bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study on Effects of Structure Parameters and Operating Conditions on the Micro-Tubular SOFC Stack Performance
Authors: Shi Jixin , Wang Yuqing , Fan Junhua , Shi Yixiang , Cai Ningsheng
Published: July 2021

A multi-physical field coupled three dimensional model of large-scale micro-tubular solid oxide fuel cell (MTSOFC) stacks was established in this study. The effects of structural parameters and operating conditions, namely configuration of the tube array, diameter, length, distance between tubes, the flow rate and flow path of air, on the stack performance were studied. The triangular array is more compact in space and can achieve higher volume specific power than the square array. However, the more concentrated arrangement also results in a higher local temperature and temperature difference, which is challenging for long-term stability. According to the simulation results, smaller tube diameter and distance between tubes lead to higher volume specific power, with the former having a marginal effect. A longer tube can reduce the axial temperature gradient, which is conducive to long-term operation stability. Increasing the air flow rate of the cathode is the most effective method to reduce the highest temperature. Furthermore, the co-flow arrangement is found to be more helpful to take away the heat generated by the stack than the counter-flow arrangement. Based on the simulation results, the structural parameters and operation conditions suitable for a large-scale micro-tubular SOFC stack are decided, considering the output power, long-term stability, and mechanical strength. The model is demonstrated as a powerful tool for the design and optimization of MTSOFC stacks.

Key words: Micro-tubular SOFC Stack; Array Configuration; Structure Parameter; Operation Condition; Volume Specific Power
Anode-Oxidizing Critical Operating Conditions of Large Planar Solid Oxide Fuel Cell
Authors: Li Hangyue , Cui Tonghui , Han Minfang
Published: July 2021

In a solid oxide fuel cell power system, large planar cells are common central parts for electric generation. In practice, the operating conditions of a planar cell may have significant impact on the electrical efficiency and the lifespan of the cell, thus the operating and maintenance cost of the power system. Given varying electric load, the power system would dynamically adjust the operating conditions of each cell or cell module, so that the energy and heat balance in the system is maintained, the fuel consumption is minimized and the cells are protected from reactant starvation, local overheating etc. To realize this functionality, we seek a fundamental understanding of the quantitative connections among fuel cell properties, operating conditions and optimal electrical efficiency.

We established a quasi-2D model for quick evaluation of fuel and oxidant concentration and current density along the flow direction. For fuel cells with very low charge transfer impedance i.e. 0.02 Ω*cm^2 operating with low fuel flow rates, the fuel concentration at the exit may reach an equilibrium where the local Nernstian potential across the cell equals the cell voltage. In such cases, the fuel utilization remains almost constant regardless of varying fuel flow rate, given a certain cell voltage. For fuel cells with local charge transfer impedance of 0.5 Ω*cm^2 operating with high fuel flow rates, such phenomenon was not observed because the fuel concentration at the exit depends strongly on the fuel flow rate. Given the fuel molar fraction at the fuel inlet, the electrical efficiency of a fuel cell has its maximum at certain cell voltage, which depends strongly on the charge transfer impedance of the fuel cell. At constant fuel flow rates, the optimal cell voltage increases with lowering charge transfer impedance. The optimal electrical efficiency appears lower with higher inlet fuel molar fraction. Given fixed and uniform fuel cell temperature, the air flow rate has little impact on the electrical efficiency for air-fuel stoichiometric ratios above 1.3.

Besides the above findings, further studies are necessary on the effects of temperature distribution as well as porous electrode diffusion resistance.

Figure 1
Numerical Study on Biogas Refining System Combined with Proton-Conducting Solid Oxide Electrolyzer
Authors: Tachikawa Yuya , Matsuzaki Yoshio , Kawabata Yasuharu , Taniguchi Shunsuke , Sasaki Kazunari
Published: July 2021

Biogas is one of the most globally distributed carbon-neutral fuels to be used as a local biomass energy source for local society energy demand. However, since the biogas from organic waste is typically a mixture of 60% methane and 40% carbon dioxide, the biogas has a lower energy density compared with coal, oil, LNG, and etc. In this study, biogas refining system including methanation reactor and proton-conducting electrolysis cell has been proposed and investigated based on the numerical calculation including mass and heat balance analysis. Using this system, hydrogen and CO2 derived from electrolysis cell and biogas, respectively, will be converted into methane via methanation reaction. Carbon deposition is a well-known problem to be resolved when carbon-rich gas is supplied to the cell cathode. Based on the calculation results, the gas humidification was found to be necessary to prevent carbon deposition at the cathode inlet. However, carbon deposition was predicted to still occur at the cathode outlet even with the gas humidification when a conventional oxide-ion conducting electrolyte is applied to the electrolysis cell due to the enhanced carbon activity caused by oxide-ion transport from the cathode to the anode. In the case of the proton-conducting electrolyte, proton transport from the anode to the cathode was found to mainly promote reverse water-gas shift reaction and methanation reaction without any carbon deposition. Even though the calculation results should be verified by comparing with experimental results, the numerical study suggested that the biogas refining system combined with p-SOEC is a promising technology for generating carbon-neutral methane with a strongly suppressed risk of carbon deposition.
Development of High-Performance Anode-Supported Planar SOFC with Large Area by 4-Layer Co-Firing Process
Authors: Hussain Amjad , Song Rak-Hyun , Joh Dong Woo , Hong Jong-Eun , Lee Seung-Bok , Lim Tak-Hyoung
Published: July 2021

