bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Redox Behaviour of Double Perovskite PrBaMn2O5+δ
Authors: Felli Andrea , Trovarelli Alessandro , Boaro Marta
Published: July 2021

Double perovskite PrBaMn2O5+δ (l-PBM) has recently shown interesting properties as electrode for solid oxide fuel cell (SOFC) technology, such as high stability, good ionic and electronic conductivity in both oxidising and reducing atmosphere [1]. It is obtainable by the reduction at high temperature of the starting mixed cubic-hexagonal perovskite Pr0.5Ba0.5MnO3-δ (m-PBM), where the Pr3+ and Ba2+ cations are stochastically disposed in the A-site of the lattice. Conversely, the double perovskite shows ordinated and alternated layers of PrO and BaO, intercalated by MnO2 planes [2].

Here, we use a multi analytical approach and temperature programmed techniques of analysis (temperature programmed X-ray diffractometry, TP-XRD, temperature programmed reduction TPR, thermogravimetric oxidation and reduction analysis, TGA) to deeply study the phase transition between the m-PBM and the l-PBM. m-PBM sample was prepared by an auto-combustion based citrate procedure [3] and exposed to consecutive oxidation and reduction cycles at high temperature to understand the effect of oxidizing and reducing atmospheres on structural changes and stabilization of the layered double perovskite. By in
situ XRD analysis we discovered the existence of a metastable cubic structure (c-PBM), which is formed from the direct oxidation of l-PBM at SOFCs operating temperatures (750 °C). Furthermore, we demonstrated the reversibility of transition from c-PBM to l-PBM during several oxidation and reduction cycles. TPR results confirmed the c-PBM to l-PBM reversibility, and the TGA characterization showed a fast transition between l-PBM to c-PBM. The oxidation of l-PBM to c-PBM seems pivotal for the stabilization of the layered structure. The results are discussed in view of a controlled exsolution of metal phase when the B site of m-PBM is doped with Co, Ni and/or Fe and in the perspective to develop versatile electrodes for SOE/SOFC applications.

References

[1] S. Afroze, A. Karim, Q. Cheok, S. Eriksson, and A. Azad, Front. Energy, 13 (2019) 770-797

[2] S. Sengodan et al.
Nat. Mater., 14 (2015) 205–209.

[3] L. Zhao, K. Chen, Y. Liu, and B. He, J. Power Sources, 34 (2017) 313-319.

Acknowledgements

Authors thank MIUR for funding (PRIN project-DIRECTBIOSOFC, 2017FCFYHK, 2019-2022)
First-Principle Study of Hole Localization in La1-XSrxFeO3-δ
Authors: Hartmann Cintia , Laurencin Jérôme , Geneste Grégory
Published: July 2021

The durability and efficiency of Solid Oxide Fuel Cells or Electrolysis Cells (SOFC/SOEC) depend on the reaction mechanisms taking place within the electrodes. These mechanisms combine a series of elementary steps including mass and charge transfers along with chemical and electrochemical reactions. These processes are still not precisely understood as they involve complex physical phenomena occurring at the atomic scale. Therefore, it is still required to carry out some fundamental studies to better unravel the basic mechanisms involved in the material properties such as the electronic or ionic conductivity, etc. For such basic investigations, the ab-initio modeling is nowadays recognized as a powerful and relevant method. In this context, this work aims to provide deeper insights into the mechanisms at atomic scale by using Density Functional Theory (DFT) calculations.

La1-xSrxCoyFe1-yO3-δ (LSCF) and LSCF-based materials are Mixed Ionic-Electronic Conductors, which are commonly used as oxygen electrode for the SOFCs/SOECs [1]. LSCF is a perovskite oxide that contains two transition metals, i.e. cobalt and iron. Owing to the complexity of this system, our work was first devoted to the parent material La1-xSrxFeO3 (LSF), which was here studied by DFT+U calculations. A special focus was paid to finely describe the localization of holes and the formation of oxygen vacancies as a function of the oxygen partial pressure.

Electronic structure calculations were carried out at different strontium contents x (x=0.0, x~0.1, x~0.4, x~0.6). Progressive changes during Sr substitution were evaluated in the Density Of State (DOS). The probability densities of the gap-state wave functions were visualized in order to describe the spatial extension of the localized electron holes. The oxygen vacancy concentration, which is related to the oxygen diffusion coefficient, was calculated and coupled to a defect model in order to give at any temperature and partial oxygen pressure the defect concentration. This work will be extended to the typical LSCF material to provide some essential insights into the chemistry of this imperfect solid.

