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A strategy to improve the performance and durability of solid oxide fuel cells (SOFCs) is to increase the cathodic activity and decrease the interfacial resistance between the cathode and electrolyte. Pulsed laser deposition (PLD) has been shown to be a promising method to engineer functional interlayers to enhance the cell's performance. In the present study, a bilayer consisting of Sm0.2Ce0.8O2−δ (SDC) barrier layer (BL) and a nanocomposite consisting of SDC-La0.8Sr0.2MnO3−δ (SDC-LSM) employed as a cathode functional layer were deposited by PLD in an anode supported SOFC. The fuel cell showed a maximum power density of 0.30 W∙cm−2 at 750 °C. Most importantly, a durability test carried out for 700 h at 750 °C showed a remarkably stable performance of the fuel cell.

Ion intercalation of perovskite oxides in liquid electrolytes is a very promising method for controlling their functional properties while storing charge, which opens the potential application in different energy and information technologies. Although the role of defect chemistry in the oxygen intercalation in a gaseous environment is well established, the mechanism of ion intercalation in liquid electrolytes at room temperature is poorly understood. In this study, the defect chemistry during ion intercalation of La0.5Sr0.5FeO3-{\delta} thin films in alkaline electrolytes is studied. Oxygen and proton intercalation into the LSF perovskite structure is observed at moderate electrochemical potentials (0.5 V to -0.4 V), giving rise to a change in the oxidation state of Fe (as a charge compensation mechanism). The variation of the concentration of holes as a function of the intercalation potential was characterized by in-situ ellipsometry and the concentration of electron holes was indirectly quantified for different electrochemical potentials. Finally, a dilute defect chemistry model that describes the variation of defect species during ionic intercalation was developed.

Poster presentation on the research onthermoelectric generators based on Nb doped STO thin films developed in the frame of the Harvestore project (GA: 824072)

The incorporation of electrochemical-based energy devices such as Solid Oxide Cells (SOC) to the renewable energy sector in the frame of a modern energy generation strategy could be beneficial, taking into account the opportunity to store renewable energy overproduction as hydrogen (SOEC operation mode) as well as to use, subsequently, this hydrogen as a fuel for energy generation in the same device (SOFC operation mode). Nowadays, the common-used SOC manufacturing approaches, in most cases, meet the limits originated by the capabilities of the techniques to produce the ceramic components with more complicated geometries, in respect to planar or tubular shapes. To overcome these constrains, the additive manufacturing (AM), commonly referred as 3D Printing, could be applied for the production of the SOC-based devices with enhanced features. The use of AM allows a high degree of design freedom and opens a wide field for fabrication of functional ceramics with high resolution of herarchical geometries, optimized through computational elements by CAD design and stereolithographic (SLA)ceramic printing. At the same time the AM, specifically the SLA in this work, allows the simplification of the whole SOC manufacturing process making it tunable in geometry and size opening a new trend for fabrication of large area SOC with enhanced features in terms of active area or other functionalities. In a more effective way in terms of time, cost and waste material reduction. The enhancement of the performance of the SOC device has been proved due to the increase of the active area by the production of complex shaped electrolytes using the 3D Printing process. To demonstrate,its scalability, large area 3YSZ electrolytes (~60-70 cm2) with the advanced geometries were fabricated by stereolithography three-dimensional printer, to be implemented as an electrolyte-supported cell using YSZ composites with lanthanum strontium manganite (LSM) as a cathode and nickel composites as an anode, i.e. Ni-YSZ/3YSZ/LSM-YSZ.

Gadolinium-doped ceria (CGO) is placed between yttrium-stabilized zirconia (YSZ) electrolyte and strontium-based electrode as a barrier layer to avoid the formation of SrZrO3 insulating phase during solid oxide fuel cell operation. This phase is observed in as-fabricated state-of-the-art cells, which evidences cation inter-diffusion during the sintering process [1]. The impact of this element to the degradation of cells is still under study, in part due to the high complexity of long-term tests necessary for the appropriate understanding of the involved phenomena. Among the efforts for improving barrier layers, the use of vacuum techniques such as sputtering and Large Area Pulsed Laser Deposition (LA-PLD) have been explored, allowing the implementation of dense layers at lower processing temperature compared with traditional deposition techniques (i. e. screen printing). CGO barrier layer thin film deposition and annealing parameters were previously optimized in a leading to an important increase of power density compared to a state-of-the-art button cell at 750ºC using a dense layer of 2 µm. Remarkable results were also obtained when the PLD barrier layer was up-scaled to large area cells of 80 cm2 and tested in short-stack configuration for long-term operation [2]. Here we present a thorough investigation of post mortem cells operated in short-stacks under realistic conditions during 15000h, comparing cells produced with state-of-the-art techniques with those produced by LA-PLD. At the light of the results, we provide tools for the improvement of the fabricated thin film layers, by finding the optimal combination between the protective role of the diffusion barrier layer, a good performance and the reduction of the PLD deposition time. Button cells with PLD barrier layer of 800 nm, 400 nm and 200 nm were fabricated and tested in SOFC mode at 750ºC. It is shown that the barrier layer thickness has no impact on the electrochemical performance and the durability which allows the use of thinner layers and a drastic reduction of the deposition time of the CGO barrier layer made by PLD. Summed to the increased performance, the durability of the layers is evaluated, subjecting the cell with the thinnest film to an aging process for 3,500 h. Post-mortem characterization of the barrier layers and interfaces was conducted by Scanning-electronic microscope and Electron Probe Micro Analysis with Wavelength Dispersive X-Ray (EPMA-WDX) to observe any microstructural changes as well as any changes in composition due to cation inter-diffusion. [1] Morales et al., Journal of Power Sources 344 (2017) 141-151. [2] Morales et al. ACS Applied Energy Materials 1 (2018) 1955-1964.

