Materiales de Aragon (INMA) focusing on optimizing the production process with conventional techniques such as tape casting and screen printing. Standard materials widely studied were employed, such as the cermet Ni-yttrium stabilized zirconia (YSZ), YSZ as electrolyte and (La 0.8 Sr 0.2 ) 0.95 MnO 3-x (LSM)-YSZ or (La 0.60 Sr 0.40 ) 0.95 Co 0.20 Fe 0.80 O 3-x (LSCF) - Gd 0.1 Ce 0.9 O 1.95 (GDC) composites [7], including in this latter case a GDC barrier layer. Button cells around 1 cm 2 were also manufactured and characterized with accelerated degradation studies in order to understand Ni migration on fuel electrode and cell components degradation. Results Tape casting was employed for the fabrication of the fuel electrode and the electrolyte. Electrolyte slurry was made from 8%mol Y 2 O 3 -stabilized ZrO 2 (8YSZ). Two different slurries were prepared for fuel electrode. The first type consists of NiO, 8YSZ powders and corn starch, which helps to decrease polarization associated with hydrogen and steam diffusion [8]. This slurry was used for making fuel-electrode support layers, resulting in a composition of 40%vol Ni, 30%vol 8YSZ and 30% porosity after reduction. The second slurry, composed by NiO and 8YSZ powders, forms the functional layer, with a final composition of 26%vol porosity, 37%vol Ni and 37% YSZ after reduction. It was tape casted on top of the electrolyte tape. Tape photographs and schemas can be seen on Figure 1a) for fuel electrode support (top) and functional layer with electrolyte (down). Then, three NiO-YSZ layers of porous substrate and one NiO-YSZ functional layer with electrolyte were roll calendered on a hot rolling press as can be seen on Figure 1b). Finally, they were sintered at 1500ºC for 2 hours, resulting in a half-SOCs which can be seen on Figure 1c). For the two types of air electrodes (LSM-YSZ and LSCF-GDC), different inks were prepared with two different compositions: 50-50%vol and 80-20%vol. Inks were homogenized using a three-roll milling process before deposition. For 5x5 cm 2 SOCs, when LSM-YSZ was used, four layers of 4x4 cm 2 were screen printed over the electrolyte as can be seen on Figure 1d): the first two with a 50-50%vol composition, while the last two with 80-20%vol composition. For LSCF-GDC air electrode, same procedure was followed, but a 4x4 cm 2 GDC barrier layer was screen printed beforehand and sintered at 1400ºC during three hours in order to minimize strontium diffusion and the formation of ionic insulating secondary phases such as strontium zirconate (SrZrO 3 ). Air electrodes were sintered at 1150ºC for two hours. Resulting SOCs can be observed on Figure 1e). After sintering, reproducible SOCs were obtained with 300 µm fuel electrode support and 50 µm functional fuel electrode (Figure 2a)), 10 µm electrolyte (Figure 2b)), 3 µm GDC barrier layer and 40 µm air electrode in both air electrodes (Figure 2c)). While thinner electrolytes could be obtained in order to reduce ohmic loses and improve performance, they may result in a decrease of the long-term performance due to electrolyte delamination and degradation in SOEC applications. SOCs were reduced at 800ºC with humidified hydrogen (~3% H 2 O) before electrochemical characterization. Characterization of 5x5 cm 2 SOCs was conducted using an Open-Flanges set-up from Fiaxell, employing Electrochemical Impedance Spectroscopy (EIS) and current density-voltage curves ( j- V curves) at different temperatures with several atmosphere conditions in both electrodes. Temperatures measured were 750, 800 and 850ºC. On fuel electrode, humidified hydrogen (~3% H 2 O and 97% H 2 ), and 50% H 2 O-H 2 were measured while atmospheric air (~20% O 2 ) and pure oxygen were used on air electrode. EIS measurements were made at Open Circuit Voltage (OCV) in the range compressed between 100 kHz to 100 mHz with an amplitude of 50 mV, while j- V curves were measured in SOFC mode (from OCV to 0.5V) and SOEC mode (from OCV to 1.5 V) using a potentiostast SP-300 from Biologic with a 30A booster. Button cells were cut with laser from 5x5 cm 2 half-SOCs (see Figure 1f)). LSM-YSZ air electrodes of 1 cm 2 were deposited on button cells following the same protocol as for squared SOCs. Resulting button cells can be seen on Figure 1g). Experiments lasted around 100h in chronoamperometry in SOEC mode (1.3 V) at temperatures comprising the range between 750 and 850ºC with high steam concentrations (at least 50% H 2 O). Characterization took place on both Fiaxell and Probostat set-ups focusing on the use of different glass, ceramic and compressive sealings, such as GO18-311 and 354, Ceramabond 571 and mica, respectively. Moreover, EIS and j- V measurements were made at different intervals in order to understand SOCs evolution. For square 5x5cm 2 SOCs, an inverse relationship