bluuebunny/crossref_metadata_2025_split 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
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.
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.
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
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
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
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