Electrochemical devices such as solid oxide fuel cells (SOFC) may greatly benefit from the implementation of nanoengineered thin-film multifunctional layers providing, alongside enhanced electrochemical activity, improved mechanical, and long-term stability. In this study, an ultrathin (400 nm) bilayer of samarium-doped ceria and a self-assembled nanocomposite made of Sm0.2Ce0.8O1.9-La0.8Sr0.2MnO3-$\delta$ was fabricated by pulsed laser deposition and is employed as a functional oxygen electrode in an anode-supported solid oxide fuel cell. Introducing the functional bilayer in the cell architecture results in a simple processing technique for the fabrication of high-performance fuel cells (power density 1.0 W.cm-2 at 0.7 V and 750 $^\circ$C). Durability tests were carried out for up to 1500 h, showing a small degradation under extreme operating conditions of 1 A.cm-2, while a stable behaviour at 0.5 A.cm-2. Post-test analyses, including scanning and transmission electron microscopy and electrochemical impedance spectroscopy, demonstrate that the nanoengineered thin film layers remain mostly morphologically stable after the operation., Comment: 24 pages, 12 figures

Extending the potential window toward the 3 V plateau below the typically used range could boost the effective capacity of LiMn

This article is part of the themed collection: Recent Open Access Articles., The NASICON superionic solid electrolyte Li1+xAlxTi2−x(PO4)3 (LATP) with 0.3 ≤ x ≤ 0.5 remains one of the most promising solid electrolytes thanks to its good ionic conductivity and outstanding stability in ambient air. Despite the intensive research for bulk systems, there are only very few studies of LATP in a thin film form (thickness < 1 μm) and its implementation in all-solid-state batteries and microbatteries. The following study fills this gap by exploring the properties of high performance LATP thin films fabricated by large-area Pulsed Laser Deposition (PLD). The as-deposited thin films exhibit an ionic conductivity of around 0.5 μS cm−1 at room temperature (comparable to the state-of-the-art of LiPON) which increases to a remarkably high value of 0.1 mS cm−1 after an additional annealing at 800 °C. A possible cause for this significant enhancement in ionic conductivity by two orders of magnitude is the formation of a glassy, intergranular phase. The performance of both as-deposited and annealed LATP films makes them suitable as solid electrolytes, which opens the path to a new family of stable and high performance all-solid-state thin film batteries., This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 824072 (HARVESTORE), from the European Regional Development Fund under the FEDER Catalonia Operative Programme 2014-2020 (FEM-IoT, 001-P-00166) and the “Generalitat de Catalunya” (2017 SGR 1421, NANOEN). FIB, HRSTEM, EDS and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. R. A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the MICINN through project grants MAT2016-79776-P (AEI/FEDER, UE) and PID2019-104739GB-I00 as well as from the European Union H2020 program “ESTEEM3” (823717). J. C. G.-R., acknowledges the financial support provided by the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 801342 (Tecniospring INDUSTRY), as well as by the Agency for Business Competitiveness of the Government of Catalonia. NMR measurements were supported and carried out at the Centre for Cooperative Research on Alternative Energies (CIC energiGUNE) as a member of the Basque Research and Technology Alliance (BRTA). Suitable Si3N4 substrates and microelectrodes have been provided by the Institute of Microelectronics of Barcelona IMB-CNM. Pt-covered Si substrates have been fabricated by the Interuniversity Microelectronics Centre (imec) in Leuven, Belgium. GI-XRD measurements have been collected at the Scientific and Technological Center (CCiT) at the University of Barcelona.