was observed between Area Specific Resistance (ASR) values obtained from EIS measurements and steam and oxygen concentrations. The higher these concentrations, the lower was ASR. Arrhenius dependency was followed with temperature. Some electrochemical results can be seen on table from Figure 2 f). For example, at 750ºC, 50% H 2 O and atmospheric air (typical SOEC operation conditions), ASR values of 0.92 Ω·cm 2 and 0.63 Ω·cm 2 for LSM-YSZ and LSCF-GDC air electrodes SOCs were measured. From j -V curves at same conditions, current densities of 0.4 A·cm -2 and 0.5 A ·cm -2 were obtained in SOEC mode at thermoneutral voltage (1.3 V), while in SOFC mode the current densities were 0.26 A·cm -2 (equivalent to 0.18 W·cm -2 ) and 0.43 A ·cm -2 (0.3W ·cm -2 ) at 0.7 V in SOFC mode. It can be confirmed that LSCF-GDC SOC presented better electrochemical performance than LSM-YSZ SOC when temperature was lowered. EIS spectra and j- V curves with these conditions can be seen on Figure 2d) (top) and 2e) (top). On the other hand, for optimal SOFC performance, humidified hydrogen (3% H 2 O) and pure oxygen (100%O 2 ) must be used. At 850ºC, ASR from EIS measurements were 0.42 and 0.41 Ω·cm 2 for both cells respectively. From j -V curves, current densities of 1.09 A·cm -2 (0.76 W·cm -2 ) and 0.87 A·cm -2 (0.61 W·cm -2 )were obtained at 0.7 V. With these conditions, a fast increase in polarization was observed in SOEC mode, caused by steam lack. Moreover, at this temperature both SOCs performed in a comparable way. EIS and j- V curves can be seen on Figure 2d) and 2e) (down). For button cells results, after 100 hours working as SOEC at 1.3 V at 750ºC with 50% H 2 O and atmospheric air, ASR was 1.02 Ω·cm 2 with a current density of 0.30 A ·cm -2 , while at 850ºC ASR was 0.97 Ω ·cm -2 with 0.50 A ·cm -2 . Finally, manufactured as well as post-mortem SEM analysis of SOCs were carried out to understand cell degradation. Conclusions Electrochemical characterization revealed that LSCF-GDC air electrodes exhibited better performance at lower temperatures than LSM-YSZ which demonstrated the effectiveness of GDC barrier layer deposited by screen printing. At higher temperatures, both air electrodes showed comparable performance, which also proved the high LSM-YSZ air electrodes performance. Moreover, long-term tests provided comparable results to commercial cells in terms of degradation rate and ASR values, validating the manufacturing processes. Future work should focus on searching optimizations for manufacturing techniques that will provide better electrochemical performance, reducing components degradation as the same time more durable long-term degradation studies (at least 1000 hours) should take place. References [1] G. Gowrisankaran, S.S. Reynolds, M. Samano, R. Clark, A. Collard-Wexler, J. Cullen, L. Davis, M. Fowlie, K. Gillingham, B. Handel, B. Hogan, P. Joskow, D. Keith, D. Lemoine, A. Pakes, P. Schmidt-Dengler, J. Teirilä, C. Wolfram, J. Wooders, M. Xiao, G. Zoettl, Intermittency and the Value of Renewable Energy, 2016. [2] M.A. Morales-Zapata, A. Larrea, M.A. Laguna-Bercero, Reversible operation performance of microtubular solid oxide cells with a nickelate-based oxygen electrode, Int J Hydrogen Energy 45 (2020) 5535–5542. https://doi.org/10.1016/j.ijhydene.2019.05.122. [3] S.C. Singhal, K. Kendal, High Temperature Solid Oxide Fuel Cells. Fundamental, Designs and Applications, 2003. [4] A. Nechache, S. Hody, Alternative and innovative solid oxide electrolysis cell materials: A short review, Renewable and Sustainable Energy Reviews 149 (2021). https://doi.org/10.1016/j.rser.2021.111322. [5] A. Tarancón, Strategies for lowering solid oxide fuel cells operating temperature, Energies (Basel) 2 (2009) 1130–1150. https://doi.org/10.3390/en20401130. [6] S.C. Singhal, Solid oxide fuel cells for stationary, mobile, and military applications, n.d. www.elsevier.com/locate/ssi. [7] A. Orera, P.R. Slater, New chemical systems for solid oxide fuel cells, Chemistry of Materials 22 (2010) 675–690. https://doi.org/10.1021/cm902687z. [8] B.I. Arias-Serrano, M.E. Sotomayor, A. Várez, B. Levenfeld, H. Monzón, M.A. Laguna-Bercero, A. Larrea, High-performance Ni-YSZ thin-walled microtubes for anode-supported solid oxide fuel cells obtained by powder extrusion moulding, RSC Adv 6 (2016) 19007–19015. https://doi.org/10.1039/c5ra28183k. Acknowledgement This research was supported by MCIN with funding from NextGenerationEU (PRTR-C17.I1) within the Planes Complementarios con CCAA (Area of Green Hydrogen and Energy) and it has been carried out in the CSIC Interdisciplinary Thematic Platform (PTI+) Transición Energética Sostenible+ (PTI-TRANSENER+). We acknowledge the financial support from the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón to Research Group T02_23R. Figure 1