Solid oxide fuel cell (SOFC) technology has attratced great attention because of higher efficiency, fuel flexibility and eco-friendly stationary power generation system. However, its commercialization is hindered due to the lack of durability and high cost. Herein, a facile and exceptionally reliable 4-layered anode supported SOFCs with a large area (12cm×12cm) was fabricated in a single step co-firing process at 1400 oC, in which tape-casted green films of NiO-YSZ, NiO-1CeScSZ, 1CeSxSZ, and GDC were laminated by isostatic press. The fabrication parameter such as viscosity of the slurries and mechanical strengths of the green films, etc. were optimized. As a result, finely porous anode layer, and highly dense 1CeScSZ electrolyte and GDC buffer layers on a robust porous anode-support were formed successfully. The LSC cathode was screen-printed on the GDC layer. The possibility of mass production of this process are verified through the fabrication of large area cells with an active area 100cm2. The single cell showed high power output of 38 W at total current 50A at 700°C and exhibits low degradation rate of 0.2% kh-1 at 25A for long-term test of 1000 hrs. This facile strategy is time-efficient, reproducible, cost-effective, and highly practical to produce SOFC system satisfying both high-performance and durability.
Intrinsic Dipole Moments and Electron Transfer at the MIEC-Gas Interfaces
Authors: Williams Nicholas , Seymour Ieuan , Leah Robert , Mukerjee Subhasish , Selby Mark , Skinner Stephen
Published: July 2021

The catalytic and transport properties of mixed ionic-electronic conducting (MIEC) electrodes for solid oxide fuel cells (SOCs) are well documented and utilised, yet poorly understood. In the current study, a novel kinetic framework for the electrochemical behaviour of hydrogen at the MIEC-gas interface will be discussed for three parallel treatments: as an ideal gas, as an adsorbate on the electrode surface and as a charge carrier dissolved in the oxide lattice. This model gives a physically meaningful reason for the enhancement in electrochemical activity of a MIEC electrode as the steam pressure is increased in both fuel cell and electrolysis modes, and is ubiquitous for any electrochemical system where the electric double layer is described as a Heaviside step function.

The process of charge transfer at the MIEC electrode/gas interface comprises of ambipolar exchange of ions and electronic species. The result of such a process causes charge separation and an associated dipole moment at the electrode surface. By applying an overpotential η to the MIEC electrode, an electrostatic surface potential shift away from equilibrium may be established where an effective double layer is formed between the electrode surface and the adsorbed species. Although no net charge transfer occurs, this surface potential shift modifies the surface chemistry and is the driving force for the ambipolar exchange of ions and electronic species.

Density Functional Theory (DFT) calculations were used to study the electrostatic potential at the ceria [111] surface, where we were able to calculate the dipole moment and adsorption energy as a function of hydroxyl coverage. The theory of the electrostatic potential at the MIEC-gas interface was then applied to predict the surface electrochemical properties as a function of local overpotential. The mechanistic understanding gained from this model is widely applicable to a range of MIEC systems and provides a basis upon which the operating conditions can be tailored.
Thermo-Mechanically Coupled Peridynamic Modelling of Fracture Formation in Solid Oxide Fuel Cell Anode
Authors: Xiang Yu , Zhong Zheng , Jiao Zhenjun
Published: July 2021

Fracture formation can be observed in brittle yttria-stabilized zirconia (YSZ) in Ni-YSZ composite anode during high-temperature operation of solid oxide fuel cells (SOFCs). It is quite difficult to predict the fracture formation in solid materials accurately based on the classical continuum mechanics theory, because of the singularity problems in partial differential equations. In this work, an ordinary state-based-peridynamic (OSB-PD) model is proposed to predict the fracture formation in SOFC anode based on real microstructures reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The key factors determining anode microstructure strength is analyzed based on the simulation results upon the comparison among different anode microstructures. The thermo-mechanical coupling effect is investigated by considering the influence of both external mechanical loads and temperature distribution.
Electrically Conductive and Protective Coating Reaction with LSCF Material
Authors: Choi Jung Pyung , Bonnett Jeff , Canfield Nathan , Hardy John S
Published: July 2021

Ferritic stainless steel interconnect materials are used in intermediate or high-temperature SOFCs because of their oxidation resistance, high formability, and low cost. Their corrosion resistance is due to the formation of a protective chromium oxide scale during operation. However, the protective oxide layer produces Cr-containing volatile species at SOFC operating temperatures and conditions, which can cause cathode poisoning. Electrically conducting spinel coatings have been developed to prevent cathode poisoning and maintain an electrically conductive pathway through SOFC stacks. Generally, Mn-Co-O spinel is used for this protective coating in SOFCs. To remove the Co and enhance the electrical conductivity, PNNL has developed a Mn-Cu-O spinel for this protective coating. This paper will focus on the electrically conductive coating’s compatibility with LSCF in high temperature operating environments.
Estimating the Impacts of Integrating a Solid Oxide Electrolyser into a Coal Power Plant
Authors: Angyus Michael , Williams Mark , Jesionowski Gary , Gemmen Randall , Gerdes Kirk , Ramezan Massood
Published: July 2021