[1] S. P. Jiang, International Journal of Hydrogen Energy, 2019, 44, 7448 – 7493
Performance and Stability of Nickelates Based Oxygen Electrodes for Solid Oxide Cells
Authors: Vibhu Vaibhav , Vinke I. C. , Eichel Rüdiger-A. , De Haart L. G. J. (Bert)
Published: July 2021

The K2NiF4-type nickelates i.e. Ln2NiO4+δ
(Ln = La, Pr, Nd) and La1.5Pr0.5NiO4+δ
have shown promising behaviour as oxygen electrodes for solid oxide cells [1]. These compounds show high anionic bulk diffusion (D*) as well as surface exchange coefficients (k*), combined with good electrical conductivity and thermal expansion properties matching with those of other components (electrolyte, interconnect etc.) of the cell. In order to further enhance the physico-chemical properties, electrochemical performance of these nickelates as oxygen electrode, we performed the substitution of nickel by other transition element such as cobalt. Two compositions of Ln2Ni1-xCoxO4+
δ
(Ln = La, Pr, Nd) and La1.5Pr0.5Ni1-xCoxO4+
δ
(x=0.1 and 0.2) were considered (as higher cobalt containing nickelates are difficult to synthesize under air atmosphere) and completely characterized using several methods. Finally, the symmetrical half-cells (8YSZ/GDC/electrode) as well as single cells (Ni-YSZ/8YSZ/GDC/electrode) were prepared and electrochemically characterized using DC- and AC-techniques in the temperature range 700 - 900 °C.

The current-voltage characteristics of the single cells show an increase in the performance with increasing cobalt content in both SOFC and SOEC operation for Ln2Ni1-xCoxO4+
δ
(Ln = La, Pr, Nd) and La1.5Pr0.5Ni1-xCoxO4+
δ
electrodes. The best cell performance is obtained with 20% cobalt substitution for all four nickelates. However, the performance of Pr2Ni0.8Co0.2O4+
δ
(PNCO20), La1.5Pr0.5Ni0.8Co0.2O4+
δ (LPNCO20) and Nd2Ni0.8Co0.2O4+
δ
(NNCO20) are similar and far better than La2Ni0.8Co0.2O4+
δ
(LNCO20) [2,3]. For instance under SOFC operation at 900 °C, the maximum power densities obtained at 0.6 V are 1.8, 1.9 and 1.91 W.cm-2 for NNCO20, LPNCO20 and PNCO20 single cells, respectively. Under SOEC conditions, the cell current densities obtained at 900 °C with an applied voltage of 1.5 V are 3.0, 2.84 and 2.8 A.cm-2, respectively for PNCO20, LPNCO20 and NNCO20 single cells with 50% H2O and 50% H2 feed gas mixture. The performance of these electrodes are better than the commercial single cell containing state of art (La,Sr)(Co,Fe)O3 oxygen electrodes. Moreover a large improvement in durability is also observed for the single cells containing cobalt substituted nickelates.

Results including physico-chemical and electrochemical properties of these materials, electrochemical performance as oxygen electrode, long term stability under electrolysis conditions and post-test analysis (using SEM-EDX, XRD) will be presented and discussed in detail.

References:

[1] V.Vibhu et al., Journal of Energy Chemistry, 46 (2020) 62.

[1] V.Vibhu et al., Journal of Power Sources, 444 (2019) 227292.

[2] V.Vibhu et al., Journal of Power Sources, 482 (2021) 228909.
Lifetime Prediction and Rapid Design Evaluation of SteelCell® Stacks Using Advanced Multiphysics Modeling
Authors: Gawel Duncan , Leah Robert , Thandi R , Reade Gavin , Howlett Jack , Lawrence Nick , Mukerjee Subhasish , Selby Mark
Published: July 2021

A major challenge in the development of SOC stacks designed for long operating lives of the order of 50-100kh is predicting through-life performance without running durability tests under a particular set of operating conditions for 5-10 years. Whilst this is ultimately necessary it is not practical for system design purposes. It is also very costly to have to repeat experimental validation for a change in operating conditions or a new generation of stack technology.

To address this issue Ceres Power has invested heavily in Multiphysics simulation capability for stacks using COMSOL Multiphysics, incorporating fluid dynamics, heat transfer, electrochemical and heterogeneous chemical reactions.