High voltage cathodes suffer from degradation phenomena that are challenging to be observed and identified during cell operation. Dense and smooth sputtered thin films electrodes with absence of binders and conductive additives allow a direct study of the active material upon Li insertion and extraction at surface and bulk. Using an operando spectroscopic ellipsometry set-up combined with a customized electrochemical-optical cell (EC-SE), the evolution of the optical absorption and thickness of LiMn2O4 and LiNi0.5Mn1.5O4 thin-film electrodes was monitored upon cycling. Mixed Mn3+/4+ valence in the electrodes and evident layer dissolution associated to Transition Metal (TM) dissolution in the non-aqueous electrolyte at the applied polarization potentials was observed. Our results reaffirm EC-SE as a convenient method to study degradation phenomena in cobalt-free transition metal oxide electrodes.

The exploration for thermoelectric thin films of complex oxides such as SrTiO

The exploration for thermoelectric thin films of complex oxides such as SrTiO3-based oxides is driven by the need for miniaturized harvesting devices for powering the Internet of Things (IoT). However, there is still not a clear consensus in the literature for the underlying influence of film thickness on thermoelectric properties. Here, we report the fabrication of epitaxial thin films of 6% Nb-doped SrTiO3 on (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) single crystal using pulsed laser deposition (PLD) where the film thickness was varied from 2 nm to 68 nm. The thickness dependence shows a subtle increase of tetragonality of the thin film lattice and a gradual drop of the electrical conductivity, the density of charge carriers, and the thermoelectric Seebeck coefficient as the film thickness decreases. DFT-based calculations show that ∼2.8% increase in tetragonality results in an increased splitting between t2g and eg orbitals to ∼42.3 meV. However, experimentally observed tetragonality for films between 68 to 13 nm is only 0.06%. Hence, the effect of thickness on tetragonality is neglected. We have discussed the decrease of conductivity and the Seebeck coefficient based on the decrease of carriers and change in the scattering mechanism, respectively., The research leading to these results has received funding from the European Union's H2020 Programme under Grant Agreement no 824072 – HARVESTORE.

The call for material systems with enhanced mass transport properties is central in the development of next-generation fuel cells, batteries and solid state energy devices in general. While two-dimensional doping by artificial heterostructuring or nanoscaling has shown great potential for overcoming kinetic limitations of ion diffusion, the length scale of interface effects requires the development of advanced tools for capturing and quantifying local phenomena in greater detail. In the present paper, an in-depth study of grain boundary oxygen conduction in Sr-doped lanthanum manganite films is presented by means of novel isotope-exchange atom probe tomography. Local pathways for fast mass transport are directly mapped by two-dimensional reconstructions and line profiles of the oxygen isotope concentration. Accurate finite element modelling is employed to retrieve the local kinetic parameters, highlighting an enhancement of two orders of magnitude for both the diffusivity and surface exchange rate with respect to the bulk (D*gb=2.1×1014 cm2 s1 and k*gb=4.3×1010 cm s1, respectively, for grain boundaries at 550 °C). Co-acquired reconstruction of the cationic distribution reveals strong inhomogeneities (dopant de-mixing) across the grain boundaries and in the sub-surface region, leading to local Sr accumulation. The findings provide unequivocal quantitative assessment of fast grain boundary oxygen diffusion in lanthanum strontium manganite, giving further insights into local stoichiometry deviations and promoting isotope exchange-atom probe tomography as a powerful tool for the study of local interface effects with high resolution. Different models for the explanation of the phenomena are critically discussed on the basis of the experimental findings.

This paper describes a specific route for the complete integration of a novel planar thermoelectric microgenerator (μTEG) that can operate under environmental conditions using commercial miniaturized heat exchangers. The proposed heat exchanger integration process is compatible with the fragility of planar micromachined silicon structures. The main structure of the μTEG is built around a micromachined silicon platform defined by silicon microfabrication technologies. Different silicon-based materials, such as bottom-up grown silicon and silicon-germanium nanowire arrays as well as top-down fabricated silicon microbeams are used as thermoelectric materials. μTEGs with those materials are characterized both before and after heat exchanger integration. The presence of the heat exchanger increases the μTEG performance significantly and power densities around 40 μW cm−2 are obtained when placed on a heat source at 100 °C and exposed under natural convection to a surrounding ambient at room temperature

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena., J.S. acknowledges the support of ICN2 (funded by the CERCA programme/Generalitat de Catalunya and by the Severo Ochoa programme SEV-2017-0706) for the XRD measurements. M.A. acknowledges the support from the Feodor Lynen Research Fellowship Program of the Alexander von Humboldt Foundation and the Isaac Newton Trust, 17.25(a). M.A. and J.D. acknowledge the support from the EPSRC Centre of Advanced Materials for Integrated Energy Systems (CAM-IES) under EP/P007767/1. J.D. also acknowledge support from EPSRC grants EP/N004272/1, EP/T012218/1, the Royal Academy of Engineering- CIET1819_24, ERC POC grant 779444, Portapower. X.W. and H.W. acknowledge the funding support from the U.S. National Science Foundation for the TEM effort at Purdue University (DMR-1565822 and DMR-2016453). This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 824072 (HARVESTORE), No 681146 (ULTRASOFC) and No 101017709 (EPISTORE) and was supported by an STSM Grant from the COST Action MP1308: Towards Oxide-Based Electronics (TO-BE), supported by COST (European Cooperation in Science and Technology).

