Testing of Pressurized Solid Oxide Single Cells

Solid oxide fuel cells (SOFCs) excel by high efficiencies in fuel cell as well as electrolysis modes, and by being able to operate in both modes as a reversible cell (solid oxide cell – SOC). This allows for production of electricity and heat from a green fuel, and for storage of electricity as gas or use as fuel. Lifetime and costs are major factors enabling such reversible SOCs to enter green energy systems. Metal supported SOCs (MSCs) provide cost-competitive materials within the cell. Furthermore, targeting the lower operating temperatures around 650 oC, MSCs will allow for cheaper stack and balance of plant components as well. Lowering operating temperatures leads to a reduction of thermally activated degradation processes, thereby prolonging the lifetime. The present study investigates the option to operate MSCs, fabricated at DTU Energy by tape casting, lamination, and screen-printing, in reversible mode between fuel cell (FC) and electrolysis (EC). Emphasis is on the effect of reversible operation on performance and durability of the MSC, compared to steady state operation in either mode, and to the behavior of state-of-the-art (SoA) fuel electrode supported SOC with Ni/YSZ fuel electrode. The MSCs are composed of a FeCr support, a Ni/GDC (gadolinium-doped ceria) infiltrated LSFNT (lanthanum-doped strontium iron nickel titanate) fuel electrode, a YSZ (yttria-stabilized zirconia) electrolyte, a GDC barrier layer, and an in situ sintered LSC (lanthanum-doped strontium cobaltite) air electrode. The reversible operation was carried out by switching between FC and EC modes at current densities of 0.25 and -0.25 A/cm2, respectively, at 650 oC using a gas mixture of 50/50 H2O/H2 to the fuel electrode and air to the oxygen electrode.Figure 1 shows the evolution of the cell voltages for the SoA cell and the MSC. The degradation rate of the SoA cell was larger during operation in EC as compared to FC mode. Similar observations were made previously, even though these tests were typically carried out at temperatures higher than 650 oC as in this work [1]. Furthermore, the degradation rate decreases over time, more particularly in EC mode, which is also a known phenomenon at this type of cells [2, 3]. In the final ca. 200 h, both degradation rates are in the range of 3%/1000 h, which is an interesting observation, i.e., the longer-term degradation rates are similar in both modes (EC and FC). The analysis of electrochemical impedance spectroscopy (EIS) recorded under current allowed to conclude that the main contribution to the degradation is the increase of polarization resistance, i.e., related to electrodes degradation.In the initial ca. 400 h hundred hours, the cell voltage degradation on the MSC is larger in fuel cell mode, while there is nearly no degradation in electrolysis mode. The good stability in EC mode over a few hundred hours confirms the findings of steady-state electrolysis tests with the same type of cells [4]. In the final period from ca. 600 h, both degradation rates increase but stay fairly constant with ca. 4%/1000 h in EC and ca. 16%/1000 h in FC mode, when calculated as linear increase. EIS reveals that both, the serial and the polarization resistances increase in parallel, which indicates a combination of degradation of electrode and probably corrosion and/or interface attachment. Details will be presented, including comprehensive EIS evaluation combined with micro-structural characterization.Figure 1. Cell voltage vs. operating time under current in reversible mode at 650 oC, 0.25 A/cm2 in fuel cell and -0.25 A/cm2 in electrolysis mode, 50/50 H2O/H2 fuel and air to the oxygen electrode, (a) SoA cell, (b) MSC, gaps in the cell voltage are interruptions of operation due to technical issues in the labReferences[1] X. Sun, B.R. Sudireddy, X. Tong, M. Chen, K. Brodersen, A. Hauch, Optimization and Durability of Reversible Solid Oxide Cells, ECS Trans. 91 (2019) 2631.[2] A. Hagen, R. Barfod, P.V. Hendriksen, Y.-L. Liu, S. Ramousse, Degradation of anode supported SOFCs as a function of temperature and current load, J. Electrochem. Soc. 153(6) (2006) A1165.[3] A. Hauch, K. Brodersen, M. Chen, C. R. Graves, S. H. Jensen, P. S. Jørgensen, P. V. Hendriksen, M. B. Mogensen, S. Ovtar, X. Sun, A Decade of Solid Oxide Electrolysis Improvements at DTU Energy, ECS Transactions, 75(42) (2017) 3.[4] A. Hagen, R. Caldogno, F. Capotondo, X. Sun, Metal Supported Electrolysis Cells, Energies 15 (2022) 2045. Figure 1