Coal plants are under tremendous stress due to the introduction of renewables, particularly solar, which create intermittent periods of power demand and lower the overall demand for coal-based power. For coal plants to operate efficiently and consistently, it has been proposed that solid oxide electrolyser cells (SOECs) be incorporated into the coal plants to produce storable hydrogen from high temperature steam and electricity. An integrated SOEC would enable the boiler to operate at maximum efficiency while borrowing a fraction of the clean high temperature steam for electrolysis. It is likely that the increase in efficiency, consistent operating hours, and revenue from hydrogen sales will outweigh the price of integration, but it is yet unknown whether this solution is profitable. One of the challenges to assessing the profitability of SOEC integration is the variability in coal plant sizes. To assess the profitability of SOEC integration in any sized coal plant, an excel sheet was developed that uses coal plant specifications to calculate coal, water and air consumption, electricity, hydrogen and oxygen production, and expected costs and revenue from each. The sheet also automatically calculates the net present value (NPV) and displays the discounted cumulative cash flow. This excel sheet can be used to model the integration of an SOEC into any selected coal plant, enabling coal plant managers to decide whether or not to invest in the project.
Development Progress at Hexis SOC Activities
Authors: Grolig Jan Gustav , Bausinger Holger , Sarda Venkatesh , Meier Christoph , Mai Andreas
Published: July 2021

HEXIS is developing and manufacturing SOFC-based micro-CHP systems for houses and / or small companies. While being a subsidiary of the Viessmann Group (until 06/2020) the company has been mostly focusing on the new generations of highly efficient (>95 % LHV) fuel cell modules – these modules are running in small quantities at customer sites - meanwhile, Hexis belongs to the h2e group and has expanded its technical activities.

This paper will present the long-term experiences on long-term and cyclic testing of fuel cell modules in lab tests as well as results on robustness and performance in the field. It was observed that degradation rates as low as approx. 0.3 % / kh, i.e. 13 mΩ cm² / kh on the short-stack level for over 50,000 h can be reached. These stacks have been analyzed with electrochemical impedance spectroscopy (EIS) at regular intervals, which can provide valuable insights in understanding fundamental degradation mechanisms for long term operation of SOFC stacks.

Moreover, the paper will include highlights of new developments since the new era for Hexis as an important part in the h2e group has started. These new developments are improvements on cell and stack level as well as new applications for the Hexis technology in general. Finally, the paper will outline some of the future challenges in Hexis’ development activities.
Commercialization of CO2 Electrolysis By Haldor Topsoe
Authors: Kungas Rainer , Blennow Peter , Heiredal-Clausen Thomas , Holt Nørby Tobias , Rasmussen Dennis , Rass-Hansen Jeppe , Moses Poul Georg , Hansen John
Published: July 2021

Electrolysis is an enabling technology for Power-to-X solutions, where X can be hydrogen or other chemicals, such as carbon monoxide (CO). When electrolysis is combined with renewable electricity, the production of fuels and chemicals can be decoupled from fossil resources which paves the way for an energy system based on 100% renewable energy. It is Haldor Topsoe’s vision to be recognized as a global leader in carbon emission reduction technologies by 2024 and electrolysis technologies will play a key role in achieving this goal.

Compared to other electrolysis technologies, SOEC allows for the conversion of CO2 into useful chemicals (such as CO) at very high efficiencies and at a faradaic yield of 100% (1,2). Haldor Topsoe is commercializing the CO2 electrolysis technology under the tradename eCOsTM: a platform for on-site, on-demand CO generation from CO2 feedstock for customers requiring a reliable and safe feed of carbon monoxide at a scale of up to 1000 Nm3/h. Two identical eCOsTM plants, each with a capacity of 96 Nm3 CO/h will be commissioned in 2021 in Ohio, USA (Fig 1). Once in operation, these two plants will not only be the largest SOEC plants in the world, but also the first SOEC plants sold and operated on fully commercial terms (i.e. without the need for subsidies) (3). Furthermore, with a total active cell area of around 40 m2, the plants will be hitherto the largest demonstration of direct electrochemical conversion of CO2 into chemicals.

In this paper, progress towards the commissioning of the two eCOs plants will be reported, as well as stack- and system-level tests demonstrating long-term operation in dry CO2 electrolysis.

References:

Hauch, R. Küngas, P. Blennow, A. B. Hansen, J. B. Hansen, B. V. Mathiesen, M. B. Mogensen, Science, 370(6513) (2020), doi:10.1126/science.aba6118.

Küngas, J. Electrochem. Soc., 167 (2020) 044508, doi:10.1149/1945-7111/ab7099

Haldor Topsoe. DeLille Oxygen Co. leases two eCOs™ units for cost-competitive onsite CO production, https://blog.topsoe.com/delille-oxygen-co.-leases-two-ecos-units-for-cost-competitive-onsite-co-production (2019)

Figure 1. An eCOsTM Plant capable of producing 96 Nm3 CO/h. The plant is built up of six modules: electrolysis unit, gas supply unit, compressor unit, gas purification unit, cooling water unit, and control unit (the control unit is not shown).