Environmental energy harvesting to power Internet of Things (IoT) systems can be achieved through thermoelectric microgenerators (μTEGs) potentially eliminating the need for batteries or extending their operational life. μTEGs are good candidates due to their scalability and their adaptability to different thermal gradients and energy densities. However, the commonly used thermoelectric materials with good thermoelectric properties (e.g. Bi 2 Te 3 ) are not compatible with down-sizing the generators to the microscale by using MEMS technology. Conversely, materials traditionally used in microelectronics (e.g. Si) have poor thermoelectric performance limiting the efficiency of thermal- to- electrical conversion due to their high thermal conductivity. The key to deal with these issues lies on silicon micromachining and nanostructuring yielding to a significant thermal conductivity reduction of the functional silicon material (nanostructuring) and the improved thermal management of the silicon-based device (micromachining). After having worked with the architectural development of the unitary μ-thermocouple, this work reports on an improved compact design of series connected silicon-based μ-thermocouples to enhance the generated power. Each thermocouple features a planar architecture with a suspended microplatform surrounded by a bulk Si rim. Bottom-up silicon nanowires are integrated as the thermoelectric active material which captures a fraction of the internally available temperature difference turning the heat flow into electricity and hence into useful power. A thin film layer of W closes the thermoelectric circuit in a uni-leg configuration. In order to multiply the output, the improved design consists of 10 μ-thermocouples arranged in series in an area of 50 mm2. For the purpose of this work, each thermocouple can be measured individually. They harvest about 3 nW when the heat source available is at 125°C. These values are low as expected for microdevices into which a heat exchanger is not integrated, the resulting bad thermal contact to the ambient avoiding an effective cooling by natural convection. In any case, the generated power is increased when connecting electrically the different μ-thermocouples in series reaching power densities of 60 nW/cm2. The fabricated all-silicon based microgenerator provides a promising energy harvester for advanced IoT systems operating in low-grade waste heat environments.

The implementation of nano-engineered composite oxides opens up the way towards the development ofa novel class of superior energy materials. Vertically aligned nanocomposites are characterized by acoherent, dense array of vertical interfaces, which allows for the extension of local effects to the wholevolume of the material. Here, we use such a unique architecture to fabricate highly electrochemicallyactive nanocomposites of lanthanum strontium manganite and doped ceria with unprecedented stabilityand straight applicability as functional layers in solid state energy devices. Direct evidence of synergisticlocal effects for enhancing the electrochemical performance, stemming from the highly ordered phasealternation, is given here for the first time using atom-probe tomography combined with oxygen isotopicexchange. Interface-induced cationic substitution, enabling lattice stabilization, is presented as the originof the observed long-term stability. These findings reveal a novel route for materials nano-engineeringbased on the coexistence between local disorder and long-range arrangement.

Unveiling point defects concentration in transition metal oxide thin films is essential to understand and eventually control their functional properties, employed in an increasing number of applications and devices. Despite this unquestionable interest, there is a lack of available experimental techniques able to estimate the defect chemistry and equilibrium constants in such oxides at intermediate-to-low temperatures. In this study, the defect chemistry of a relevant material such as La1-xSrxFeO3-d (LSF) with (x = 0.2, 0.4 and 0.5 (LSF20, LSF40 and LSF50 respectively) is obtained by using a novel in situ spectroscopic ellipsometry approach applied to thin films. Through this technique, the concentration of holes in LSF is correlated to measured optical properties and its evolution with temperature and oxygen partial pressure is determined. In this way, a systematic description of defect chemistry in LSF thin films in the temperature range from 350dC to 500dC is obtained for the first time, which represents a step forward in the understanding of LSF20, LSF40 and LSF50 for emerging low temperature applications., Front cover of the journal