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

Fatigue resistance of steels: Boardman, B. Metals Handbook 10th Edn (ASM International, Materials Park, Ohio, 1990) Vol. 1, pp 673–688

Mathematical approaches to modelling the mass transfer process in solid oxide fuel cell anode

Chromium poisoning of the air electrode is a primary degradation mechanism for solid oxide cells (SOCs) operating under fuel cell mode. Recent experimental findings show that reversed pulse operation for SOCs operated as electrolyser cells can reverse this degradation and extend the lifetime. Here, we use a multiphysics model of an SOC to investigate the effects of reversed pulse operation for alleviating chromium poisoning of the air electrode. We study the effects of time fraction of the operation under fuel cell and electrolysis modes, cyclic operation starting after a certain duration, and fuel cell and electrolysis current densities on the cell lifetime, total power, and hydrogen production. Our modeling shows that reversed pulse operation enhances cell lifetime and total power for all different cases considered in this study. Moreover, results suggest that the cell lifetime, total power, and hydrogen production can be increased by reversed pulse operation at longer operation times under electrolysis mode, cyclic operation starting from the beginning, and lower electrolysis current densities. All in all, this paper documents and establishes a computational framework that can serve as a platform to assess and quantify the increased profitability of SOCs operating under a co-production operation through reversed pulse operation.

Solid oxide cells (SOCs) represent a highly promising energy conversion and storage technology, potentially serving as a cornerstone of sustainable development strategies by significantly increasing the share of clean energy. During periods of surplus energy from renewable sources, hydrogen can be generated in the electrolysis mode, and subsequently consumed to produce electricity and heat when the demand is high in fuel cell mode. However, the conventional operating temperature of the cells, typically above 800 °C, poses challenges associated with thermal compatibility and material degradation, substantially inflating costs and hindering widespread commercialization. At the targeted operating temperatures below 600 °C, most electrode materials suffer drastic reductions in electrochemical performance, underscoring the need for innovative electrodes capable of maintaining high efficiencies at lower temperatures. Recent researches have highlighted the potential of a range of new electrodes engineering strategies, including mechanical milling, infiltration, in situ assembling, in situ exsolution of nanoparticles and morphology modification of materials to boost the electrode materials performance. It has been observed that materials possessing the same crystal structure yet an altered morphology can exhibit significantly distinct electrochemical characteristics, thereby enhancing processes such as the surface exsolution of nanocatalysts. A key advantage of these electrodes lies in their elevated catalytic activity, which bolster performance.In this study, we examine how transforming material morphology from a powder-based form to a nanofibrous structure influences electrochemical performance. Additionally, we investigate techniques such as the in situ exsolution of nanoparticles on material surfaces, evaluating whether morphological changes affect this process and assessing the impact of phase transitions on its effectiveness. While our primary focus is on perovskite-based materials and their derivatives for application in solid oxide cells, the insights gained may also be applicable to other domains within materials engineering. Using the example of the composite material GdBa0.5Sr0.5CoCuO5+δ (GBSCC) - Ce0.9Gd0.1O1.95 (GDC) and Sr1.8Fe1.4Ti0.2Cr0.2Ni0.1Co0.1O6-δ perovskite, we demonstrate how changes in morphology (from powder to nanofiber) influence the material's performance, for example, the nanofibrous GBSCC-GDC electrode exhibits a polarization resistance (Rp) over 60% lower compared to the powder-based material electrode at 600 °C (0.186 Ω·cm² vs 0.493 Ω·cm²). Additionally, we show whether morphological modifications can impact the quantity and quality of in situ exsolved nanoparticles, as well as the elemental concentration after reoxidation. Exsolved nanoparticles from nanofiber materials have diameters over 50% smaller compared to powder-based perovskites.Acknowledgements:The work is funded by the National Science Centre Poland (NCN) based on the decision number UMO-2021/43/D/ST5/00824. Michał Gogacz also acknowledges the financial support of research project supported by the program „Excellence Initiative – Research University” for the AGH University of Krakow.HRTEM, EDS and SAED results were a part of CERIC-ERIC grant no. 20242238 and were conducted in National Institute of Materials Physics, Măgurele in Romania. Figure 1

Solid oxide cells (SOCs) can operate in fuel cell and electrolysis mode, allowing for production of electricity and heat from a green fuel, and for storage of electricity as gas or use as fuel. Lifetime and costs are major factors enabling commercialization. Metal supported SOCs (MSCs) provide cost-competitive materials within the cell. The present study investigates the reversible operation of MSCs, fabricated by tape casting, lamination, and screen-printing, at 650 oC in 50/50 steam/hydrogen gas. In the initial few hundred hours, the MSC show a lower degradation rate compared to a state-of-the-art (SoA) fuel electrode supported cell in the electrolysis mode, while it is ca. comparable in fuel cell mode. Electrochemical impedance evaluation revealed that the degradation is due to a simultaneous increase of the serial and polarization resistances in the MSC while it is mainly due to increase of the polarization resistance in the SoA cell.