Despite its high efficiency, SOEC technology faces a critical challenge: maintaining long-term stability, often undermined by interfacial degradation and unwanted chemical interactions between air electrodes and the electrolyte. During cell operation, strontium is segregated from the electrode and diffuses towards the electrode-electrolyte interface, where it reacts with zirconium, forming insulating layers. The introduction of rare-earth-doped ceria interlayers at the interface has been proven to prevent strontium migration and improve long-term performance of the cell, enhancing air electrode-electrolyte compatibility. High density and absence of defects are crucial properties for these layers, in order to effectively prevent strontium diffusion towards the interface, limiting cell degradation. In this line, this work explores the deposition of dense, thin, homogeneous and defect-free rare-earth-doped ceria layers at the air electrode-electrolyte interface. The impact of different dopants on the interlayer: samarium, lanthanum and gadolinium, was analyzed. The films were deposited by means of magnetron sputtering techniques: direct current (DC) and high power impulse magnetron sputtering (HiPIMS). Magnetron sputtering offers precise control over the films’ properties: thickness, composition, uniformity and finishing, allowing for the deposition of high-quality and efficient films. Additionally, the scalability of magnetron sputtering makes it compatible with potential large-scale manufacturing. The implications of magnetron sputtering parameters on coating-surface interface and coating properties were examined. Scanning electron microscopy (SEM) was used to evaluate the film’s physical features. Focused ion beam (FIB) was employed for high resolution interface visualization. Energy dispersive spectroscopy (EDS) was used to verify the chemical composition of the coatings. X-ray diffraction (XRD) was employed to determine ceria’s adequate doping. In order to test the quality of the developed ceria interlayers, anode supported half cells of NiO-YSZ/YSZ were supplied by INMA, different deposition conditions for the interlayers were tested, and finally standard LSCF/CGO air electrodes were deposited by screen-printing. Electrochemical impedance spectroscopy (EIS) and current-voltage (I-V) characterization in both fuel cell and electrolysis mode were performed to evaluate electrochemical performance, including long-term stability. Glow discharge optical emission spectrometry (GDOES) was employed to verify the prevention of strontium migration after electrochemical testing. Overall, the study focuses on the deposition and optimization of rare-earth-doped ceria interlayers to enhance air electrode-electrolyte compatibility, addressing the degradation challenge SOEC technology faces. Tackling this issue by means of magnetron sputtering, it aims to produce superior quality films, and compare these results to those achieved by other deposition techniques. In this way, the study aspires to further explore and contribute to the optimization of SOEC technology, supporting its transition to industrial-scale applications.

