Sunfire (Germany)

It is widely accepted that sulfur-induced resistance increase is mitigated by the anodic current density in the fuel cell mode. On the other hand, the role of cathodic current in the electrolyzer mode is yet only poorly explored. This study therefore aims to identify the role of cathodic current on the poisoning behavior in solid oxide electrolyzers. We have performed an electrochemical impedance spectroscopy-based study on a commercial Ni/GDC electrode in a H 2 S concentration range from 0.1 ppm to 1 ppm and current densities from 0 Acm −2 up to −1 Acm −2 in steam-electrolysis and up to −0.8 Acm −2 in CO 2 -electrolysis. Results at OCV show a critical influence of H 2 and CO concentration on the poisoning response. Under cathodic polarization, the impact of sulfur on the resistance is lower when load is applied, compared to the OCV case, and this effect is more pronounced during CO 2 -electrolysis than in H 2 O-electrolysis. In poisoned H 2 O-electrolysis, the electrode overpotentials match expectations from the inherent Tafel behavior of the electrode. In contrast, overpotentials during poisoned CO 2 -electrolysis appear to be lower than one would expect from the inherent Tafel behavior of the electrode, demonstrating a mitigation effect of cathodic current on the H 2 S poisoning in CO 2 -electrolysis. • H 2 S poisoning of Ni/GDC electrodes under steam and CO 2 electrolysis conditions. • Interrelations between poisoning response, concentration and current resolved. • Tafel behavior explains mitigation of resistance increase in H 2 O electrolysis. • In CO 2 electrolysis, cathodic current was found to mitigate H 2 S poisoning.

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria layers deposited via EB-PVD method at 600 oC were assembled and electrochemically investigated in a so-called “rainbow” stack with 30 repeat units (RUs). At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65 % at 75 % steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +10.9 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films demonstrated similar initial performance and degradation rate to the state-of-the-art cells. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers.

The solid oxide cell technology allows to produce synthesis gas (CO+H2), a precursor for e-fuels and other chemicals. This work reports on the long-term performance of an electrolyte supported cell (Ni-CGO/3YSZ/LSCF-CGO), operated at industrially relevant co-electrolysis conditions (32.5 % H2, 35 % H2O, 8.1 % CO, 24.4 % CO2, -0.5 A/cm2, 815 °C). The cell had a Ni-CGO fuel electrode (~30 μm thick), a 3YSZ electrolyte (~90 μm) and an LSCF-CGO oxygen electrode (~35 μm thick) plus a thin CGO barrier layer in-between. The cell was operated for 2300 h at constant galvanostatic conditions, with an overall degradation of 80 mΩcm2/kh. At the start of the test, the ohmic resistance contributes to almost 90 % of the ASR (area-specific resistance), but the increase in Rp (polarization resistance) is what contributes the most to the increase in total cell ASR during the long-term operation. This increase in ASR is not constant over the entire test time. On the contrary, it is considerably higher during the first 300 hours (180 mΩcm2/kh) and then it levels off and stabilizes to 32 mΩcm2/kh during the remaining approx. 2 kh of the long-term operation. The measured electrochemical impedance spectra showed a decrease in the performance of the Ni-CGO fuel electrode. A possible explanation for the observed fuel electrode degradation was found via SEM-EDS, where a considerable quantity of silicon-containing compounds was found in the active area of the Ni-CGO fuel electrode.

In this work, an ultra-thin glass substrate based absolute pressure sensor was developed and manufactured to study the implementation of different build-up technologies with focus on high-temperature sensor application. Physical vapour deposition was used to realise strain gauge sensor structures as well as several protective layers. Screen printed thick-film layers were applied to deposit routing traces. Also, a housing assembly using two ultra-thin glass substrates was achieved this way. The electrical connection to the measurement instrumentation was realised by either platinum or high purity nickel wires. Wires were connected to the contact pads by thick-film sintering. The measured overall thickness of the sensor is 390 µm. Furthermore, the ultra-thin glass substrates were cut by Laser and saw dicing resulting in a recommendation to prefer Laser dicing for future work. To characterise the pressure sensor, a customised pressure chamber with integrated muffle furnace was used. First tests showed that the manufactured sensor proved to be functional at temperatures of up to 450 °C while applying a pressure range of 1 to 5 bar (absolute).