The multiphysics model has the capability to simulate multiple scales from a single cell to a full-size 5kW stack. Start-of-life cell performance as a function of temperature and fuel composition is calibrated from extensive high-resolution AC impedance measurements on button cells, with the predicted stack performance experimentally validated using highly instrumented stacks.

A further challenge in stack simulation is to simulate through life performance changes due to multiple cell degradation mechanisms, to predict stack life and through-life performance and efficiency. To address this issue, Ceres Power has invested significant effort into understanding mechanisms of performance degradation at the fundamental cell level, generating mathematical models of degradation as a function of time, temperature and current density. Most degradation mechanisms observed are common to all SOFCs cells, such as poisoning of both electrodes and increases in ohmic resistance due to oxide scale growth.

A pseudo-dynamic solver has been applied to the multiphysics model applying the models of cell degradation to be applied to a full stack, including a control loop changing the thermal boundary conditions through life to maintain a constant nominal stack temperature. To maintain tractable simulation times, most of the physics of the stack is treated as steady-state, with only those mechanisms changing over a timescale of hundreds to thousands of hours solved dynamically. Using this approach, tens of thousands of hours stack operation can be simulated in a few tens of hours of CPU time on a high-performance server even at the full 5kW stack scale.

The dynamic multiphysics degradation model has been validated against through-life performance tests. This is a powerful tool which allows rapid evaluation of the likely impact of operating a stack in a condition other than ones in which extensive test data already exist.
Effects of Flow Channel Arrangement and Electrolyte Thickness on Thermal Stress for Planar Solid Oxide Fuel Cell Stacks
Authors: Zheng Jianmin , Xiao Liusheng , Chen Ming , Yuan Jinliang
Published: July 2021

Typical operating temperature for solid oxide fuel cells (SOFC) is between 700~800°C. A large temperature gradient and thermal stress caused by internal losses and electrochemical reactions may cause SOFC stack performance degradation and even structural damage, which has become a hindrance to its applications.

In this study, a three-dimensional multiphysics CFD (computational fluid dynamics) model is developed and applied for a planar SOFC stack to study the temperature and thermal stress distribution, as well as effects of structure and design parameters, including the flow channel arrangement (e.g., co- and count-flow) and thickness of the electrolyte layer. The stack is composed of three-unit cells, metallic interconnect layers, sealing and anode/cathode current collectors.

The simulation results reveal that the temperature difference in the counter-flow mode is smaller and the thermal stress is lower than those in the co-flow mode. The overall performance of the stack is better when the electrolyte layer thickness becomes smaller, but the stack temperature and the temperature gradient become higher. In addition, a large temperature gradient due to the thin electrolyte layer leads to a significant increase of the thermal stress in the electrolyte. The findings and research method from this study can be applied to optimize the design of the stack structures, by consideration of the maximum thermal stress and its distribution.

Acknowledgements

This work is supported by the National Key Research and Development Project of China (2018YFB1502204), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048).

References

1. M. Peksen, Progress in Energy and Combustion Science, 2015; 48: 1-20.

2. K. Eichhorn Colombo, V. Kharton, F. Berto, et al., Computers and Chemical Engineering,2020; 140: 106972.

3. P. Pianko-Oprych, T. Zinko, et al., Journal of Power Sources, 2015; 300: 10-23.

4. J. Robinson, L. Brown, R. Jervis, et al., Journal of Power Sources, 2015; 288: 473-481.

5. L. Chang, H. Liu, Y. Shiu, et. al., Journal of Power Sources, 2010; 195: 1895-1904.

6. A. Selimovic, M. Kemm, T. Torison, et. al., Journal of Power Sources, 2005; 145: 463-469.

7. M. Xu, T. Li, M. Yang, et. al., Science Bulletin, 2016; 61: 1333-1336.

8. C. Lin, L. Huang, L. Chiang, Y. Chyou, Journal of Power Sources, 2009; 192: 515-524.

9. M. Peksen, International Journal of Hydrogen Energy, 2013; 38: 553-561.

10. X. Fang, Z. Lin, Applied Energy, 2018; 229: 63-68.

11. D. Cui, M. Cheng, Journal of Power Sources, 2009; 192: 400-407.

12. Q. Li, Z. Xu, M. Cheng, et al., Modern Physics Letters B, 2020; 34(15): 23.

13. W. Zhang, D. Yan, J. Duan, et al. International Journal of Hydrogen Energy, 2013, 38(35): 15371-15378.

14. Y. Zhang, W. Jiang, S. Tu, et al., International Journal of Hydrogen Energy, 2018, 43(9): 4492-4504.

Figure 1
First-Principles Calculation and Multi-Scale Observation for a Carbon Deposition on a SOFC Anode Near the Interface
Authors: Watanabe Hirotatsu , Ogura Teppei , Hanamura Katsunori
Published: July 2021