Figure 1
AVL’s SOC Solutions Addressing Current Technology Trends and Drivers Towards Green Electricity Generation and Fuel Production
Authors: Hauth Martin , Reiter Bernd
Published: July 2021

This work presents an overview of AVL’s most recent development activities in the field of SOC based power generation and fuel production. In particular, highlights from ongoing projects will be discussed. Detailed results will be presented in separate papers in the course of this conference to address the main technology and application trends which are currently driving the SOC industry. The main highlights will be the development of a 1 MW Power-to-Liquid plant, a reversible SOC system based on hydrogen operation as well as an ammonia fueled SOFC system.

A thermodynamic analysis as well as the basic plant concept of a fully integrated SOEC-Fischer-Tropsch Power-to-Liquid plant for a highly efficient production of diesel was carried out. The project provides the unique possibility to design the plant by optimizing and integrating both processes, SOEC and Fischer-Tropsch, in the most efficient manner. Compared to existing concepts based on the connection of existing SOEC and FT systems, this approach will enable a significant efficiency boost of the overall plant. Especially, the coupling of the heat integration of both processes will be the key for overall efficiencies of 50-55 %. Eventually, estimates of diesel prices in the range of 1-3 EUR/L are discussed as an alternative to fossil based diesel.

Local hydrogen production and re-electrification via a reversible operated SOC system are investigated in order to capture excess electricity from renewable power generation. The development addresses a 15 kW rSOC system which will be operated in combination with PV under real conditions. Innovative system architectures towards highest total efficiencies (electricity and hydrogen production) are the core of the first phase of the project. Application specific boundary conditions are discussed with respect to its impact on system design.

One of the most heavily discussed trends is the direct utilization of ammonia for power generation in an SOFC system. Green ammonia production is seen as a very promising alternative to conventional fuels to address CO2 reduction while keeping the energy density at a relatively high level as it is needed for example in maritime applications. AVL will present the results of its ammonia based SOFC system development and discuss it in the context of power propulsion and auxiliary power for different ship applications. Furthermore, the efficiency chain as well as a comparison with other technologies such as ICE and PEM will complete the detailed investigation.
The Correlation of EIS and Performance of Button-Size and Industrial-Size Planar SOFCs Under Different Operating Conditions
Authors: Liang Jingjing , Wang Yige , Lyu Zewei , Cui Tonghui , Sun Zaihong , Han Minfang
Published: July 2021

Reversible solid oxide cell (RSOC) is a new technology for energy storage with the advantages of high efficiency and high energy density, combining solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode to achieve two functions in one device. The commercialization of RSOC is limited by the severe degradation of air electrodes during the operation of SOEC. Anode supported cells with yttria-stabilized zirconia (YSZ) electrolytes, Ni/YSZ hydrogen electrodes and perovskite oxygen electrodes with lanthanum strontium cobalt ferrite (LSCF) were tested and the reversible operation has been demonstrated. The electrochemical performance and stability in reversible mode of the cells are demonstrated under 650℃，700℃，750℃ with different composition of fuel gas (30% H2O/70%H2, 50% H2O/50%H2 and 70%H2O/30%H2) and current density (0.5A/cm2 and 1.0 A/cm2) through the experiment research. Post-test is also used to assist in analyzing the degradation mechanism. It is found that the degradation is more severe under SOEC mode at high current density (1.0 A/cm2) and the alternative operation of two modes helps to mitigate the degradation of cells comparing with operating in SOEC mode. Operation under SOFC mode plays a restorative role through reducing the high oxygen partial pressure at the oxygen electrode caused by SOEC mode operation, thus mitigating the degradation of the cell. This study signifies the difference between the SOEC and SOFC mode and provides insight in the operating mechanism of RSOC.
Performance and Processes of Pure CO2 Electrolysis in Solid Oxide Cells
Authors: Dittrich Lucy , Duyster Tobias , Foit Severin , Vinke I. C. , Eichel Rüdiger-A. , De Haart L. G. J. (Bert)
Published: July 2021

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
Performance Investigation and Optimization of a SOEC Stack Operated Under Industrially Relevant Conditions
Authors: Königshofer Benjamin , Höber Michael , Boškoski Pavle , Nusev Gjorgji , Juričić Ɖani , Hochenauer Christoph , Subotic Vanja
Published: July 2021