An in-depth investigation was performed on a metallic interconnect extracted from an SOFC stack operated for 40,000 h. The characterization was performed on the surface and the cross-section, paying attention to the evolution of the materials due to the interaction with the dual atmosphere of the stack under operating parameters. The interaction between materials (i.e., metal substrate, coatings and atmospheres) and stack components (i.e., current collectors and MIC) generated several modifications that affected the surface and, in some cases, the bulk of the interconnect. The careful metallographic preparation allowed for the performance of an intensive microscopical characterization of the cross-sections all along the interconnect profile, from the inlet to the outlet of the fuel stream. The formation of thermal grown oxides on both sides and their evolution were studied and described. The interconnect, after 40,000 h, was still suitable for operation, but the few bulk changes due to the diffusion of Ni and the TGO that formed at the fuel side suggest the introduction of fuel side coatings to increase the life expectations of the whole stack.

High-temperature reactions between glass–ceramic sealants and Fe-Cr alloy interconnects may lead to the formation of undesirable phases, and consequently degradation of solid oxide fuel/electrolyser devices. In this work, three different glass–ceramic sealants (Na-containing, Ba-containing, Sr-containing compositions) and Fe22Cr stainless steel powders (raw and pre-oxidised) are considered in order to test their chemical reactivity at 750 °C and 850 °C for 500 h in static air. The novelty of this approach is related to the use of powder mixtures instead of studying the reactivity on planar interfaces, which allows a better evaluation the materials’ reactivity. Oxidation tests indicate that the Sr-containing glass–ceramic/steel couple is the least reactive among the aged samples. For the Ba-containing samples, the formation of an undesirable phase of BaCrO4 is observed by diffractometry and photoelectron spectroscopy analyses. The present research explores, for the first time, the effects of exposing the high surface area of the alloy powder and glass–ceramic sealant interface, assessed by oxidation testing and microstructural analysis. The results show that by using mixed powders with large interface surface areas, degradation of the materials can be observed after relatively short times, allowing accelerated screening of the reactivity of materials, and thus their further development.

The degradation of metal interconnects (ICs) is one of the main lifetime limiting issues in Solid Oxide Cells (SOCs). Chromium oxide thermally grows on the substrate surface that causes ohmic loss and its vapors poison the oxygen electrode reaction (OER). Mn-based spinels are presently among the materials of choice to protect ICs to prevent Cr diffusion.As the target lifetime is around 40000h, it is of interest to design accelerated ageing tests, under harsher than nominal operating conditions, to simulate the long-time ageing behavior at nominal conditions.In this study, the performance of IC coatings was investigated with accelerated ex-situ corrosion ageing tests, in which the operating condition of the air-side interconnect was simulated. Temperature and humidity were selected as test variable parameters. Area Specific Resistance (ASR) and Cr depletion/migration were studied for the stressed conditions. Tests were carried out on stainless steel substrate with Mn-Cu-Oxide and Mn-Co-Oxide as protective coatings.Ageing tests over 1000h at different temperatures (750-950°C) and humidity (above 15%RH) were run while monitoring the ASR of the samples. Fig. 1 shows the ASR results for the samples run at different temperatures and in dry condition. Based on Fig. 1a-e, it is observed that the ASR trends remain constant during the test time. Although 916°C is well above nominal operating temperature, the ASR showed constant value within a reasonable range. At a test temperature 950°C (Fig. 1f), the ASR behavior of samples containing Co-Mn Oxide protective coating is the same found for lower temperatures; however, a sharp ASR increase in Mn-Cu Oxide coated samples can be observed. Applying humidity to high-temperature conditions also may help to accelerate the test, and its results will be presented. SEM/EDX post-test characterization provides information on the scale morphology and helps to understand the different behaviors at different stressed conditions.Keywords: SOC; interconnect; protective coating; ageing test; accelerating test; Cr diffusion; ASR; Figure 1