Aqueous rechargeable lithium-ion batteries have attracted great attention as an alternative to traditional battery technologies, being able to overcome the issues caused by flammable and expensive organic electrolytes. In particular, LiMn2O4 has reached very fast second-level charge capability by the synthesis of unconventional morphology and particle sizes, allowing charging rates up to 600 C and 93% retention of the capacity after 10,000 cycles. However, the self-discharge process and aging mechanisms for aqueous batteries have been rarely studied, which contrasts with the extensive bibliography of the same phenomena in LMO cells based on organic electrolytes. In this article, the mechanisms involved in the loss of reversible specific charges were studied by diverse techniques like OCV, EIS, and In-situ Raman. The results revealed a more favorable self-discharge process compared with using organic electrolytes owing to the lower stability of water. The self-discharge process can be divided into three different regions with a sequential lower decay rate of voltage and capacity as well as two different evolutions of the electric parameters. This study opens new questions about the nature, composition, and mechanisms of the self-discharge in aqueous media which will play a critical role in the electrochemical performance of novel aqueous Li-ion batteries., This work has been funded by the FP7-NMP-2013-SMALL-7, SiNERGY (Contract 604169), CERCA Programme/Generalitat de Catalunya. A.S., MSCA grant agreement No. 658057 and European Research Council (ERC, grant agreement number 772579). We greatly thank these entities for their economical support as well as the support of the Severo Ochoa FUNFUTURE (CEX2019-000917-S) Exellence Centre distinction.

Tuning oxygen mass transport properties at the nanoscale offers a promising approach for developing high performing energy materials. A number of strategies for engineering interfaces with enhanced oxygen diffusivity and surface exchange has recently been proposed. However, the origin and the local magnitude of such local effects remain largely undisclosed to date. This is ascribed to the lack of direct measurement tools with sufficient resolution. In this work, we use atom probe tomography with sub-nanometric resolution to study oxygen mass transport on oxygen-isotope exchanged thin films of lanthanum chromite. We present a direct visualization of nanoscaled highly conducting oxygen incorporation pathways along grain boundaries, with reliable quantification of fast oxygen diffusion at grain boundaries and correlative link to local chemistries. Combined with finite element simulations of the precise 3D nanostructure, we quantify an enhancement in the grain boundary oxygen diffusivity and in the surface exchange coefficient of lanthanum chromite of about 4 and 3 orders of magnitude, respectively, compared to the bulk. This remarkable increase of the oxygen diffusivity in an interface-dominated material is unambiguously attributed to grain boundary conduction highways thanks to the use of a powerful technique that can be straightforwardly extended to the study of currently inaccessible multiple nanoscale mass transport phenomena.

The thermoelectric performance of nanostructured low dimensional silicon and sili-con-germanium has been functionally compared device-wise. The arrays of nanowires of both materials, grown by a VLS-CVD (Vapor-Liquid-Solid Chemical Vapor Deposition) method, have been monolithically integrated in a silicon micromachined structure in order to exploit the im-proved thermoelectric properties of nanostructured silicon-based materials. The device archi-tecture helps to translate a vertically occurring temperature gradient into a lateral temperature difference across the nanowires. Such thermocouple is completed with a thin film metal leg in a unileg configuration. The device is operative on its own and can be largely replicated (and in-terconnected) using standard IC (Integrated Circuits) and MEMS (Micro Electro Mechanical Sys-tems) technologies. Despite SiGe nanowires devices show a lower Seebeck coefficient and a higher electrical resistance, they exhibit a much better performance leading to larger open cir-cuit voltages and a larger overall power supply. This is possible due to the lower thermal con-ductance of the nanostructured SiGe ensemble that enables a much larger internal temperature difference for the same external thermal gradient. Indeed, power densities in the μW/cm2 could be obtained for such devices when resting on hot surfaces in the 50–200 °C range under natural convection even without the presence of a heat exchanger.

In the following the raw data used for the paper entitled “Operando Probing of Li-insertion on LiMn2O4 Cathodes by Spectroscopic Ellipsometry” (Morata et al.) published in J. Mater. Chem. A, 2020,8, 11538-11544 in 2020 are described. They were obtained under the funding of the European Union`s Horizon 2020 research and innovation program under the grant agreement No. 824072 and consist of the implementation of operando spectroscopic ellipsometry on Li-ion cathode material (LiMn2O4). The deposition of LiMn2O4 thin films was carried out using a Large Area PLD5000 by PVD Products, Inc. equipped with a KrF excimer laser with 248 nm wavelength. The PLD process was performed in an oxygen atmosphere at a pressure of 20mTorr. The deposition temperature was 20 mTorr. a laser fluency of 650 mJ cm−2 was used, with a pulse frequency of 10 Hz. LiMn2O4 and Li2O materials were deposited alternatively in a pulse ratio of 2:1 until the desired thicknesses was reached. XRD measurements were carried out using Bruker-D8 Advance equipment with Cu Kα radiation source and a Lynx Eye detector. The SEM images were taken in a Zeiss Auriga. The spectroscopic ellipsometry measurements were recorded by a phase modulation system (UVISEL equipped with a Horiba spectrometer) at wave- lengths ranging from 260 to 2100 nm (4.77 to 0.59 eV). The ellipsometer beam angle of the incidence was fixed at 70.0°, and the spot size was fixed at 2 mm2. A homemade electrochemical chamber has been fabricated with a Prusa i3 style 3D printer, using Acrilonitril Butadiene Styrene. &nbsp