The nickel/yttria-stabilized zirconia (Ni/YSZ) and nickel/scandia-stabilized zirconia (Ni/ScSZ) have widely used as an anode for solid oxide fuel cells (SOFCs). The high operation temperature allows an SOFC to operate on a wide range of fuels, including hydrocarbons and coal syngas. Ni is also a catalyst for carbon deposition reactions which destroy the anode microstructure. Meanwhile, the carbon deposited on the electrode can be used for different ways. It is important to control the carbon deposition on the electrode; therefore, the carbon deposition model needs to be developed.

In this study, carbon deposition site in the Ni/YSZ and Ni/ScSZ was studied through first-principles calculation and multi-scale observation using SEM and TEM. Observation showed that the carbon deposition was progressed not in the overall Ni surface but in the specific sites such as the interfaces and Ni(211) facet at low temperature. The carbon deposition rate strongly depended on the electrode structure at microscales. All calculations here are performed employing the periodic density functional theory (DFT) method implemented in the Vienna Ab-Initio Simulation Package (VASP). The Ni/YSZ and Ni/ScSZ atomic models are developed to discuss the CH adsorption which is the initial step of the carbon deposition. The CH adsorption energy in the concentrated vacancies at the Ni/YSZ interface was much lower than that in the Ni(111) facet, indicating that concentrated vacancies become the active site of the carbon deposition. However, the CH adsorption energy in the dispersed vacancies are almost the same as that in the Ni(111) facet. It is shown that vacancy patterns play an important role in the carbon deposition rate. The impact of dopant in the anode on the carbon deposition is also studied. DFT calculation gives an useful hint to develop the carbon deposition model with considering the electrode structure.
The Influence of Humidity Content on Ferritic Stainless Steels Used in Solid Oxide Fuel Cell Under Dual Atmosphere Conditions at 600°C
Authors: Gagliani Luca , Visibile Alberto , Gündüz Kerem Özgür , Svensson Jan-Erik , Froitzheim Jan
Published: July 2021

In the last few years, the interest in the development and application of green energy harvesting, storage and production technologies, boosted the research activities to fulfill the demand of better performing, more reliable and cost-effective materials. In the field of Solid Oxides Fuel Cells (SOFC), many efforts have been spent on the interconnects, that are used to electrically connect single cells to obtain stacks for higher output voltages. Interconnects are exposed simultaneously to fuel gas (i.e., H2) and oxidizing (humid air) atmospheres (dual atmosphere) at a working temperatures in the range between 600°C and 800°C. Nowadays, chromia forming ferritic stainless steel (FSS) has been selected as material for interconnects due to its ease of fabrication, affordability and electrical conductivity. In air the material forms a protective chromia layer that reduces further corrosion. However, in dual atmosphere conditions, FSS commonly show fast and unexpected degradation, on the air side, especially at 600°C.

The mechanism behind the dual atmosphere effect is still not fully clear, but previous works highlighted the importance of pre-oxidation time, exposure temperature, humidity and surface finishing. Until now, major efforts have been spent in studying the long-term behaviour, with the aim to identify a long-lasting interconnect material. To successfully overcome the effects of dual atmosphere-induced corrosion, it is of fundamental importance to investigate how the corrosion phenomenon starts and evolves. In this work, the initial stages of dual atmosphere breakaway corrosion at 600°C were investigated for selected FSS alloys. The samples were exposed under controlled conditions which resemble those of SOFC (Ar-5%H2 + 3%H2O//FSS//air + 3%H2O). The oxide scales were further investigated by means of Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) analysis. Experiments with different exposure times were performed (i.e., up to 12 hours) and the influence of temperature ramping was studied.

