Izaak Vinke

In solid oxide electrolysis cells (SOECs) carbon dioxide (CO2) is converted to carbon monoxide (CO). In the chemical industry CO is an important reactant to produce base chemicals such as acetic or formic acid or fine chemicals produced by carbonylation processes. CO is also used in the reduction of oxides to metals. Conventional processes for CO production are based on fossil resources such as coal or natural gas. CO2 electrolysis presents a sustainable method to utilize renewable energy for CO production and additionally transforms the greenhouse gas CO2 into a resource. Carbon dioxide is already used and investigated in the co-electrolysis process where it is converted alongside steam to produce syngas, a mixture of hydrogen and carbon monoxide. However, the analysis of pure CO2 electrolysis for CO production hasn’t been investigated in detail. Some studies report alternative materials or first degradation results. In this contribution the CO2 electrolysis is discussed in-depth from an electrochemical point of view. A detailed analysis by current-voltage characteristics (IV curves) and electrochemical impedance spectroscopy (EIS) was performed on commercially available cells by Elcogen consisting of a Nickel/ 8 mol % Yttrium-Stabilized Zirconia (8YSZ) cermet fuel electrode, a 8YSZ electrolyte, a Cerium Gadolinium Oxide barrier layer and a Lanthanum Strontium Cobaltite air electrode. IV curves and EIS spectra were measured at varied CO2/CO ratios, temperatures, flow rates and current densities. The results show that with increasing CO2/CO ratio the total area specific resistance (ASR) increases at open circuit voltage and decreases under load (Figure 1). A similar decrease of resistance is seen for increasing flow rates. The main resistance contribution determined from impedance analysis comes from diffusion/concentration losses[1]. The analysis by impedance spectroscopy provides information on the underlying processes and is not only of relevance for understanding pure CO2 electrolysis but also for understanding the role of CO2 reduction during co-electrolysis. Figure caption: Figure 1: ASR, |i|1.4 V and OCV for varied CO2/CO ratios at 800 °C[1]. 1Two values are given due to a hysteresis. The first value represents the forward scan and the second value represents the backward scan of the IV curve. Literature [1] S. Foit, L. Dittrich, T. Duyster, I. Vinke, R.-A. Eichel, Haart, L. G. J. de, Processes 2020, 8, 1390. Figure 1

High-temperature co-electrolysis of CO2 and H2O at elevated temperatures between 700 °C and 900 °C valorises CO2 to produce a mixture of carbon monoxide (CO) and hydrogen (H2), called syngas. Co-electrolysis has the great advantage over conventional processes, that the desired syngas ratios of downstream processes can be realized by varying process parameters such as temperature and feed gas composition accordingly in a one step process. Co-electrolysis can also play a vital role in counteracting power fluctuations of renewable energy sources by storing temporarily unused electricity through conversion to other energy resources like chemicals or heat for later use. The underlying processes in co-electrolysis for CO production are direct electrochemical CO2 reduction and reverse water gas shift equilibrium (RWGS). Their specific significance has not been clarified in detail yet and was controversially discussed in literature up to this day [1,2]. The impact of the equilibrium partial pressure of H2O on the physical processes in the transition boundary of co-electrolysis towards direct CO2-electrolysis was investigated by AC and DC measurements for various gas compositions. The analysis led to identifying the role of the underlying electrochemical processes during co-electrolysis, in particular the electrochemical CO2 reduction compared to the conversion of CO2 in the reverse water-gas shift reaction and the electrochemical H2O reduction. The area specific resistance (ASR) was, amongst others, taken as an indicator to determine, which of the reduction reactions (H2O or CO2 reduction) is dominant depending on the gas composition. The experiments were conducted using commercially available cathode-supported full cells (Elcogen) made of Ni-8YSZ/8YSZ/CGO/LSC. Results as seen in Figure 1 show that the ASR for an equilibrium concentration of 5 % H2O is considerably larger than for higher H2O contents. Above 15 % H2O, the ASR shows no dependency on the gas composition and is comparable to pure H2O-electrolysis [3]. These observations underline the hypothesis that CO2-electrolysis becomes pre-dominant compared to H2O-electrolysis for low H2O content during co-electrolysis. With increasing H2O content, CO2-electrolysis becomes less significant and carbon dioxide is converted in the reverse water gas shift equilibrium. The origin of the discrepancy in literature was found to be the different operating H2O concentrations. A threshold has been established for the perception of CO2-electrolysis during co-electrolysis experiments. figure caption: Arrhenius plot of ASROCV for different steam concentrations at 6 l·h-1. [1] C. Stoots, J. O'Brien, J. Hartvigsen, Int. J. Hydrogen Energy 2009, 34, 4208. [2] S. D. Ebbesen, R. Knibbe, M. Mogensen, J. Electrochem. Soc. 2012, 159, F482-F489. [3] L. Dittrich, M. Nohl, E. E. Jaekel, S. Foit, L.G.J. (Bert) de Haart, R.-A. Eichel J. Electrochem. Soc. 2019, 166, F971-F975. Figure 1