The Forschungszentrum Jülich GmbH has successfully developed a 5/15 kW-class reversible Solid Oxide Cell (rSOC) system in recent years, promising a high system efficiency in fuel cell and electrolysis mode [1]. The core element of the system is the well-known Integrated Module developed, which has been adapted from fuel cell to the rSOC operation. This Module consisted of four 10-layer sub stacks, in which each layer had an active cell area of 320 cm². It also contained fuel and air heat exchangers, arranged on top and underneath the stacks, to bring the incoming gases to the operating temperature. In addition, three electrically operated heating plates were implemented to heat up the system at the beginning of the operation and to adjust the stack temperature during the endothermic electrolysis operation. Other components necessary for the system operation such as the evaporator, blowers, condenser and control system are attached near the Integrated Module in a compact and suitable manner. This system was extensively examined after its completion. A maximum power of 5.3 kWDC at a current density of 0.5 A cm-2 and a fuel utilization of 97.3% could be achieved in fuel cell mode. Under these conditions, an electrical efficiency of 62.7% (LHV, DC) was reached. Furthermore, a maximum electrical input power of - 14.3 kWDC could be achieved in electrolysis mode with a current density of -0.89 A cm-2 at a steam conversion rate of 85%. An electrical efficiency of 70% (LHV, DC) was measured for this operating point. In the further course of the tests, the switching between the operating modes was investigated and optimized. The change from fuel cell to electrolysis mode took approximately 13 minutes limited by steam generation and the opposite direction took less than 3 minutes [2]. In the fuel cell mode, a maximum system fuel utilization of more than 99% was achieved through the use of an off-gas recirculation. Such a high utilization could be realized because the steam content has been removed from the recirculated gas stream by condensation before feeding back to the stack inlet. Furthermore, the system behavior during load variation was examined. With this system design, a minimum part load of 0.1 A cm-2 in the fuel cell and - 0.05 A cm-2 in the electrolysis mode could be demonstrated [3]. Based on these experiences, a new rSOC system with a power of 10 kW in fuel cell and 40 kW electrolysis mode will be constructed. For this purpose, the stacks used and the supporting components have to be adapted. In addition, the efficiency in the electrolysis mode will be increased by using a more effective steam generation process. The new developed system as well as its test results will be presented at the conference for the first time.[1] M. Frank, R. Deja, R. Peters, L. Blum, D. Stolten, Applied Energy, 217 (2018) 101-112.[2] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, V.N. Nguyen, L. Blum, D. Stolten, ECS Transactions, 91 (2019) 2495-2506.[3] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, N. Kruse, Q. Fang, L. Blum, R. Peters, Journal of the Electrochemical Society, (2021).

This report presents the preliminary documentation of a 10 MWe DC reversible solid oxide cell (rSOC) system designed to use both electrical and thermal energy from a nuclear power plant (NPP). The system is designed to consume 10 MWe DC in electrolysis mode while producing hydrogen from demineralized feedwater. In fuel cell mode, the same stacks produce 2.37 MWe DC of electricity by reacting hydrogen and oxygen, while generating water as a byproduct which is recycled to be used later in the electrolysis mode. The system detailed in this specification is a high-temperature steam electrolysis (HTSE) system when operated in the electrolysis mode. HTSE systems have the benefit of producing hydrogen at a higher efficiency than conventional low-temperature electrolysis (LTE) systems. In this report it is assumed that some of the heat required for HTSE operation comes from an NPP. Heat extraction from an NPP for use in electrolysis mode of the rSOC system allows preheating and vaporization of feedwater before recuperators and trim heaters raise the feed temperature to the approximately 800 ?C before entering the solid oxide stacks. The purpose of an rSOC system in a utility company setting is to employ energy arbitrage with a dispatchable demand load which can consume excess electricity generation during times of low grid demand / high generation and can produce electricity for the grid during times of high grid demand / low generation. There is a wide range of energy storage technologies that could be used for utility-scale energy arbitrage (utility-scale battery storage is considered the baseline technology), the object of this work is not to compare and contrast rSOC technology with any of these other technologies, but only to present this preliminary design for consideration and for use in future conceptual or front end engineering design (FEED) work. This document is not meant to be a final specification or definitive description of the rSOC system, but it is meant to showcase preliminary process modeling results, provide boundary conditions and interface requirements such as input feed and utility stream flowrates, temperatures, and pressures as well as thermal and electrical energy requirements, and output conditions in both electrolysis mode and fuel cell mode. These results are intended to inform the future development of a conceptual demonstration-scale study to assess the technical and economic feasibility of a future demonstration of an rSOC integrated project at an NPP.