Several parameters were evaluated, like the effects of chromium content, the role of sample thickness and the influence of trace elements in different alloys and different batches of the same alloy. Implications of grain orientation at the surface, as well as of pre-oxidation treatment were investigated too.
Lanthanum Strontium Cobaltite-Alumina Fiber Composite Contact Material for Solid Oxide Fuel Cells
Authors: Chou Yeong-Shyung , Jin Tongan , Canfield Nathan L , Bonnett Jeff , Choi Jung Pyung , Hardy John S
Published: July 2021

Lanthanum strontium cobaltite (LSCo) is considered a good candidate as cathode contact materials for SOFC applications, due to its high electrical conductivity as compared to the standard LSM materials. However, it suffers very poor thermal cycle stability because large mismatch in CTE. To overcome the large residual stress, we proposed to use strong and short alumina fiber to enforcement the LSCo matrix. Alumina in vol% from 2.5 to 20% were formulated and prepared for sintering study, thermal expansion coefficient measurement, phase characterization, bulk strength, and contact strength evaluation before and after 10 deep thermal cycles. Results showed the presence of rigid alumina fiber did retard the densification of LSCo matrix substantially at high alumina content. Bulk strength showed increasing trend at low alumina content but decreased at high alumina v%, likely due to severe retardation in densifications. Contact strength on 1”x1” bilayer showed the strong bonding at low alumina v% while good thermal cycle stability was observed. The candidate composite was further tested in a stack fixture using 2”x2” cell. Results of impedance versus cycling and microstructure and fracture analysis will be discussed to assess the validity of fiber reinforced LSCo as contact material.
Repair Joining of Glass-Ceramic Sealants for SOC Stacks
Authors: Gross-Barsnick Sonja , Malzbender Jürgen , Fang Qingping
Published: July 2021

A new concept has been developed to repair leaking solid oxide cell (SOC) stacks. Conventionally, the stacks are joined with a glass-ceramic sealant before they are taken to operation. Once they start leaking through the sealant, they have become unusable. This approach aims to prevent the scrapping of valuable aggregates.

A composite sealing material composed of a glass matrix “H” based on the BaO-CaO-SiO2 system with yttrium-stabilized zirconia fibers as filler material was used for this study. The sealant tends to crystallize slowly at 800 °C forming a multi-component glass-ceramic of a finely dispersed microstructure. The melting temperature of the crystallized material was investigated by means of differential scanning calorimetry (DSC). Beside of the glass matrix powder which was crystallized by heating to 850°C and dwelling for 100 h, the state-of-art sealing material was used as green foils of the composite mixture with fibers. Sandwiched samples of two Crofer22APU plates of 50x50 mm² were joined with the two types of sealing materials, followed by forcibly breaking of the samples and repair joining at different temperatures between the onset and peak temperature of melting of the glass-ceramic obtained by DSC. Gas-tightness measurement was performed by helium leakage detection at room temperature and the broken samples were investigated by optical microscopy. The optimal thermal treatment parameters were chosen on behalf of gas-tightness and porosity. Cross-sections were prepared after repair joining at 930°C for 10 h and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) was carried out. The microstructure shows a high amount of residual glass phase with clusters formed of zirconia-silicate needles. The reaction zone to the steel is of a similar thickness in comparison to standard joining at 850°C, but is clearly delineated from the sealing material. Close to the three-phase boundaries of metal/glass/air a homogeneously distributed closed porosity is found while the pores have gathered to flattened enlarged voids in the middle of the joining gap.

The impact of these microstructural findings on the strength of the joints are now investigated by means of torsion shear tests on hour-glass shaped Crofer22H samples joined in a ring contour. The strength data will be compared to the standard joining procedure and thermally aged samples (800°C for 1000h). Meanwhile an upscaling of the joining geometry using dummy plates of the size of window frame design (H20-design) stacks was performed and the result of gas-tightness measurements will be reported. In case of successful repair of dummy plates, this promising concept will be proofed with a 20-layer stack (internal number: H2020-02), which showed measurable leakage through sealant after start-up procedure.
Improving Current Collection of Tubular Solid Oxide Fuel Cells
Authors: Feng Hai , Panthi Dhruba , Du Yanhai
Published: July 2021

Solid Oxide Fuel Cells (SOFCs) are electrochemical devices with solid electrolyte materials that convert chemical energy in fuels into electrical energy. Tubular SOFCs (T-SOFCs) is one of the major SOFC configurations which has the advantages of good thermal conductivity, easy to seal and shorter start-up time. However, challenges remain in effectively collecting the current inside the tubular cells. Developing an efficient, easily applicable and cost-effective collector is imperative. The properties of a desired current collector are to: reflect the fuel cell performance, be able to withstand the fuel cell’s high working temperature environment, protect the fuel cell from damage, simplify the current collector application procedure, expand the contact surface between the tube and the current collector, and save cost.