Physico-chemical processes in batteries are taking place on a broad time scale from fractions of seconds to the order of days [1]. Thus, for an accurate characterization of transport and mobility processes in batteries using electrochemical impedance spectroscopy (EIS), a large frequency range of up to ten decades must be covered. This implies measurement durations on the order of days for low frequency measurements, yielding the risk of distorting electrochemical instabilities in the battery and a considerable change of its state of charge (SOC) due to the probing ac current excitation. It is shown that the SOC change is frequency dependent and with 10-15% of the nominal battery capacity for the sub-millihertz range hardly a small perturbation. Nevertheless, these obstacles can be mitigated by the time domain measurement (TDM) technique [2-4]. TDM is limited to impedance measurements at low frequencies, with a small and frequency-independent SOC change. The combination of TDM and EIS, called time-domain supported electrochemical impedance spectroscopy (TD-EIS), opens up the possibility for a time-efficient implementation of impedance spectroscopy over a large frequency range down to microhertz frequencies [5]. In this work, TD-EIS at varying temperatures in combination with data fitting using an electrical equivalent circuit battery model, is used for the high-accuracy quantification of low-frequency mobility parameters in lithium-ion batteries. It is experimentally demonstrated, for the first time, that the phase of the impedance measurements converges in the sub-millihertz range, which permits a reliable quantification of diffusion kinetics. Moreover, it is shown that with TD-EIS time savings of up to 80% compared to the standard EIS measurement are feasible. From the electrical equivalent circuit battery model fit, an accurate estimate of charge transfer resistance and, in particular, also solid-state diffusion rate are obtained. Both processes follow an Arrhenius law, allowing the determination of activation energies with small variance. The results for the charge transfer process and for the solid-state diffusion process are within the range of literature values measured for similar systems. This work has been published in JECS [6]. References [1] A. Jossen, “Fundamentals of battery dynamics”, Journal of Power Sources 154 (2) (2006) 530-538 [2] S. C. Creason, J. W. Hayes, D. E. Smith, “Fourier transform faradaic admittance measurements - III. Comparison of measurement efficiency for various test signal waveforms”, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 47 (1) (1973) 9-46 [3] J.-S. Yoo, S.-M. Park, “An electrochemical impedance measurement technique employing Fourier transform”, Analytical Chemistry 72 (9) (2000) 2035-2041 [4] D. Klotz, M. Schönleber, J. Schmidt, E. Ivers-Tiffée, “New approach for the calculation of impedance spectra out of time domain data”, Electrochimica Acta 56 (24) (2011) 8763-8769 [5] J. Illig, J. Schmidt, M. Weiss, A. Weber, E. Ivers-Tiffée, “Understanding the impedance spectrum of 18650 LiFePO4-cells”, Journal of Power Sources 239 (2013) 670-679 [6] A. Mertens, I.C. Vinke, H. Tempel, H. Kungl, L.G.J. de Haart, R.-A. Eichel, J. Granwehr, "Quantitative Analysis of Time-Domain Supported Electrochemical Impedance Spectroscopy Data of Li-Ion Batteries: Reliable Activation Energy Determination at Low Frequencies", Journal of the Electrochemical Society 163 (7) (2016) H521-H527 Figure caption: Arrhenius plot of the solid-state diffusion rate obtained from battery model fits of impedance data from three batteries measured at different temperatures. The activation energies are determined from the gradients. Figure 1