3D printing of functional materials will revolutionize the energy sector by introducing complex shapes and novel functionalities never explored before. This will give rise to the next generation of enhanced devices ready for mass customization. Among others, electroceramic-based energy devices like solid oxide fuel and electrolysis cells are promising candidates to benefit from using 3D printing to develop innovative concepts that overcome shape limitations of currently existing manufacturing techniques. In this work, a new family of highly performing electrolyte-supported solid oxide cells were fabricated using stereolithography. Conventional planar and high-aspect ratio corrugated electrolytes were 3D-printed with yttria-stabilized zirconia to fabricate solid oxide cells. Corrugated devices presented an increase of 57% in their performance in fuel cell and co-electrolysis modes, which is straightforwardly proportional to the area enlargement compared to the planar counterparts. This enhancement by design combined to the proved durability of the printed devices (less than 35 mV/1000 h) represents a radically new approach in the field and anticipates a strong impact in future generations of solid oxide cells and, more generally, in any solid state energy conversion or storage devices.

Diffusion barrier layers are typically introduced in solid oxide fuel cells (SOFCs) to avoid reaction between state-of-the-art cathode and electrolyte materials, La1–xSrxCo1–yFeyO3-δ and yttria-stabilized zirconia (YSZ), respectively. However, commonly used layers of gadolinia-doped ceria (CGO) introduce overpotentials that significantly reduce the cell performance. This performance decrease is mainly due to the low density achievable with traditional deposition techniques, such as screen printing, at acceptable fabrication temperatures. In this work, perfectly dense and reproducible barrier layers for state-of-the-art cells (∼80 cm2) were implemented, for the first time, using large-area pulsed laser deposition (LA-PLD). In order to minimize cation interdiffusion, the low-temperature deposited barrier layers were thermally stabilized in the range between 1100 and 1400 °C. Significant enhanced performance is reported for cells stabilized at 1150 °C showing excellent power densities of 1.25 W·cm–2 at 0.7 V...

The degradation mechanism of micro-tubular Solid oxide fuel cells (mSOFC) has been studied as a function of the fuel utilization (FU from 40 to 80%) along the tube (inlet, center and outlet). La0.6Sr0.4Co0.5Fe0.5O3/Sm0.2Ce0.8O2/8YSZ/Ni-YSZ pristine cells undergone to different galvanostatic tests were carefully characterized by Raman spectroscopy as well as scanning electron microscopy and energy dispersive X-ray spectroscopy analyses. In this work, remarkable cation diffusion through the barrier layer – electrolyte interface and Ni-reoxidation have been detected as main degradation mechanisms. These phenomena, strongly enhanced by the high fuel utilization, promote Y-segregation through electrolyte and anode, enhancing the reduction of the Ni-percolation paths and, eventually, leading to the reduction of the barrier layer thickness. The most significant microstructural modifications have been identified in the outlet part of the tube where especially harsh operating conditions, in terms of temperature, fuel utilization and polarization gradients, occur. An increase of the total gas flow has shown beneficial effects on the described phenomena reducing the effects of the degradation. Increasing the carrier gas flow allows lower degradation rates for cells operating under high fuel utilization up to 80% for 1000 h.

LiMn2O4 thin films were deposited via a pulsed laser deposition (PLD). For the first time a multi-layer PLD approach was applied to compensate for the lithium loss, with superior properties such as high stoichiometric flexibility and facile handling compared to conventional approaches. We highlight the influence of the main deposition parameters; fluency and oxygen background pressure on the oxidation state of Mn within the Li-Mn-O system, as well as its stoichiometry and hence its crystallographic phase. Furthermore we show that LMO films maintain characteristic twin peak electrochemical signature even at elevated sweep rates in combination with meagre polarization. These are encouraging results proving that multi-layer PLD is a facile and convenient approach to overcome the intrinsic drawback of lithium deficiency, assuring deposition of Li containing thin films electrodes with high electrochemical activity.