We have analysed, through neutron diffraction experiments with the volume-gauge technique, the operando performance of lead cells composed of industrial positive and negative electrodes, previously tank formed in the manufacturing plant. The cells, 6.7 cm x 11.5 cm in surface, comprised a 3.4 mm thick positive electrode sandwiched between two 2.3 mm thick negative electrodes. The electrolyte was sulphuric acid diluted in water, both deuterated, and the separators were industrial grade absorptive glass mat (AGM). The experiments, carried out using the VULCAN instrument at the Oak Ridge National Laboratory (TN, USA), showed the evolution of alpha-PbO2, beta-PbO2 and PbSO4 phases in the positive active mass during charge/discharge cycling, comparing the behaviour of fresh and cycled cells. No evidence of PbSO4 phase in fully charged plates or PbO in any state of charge were found above 1% by weight. Significant inhomogeneity of phase distribution and transition rates inside the positive electrode was observed. The experiments allowed estimation of the energy efficiency by comparing the external energy provided to the cell with the energy stored in the PbSO4 to PbO2 transformations.

We have analyzed by operando neutron diffraction the charge/discharge crystallographic transformation processes inside the positive active mass (PAM) of industrial lead batteries, getting information onthe spatial distribution of the phases. Our study was focused on the positive electrode because it is there where the main limitations to the charge/discharge efficiency are originated. The experiments were carried out in the VULCAN instrument at the Spallation Neutron Source of the Oak Ridge National Laboratory (Tennessee, USA) using the volume gauge technique. VULCAN is a high brightness time-of-flight diffractometer which provides fast volumetric mapping and, therefore, the possibility to study kinetic behaviors. Accordingly, both static and dynamic mapping experiments were performed during charge-discharge cycles, comparing fresh and cycled cells. The diffractograms obtained were analyzed using VDRIVE and GSAS software, together with dedicated Python scripts. In addition to compositional maps (Figure 1), information on lattice parameters, crystallinity, stoichiometry and hydration was also obtained as a function of the state of charge. Local inhomogeneities and differences in the behavior between fresh and cycled cells were observed. Moreover, we have used the Pb signal from the positive grid as internal calibrating element to obtain the absolute molar concentration of the component phases, comparing the PbSO 4 PbO 2 transformation with the effective charge driven by the cell during charge and discharge processes. The b-PbO 2 mass utilization during the C5 100% to 20% discharge was about 0.3. In the same way, the charge factor was estimated to about 70%, from the start of charging until the PbO 2 concentration reaches a near flat regime, and about 5% after reaching the flat regime. Giving for the full charging cycle a value about 50%. As far as we know, this is the first time that diffraction information has been obtained from inside commercial thick electrodes (3.4 mm in thickness) during real operation conditions, mapping the PbO 2 and PbSO 4 evolution in a 2.24 cm x 7.2 cm region of the positive electrode. Figure 1

The laser is a powerful tool for materials processing, incorporated already in many industrial processes and laboratory procedures. In this work, we are concerned with laser processing applied to research and development of ceramics for electrochemical cells and other high temperature oxide ceramics for energy applications. Solidification of single crystals or composites of relevant oxides can be performed by the laser assisted floating zone method, providing samples for structural, mechanical or functional fundamental research, as well as knowledge about its manufacture by melt processes. Selective laser melting of these ceramic oxides is a very promising technology, at the research level. Successful examples of surface laser melting of oxide eutectic composites are presented. The technologies of sub-tractive laser processing of ceramics (cutting, drilling, structuring, cleaning, etc.) are more developed, and the research is directed towards the optimization of mechanisms, increase of resolution and efficiency and the investigation of the effects of the laser treatment on the functional performance. Different laser processes of SOC (solid oxide cell) components are shown to decrease the ohmic, concentration and activation losses. The manuscript describes the state-of-the art of the technologies as applied to oxide and composite materials present in solid oxide electrochemical devices (SOFC, SOEC, and batteries) and selective emitters for thermophotovoltaics, with emphasis on the last achievements by the authors team. (c) 2021 SECV. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Pr and Mn infiltrated oxide nanoparticles are confirmed as excellent candidates for boosting the performance of standard lanthanum strontium manganese oxygen electrodes.