In future there will be a strong demand for large capacity rechargeable batteries to store electrical energy (e.g. from renewable power sources) in long-term stationary applications  [1]. A high temperature metal / metal oxide battery can be built up by combining solid oxide fuel cell (SOFC) technology and a metal/metal oxide storage system [2]. Such a type of battery promises charging and discharging capacities of more than 250 W/cm2 [3]. Requirements for a reversible working solid oxide cell (SOC) are a high performance, minimum internal resistance of the cell, and long-term stability at operating conditions. In the present work the performance of solid oxide cells (SOC) operating in fuel cell and steam electrolysis mode over a temperature range of 650-900 °C and as a function of humidity were studied. Results presented were obtained from single SOCs, with an active area of 16 cm2 and button cells with an active area of 0.5 cm2. The SOCs investigated were anode substrate cells (ASC), with nickel-YSZ-cermet steam/hydrogen electrodes, yttria-stabilized zirconia (YSZ) electrolytes, and lanthanum strontium iron cobalt perovskite (LSCF) air electrodes. Current-voltage measurements were coupled with electrochemical impedance spectroscopy (EIS), in order to identify the different loss terms in cell behaviour during the fuel cell and electrolysis mode. EIS measurements are conducted under practical load conditions in SOCs in both modes. The cells show stable current-voltage curves during cycling between fuel cell and electrolysis mode at short cycling times between 2.5 h and 5 h. Measurements at different humidity show that high electrical-to-hydrogen energy conversion efficiencies are achieved and the amount of steam content is the limiting factor for the electrolysis mode. During electrolysis mode remarkable high current densities around -1.3 A/cm2 were achieved at a cell voltage of 1.3 V and a temperature of 800 °C. Below 50 % steam content, however, a strong efficiency loss was observed. It is also well known that the degradation of the SOC during steam electrolysis is still a limiting factor for the long term application [4]. Hence the focus of interest was also the degradation of the air electrode. Increasing the current density and elongating the duration of electrolysis experiments resulted frequently in a very fast delamination of the LSCF electrode.