Nowadays, renewable energy increases its contribution to the present energy scenario. In this regard, the implementation of energy storage and sources as the electrolysers and fuel cells gives the opportunity to transform the surplus of renewable energy to the form of hydrogen, by water electrolysis and the use of this hydrogen as a fuel for energy generation by the reverse mode of the same devices, in the so-called power to gas and gas to power routes. Among the different technologies of fuel cells and electrolysers, the high temperature technology based on ceramic solid oxides presents the best efficiencies. However, the fabrication of this devices implies several manufacturing procedures and multiple intermediate steps of fabrications, such as tape-casting, screen-printing, annealing, manual stacking, joining, sealing, etc. As a result, the SOC production process becomes more expensive and time-consuming. Recently, it has been demonstrated that the application of additive manufacturing (AM) technologies for functional ceramics fabrication, specially to SOC production, leads to significant improvement of the process. AM represents freedom of design, that allows to enhance the performance of the SOC-based device, an increase of manufacturing speed and productiveness, while the waste material is reduced. As a final result, one-step printed monolithic SOFC stack could be produced combining different AM technologies in a single printing process. For this purpose, hybrid 3D printing technology which combines stereolithography (SLA) and robocasting (direct ink writing, DIW) has been developed. Thus, the technique uses 8YSZ for the electrolyte fabrication by SLA and deposition of electrodes and interconnectors by DIW. The elaborated hybrid multimaterial 3D printing technology renders possible complete SOC stack fabrication as a single-step process. Complete fully printed SOFC cells, their co-sintering process and their characterization are here presented while the advantages and limitations of the fabrication process are discussed.

The development of alternative sources for electric power generation and energy storage to meet the growing demand and ensuring environmental sustainability for the next decades is still being a challenge for the scientific community. In this context, fuel cells are of great interest in enabling sustainable generation of electricity, being highly efficient and being a reliable, efficient and safe technology during its operation. Fuel cells are electrochemical devices that directly convert chemical energy into electrical energy and heat by continuously feeding a fuel and an oxidant, and can also use surpluses of energy to reduce water to hydrogen as a chemical storage route when working on reverse mode. These devices are made up of two electrodes (fuel electrode and oxygen electrode) separated by an electrolyte. It has been shown that the use of additive manufacturing (AM) technologies combined with ceramic fabrication techniques to optimize the microstructures and geometries of the SOC devices enhance its performance and reliability. New printable formulations for ceramic pastes have been developed for electrolytes in order to enhance the active area of reaction. Among different strategies to improve the performance, the use of composite electrodes base on porous scaffold of the ionic conductor phase to be infiltrated by the catalytic active phase is widely used. With the advance of the AM technology, 8YSZ electrolytes and scaffolds with different configurations can be also fabricated by 3D printing method. In this present work, we aim to fabricate an innovative and complex structure for YSZ electrodes with dense and porous parts and optimize the fabrication parameters for different 3D-printing process to obtain enhanced features of the ceramic supports that will be applied for SOC. Focusing on optimize the 3D processing of combined porous and dense structures for SOFC/SOECs, dense (δ>95%) monolithic gas-tight YSZ thin electrolytes supported by porous scaffolds on both sides will be fabricated for later functionalization by infiltration of the electrodes. The fabrication of the porous dense porous electrolyte will be generated by: porosity integrated by the CAD design, generation of porosity by development of new ceramic pastes and tuning of the printing parameters.

Strontium titanate (SrTiO3 ) has received much attention due to its wide range of potential applications, including in electrochemical devices such as solid oxide fuel cells and capacitors. The stability and safety features of SrTiO3 led to the development of promising electrodes for Li-ion batteries. Here, we use density functional theory simulations to examine the incorporation of lithium from its gas-phase and bulk forms. The results show that a single Li atom is thermodynamically stable in bulk SrTiO3 with respect to its gas-phase and slightly unfavorable compared to its bulk. Multiple Li incorporation up to six is also considered, and the incorporation is exoergic with respect to both gas-phase and bulk forms. Charge analysis confirmed the presence of Li+ ions in the lattice. Li incorporation turns the insulating nature of SrTiO3 into metallic and non-magnetic into magnetic. Lithium incorporation facilitates the formation of Sr, Ti, and O vacancies. The loss of Li2 O is exoergic, suggesting that oxygen vacancy mediated self-diffusion will be promoted.

A set of long-term tests (t ≥ 1000 h) have been carried out in fuel cell and electrolysis modes on typical Ni-YSZ//YSZ//LSCF-CGO cells. The degradation rates were found to be higher in electrolysis than in fuel cell operation. Post-test analyses have revealed that Sr diffusion and formation of SrZrO3 at YSZ/CGO interface occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode. As a consequence, LSCF destabilization is found to be not involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. An in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF demixing mechanism. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in LSCF material (while the fuel cell condition results in an increase in the concentration of oxygen vacancies). It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation is detailed.