We have designed a current collector and identified the materials for inside tube current collection with desired characteristics such as high temperature tolerance, low electrical resistance, and low cost. The research focused on the effectiveness of the current collector and its durability at various fuel cell operation conditions. The design achieved a peak power density at 0.7V of 0.21W/cm2 at the temperature of 700oC for a conventional tubular SOFC with material set of Ni+8YSZ‖YSZ‖LSM. Comparing to the general metal (nickel, silver) current collectors, the studied material can reduce the cost from hundreds of dollars per yard to $0.13/yard. The paper will discuss the design and the cost-effective material selection of the current collector which provides a potential path for the commercialization of tubular SOFC technology.
Electrochemical Characterization of Intermediate-Temperature Solid Oxide Fuel Cells with PVD-Coated Electrolyte
Authors: Solovyev Andrey , Burmistrov Ilya Nikolaevich , Rabotkin Sergey , Shipilova Anna , Yalovenko Dimitriy Vladimirovich , Semenov Vyacheslav , Bredikhin Sergey Ivanovich
Published: July 2021

Intermediate temperature solid oxide fuel cells (SOFCs) working in the range of 600–800°C are interesting because they allow the expansion of the choice of materials that can be used, decrease system cost, and reduce the corrosion rate of system components [1]. The thickness of the electrolyte should be reduced, so reducing the area-specific resistance of the fuel cell for working in this temperature range. Physical vapor deposition methods, such as magnetron sputtering are used to produce thin-film electrolytes [2].

This work is an extension of our previous efforts focusing on scaling the technology of magnetron deposition of electrolyte to large-area cells [3]. It is known that area-specific resistance of small button cells is much less than that of industrial-sized planar anode-supported SOFC cells (10 cm×10 cm or greater). Such difference in ASR is due to large ohmic losses in a SOFC stack that are highly dependent on contact resistance at the cathode/bipolar plate interface. For example, the power density of our 10 cm×5 cm cell with magnetron sputtered yttria-stabilized zirconia (YSZ)/gadolinium-doped ceria (GDC) bilayer electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Gd0.1Ce0.9O1.95 (LSCF/GDC) cathode was 430 mW/cm2 at 0.7 V and at 750°C [4]. This value was about 40% of that of the 2 cm diameter button cell (1025 mW/cm2) with a similar structure and composition. The area-specific resistance of the former cell was 0.54 Ohm·cm2, while it was 0.2 Ohm·cm2 for the latter one.

The goal of this work is to increase the performance of the large-area cell with PVD-deposited electrolyte by improving the structure and composition of the cathode active and contact layers. 4-µm-thick YSZ electrolyte and 2-µm-thick GDC barrier layer were deposited on the 5 cm×5 cm commercial NiO/10ScCeSZ anodes (KCERACELL CO., Korea) by means of reactive magnetron sputtering. LSCF/GDC cathode active layer with an active area of 4 cm×4 cm was screen printed onto the electrolyte. Electrochemical investigations were performed in the temperature interval of 600–800 °С. Figure shows the resulting performance – I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte. High power densities of 0.29, 0.55, 0.83, 1.16 и 1.4 W/cm2 were achieved at 0.7 V and at 600, 650, 700, 750 and 800°C, respectively.

Acknowledgements. This work was funded by the Russian Science Foundation (Grant No. 17-79-30071).

[1] D. J. L. Brett et al., Chem. Soc. Rev., 37, 1568 (2008)

[2] S. Sønderby et al., Surf. Coat. Technol., 240, 1 (2014)

[3] A. Solovyev et al., J. Electrochem. En. Conv. Stor., 15(4), 044501 (2018)

[4] A. Solovyev et al., Fuel Cells, 17(3), 378 (2017)

Figure 1: I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte.