Co-electrolysis as value chain process can contribute to various sectors like the chemical industry [1] or the energy sector [2] due to its high flexibility [3]. With its product syngas (a mixture of hydrogen (H2) and carbon monoxide (CO)), co-electrolysis acts as an upstream process to meet changing demands within the respective downstream supply chains [3]. Additionally, when 100% of renewable energy sources are used, green syngas can be produced thus coupling and connecting renewables into the existing value chains [4,5]. In order to fulfill industrial needs, the process of co-electrolysis has to be examined in detail. This work presents a 3D model of a simplified Solid Oxide Electrolysis Cell (SOEC) operating at high temperatures in the co-electrolysis mode. In this model, we evaluate the boundaries of co-electrolysis, the steam and CO2 electrolysis, as well as a detailed description of the co-electrolysis process with the help of a proposed reaction scheme. The model is fully coupled including electrochemical, chemical, heat and transport phenomena occurring at single cell level. We consider the heat of the reaction(s), accompanying reactions including possible surface reactions in co-electrolysis operation mode, Maxwell-Stefan interaction and electrochemical charge transfer reactions of the Butler-Volmer type. With calculating experimental characteristics like i-V curves (see Figure) or electrochemical impedance spectroscopy (EIS) curves, the influence of every parameter considered in each reaction step can be evaluated according to its value range. The model is in first instance validated with the pure electrolysis types. With the model, we can visualize the particle distribution within the porous cell, see the development of overpotential (see Figure) and obtain experimental characteristics which allow us to identify the contributions of each mechanism to them. This is an important step towards fundamental understanding of the co-electrolysis process on a small scale which can then be transferred to the large scale applications on stack level. Effects of degradation are envisioned to be incorporated into the model as well. Figure caption: Figure 1: Plot of the overpotential distribution at 0.6 A∙cm-2 within the porous cell electrodes with appropriate dimensions (left) and corresponding polarization curve with a current sweep from 0 to 3 A∙cm-2 in steps of 0.2 A∙cm-2 (right) both for steam electrolysis at 800°C. References [1] Foit, S.R.; Vinke, I.C.; Haart, L.G.J. de; Eichel, R.-A. (2017): Power-to-Syngas: An Enabling Technology for the Transition of the Energy System? In: Angewandte Chemie (International ed. in English) 56 (20), pp. 5402–5411 [2] Baerns, A.B.M.; Brehm, A.; Gmehling, J.; Hinrichsen, K.-O.; Hofmann, H.; Onken, U.; Palkovits, R.; Renken, A. (2014): In: Technische Chemie, Vol. 2, Wiley-VCH, Weinheim, p. 573 [3] Dittrich, L.; Nohl, M.; Jaekel, E.E.; Foit, S.; Haart, L.G.J. de; Eichel, R.-A. (2019): High-Temperature Co-Electrolysis: A Versatile Method to Sustainably Produce Tailored Syngas Compositions. In: J. Electrochem. Soc. 166 (13), F971–F975 [4] Jensen, S.H.; Sun, X.; Ebbesen, S.D.; Knibbe, R.; Mogensen, M. (2010): Hydrogen and synthetic fuel production using pressurized solid oxide electrolysis cells. In: International Journal of Hydrogen Energy, vol. 35, no. 18, pp. 9544–9549 [5] Li, W.; Wang, H.; Shi, Y.; Cai, N. (2013): Performance and methane production characteristics of H2O–CO2 co-electrolysis in solid oxide electrolysis cells. In: International Journal of Hydrogen Energy, vol. 38, no. 25, pp. 11104–11109 Figure 1

The degradation of anode supported cells with LSM cathodes exposed to various chromium sources was analyzed and post-test analyses were conducted to observe the cathode microstructure and to determine the chromium content. Three different degradation phases could be identified each corresponding to a different process. The analyses showed that severe chromium poisoning can be alleviated but not generally avoided.

The state-of-the-art fuel electrode materials for solid oxide electrolysis cells (SOECs) are Ni-cermets due to their high electro-catalytic activity, high electrical conductivity and the low price. However, one major concern that must be solved for a widespread commercialisation is their poor degradation behaviour during electrolysis operation caused by for example Ni migration, depletion and agglomeration in the fuel electrode. One strategy to improve the durability of SOECs is the usage of alternative fuel electrode materials. For instance, completely Ni-free fuel electrodes may solve the problems of morphological degradation during operation and further could enhance redox cycling stability. Within possible candidates, gadolinium doped ceria (GDC) is an interesting material due to good stability towards carbon deposition and the possibility to host electro catalysis in electrolysis reactions [1, 2]. Furthermore, GDC (Ce0.8Gd0.2O2-δ) shows electronic conducting (700 °C, 0.028 S·cm...