The redox behavior of terbium and praseodymium doped yttria-stabilized zirconia (YSZ) is studied. The aim is to identify spectroscopic probes and a suitable experimental procedure to monitor the oxygen activity in YSZ electrolytes in solid oxide cells with spatial resolution and at operation conditions (e.g. at high temperatures). Sintered ceramics and crystals with 0.3 to 10 at% content of Pr or Tb ions in YSZ were prepared. Upon equilibration in atmospheres from 10 −20 to 100 bar P O 2 around 800 °C, the majority of these rare earth ions are in the 3 + oxidation state. At oxygen pressures above 0.001 bar, the small proportion of Tb 4+ and Pr 4+ formed give rise to intense optical absorption around 300–500 nm and to decreased reflectance. From the reflectance measurements it is shown that the Tb 4+ concentration increases as P O 2 1/4 , as correspond to the trapping of the holes generated upon the oxygen incorporation as Tb 4+ . This competitive absorption causes a decrease of the Tb 3+ luminescence. A quantitative relationship of the Tb 3+ luminescence intensity with P O 2 at 800 °C has been found, which is compatible with the trapping model. The spatial resolution of the experimental procedure could be very roughly estimated of the order of 100 μ m.

Oxide eutectics have great potentiality as structural or functional materials, owing to the outstanding properties derived from the eutectic microstructure. Among them, the eutectic of the ZrO2 - MgO system is particularly noteworthy because of the unusual combination of thermomechanical, optical and electrical properties. In a recent application, Zr1-delta Mg delta O2-delta - MgO eutectic oxides have been used to produce porous supports for molten -carbonate based CO2 separation membranes. Here we explore composite ceramic oxides of the CexZr1-xO2 - MgO (x < 0.5) system with eutectic microstructure, with the motivation that incorporating cerium may enhance the CO2 permeation properties. Eutectic composites with different cerium content are produced by a laser-assisted directional solidification technique at variable solidification rate, v. In all cases the composite bicrystal consists of two phases, MgO and a fluorite-like (CexZr1-x)1-yMgyO2-y phase. A purely fibrilar microstructure is found for x >= 0.3 at v = 25 mm/h, with MgO fibres embedded within the fluorite-like matrix. The MgO mol% in the eutectic composites decreases from-53% for x = 0 to-48% for x = 0.5. X-ray and Raman results evidence long-range ordering in a quasi-tetragonal monoclinic symmetry for x = 0.5. Impedance spectroscopy results are consistent with a change from ionic to mainly electronic conductivity when the atmosphere is changed from air or Ar to 5% H2-Ar.

Due to the limitations of bone autografts, we aimed to develop new composite biomaterials with pro-angiogenic and osteogenic properties to be used as scaffolds in bone tissue engineering applications. We used a porous, cross-linked and slowly biodegradable fibrin/alginate scaffold originally developed in our laboratory for wound healing, throughout which deposits of calcium phosphate (CaP) were evenly incorporated using an established biomimetic method. Material characterisation revealed the porous nature and confirmed the deposition of CaP precursor phases throughout the scaffolds. MC3T3-E1 cells adhered to the scaffolds, proliferated, migrated and differentiated down the osteogenic pathway during the culture period. Chick chorioallantoic membrane (CAM) assay results showed that the scaffolds were pro-angiogenic and biocompatible. The work presented here gave useful insights into the potential of these pro-angiogenic and osteogenic scaffolds for bone tissue engineering and merits further research in a pre-clinical model prior to its clinical translation.

Solar perovskites have received phenomenal attention and success over the past decade, due to their high power conversion efficiencies (PCE), ease of fabrication and low cost which has enabled the prospect of them being a real commercial contender to the traditional silicon technology. In one of the several developments on the archetypal MAPbI3 perovskite absorber layer, FAPbI3 was found to obtain a higher PCE, likely due to its more optimum band gap, with doping strategies focusing on the inclusion of MA+/Cs+ cations to avoid the unfavourable phase transformation to a photoinactive phase. To better understand the phase change from the photoactive cubic (Pm3[combining macron]m) black (α) phase to the unwanted photoinactive (P63/mmc) yellow (δ) phase, we make use of variable temperature Raman spectroscopy to probe the molecular species and its relationship to the inorganic framework. We show for the first time there to be no Raman active modes for the α phase up to 4000 cm-1, which can be correlated to the Pm3[combining macron]m cubic symmetry of that phase. Our detailed studies suggest that previous reports of the observation of Raman peaks for this phase are likely associated with degradation reactions from the localised laser exposure and the formation of Raman active lead oxide. In addition, we have identified water as a contributing factor to the transformation, and observed a corresponding signal in the Raman spectra, although confirmation of its exact role still remains inconclusive.

