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Digital, additive printing processes are increasingly used to produce electronic components due to their cost-saving opportunities and flexibility in design, compared to established thin-film technologies. Inkjet compatible materials like metals (e.g. silver, gold, copper), carbons and polymers are in evaluation and application for printed electronics. However, the range of printable materials for inkjet is limited, mainly due to the needed small particle size (< 1 μm) to avoid a nozzle clogging and print failure. Silicon is a very versatile material useful in most electronic applications like solar cells, semiconductor, and lithium-ion batteries. World record solar cells (> 25 %) were demonstrated with thin-film concepts (TOPCon), where a doped silicon contact is formed on the cell backside in laborious and costly vacuum production steps. The availability of a doped and inkjet printable silicon ink would allow the direct printing of such contacts, which would simplify the production effort. Boron-doped silicon powder (< 100 μm particle size), as a recycling product from PV-industry, was intensively milled in ceramic media. A hydrofluoric acid etching procedure was developed to reduce the oxygen content of the powder. Silicon inks were formulated and evaluated with variation in type of solvents and organic binders. Important ink properties like rheological behavior and inkjet compatibility were characterized (Dimatix DMP). The ink wetting behavior on monocrystalline silicon wafers (n-type 51015 cm-2) was characterized by wetting angle and surface energy measurements (Krüss DSA 100) with an optional plasma pre-treatment. Furnace and photonic sintering methods (line laser LIMO, flash-lamp Novacentrix) were compared to demonstrate the sintering of printed Si-films. The film microstructure was characterized by SEM, XRD and Photoluminescence (PL) Imaging (charge carrier lifetime). A two-step grinding procedure significantly reduced the mean particle size to 200 nm. By HF etching the oxygen content of the powder was reduced to 0.6 wt.-%, which equals to an oxide shell of only 0.4 nm. By choosing a proper solvent, the ink wetting was optimized to achieve good print quality for dots, straight lines, and full areas. The developed ink has 10 wt.-% Si-particle loading, a viscosity of 13.5 cP and a surface tension of 29 mNm. In single pass printing the film thickness after sintering was 0.8 μm. By sintering under forming gas, a visible sintering effect of the Si-particles was observed at rather high temperatures of 1150 °C. XRD analysis reveals no crystalline oxide formation, although the samples change color from dark grey to yellow greenish. An even better sintering effect was observed for photonic laser sintering within a millisecond processing time. The functionality of such printed Sifilms for solar cell applications was evaluated by PL Imaging and life-time measurements.

Oxidation of the surface of metallic chromium oxide forming metallic interconnect (MIC) can cause up to one third of the total SOFC stack degradation during the long-time operation at elevated (750 - 850 C) temperatures. The application of protective coatings is the most effective method not only for reduction of the growth of oxide scales but also for prevention of evaporation of Cr-containing species from MIC and of the poisoning of the air electrode. Two approaches to form the protective layers on the surface of CFY interconnect material with high chromium content ( 94 %) have been tested. The CuNiMn-spinel (CNM) coatings were deposited using the wet powder spraying (WPS) of the slurries. As an alternative approach physical vapour deposition (PVD) method was used to apply thin metallic films on the surface of MIC and to form the protection layer by in-situ oxidation under the stack relevant conditions. The experiments were carried out at first using the model samples of different geometries to evaluate the properies and efficiency of the coatings. Composite pastes with addition of perovskite powders were also tested, because the CNM layers densify at SOFC operating conditions and shrinkage during long-term operation can cause the decrease of the contact area between the components and accelerate the degradation of the stack performance. The experiments have shown that the perovskite additive can efficiently reduce the shrinkage compared to the pure CNM material and match it well to the shrikage of other stack components. Moreover, the perovskite additive do not deteriorate the electrical properties of the composite since the perovskites have electrical conductivity comparable to CNM. The PVD coatings were tested in combination with CNM containing contacting layers applied by screen printing to reduce the chromium release rate. The experiments have shown a good compatibility and mechanical stability between the contacting layer and PVD protective coating during operation and thermal cycling. The materials and composites have been characterized by scanning electron microscopy (SEM/EDX), optical dilatometry and electrical conductivity measurements. Finally, the most promising material combinations obtained for model samples were transferred to SOFC stacks MK35x and evaluated under real operation condition.

Continuous improvement of AVL’s natural gas operated SOFC CHP platform towards residential and small industrial applications led to first operational tests of a completely new hardware generation, targeting 5kWEL, 55% AC net electrical efficiency and 5000h of operation. Within the scope of the publicly funded project “SOFC5-60” (FFG: 864851 / PtJ: 03ET6120A), conducted in cooperation with FraunhoferIKTS, High Tech Coatings, BIOSBioenergiesystemeGmbH, Viessmann, AVL Schrick and ForschungBurgenland from 2017to2021, the aim is to fully integrate and operate the system in an office building for the provision of electricity and hot water. Further target applications are hotels and apartment buildings. Therefore, electricity and heat demand profiles of such applications were analyzed to identify the optimal building sizes for a 5kW system as well as the requirements for the operating procedure. AVLs existing system architecture based on hot anode gas recirculation, steam reforming and a modular interface between the gas processing unit and the stack module has been expanded with functionalities like a heat recovery for hot water production, an exhaust gas condensate recovery unit, and power electronics for grid feed-in. Besides that, an optimized integration of the BoP components such as the hot anode gas recirculation blower, development of periphery components for stand-alone applications, activities towards design to manufacture as well as load following operation capabilities and long term operational durability are in the center of development activities. This work gives an insight into the development achievements that are the next step towards industrialized SOFC CHP systems as well as operational data for full- and part load operating points, as well as transient- and load following operation.