Figure 1
Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)
Authors: Williams Mark , Song Xueyan , Gemmen Randall
Published: July 2021

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression. SOEC and EHC have been integrated into an ECN in a series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC H-SOEC EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence such an optimum. It is important to understand in general that heat removal can allow increase hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC H-SOEC EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear or geothermal energy. The goal of HT electrolysis research and development should be to lower ASR and improve heat conduction or heat transfer into and out of the SOEC. The promise of the H-SOEC electrochemical hydrogen compressors depends on its stability, durability and improved transference numbers. The goal of future research should be to improve the potential of this new SOEC H-SOEC EHC ECN.
Boundaries of High-Temperature Co-Electrolysis Towards Direct CO2-Electrolysis
Authors: Wolf Stephanie Elisabeth , Dittrich Lucy , Nohl Markus , Foit Severin , Vinke Izaak , De Haart L. G. J. , Eichel Rudiger-A
Published: July 2021

High-temperature co-electrolysis of CO2 and H2O at elevated temperatures between 700 °C and 900 °C valorises CO2 to produce a mixture of carbon monoxide (CO) and hydrogen (H2), called syngas. Co-electrolysis has the great advantage over conventional processes, that the desired syngas ratios of downstream processes can be realized by varying process parameters such as temperature and feed gas composition accordingly in a one step process. Co-electrolysis can also play a vital role in counteracting power fluctuations of renewable energy sources by storing temporarily unused electricity through conversion to other energy resources like chemicals or heat for later use.

The underlying processes in co-electrolysis for CO production are direct electrochemical CO2 reduction and reverse water gas shift equilibrium (RWGS). Their specific significance has not been clarified in detail yet and was controversially discussed in literature up to this day [1,2].

The impact of the equilibrium partial pressure of H2O on the physical processes in the transition boundary of co-electrolysis towards direct CO2-electrolysis was investigated by AC and DC measurements for various gas compositions. The analysis led to identifying the role of the underlying electrochemical processes during co-electrolysis, in particular the electrochemical CO2 reduction compared to the conversion of CO2 in the reverse water-gas shift reaction and the electrochemical H2O reduction. The area specific resistance (ASR) was, amongst others, taken as an indicator to determine, which of the reduction reactions (H2O or CO2 reduction) is dominant depending on the gas composition. The experiments were conducted using commercially available cathode-supported full cells (Elcogen) made of Ni-8YSZ/8YSZ/CGO/LSC.

Results as seen in Figure 1 show that the ASR for an equilibrium concentration of 5 % H2O is considerably larger than for higher H2O contents. Above 15 % H2O, the ASR shows no dependency on the gas composition and is comparable to pure H2O-electrolysis [3]. These observations underline the hypothesis that CO2-electrolysis becomes pre-dominant compared to H2O-electrolysis for low H2O content during co-electrolysis. With increasing H2O content, CO2-electrolysis becomes less significant and carbon dioxide is converted in the reverse water gas shift equilibrium. The origin of the discrepancy in literature was found to be the different operating H2O concentrations. A threshold has been established for the perception of CO2-electrolysis during co-electrolysis experiments.

figure caption: Arrhenius plot of ASROCV for different steam concentrations at 6 l·h-1.

[1] C. Stoots, J. O'Brien, J. Hartvigsen, Int. J. Hydrogen Energy 2009, 34, 4208.

[2] S. D. Ebbesen, R. Knibbe, M. Mogensen, J. Electrochem. Soc. 2012, 159, F482-F489.

[3] L. Dittrich, M. Nohl, E. E. Jaekel, S. Foit, L.G.J. (Bert) de Haart, R.-A. Eichel J. Electrochem.
Soc. 2019, 166, F971-F975.

Figure 1
Influence of Active Layer Thickness of Reversible Solid Oxide Cells on the Electrochemical Performance of Water Electrolysis
Authors: Kukk Freddy , Pylypko Sergii , Lust Enn , Nurk Gunnar
Published: July 2021

As energy storage becomes increasingly more important in contemporary and future energy solutions, the ability of a solid oxide cell (SOC) to work reversibly as an electrolyzer/fuel cell gives this technology great potential for use in large energy storage projects1,2. In theory, it is possible to use the state-of-the-art solid oxide cells in electrolysis operation to produce fuel (i.e. split water into oxygen and hydrogen) or generate electricity and heat using the so-called fuel cell regime. In addition, it is possible to produce syngas (H2 + CO)1,2 by co-electrolyzing water and CO2.

While the performance and stability of the solid oxide fuel cell (SOFC) are in focus of most research regarding this technology, the technological possibilities of reversible solid oxide cells (RSOC) are far less studied. Although both technologies mostly share their device composition and main architecture, using the SOC in electrolysis mode creates new degradation mechanisms and technological problems3,4.