The insight into the mechanism of the unprecedented formation of pure anatase TiO2 from the macromolecular (Chitosan)•(TiOSO4)n precursor has been investigated using micro Raman spectroscopy, Scanning Electron Microscopy (SEM) and thermogravimetric/differential thermal analysis (TGA/DTA). The formation of a graphitic film was observed upon annealing of the macromolecular precursor, reaching a maximum at about 500 °C due to decomposition of the polymeric chain of the Chitosan and (PS-co-4-PVP) polymers. The proposed mechanism is the nucleation and growth of TiO2 nanoparticles over this graphitic substrate. SEM and Raman measurements confirm the formation of TiO2 anatase around 400 °C. The observation of an exothermic peak around 260 °C in the TGA/DTA measurements confirms the decomposition of carbon chains to form graphite. Another exothermic peak around 560 °C corresponds to the loss of additional carbonaceous residues.

Solid oxide fuel cells (SOFC) are reversible devices that generate electric energy by oxidation of a fuel, commonly hydrogen. In electrolyser mode (SOEC), a voltage is applied and hydrogen is generated from water. These processes are highly efficient, although one of the main sources of degradation in these devices arises from extreme oxygen activity inside the electrolyte at the interfaces with the electrodes [1, 2], developed because of inappropriate operating conditions or poor electrode performance. In particular, high oxygen partial pressure in the oxygen electrode/electrolyte interface can lead to electrode delamination when working in SOEC mode at high voltages. The purpose of this work is to investigate the oxygen activity profile established across a yttria-stabilized zircona (YSZ) electrolyte upon different polarization conditions. To achieve this goal, several redox ions were studied as spectroscopic probes inside a YSZ matrix and among them terbium was found to be a suitable dopant as optical spectroscopic probe for intermediate and high ranges of oxygen activity [3]. By means of optical absorption and diffuse reflectance, 3+/4+ terbium oxidation states could be identified in samples annealed in different atmospheres. Tb3+ luminescence signals can be used to follow the 3+/4+ dopant redox couple, and using the strong 5D4 → 7F5 Tb3+ luminescence emission [4], a quantitative relation between its intensity and oxygen partial pressure in equilibrium with the doped electrolyte could be established (Fig. 1). Therefore, this signal can be used to quantify the p O 2 in equilibrium at different positions inside the electrolyte. Several experiments were designed in order to obtain different electrochemical parameters from the YSZ-Tb system. First of all, ionic conductivity of the terbium doped YSZ electrolyte was determined with symmetrical cells with platinum electrodes and testing them by impedance spectroscopy under oxygen and hydrogen atmospheres in a wide range of temperatures. Electronic conductivity of YSZ-Tb could be determined using Hebb-Wagner cells with a LSM/YSZ electrode on the oxygen side and an ion-blocking Pt electrode. Similar cells were also polarized under different conditions and cooled down to freeze the oxygen activity gradient. The quenched O2 activity profile was quantified using Tb3+ luminescence signal intensity, and analysed taking into account the actual conductivity of the minority carriers, as determined in the previous experiments. Cells with a LSM/YSZ cermet air electrode and a Ni/YSZ cermet hydrogen electrode were tested in SOEC mode. When in stationary state, cells were quenched, freezing the high-temperature under-voltage terbium oxidation state, as shown in Fig. 2. By analysing the terbium luminescence signal, oxygen activity and oxygen partial pressure across the electrolyte thickness could be determined under different polarization conditions. The results and capabilities of the method will be discussed. [1] A. Virkar, Int. J. Hydrogen Enery 35 (2010) 9527. [2] M.A. Laguna-Bercero et al., Int. J. Hydrogen Energy 36 (2011) 13051. [3] R.I. Merino et al. (2018) https://digital.csic.es/handle/10261/182893. [4] M.R.N. Soares et al., Materials Letters 65 (2011) 1979-1981. Figure 1

CO2 utilisation as a feedstock is presented as an encouraging pathway to mitigate atmospheric pollution. This chapter summarises recent advances in a novel approach for the production of valuable products, such as synthetic fuel, by co-electrolysis of steam and CO2 using the existing technology of solid oxide cells. In this regard, this chapter covers the general aspects of the co-electrolysis process, its history and the industrial state-of-the-art technology. It also gathers some recent studies and developments covering various aspects with special focus regarding current and novel materials and configurations, operational parameters, durability tests and degradation issues, including economic considerations and scalability studies. It is concluded that CO2-recycled hydrocarbon fuels could replace the actual fuels for transportation or industrial use, with feasible technology development and mass production of the different components. The sustainability of the former could provide a key issue for their introduction into the market.