High temperature solid oxide fuel cell (SOFC) is regarded as a unique electrochemical device to convert the chemical energy of a large diversity of fuels into electricity and heat with high efficiency and low emission. The electrolyte-supported cell (ESC) design is proven to be one of the most feasible SOFC technologies for commercial applications. Thickness reduction of yttria stabilized zirconia (YSZ) electrolyte supports without sacrifice of mechanical strength is favorable for cell performance enhancement.In this work, dense gadolinium-doped ceria (GDC) thin-films with thickness in the range of 0.15-0.5 µm were fabricated as Sr-barrier layers on the cathode side, and as strength-balance and adhesion layer on the anode side by electron beam physical vapor deposition (EB-PVD) method. Replacing the state-of-the-art screen-printed GDC layers, the approach with YSZ substrate sandwiched in between two GDC thin-films was proposed not only to prevent the formation of interfacial secondary phase on the cathode side, but also to increase the overall robustness of ESCs. Investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), it was confirmed that 0.5 µm thick GDC thin-films were effective to suppress the formation of Sr-zirconate phase at the YSZ/GDC interface. In comparison to reference cells with screen-printed GDC layers, higher breaking loads were recorded on the cells with PVD-GDC thin-films by Ring-On-Ring bending tests, showing considerably improved mechanical properties. Current-voltage characteristics and electrochemical impedance spectroscopy demonstrated that the performance of the as-prepared ESCs with GDC thin-films was comparable to the reference cells. Operated at 860 °C, the ESC with 0.5 µm GDC thin-film outperformed other tested cells with 0.15 µm or 0.3 µm GDC layers, and delivered a power density of 0.55 W•cm-2 at a cell voltage of 0.7 V. The results achieved in this work can be considered as step stones for the further development of ESCs with reduced electrolyte thickness, sufficient robustness and improved performance.This work is financially supported by the German Ministry for Economic Affairs and Energy (BMWi) within the framework of the project “Kostenoptimierter Stack und verbessertes Offgrid-System (KOSOS)” with grant number of 03ETB005C.

Introduction Sunfire develops and produces high-temperature fuel cell (SOFC), electrolyzer (SOEC) and co-electrolysis (Co-SOEC) systems. SOFCs convert fuels and gases into electricity and heat for residential, commercial and industrial applications. SOECs and Co-SOECs convert water and/or CO2 with preferably renewable electricity into hydrogen or syngas. With these technologies, Sunfire addresses a multitude of challenges in our energy systems. Development and industrial outlook Sunfire continuously improves its technology on stack as well as at system integration level. For the stack technology, a decrease of the combined life cycle costs (€ kW-1 h-1) is the key driver for development. Recent improvements in this KPI as well as updates to our long-term stack tests in SOFC (~25kh), SOEC (~10kh) and Co-SOEC (~5kh) will be shown and discussed.Furthermore, updates on production scaling will be shown. This includes improvement of various processes as well as buying and commissioning new equipment for automated production.Sunfire’s products are also continuously being improved. Our existing micro-CHP solution (Sunfire-Home) offers a rated electrical output of 750 W and a thermal output of 1,300 W. In addition to reducing emissions, the advantages of Sunfire-Home include high efficiency, fully automatic operation with remote access and simple integration with modern building technology. Updates on the running units within the scope of the PACE-project and next steps will be shown.With Sunfire-Remote, we provide a compact SOFC-system for self-sufficient and off-grid power supply from pipeline gas and Propane. The units are battery chargers primarily and provide continuous power for a wide range of applications with an average power consumption up to 400 W. Flexibility in the kilowatt range can be covered by batteries that has to be selected according to the needed capacities and specific requirements. Also here, updates of the market status will be given.Furthermore, Sunfire is the leading provider of SOEC systems worldwide, quickly moving into the multi-megawatt market for industrial applications. By focusing on the utilization of industrial off-heat to maximize overall electrical efficiency, the operational cost for continuous hydrogen production can be kept at a minimum. Sunfire units are therefore specifically suited for brown-field industrial applications, as demonstrated at the steel plant of Salzgitter. There, a 730 kWelAC SOEC system was installed in 2020 within the GrInHy2.0 project, after successfully operating a 150 kWelAC rSOC system since 2017.(1) The electrolyzer is expected to be in operation for at least 13,000 hours by the end of 2022, while producing at least 100 tons of green hydrogen from renewable electricity. Additionally, a 2,6MW SOEC System for the operation at a refinery of Neste in Rotterdam is currently being planned within the framework of the MULTIPHLY project as will be shown.In addition to pure hydrogen electrolysis (HyLink), Sunfire is also developing the Co-SOEC (SynLink) providing renewable syngas, a mixture of H2 and CO, for chemical applications and Power-to-Liquid processes. The operation with Sunfires technology has been successfully demonstrated within the Kopernikus PtX project and the next step will be the supply of a 1 MW Co-SOEC unit within MegaSyn. References (1)Schwarze, O. Posdziech, J. Mermelstein, S. Kroop, Fuel Cells, (2019).