Solid oxide electrolysis cells (SOEC) are a highly efficient technology for producing green hydrogen using only steam and electricity from renewable sources. However, a variety of different applications and associated operating conditions can cause performance deterioration and microstructural degradation of SOECs. Hereby, various factors such as inlet gas composition, operating temperature or supplied current profile can have a significant different impact on the performance and long-term stability of SOECs. In order to investigate the influence of different industrially relevant operating conditions on the performance of SOECs, a series of experiments was performed on a ten-layer electrolyte-supported stack with an active area of 127 cm2/cell. With the aim of creating a test and results matrix that includes all relevant operating parameters, their influence on performance and optimization potential. As the first dimension of the test matrix, the performance of the stack was investigated at different steam/hydrogen-ratios of between 1 – 9 of the inlet gas composition, thus focusing on high-efficient electrolysis operation at low hydrogen partial pressures at gas inlet. Another dimension was added to the test matrix by varying the operating temperature of the stack between 785 – 835 °C since operation at lower temperatures can hold potential advantages because the total energy demand for maintaining the operating temperature can be significantly reduced. Furthermore, different combinations of anodic and cathodic volume flow were fed to the stack. Hereby, the steam flow was lowered in order to achieve higher steam conversion rates at lower power input. Additionally, the performance of the stack was investigated at varying air volume flows. During the experiments polarization curves and electrochemical impedance spectroscopy (EIS) in combination with analysis via distribution of relaxation times (DRT) were used for characterizing the performance of the single cells within the stack at current densities up to 0.8 A/cm2. The monitoring of the temperature distribution within the stack was realized through thermocouples integrated at the in- and outlet of the gas flow channels as well as through three additional thermocouples mounted within the stack. This study presents correlations between the performance of a SOEC stack and specific industrially relevant operating conditions and proposes optimal operating conditions for different applications with a specific focus on high efficiency as well as low degradation potential.

Figure 1
Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing
Authors: Hedayat Nader , Du Yanhai
Published: July 2021

Tubular solid oxide fuel cells (SOFCs) with one closed-end configuration have high tolerance of thermal cycling owing to the capability of expanding and shrinking freely in response to thermal stresses. Additionally, tubular cells with one closed-end have simple sealing requirements, and enable making the stacks with uniform temperature distribution. In this study, anode supported micro-tubular SOFCs with one closed-end were manufactured successfully by dip-coating and co-firing methods using carbon rods with round end as a template. A dense electrolyte layer was obtained at a co-firing temperature of 1400 °C, followed by cathode deposition and sintering. The prepared micro-tubular SOFCs comprised of Ni-yttria-stabilized zirconia (YSZ), Ni–scandia-stabilized zirconia (SSZ), strontium-doped lanthanum manganite (LSM)-SSZ, and LSM as the anode support, anode functional layer, electrolyte, cathode functional layer, and cathode current collector, respectively. The electrochemical performance and microstructure of fabricated closed-end micro-tubular SOFC was evaluated by electrochemical characterization and scanning electron microscopy. The developed dip-coating method is fast in turnaround time and enables fabricating the one closed-end tubes of various lengths and diameters by co-firing.
Experimental Investigation of Efficiency Maximization in Solid Oxide Electrolysis Systems by Internal Steam and Heat Recovery
Authors: Kruse Nicolas , Tiedemann Wilfried , Hoven Ingo , Deja Robert , Peters Roland , Blum Ludger , Peters Ralf
Published: July 2021

Solid oxide electrolysis cells (SOEC) recently experienced increasing attraction in the context of producing hydrogen from renewable energy. SOEC systems provide one of the highest efficiencies for hydrogen production from water and electrical power. With current cell-technology they can be operated at thermal neutral condition, which means that the cell itself generates no waste heat at all. Therefore the efficiency of the solid oxide electrolysis system is determined by the systems capability to recover heat and steam from the off-gas. The key component for heat recovery in an SOEC system is the steam generator because it is by far the largest consumer of energy beside the solid oxide electrolysis cell stack itself.

In this contribution, the development of a scalable steam generator (Figure 1) and results with a prototype for a reversible solid oxide cell (rSOC) system with 40 kW of power in electrolysis mode will be presented. The steam recovery in this design is accomplished indirectly by reusing the heat of vaporization from condensation of the remaining steam in the off-gas to preheat the feed water (in HX1). The design is based on our long term experience with different types of steam generators for SOEC and a multiphase, multi-component pinch analysis. The pinch analysis shows clearly that a high degree of energy recovery requires focusing on the water preheating and steam superheating. Besides evaluating the optimal heat and steam integration, the prototype allows to investigate other design goals as stability, low steam contamination and high dynamic responsiveness.

Furthermore this contribution discusses the benefits and drawbacks comparted to other approaches and the combination with off-gas recirculation. In the studied configuration a reduction in electrical energy for supplying superheated steam of about 20% is expected. That means at 70% steam utilization a reduction of about 5% of the specific energy demand of the SOEC system.

Besides the cost reduction for cells and stacks, the development of a simple but highly efficient system designs is the key requirement to match the forthcoming demand for viable hydrogen production solutions based on SOEC. The steam supply is a major building block in that respect.