All solid-state batteries offer the possibility of increased safety at potentially higher energy densities compared to conventional lithium-ion batteries. In an all-ceramic oxide battery, the composite cathode consists of at least one ion-conducting solid electrolyte and an active material, which are typically densified by sintering. In this study, the reaction of the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) and the active material LiNi0.6Co0.2Mn0.2O2 (NCM622) is investigated by cosintering at temperatures between 550 and 650 °C. The characterization of the composites and the reaction layer is performed by optical dilatometry, X-ray diffractometry, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, as well as scanning transmission electron microscopy (STEM). Even at low sintering temperatures, elemental diffusion occurs between the two phases, which leads to the formation of secondary phases and decomposition reactions of the active material and the solid electrolyte. As a result, the densification of the composite is prevented and ion-conducting paths between individual particles cannot be formed. Based on the experimental results, a mechanism of the reactions in cosintered LATP and NCM622 oxide composite cathodes is suggested.

International audience; Operating solid oxide fuel cells (SOFC) in a specific industry-relevant environment can result in undesired performance alterations and subsequent morphological changes. Conventional characterization tools, such as polarization curve or electrochemical impedance spectroscopy, can be employed to gain a rough overview of the cell performance. Nevertheless, if these conventional tools fail and seemingly invisible degradation mechanisms occur inside the cell and system, such degradation cannot be identified. Eventually, these mechanisms can cause the system to collapse abruptly and irreversibly. In this study, novel online-monitoring tools based on total harmonic distortion analysis (THD) were employed to identify the most relevant degradation mechanism when using carbon-containing fuels, i.e. carbon deposition. The examination was performed on SOFCs of industrial size, methane was used as a fuel, and the cells were operated under a constant current load. The operating conditions were designed as required for application in auxiliary power units (APUs). The results reveal that the preliminary stage of degradation can be most quickly identified using the frequencies: 1 Hz, 10 Hz, 100 Hz, 2 kHz, 2.5 kHz, 4 kHz and 8 kHz. If the lower frequencies are removed and only the frequencies equal to or higher than 2 kHz are applied, almost the same information is obtained, and the measuring time can be significantly reduced. In addition, this study enabled us to identify a highly efficient strategy that can be used to remove carbon and to regain the initial cell performance. Carbon removal during the regeneration process was also successfully detected by applying the THD methodology.

Oxidation of the surface of metallic chromium oxide forming metallic interconnect (MIC) can cause up to one third of the total SOFC stack degradation during the long-time operation at elevated (750 - 850 °C) temperatures. The application of protective coatings is the most effective method not only for reduction of the growth of oxide scales but also for prevention of evaporation of Cr-containing species from MIC and of the poisoning of the air electrode. Two approaches to form the protective layers on the surface of CFY interconnect material with high chromium content (~ 94 %) have been tested. The CuNiMn-spinel (CNM) coatings were deposited using the wet powder spraying (WPS) of the slurries. As an alternative approach physical vapour deposition (PVD) method was used to apply thin metallic films on the surface of MIC and to form the protection layer by in-situ oxidation under the stack relevant conditions. The experiments were carried out at first using the model samples of different geometries to evaluate the properies and efficiency of the coatings. Composite pastes with addition of perovskite powders were also tested, because the CNM layers densify at SOFC operating conditions and shrinkage during long-term operation can cause the decrease of the contact area between the components and accelerate the degradation of the stack performance. The experiments have shown that the perovskite additive can efficiently reduce the shrinkage compared to the pure CNM material and match it well to the shrikage of other stack components. Moreover, the perovskite additive do not deteriorate the electrical properties of the composite since the perovskites have electrical conductivity comparable to CNM. The PVD coatings were tested in combination with CNM containing contacting layers applied by screen printing to reduce the chromium release rate. The experiments have shown a good compatibility and mechanical stability between the contacting layer and PVD protective coating during operation and thermal cycling. The materials and composites have been characterized by scanning electron microscopy (SEM/EDX), optical dilatometry and electrical conductivity measurements. Finally, the most promising material combinations obtained for model samples were transferred to SOFC stacks MK35x and evaluated under real operation condition., Federal Ministry for Economic Affairs and Energy (BMWi) for funding of these researches (support code 03ET6120A).

The glass crystallization route for Na‐ion conducting glass ceramics with conductive N5 modification of Na5YSi4O12 has been explored. P2O5 is used to modify the glass frit for optimization of the sintering and crystallization process. Mass spectroscopy reveals that the evaporation of CO2 in the sintered microstructure is responsible for enhanced porosity. The glass is not fully transformed to the highly conductive phase (N5) by crystallization and thereby lower conductivities in sintered samples is observed. A pre‐crystallization step of the initial glass powder is evaluated as suitable to eliminate the gas evolution and subsequent sintering of material crystallized in desired N5 modification is successfully performed. With the powder of the pre‐crystallized material, homogenous sintered microstructures consisting of crystalline and glassy phases are obtained. Despite the higher temperature needed for sintering, low porosity and a mechanical strength up to 60 N mm−2 are achieved for samples from pre‐crystallized powder. The analysis of impedance spectra of sintered samples reveal high impact of grain boundaries on total ionic conductivity. Samples made from pre‐crystallized powder show higher overall ionic conductivity of 8.3 × 10−6 S cm−1 at room temperature which is lower than the conductivity of crystallized N5 phase grains (1.4 × 10−4 S cm−1).