This present study aims to investigate and compare the long-term stability of Ni-GDC and Ni-YSZ under three different electrolysis modes; steam electrolysis, co-electrolysis and CO2 electrolysis. Firstly, electrolyte-supported single cells of Ni-GDC (NiO-GDC//8YSZ//GDC//LSCF) and Ni-YSZ (NiO-GDC//8YSZ//GDC//LSCF) were fabricated and investigated using electrochemical impedance spectroscopy (EIS). Furthermore, the impedance data were also recorded under polarization (0.7 to 1.4V) as well as at OCV. Finally, stability tests of the single cells were carried out under steam (H2O:H2, 50:50), co- (H2O:CO2:CO, 40:40:20) and CO2 electrolysis (CO2:CO, 80:20) conditions at 900 °C with -0.5 A/cm2 current density. The results reveal that Ni-GDC exhibits higher current density and lower polarization resistance (Rp) than Ni-YSZ in all the electrolysis modes. Furthermore, the Ni-GDC cells show a lower degradation rate than Ni-YSZ. However, Ni migration and agglomeration were observed in both elect...

Lanthanide Nickelate Ln2NiO4+δ (Ln = La, Pr or Nd) has drawn significant attention as an oxygen electrode for solid oxide cells (SOCs) due to its mixed ionic and electronic conductivity (MIEC) property. They exhibit very good electro-catalytic activity as well as high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values [1]. Earlier reported results [2, 3] show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) lead to an enhancement in the transport and electrochemical properties of the material. The present study aims to investigate the effect of Sr2+ substitution at A-site in LNCO i.e. La2-xSrxNi0.8Co0.2O4+δ (LSNCO) in order to further investigate the structural, physico-chemical and electrochemical properties of the materials. Three different compositions i.e. LSNCO5, LSNCO10 and LSNCO20 were studied with x = 0.05, 0.10 and 0.20 respectively. First the materials were characterized by XRD, TGA and SEM. Then, the electrochemical cha...

The K2NiF4-type nickelates i.e. Ln2NiO4+δ (Ln = La, Pr, Nd) and La1.5Pr0.5NiO4+δ have shown promising behaviour as oxygen electrodes for solid oxide cells [1]. These compounds show high anionic bulk diffusion (D*) as well as surface exchange coefficients (k*), combined with good electrical conductivity and thermal expansion properties matching with those of other components (electrolyte, interconnect etc.) of the cell. In order to further enhance the physico-chemical properties, electrochemical performance of these nickelates as oxygen electrode, we performed the substitution of nickel by other transition element such as cobalt. Two compositions of Ln2Ni1-xCoxO4+ δ (Ln = La, Pr, Nd) and La1.5Pr0.5Ni1-xCoxO4+ δ (x=0.1 and 0.2) were considered (as higher cobalt containing nickelates are difficult to synthesize under air atmosphere) and completely characterized using several methods. Finally, the symmetrical half-cells (8YSZ/GDC/electrode) as well as single cells (Ni-YSZ/8YSZ/GDC/elect...

The Distribution of Relaxation Times (DRT) is an important analytical tool that is capable of giving initial information from Electrochemical Impedance Spectra (EIS) with respect to the number of relaxation processes occurring in the system and their corresponding relaxation frequencies. The DRT transformation with the Tikhonov regularization is used for analysis of EIS data obtained from the characterization Solid Oxide Fuel and Electrolysis Cells (SOFC/SOEC) operating at high temperatures. The effects of this transformation together with occurring pitfalls on the most commonly implemented circuit elements used to describe EIS data was investigated to gain a better understanding. The behavior of the DRT transformation as a function of the individual circuit elements is reported, the regularization parameter λ is taken as a sweep parameter to investigate its influence and optimal ranges for the selection of λ are presented.

Solid oxide fuel cell (SOFC) development work at Forschungszentrum Juelich (FZJ) is extensive, ranging from fundamental materials' design through to near‐commercial prototype CHP systems. Considerable advances have been demonstrated in the past years concerning the improvement of device performance by identifying performance degradation mechanisms and reducing or eliminating those problems, and in designing, developing and manufacturing core SOFC components. At the time of this writing, the first, fully integrated SOFC combined heat and power generation prototype system is awaiting completion. FZJ is involved in significant national and international programs and coordinates major international projects.