Figure 1. Steam generator with heat and (indirect) steam recovery

Figure 1
Highly Active and Stable a-Site Deficient La0.4Sr0.4Ti0.94Ni0.06O3-δ SOFC Anode Material with in-Situ Exsolved of Ni Nanoparticles
Authors: Kim Kyeong Joon , Lee Jong Jun , Lee Kang Taek
Published: July 2021

La-doped strontium titanates with a perovskite structure are promising candidates of the anode materials for solid oxide fuel cells (SOFCs) owing to their good chemical compatibility with other components and superior redox-stability. Among these La-doped SrTiO3 (LST), A-site deficient LST materials have attracted much interest due to their improved electrochemical characteristics. Recently, exsolution in A-site deficient LST has been intensively studied, because catalytic active and durable metal nanoparticles can be exsolved on the LST surface. In this study, we developed the A-site deficient Ni-doped La0.4Sr0.4TiO3 (LSTN)-Ce0.9Gd0.1O1.95 (GDC) composite anodes, and investigate their electrochemical performance and redox stability on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte-based SOFCs. The maximum power density(MPD) of LSTN44-GDC anode based cell was 0.698 mW cm-2 at 900℃ in wet H2 fuel (3% H2O). Also, during redox cyclic tests combined with long-term stability test, The LSTN44-GDC cell maintained its performance without any degradation. All these results demonstrate that the A-site deficient LSTN-GDC is a promising material for an efficient and stable SOFC anode.
Bi-Layer Structured Co-Ionic Composite Electrolytes Solid Oxide Cells for Stable Fuel Cell and Electrolysis Operations
Authors: Niaz Atif Khan , Lim Hyung-Tae
Published: July 2021

A bilayer comprising BCY (BaCe0.85Y0.15O3-d) - GDC (Gd0.2Ce0.8O2-d) at anode side and BZY (BaZr0.85Y0.15O3-d) - NDC (Nd0.1Ce0.9O2-d) at cathode side, was designed for improving the stability for intermediate solid oxide fuel cells. Two Pt probes were embedded in each electrolyte layer close to anode and cathode sides of electrolyte for the estimation of the local electronic conduction, which is correlated to the cell stability under negative voltage operation caused by cell imbalance. Mixed ionic and n-type electronic conduction was locally developed in the BCY-GDC region near the anode side while mixed ionic and p-type electronic conduction was locally developed in the BZY-NDC near the cathode side. On the other hand, the middle electrolyte region exhibited predominantly ionic conduction which was an effective electrolyte region. Contrary to single layer structured composite electrolytes, the bi-layered composite electrolyte cell was stably operated without electrode/electrolyte delamination under negative voltage conditions, by means of local electronic conduction. Hence, we suggest the composite electrolytes configuration, such as cathode/ BCY-GDC / BZY-NDC / anode, for stable fuel cell and electrolysis operations.
Effect of Sc-Segregation on Transport and Durability Properties of Solid Oxide Fuel Cells
Authors: Kim Hye-Sung , Hussain Amjad , Kwon Beom-Su , Lee Seung-Bok , Lim Tak-Hyoung , Hong Jong-Eun , Park Seok Joo , Joh Dong Woo , Bae Hyung Bin , Song Rak-Hyun
Published: July 2021

In solid oxide fuel cells (SOFC), strontium zirconate (SrZrO3) insulating phase formation between Sr-containing cathode and yttria-stabilized zirconia (YSZ) electrolyte was a long-standing unsolved problem. Though a bilayer strategy with gadolinium doped ceria (GDC), or the use of samarium doped ceria (SDC) as a protective layer have been reported to improve stability and performance, the effectiveness of these processes at preventing secondary phase formation is still open to debate. In this study, focusing on Sc and Ce co-doped ZrO2 (ScCeSZ), we found that nanometer-scale Sc-segregation layers are present at co-sintered GDC/ScCeSZ interfaces. Utilizing atomic-column resolved scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical measurements, we successfully demonstrate that SOFC cells consisting of Sc-segregated interfaces show a remarkable increment of long-term durability.
Perovskites Doped with Small Amounts of Noble Metals for IT-SOFCs
Authors: Marasi Martina , Panunzi Anna Paola , Duranti Leonardo , D'Ottavi Cadia , Di Bartolomeo Elisabetta
Published: July 2021

Solid oxide fuel cells (SOFCs) have a great potential among the emerging energy conversion technologies because they can efficiently convert various types of fuel (hydrogen, methane, CO, biogas) into electrical energy in the 750-850 °C temperature range. The choice of electrodes remains a challenge because most metal oxides suffer from low chemical stability and low electrocatalytic activity toward oxygen reduction reaction (ORR) in the intermediate temperatures (IT) range (500-700 °C) [1]. In this view, perovskite oxides (ABO3) have shown excellent properties in terms of thermal stability, compatibility with other cell components, low production cost and, most importantly, great flexibility [1]. La0.6Sr0.4FeO3-δ, (LSF) perovskite oxide have been widely investigated for the high electrical conductivity and the electrochemical properties [2]. However, the main drawback is the poor activity towards ORR in the IT range, as most iron-based perovskite oxides [3]. The B-site doping with noble metal catalysts can sensitively improve the properties and make the compounds suitable for electrode application.

The addition of small amounts of Ru or Pt into LSF structure can be an effective approach to improve the electrocatalytic properties [4,5]. Specifically, we synthesized B-site doped LSF powders with very low amounts (<5%mol) of Ru and Pt by using solution combustion synthesis (SCS) method. The synthesized powders were calcined at quite low temperature (750 °C) to get as high as possible surface area (>15 m2/g). All compounds showed a single perovskite phase. As reported in Fig. (a), the addition of Ru and Pt in the structure causes a progressive shift of the XRD peaks to lower 2θ angles indicating the perovskite lattice expansion due to the substitution of Fe4+/ Fe3+ sites with larger Ru and Pt ions.