Enhancing the performance of unitized regenerative proton exchange membrane fuel cells through microwave-synthesized chitosan based nanocomposites

A Ni/Yttria‐stabilized zirconia (YSZ) cell with a (La0.60Sr0.40)0.95Co0.20Fe0.80O3–δ cathode is tested both in fuel cell and electrolysis modes. In fuel cell mode under dry air and wet H2, the cell is operated between the open circuit voltage (OCV) and 0.4 V and reaches 330 mW cm−2 at 850 °C for 157 mL min−1 H2 supply. The influence of temperature and air or hydrogen flow rate is studied, and impedance measurements show that below 0.8 V the electrolyte becomes the more resistive part of the cell. Nevertheless, fuel utilization yields are higher under oxygen or hydrogen depletion. If it is possible at 750 °C to work at low voltage during several hours in the entire voltage range, the voltage decrease must be limited at 850 °C. The cell can also be operated under wet air. The same cell can be operated in electrolysis mode, and a power density of 340 mW cm−2 can be obtained at 0.3 V/OCV under 100 mL min−1 wet (3% H2O) 5% H2–95% Ar mixture on the fuel side and dry or wet 100 mL min−1 air flow on the air side. Nevertheless, bubbling air providing the air electrode in saltwater has an irreversible detrimental effect on the cell.

Reversible solid oxide electrochemical cell (RSOC) is a competitive option which has attracted increasing focus on alleviating some environmental problems and energy crisis with the capability of reversibly operating in solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode [1].Solid oxide cells (SOCs) have received increasingly attention due to their high efficiency and broad applications. However, electrodes with rapid hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), oxygen evolution reaction (OER) and sufficient durability play a key role in solid oxide cells. A multifunctional perovskite oxide La0.6Ca0.4Fe0.8Ni0.2O3-δ (LCFN) has been investigated as an electrode for SSOCs in our previous work. The results confirm that LCFN shows excellent ORR, OER, CO2-RR and HOR catalytic activity [2-3]. However, the investigation of LCFN for SOCs has been hindered due to the lack of stability. Herein, a novel perovskite La0.6Ca0.4Fe0.7Sc0.1Ni0.2O3-δ (LCFSN) is investigated as an electrode of SOCs. Its structural stability has been improved under H2 atmosphere. The polarization resistance (Rp) of the electrode LCFSN is only 0.147 Ω cm2 at 800 °C under air. The single cell Ni-YSZ/YSZ/GDC/LCFSN displays a peak power density of 1.36 W/cm2 in fuel cell mode and a low Rp value of 0.131 Ω cm2. Most importantly, the cell exhibits admirable durability of 130 h without apparent degradation. All these results suggest that LCFSN is a promising candidate electrode for SOCs.

Comparison of gas phase transport effects between fuel cell and electrolysis cell modes of a 100 cm2 class molten carbonate cell

Review: 22 refs.

Synthesis of biofuels is an important step in the phase out of fossil fuels in the transportation sector, especially in long-distance sea, air and road transport where direct electrification seems unfeasible. Integration of renewable electricity enables efficient electricity storage as well as an increased utilization of the biomass carbon, which lowers the biomass demand. This paper presents a flexible system for the conversion of biomass and electricity to methanol. The system is based on the deep integration of a Two-Stage gasifier and solid oxide cells (SOC). The integration enables efficient production of a nitrogen-free high-quality syngas, suitable for methanol production. This study focuses on the system in electrolysis mode, and analyzes the effects of recirculating CO2 from the gas conditioning and methanol synthesis process back to the SOC, as well as the effects of pressurized operation of the gasifier and increased H2O content in the gasifier. Thermodynamic modeling shows that CO2-recirculation allows an increase in conversion of the carbon in the biomass to methanol from 80 % up to 92 %, with an energy efficiency of 71 %. Only a slight pressurization seems feasible, as an increase in pressure beyond ~3 bar results in significant methane formation inside the SOC.