Ni-YSZ is known as the state-of-the-art fuel electrode material for solid oxide cells. However, this conventional fuel electrode experiences severe degradation due to Ni- agglomeration and migration away from the electrolyte. Therefore, to avoid such issues, we have considered Ni free electrodes i.e. La0.6Sr0.4MnO3 (LSM) based perovskite oxides as fuel electrode. Under reducing atmosphere, the LSM perovskite phase transforms into a Ruddlesden-Popper (La0.6Sr0.4)2MnO4±δ phase. In addition to pure LSM fuel electrode, we have also investigated the performance of LSM+YSZ (50:50 wt %) and LSM+GDC (50:50 wt %) composite electrodes. The electrolyte-supported single cells were prepared using 8YSZ electrolyte supports, and in all cases, LSM+YSZ/LSM oxygen electrodes were used. The current-voltage characteristics show good performance for LSM and LSM+GDC fuel electrode containing single cells. However, a lower performance is observed for LSM+YSZ fuel electrode containing single cell. For inst...

High-temperature electrolysis using solid oxide electrolysis cells (SOECs) is an innovative technology to temporarily store unused electrical energy from renewable energy sources. However, they show continuous performance loss during long-term operation, which is the main issue preventing their widespread use. In this work, we have performed the long-term stability tests up to 1000 h under steam and co-electrolysis conditions using commercial NiO-YSZ/YSZ/GDC/LSC single cells in order to understand the degradation process. The electrolysis tests were carried out at different temperatures and fuel gas compositions. Intermittent AC- and DC- measurements were performed to characterize the single cells and to determine the responsible electrode processes for the degradation during long-term operation. An increased degradation rate is observed at 800 °C compared to 750 °C under steam electrolysis conditions. Moreover, a lower degradation rate is noticed under co-electrolysis operation in ...

ABSTRACT In order to gain insight into the mechanism causing performance degradation and/or failure, stacks of planar solid oxide fuel cells (SOFC) are routinely dismantled and examined after operation at Forschungszentrum Jülich. The post-operation inspection focuses in particular on the chemical and mechanical compatibility aspects of cell and stack materials.In the present work a short-term degradation effect is addressed, which was found to be caused by unwanted chemical interactions between glass–ceramic sealants and ferritic steel interconnects. The post-operation inspection revealed severe steel corrosion along the seal rims. Under SOFC stack conditions rapidly growing oxide nodules were observed bridging the 200 μm seal gap between the metallic components after a few hundred hours of operation. These oxide nodules, rich in iron, gave rise to local short-circuiting effects eventually resulting in stack failure.The present study, combined with recent model investigations triggered by the stack results, indicates that severe degradation only occurs in the case of glass–ceramic sealants which contain minor amounts of PbO. Furthermore, the rate of corrosion attack of the metallic components strongly depends on the silicon (Si) content of the ferritic steel. The stack tests suggest that increasing the Si content increases the corrosion rate, and thus detrimentally influences the stack performance.

Ni-gadolinia-doped ceria (GDC) based electrode materials have drawn significant attention as an alternative fuel electrode for solid oxide cells (SOCs) owing to mixed ionic conductivity of GDC and high electronic and catalytic activity of Ni. Moreover, the catalytic activity and electrochemical performance of the Ni-GDC electrode can be further improved by dispersing small quantities of other metal additives, such as gold or molybdenum. Therefore, herein, we considered gold and molybdenum modified Ni-GDC electrodes and focused on the upscaling; hence, we prepared 5 × 5 cm2 electrolyte-supported single cells. Their electrochemical performance was investigated at different temperatures and fuel gas compositions. The long-term steam electrolysis test, up to 1700 h, was performed at 900 °C with −0.3 A·cm−2 current load. Lastly, post-test analyses of measured cells were carried out to investigate their degradation mechanisms. Sr-segregation and cobalt oxide formation towards the oxygen e...