Ceramic high-temperature fuel cells and electrolysers are efficient energy conversion systems for electrical power generation and hydrogen production. Their core components are constituted by a stack of electroactive Solid Oxide Cells (SOCs) in which the electrochemical reactions take place. Thanks to their flexibility, the same stack can be alternatively operated in both fuel cell and electrolysis modes. However, the insufficient durability of SOCs still constitutes a major limitation for the technology. The present study addresses this issue and aims to bring some new insights on the effect of the Solid Oxide Fuel Cell (SOFC) versus Solid Oxide Electrolysis Cell (SOEC) operating modes on degradation of a typical Ni-YSZ//YSZ//CGO//LSCF-CGO cell. The electrochemical degradations are generally attributed to several underlying phenomena such as electrode microstructural evolution, material chemical decomposition or electroactive sites poisoning by contaminants. Among them, it is generally considered that Ni agglomeration in the Ni-YSZ cermet and Lanthanum Strontium Cobalt Ferrite (LSCF) material destabilization are two prevalent mechanisms involved in the cell performance deterioration. Therefore, these two mechanisms have been specifically investigated by a coupled approach of long-term testing in both SOFC and SOEC modes (1000 ≤ t (h) ≤9000) and post-test characterizations. The experimental results have then been analyzed in the frame of an in-house multi-scale model with the purpose to interpret them and to quantify the effect of material ageing on cell performances. The extent of Ni agglomeration has been characterized by three-dimensional electrode reconstructions obtained by X-ray nano-holotomography at European Synchrotron Radiation Facility (ESRF) (on the new Nano-Imaging beamline ID16A-NI). The new set-up and protocol enable the reconstructions of valuable 3D volumes (Fig. 1) with a large field of view (~50 µm) along with a high spatial resolution (~50 nm). The electrode morphological properties, which have been measured on the 3D volumes, have revealed a substantial Ni coarsening over time at 850°C and 750°C, whereas no Ni depletion was detected at the electrolyte interface. The increase of the Ni particle size is found to induce a decrease in both (i) the density of Triple Phase Boundary (TPBs) lines and (ii) the interfacial surface area between Ni and gas. Moreover, it was found that the Ni/YSZ interfacial surface area does not evolve during the experiments. This statement indicates that the ceramic backbone in the cermet prevents a massive Ni agglomeration at the SOFC/SOEC operating temperature. The compilation of all experimental data have allowed fitting the parameters of a physically-based law for Ni coarsening that was introduced in the modelling framework. The simulations have revealed that Ni agglomeration explains around 20-25% of the electrochemical degradation at 850°C after 1000 hrs of operation. However, the electrode microstructural evolution is found not to be affected by the cell polarizations. Therefore, the mechanism cannot explain the higher degradation rates recorded in electrolysis mode compared to the fuel cell ones. To explain the impact of the operating modes (SOFC or SOEC) on the degradation rates, several post-test analyses (i.e. Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray µfluorescence and µdiffraction techniques) have been employed to investigate the phase reactivity in the region of the CGO barrier layer. The characterizations have revealed that Sr diffusion across the barrier layer and formation of SrZrO3 secondary phase occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode (Fig. 2). As a consequence, LSCF destabilization is found not to be involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. The post-test analyses have also revealed a diffusion and an accumulation of Co in the region of the barrier layer which is concomitant with the formation of SrZrO3. The formation of these Co-rich segregates in contact with SrZrO3 grains have been identified as cobalt-ferrite type compound. The in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF destabilization mechanism. The cell polarization curves and the local quantities within the O2 electrode have been computed in both fuel cell and electrolysis modes. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in the LSCF material. It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation has been detailed. Figure 1

Nanostructured metal oxides have received increasingly more attention due to their high specific surface area that may increase the active region of the material and hence enhance the performance of many electrochemical devices such as gas sensors or solid oxide fuel cells. However, it is still a major issue to keep these nanostructures stable at the high fabrication and operating temperatures of the electrochemical devices (e.g., solid oxide cells), typically over 1000 °C and 700 °C, respectively. In this work, thermally stable Ce0.8Sm0.2O1.9 mesoporous scaffolds were infiltrated with a Sm0.5Sr0.5CoO3-δ catalyst, which were then used as electrodes for solid oxide cells. The electrochemical properties of these nanocomposite electrodes in a symmetrical cell at 500–750 °C were evaluated using electrochemical impedance spectroscopy. When tested at 700 °C for a long period of time, the cells showed no performance degradation but a 50 % reduction in the area specific resistance (ASR = 0.08 Ω·cm2) after more than 200 h of operation, suggesting that the mesoporous composites are promising electrodes for high-temperature electrochemical devices.

This work evaluates the relevance of the carrier gas in the performance of micro-tubular SOFCs and describes its role in improving the fuel cell efficiency of these systems. Initial dual operation mode analyses revealed a strong influence of the carrier gas flow on the fuel cell degradation rate, showing a higher degradation rate when low fuel utilization (FU) conditions were employed under low total flow conditions. These experiments evidenced that a suitable fuel-to-carrier gas ratio must be satisfied in order to avoid mass transport limitations. A decrease of this relation, accomplished in this case by an increase in the amount of gas carrier flow (high total flow conditions), allowed to reduce the degradation rate even at high fuel utilization conditions (80%), breaking the limitations traditionally observed for this technology. This approach improves system efficiency –in terms of fuel consumption– while decreases the degradation rate.