espanolLa aplicacion de baterias acopladas a sistemas de conversion de energia renovable en las ciudades ayudara en gran medida a superar algunos de los retos tecnologicos para la electrificacion de la red y el transporte, como la dificil accesibilidad a puntos de carga, y de coste, mejorando sus capacidades tecnicas y haciendo que el sistema energetico a nivel global sea mas sostenible. Ademas, su aplicacion tendra un efecto inmediato en la salud de los ciudadanos debido a la disminucion de las emisiones de gases de efecto invernadero a la atmosfera, asi como otros contaminantes. A continuacion, presentamos una revision de los esfuerzos recientes para desarrollar nuevas tecnologias avanzados para las futuras baterias sostenibles. Tambien destacaremos las estrategias actuales de reciclado de baterias que se aplican hacia un futuro con cero emisiones de carbon EnglishThe application of batteries coupled to renewable energy conversion systems in cities will greatly help to overcome some of the technological challenges for grid electrification and transport, such as difficult accessibility to charging points, and cost, by improving their technical capabilities and making the energy system globally more sustainable. Furthermore, its implementation will have an immediate effect on citizens’ health due to the reduction of greenhouse gas emissions into the atmosphere, as well as other pollutants. Below is a review of recent efforts to develop new advanced technologies for future sustainable batteries. We will also highlight current battery recycling strategies that are being implemented towards a zero-carbon future based on the concept of the circular economy.

Aluminium-doped lanthanum silicate (LSAO) apatite-type compounds have been considered as promising candidates for substituting yttria-stabilized zirconia (YSZ) as electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFC). Nevertheless, not many materials have been reported to work as cathodes in a LSAO apatite-based cell. In the present work, eight different strontium and cobalt-free compounds with a perovskite-type structure and the general composition LaM1-xNxO3-δ (where M = Fe, Cr, Mn; N = Cu, Ni; and x = 0.2, 0.3) have been tested. This study includes the synthesis and structural characterization of the compounds, as well as thermomechanical and chemical compatibility tests between them. Functional characterization of the individual components has been performed by electrochemical impedance spectroscopy (EIS). Apatite/perovskite symmetrical cells were used to measure area-specific resistance (ASR) of the half cell in an intermediate temperature range (500-850 °C) both with and without DC bias. According to its electrochemical behaviour, LaFe0.8Cu0.2O3-δ is the most promising material for IT-SOFC among the compositions tested since its ASR is similar to that of the traditional (LaxSr1-x)MnO3 (LSM) cathode.

The application of batteries coupled to renewable energy conversion systems in cities will greatly help to overcome some of the technological challenges for grid electrification and transport, such as difficult accessibility to charging points, and cost, by improving their technical capabilities and making the energy system globally more sustainable. Furthermore, its implementation will have an immediate effect on citizens' health due to the reduction of greenhouse gas emissions into the atmosphere, as well as other pollutants. Below is a review of recent efforts to develop new advanced technologies for future sustainable batteries. We will also highlight current battery recycling strategies that are being implemented towards a zero-carbon future based on the concept of the circular economy.

Ionic charge balance at the interface of Gd-doped CeO2/CoO eutectic ceramics produces Gd segregation and increases the interfacial ionic conductivity.

In this work we report a detailed structural study of theK(2-x)Na(x)Mg(2)(SO4)(3) series in order to evaluate the effect of Na incorporation on the structure. The results show that the cubic langbeinite structure is observed at room temperature for high Na levels; K2-xNaxMg2(SO4)(3) (0 <= x <= 1.8). Increasing the Na content further, 1.8 < x <= 1.9, leads to significant structural distortions, with the observation of an enlarged orthorhombic cell. These latter systems resemble a highly distorted variant of the langbeinite structure, and this relationship is also illustrated by the fact that they transform to the cubic langbeinite structure at relatively low temperature (approximate to 200 degrees C). In conjunction with our prior studies on Na2Mg2(SO4)(3) (complex monoclinic cell, which also transforms to langbeinite at elevated temperature), this work highlights the flexibility of the langbeinite structure to accommodate high levels of Na ions, thus offering another potential avenue to manipulate the properties of materials with this structure-type.

The authors acknowledge the financial support from the Spanish Ministerio de Economia y Competitividad and Feder Funds under project MAT2016‐77769‐R.