To assess the electrocatalytic activity, the compounds were investigated in oxidizing conditions using electrochemical impedance spectroscopy (EIS) analysis. Fig. (b) shows the Arrhenius plot of area specific resistance (ASR) values of LSFRu and LSFPt perovskite oxides. The ASR values were measured on LSFM/La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)/LSFM (M=Ru, Pt) symmetric cells in the temperature range 550-800 °C. The insertion of a very low amount (1%mol) of Pt or Ru significantly reduces the polarization resistance, confirming the beneficial effect of noble metal ions on ORR activity. All these features suggest that very low Pt and Ru doping positively affects the structural and electrocatalytic properties valuably for cathodic applications.

[1] Hwang J, Rao R.R. (2017). Science 358:751-756

[2] Hansen KK, Mogensen M (2008). ECS Trans 13:153–160

[3] Chavan SV, Singh RN (2013). J Mater Sci 48:6597–6604

[4] Fan W, Sun Z. (2016) RSC Adv 6:34564

[5]Shaoli G., Hongjing Wu, (2015),Catalysts, 5, 366-391

Figure 1
Influence of La0.5Ba0.5CoO3 Anode Thickness on Hydrogen Production for Solid Oxide Electrolyzer Cells
Authors: Chin Wei-Cheng , Lee Yi Hsuan
Published: July 2021

In this study, La0.9Sr0.1Ga0.8Mg0.2O3-
d (LSGM) and Ni-LSGM were applied as the electrolyte and cathode materials for solid oxide electrolyzer cell (SOEC), respectively. The different thicknesses of anode material, La0.5Ba0.5CoO3 (BLC5), were utilized to observed cell performances under 20% H2O-2% H2-78% N2 atmosphere at 800°C. The correlations between the faradaic efficiency of hydrogen production and anodic thickness were observed. Also, I-V curves were measured with different anodic thickness samples. According to I-V curve results, cell performances could be considered as similar regardless of thickness. However, the faradaic efficiency of hydrogen production was relatively low with the thin-thickness sample. It is indicated that insufficient reaction areas induced to lower hydrogen generation efficiency.
Performance Analysis of Ammonia in Solid Oxide Fuel Cells
Authors: Nuggehalli Sampathkumar Suhas , Sun Xiufu , Joris Steve , Van herle Jan , Middleton Peter Hugh , Frandsen Henrik Lund
Published: July 2021

The transition of the marine propulsion system towards alternative fuels is mandatory to offset carbon emission. Among the alternative fuels, ammonia is carbon-free and can be produced in sustainable ways. Ammonia has 17.8% hydrogen (wt %) and is easily liquified at 25°C and 8 bar pressure. The two-stroke internal combustion engines currently used in the marine sector reach efficiencies of about 50% but generate substantial polluting emissions. Solid oxide fuel cells generate electricity with efficiencies greater than 50 % and can use ammonia as fuel.

In this work, a single-cell SOFC was characterised using in-situ ammonia decomposition reaction (Int-ADR) and compared with ex-situ ammonia decomposition reaction (Ext - ADR; composition - N2:H2 = 1:3), and pure hydrogen (H2 100%; composition - H2 = 100%), between temperatures of 750 °C to 850°C. The constant load tests performed at 750°C with 84% fuel utilization revealed that the LHV efficiency of the ammonia fed SOFC was 58%. The J-V characteristics showed similar performances for the three compositions at different temperatures and flowrates. The open-circuit voltage (OCV) of Int-ADR was similar to that of Ext- ADR, confirming that usage of ammonia as fuel in the Ni-YSZ anode involved two steps, (i) decomposition of ammonia into nitrogen and hydrogen, followed by (ii) electrochemical conversion of the hydrogen into steam.

The electrochemical impedance spectroscopy (EIS) results showed that the polarisation resistance (Rp) decreased by 15% over this temperature range. The total flowrate of 80 Nml
min

-1
of ammonia for Int-ADR, 160 Nml
min

-1
for Ext ADR and 120 Nml
min

-1
for H2 100% were chosen after performing distribution of relaxation time (DRT) analysis on changing total flowrates at 775 °C. The DRT coupled with complex nonlinear least-square (CNLS) analysis for the temperature range of 750-850°C revealed that the charge transfer resistance reduced by 66%, while the gas conversion resistance increased by 12% due to better evacuation of steam. The Arrhenius plot of DRT peak resistances revealed that the polarisation activation energy was the same for the three gas compositions, at 16 kJ
mol

-1

.