Lanthanide nickelate Ln2NiO4+δ (Ln = La, Pr, or Nd) based mixed ionic and electronic conducting (MIEC) materials have drawn significant attention as an alternative oxygen electrode for solid oxide cells (SOCs). These nickelates show very high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values and hence exhibit good electrocatalytic activity. Earlier reported results show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) leads to an enhancement in the transport and electrochemical properties of the material. Herein, we perform the substitution at A-site with Sr, i.e., La2−xSrxNi0.8Co0.2O4+δ, in order to further investigate the structural, physicochemical, and electrochemical properties. The structural characterization of the synthesized powders reveals a decrease in the lattice parameters as well as lattice volume with increasing Sr content. Furthermore, a decrease in the oxygen over stoichiometry is also observed with Sr substituti...

High-temperature co-electrolysis of CO2 and H2O at elevated temperatures between 700 °C and 900 °C valorises CO2 to produce a mixture of carbon monoxide (CO) and hydrogen (H2), called syngas. Co-electrolysis has the great advantage over conventional processes, that the desired syngas ratios of downstream processes can be realized by varying process parameters such as temperature and feed gas composition accordingly in a one step process. Co-electrolysis can also play a vital role in counteracting power fluctuations of renewable energy sources by storing temporarily unused electricity through conversion to other energy resources like chemicals or heat for later use. The underlying processes in co-electrolysis for CO production are direct electrochemical CO2 reduction and reverse water gas shift equilibrium (RWGS). Their specific significance has not been clarified in detail yet and was controversially discussed in literature up to this day [1,2]. The impact of the equilibrium partial...

Understanding degradation mechanisms in SOCs remains an ongoing issue for its mitigation and to reach levels that will bring the technology closer to commercialization. Benefiting from our experience in performing long-term tests on stacks (up to 100,000 h) post-test examination of the components of several of these stacks gave a better understanding about various degradation effects. Among others the chromium poisoning of La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) and La0.6Sr0.4CoO3-δ (LSC) air electrodes used over the past decade in the cells will be presented. In parallel alternative air electrode materials for low-temperature application based on La2Ni1-xCoxO4+δ (LNCO) are being developed and the influence of A- and B-site substitution on the structural, physico-chemical and electrochemical properties of the materials is investigated. First promising results of a short-stack with Ni/YSZ substrate cells with La2Ni0.8Co0.2O4+δ air electrodes will be presented. Based on the earlier experienc...

Chemical industries rely heavily on fossil resources for the production of carbon-based chemicals. A possible transformation towards sustainability is the usage of carbon dioxide as a source of carbon. Carbon dioxide is activated for follow-up reactions by its conversion to carbon monoxide. This can be accomplished by electrochemical reduction in solid oxide cells. In this work, we investigate the process performance of the direct high-temperature CO2 electrolysis by current-voltage characteristics (iV) and Electrochemical Impedance Spectroscopy (EIS) experiments. Variations of the operation parameters temperature, load, fuel utilization, feed gas ratio and flow rate show the versatility of the procedure with maintaining high current densities of 0.75 up to 1.5 A·cm−2, therefore resulting in high conversion rates. The potential of the high-temperature carbon dioxide electrolysis as a suitable enabler for the activation of CO2 as a chemical feedstock is therefore appointed and shown.

Several combinations of glass-ceramic and steel compositions with excellent chemical and physical properties have been tested in the past in solid oxide fuel cell (SOFC) stacks, but there have also been some combinations exhibiting pronounced chemical interactions causing severe stack degradation. Parallel to the examination of these degradation and short-circuiting phenomena in stack tests, recently less complex model experiments have been developed to study the interaction of glass-ceramic sealants and interconnect steels. The sealants and steels were tested in the model experiments at operation temperature using a dual air/hydrogen atmosphere similar to stack conditions. The present work compares electrochemical performance under constant current load of SOFC stack tests with the resistance changes in model experiments. In addition, microstructural results of post-operation inspection of various sealant–steel combinations are presented. The model experiments have shown that under...