Figure 1
Operando Diagnostics of Solid Oxide Fuel Cell Stack Via Electrochemical Impedance Spectroscopy Simulation-Informed Machine Learning
Authors: Le Giang Tra , Mastropasqua Luca , Adler Stuart B. , Brouwer Jack
Published: July 2021

Electrochemical energy conversion based on electrolysis and fuel cells offers one possible technological route to long term storage of renewable electricity. However, a major factor limiting commercial deployment is uncertainty about the long-term durability of these technologies in real-world operation. To be successful, these technologies must incorporate ways to pre-detect and mitigate failure. By coupling well-known electrochemical techniques with novel data analysis tools, we believe it is possible to identify key defects and pre-failure conditions in operating fuel cell systems, allowing these systems to be serviced or replaced before catastrophic failure and downstream consequences can occur. Through experimental study on a solid oxide fuel cell (SOFC) short stack of 6 cells, we identify the mechanisms contribute to this system electrochemical impedance spectroscopy (EIS), by carrying out pristine cell/stack tests at different operating conditions (gas partial pressure, current, temperature). Information gathered from the experiments informs a coarse-grained physics-based model, which provides good agreement with experimental data. We use our coarse-grained model to simulate different possible failures in the cell to explain the EIS we collected of failed/degraded cells. We applied a machine learning approach to this process of failure identification by training a model to detect failure on a database of simulated impedance of healthy and failed SOFC. The model robustness is demonstrated as it well predicts experimental data.

Figure 1
The 3D Reconstruction and Simulation of Solid Oxide Fuel Cell Anode
Authors: Liu Shixue , Liu Zhijing , Yang Ying , Zhang Lin , Huang Rui , Zhu Jiang , Zhang Shuxing
Published: July 2021

The 3D Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) technique has been used to study the ceramic microstructures with the accuracy of tens of nanometers. There are several reports about the 3D reconstruction about the Ni-YSZ electrode in SOFC or SOEC mode (1-3). In this work, samples taken from full size, 10×10 cm2, solid oxide fuel cell (SOFC) single cells were reconstructed with the FIB-SEM tomography. Three samples were chosen from the same production batch, including a cell without reduction, a cell with 5 hours reduction and a cell with 100 hours test with humidified hydrogen, respectively. Figure 1 shows the SEM micrograph and reconstructed anode for the cell after 100 hours test. Different from the button cells, the full size anode-supported SOFC need a strong support layer and a smaller porosity is also acceptable. The lattice Boltzmann method (LBM) was used to simulate the physical processed in the reconstructed porous electrode. The 3D microstructure was remeshed to cubic voxels for numerical analysis. The triple-phase-boundary length was automatically identified and the parameters in the exchange current density equation were fitted to the polarization curves. Detailed results will be submitted in the full length draft.

References

1. Z. Jiao, N. Shikazono, and N. Kasagi, J. Electrochem. Soc., 159 (3), B285 (2012).

2. M. Trini, P.S. Jørgensen, A. Hauch, J.J. Bentzen, P.V. Hendriksen, M. Chen, 3D microstructural characterization of Ni/YSZ electrodes exposed to 1 Year of electrolysis testing, J. Electrochem. Soc., 166 (2), F1 (2019).

3. M. Trini, A. Hauch, S. De Angelis, X. Tong, P. Vang Hendriksen, and M. Chen, J. Power Sorces, 450, 227599 (2020).

4. D. Kanno, N. Shikazono, N. Takagi, K. Matsuzaki, and N. Kasagi, Electrochimi. Acta, 56, 4015, 2011.

Figure 1
Initial-Stage Performance Evolution of Solid Oxide Fuel Cells Based on Polarization Analysis
Authors: Wang Yige , Lyu Zewei , Han Minfang , Sun Zaihong , Sun Kaihua
Published: July 2021

Solid oxide fuel cell (SOFC) has attracted more and more attention in recent years due to its high efficiency and low pollution. However, lifetime and stability are still limitations that affect further commercial applications of the SOFC technology. Therefore, it is critical to establish an online monitoring and analysis method to study the mechanism of SOFC performance evolution. The initial performance evolution of SOFCs is more apparent and non-linear than the subsequent stages, affecting the performance calibration and trading, especially for the industrial large-size cells and stacks. In this study, a single cell with an effective area of 100 cm2 was tested in Xuzhou HuaTsing Jingkun Energy Co. Ltd. under the constant current condition with humidified H2 for 80 hours after the NiO-YSZ anode was reduced for 4 hours. During the operation, the EIS data under different DC electrical current biases (0, 20, 50, 100, 300 mA cm-2) and j-V curve were recorded at 24-hour intervals. The EIS data were decomposed by the distribution of relaxation time (DRT) method, and the evolution of each electrode process under different polarization conditions was obtained. For the first 22 hours, the voltage under galvanostatic test and the power density at 0.7 V increased. The performance improvement is mainly due to the increase of the OCV and the decrease of the anode gas diffusion as well as gas conversion resistance, which can be attributed to the further anode reduction. The long reduction time is related to the low porosity and fine granularity of the Ni-YSZ anode, which was preliminarily verified by FIB-SEM. During the next 60 hours, the voltage dropped rapidly, and the power density at 0.7 V decreased by 27%. This nonlinear degradation was mainly caused by the weakening of the charge transfer reactions at the anode and the O2 surface exchange kinetics at the cathode. With the increase of current density, the deterioration of anode reaction gradually became the dominant factor for the increase of polarization impedance.