In this work the authors focus on the electrolysis performance of the RSOC. The authors analyzed the influence of active layer thickness on SOC performance in electrolysis mode by using a commercial solid oxide cell (Ni-3YSZ|Ni-8YSZ|8YSZ|GDC|LSC). The study has been performed to establish the optimal active layer thickness and therefore to maximize the SOC performance in electrolysis mode.

Electrochemical characterization of SOC button cells has been conducted using electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic methods at several operating conditions including different temperatures and different water vapor contents in the gas stream. The gas compositions have been exchanged to simulate working conditions at different locations in the RSOC stack during electrolysis work. The results of the electrochemical studies have been analyzed using equivalent circuit fitting method of Nyquist plots. Complex analysis of different porous architectures and chemical compositions at different operating conditions gave more information on how the structure of the SOC determines the electrochemical performance of the water electrolysis process.

References:

Giulio Vialetto, Marco Noro, Paolo Colbertaldo, Masoud Rokni, International Journal of Hydrogen Energy, 44, 9608-9620 (2019)

M. B. Mogensen, M. Chen, H.L. Frandsen, C. Graves, J.B. Hansen, K.V. Hansen, A. Hauch, T. Jacobsen, S.H. Jensen, T.L. Skafte and X. Sun, Clean Energy, 3, 175–201 (2019)

P. Mocoteguy and A. Brisse, International Journal of Hydrogen Energy, 38 (36), 15887-15902 (2013)

Y. Tao, S. D. Ebbesen, M. B. Mogensen, Journal of Power Sources, 328, 452-162 (2016)
Tuning Transport Mechanisms in Fuel-Assisted Solid Oxide Electrolyzers for Enhanced Performance and Product Selectivity
Authors: Nielsen Anders S , Pharoah Jon G
Published: July 2021

The demand for renewable energy storage systems and CO2-utilization technologies has become apparent in recent decades due to concerns related to the continuous emission of anthropogenic greenhouse gases. A promising technology that can help alleviate some of these concerns are solid oxide electrolyzers, since they have the ability to convert CO2 and steam into valuable chemicals and fuels from the electricity generated by renewable sources, including wind and solar energy. Furthermore, these devices can operate in fuel-assisted mode, wherein a reactant, such as methane, hydrogen, and/or carbon monoxide, is delivered to the anode in order to reduce its operating potential. This simple modification has been shown to decrease the operating potential by nearly one order of magnitude [1-3], and, in some instances, has enabled the cell to generate power and synthesis gas simultaneously [4-6]. Fuel-assisted solid oxide electrolyzers have therefore emerged as a compelling option for renewable energy storage and large-scale chemical production, and have begun to draw significant attention from researchers and designers. But despite previous efforts, an understanding of how to attain a desired product composition and efficiency remains unclear. The objective of the presented work, then, is to perform a scaling analysis of the transport phenomena pertinent to fuel-assisted cells, in order to develop a set of dimensionless ratios that characterize the interplay between chemical and electrochemical reactions, and advective and diffusive transport. These dimensionless ratios provide crucial information on how to control the contribution of chemical and electrochemical reactions, as well as strategies to mitigate concentration and temperature gradients within the electrodes and flow channels. This approach is intended to provide an enhanced understanding of how to increase the product selectivity and performance of fuel-assisted solid oxide electrolyzers, which will hopefully lead to enhanced electrode and cell designs.

[1] A. Q. Pham, P. H. Wallman and R. S. Glass, US Patent 6,051,125 (2000).

[2] F. Chen and Y. Wang, US Patent 9,574,274 (2017).

[3] Y. Wang, T. Liu, S. Fang, G. Xiao, H. Wang and F. Chen, J. Power Sources, 277, 261 (2015).

[4] H. Xu, B. Chen and M. Ni, J. Electrochem. Soc., 163, F3029 (2016).

[5] Y. Patcharavorachot, S. Thongdee, D. Saebea, S. Authayanun and A. Arpornwichanop, Energy Convers. Manage., 120, 274 (2016).

[6] H. Xu, B. Chen, J. Irvine and M. Ni, Int. J. Hydrogen Energy, 41, 21839 (2016).
Spatial Current and Temperature Variations in a Microtubular Solid Oxide Electrolysis Cell In-Situ Analyzed with Electrode-Segmentation Method
Authors: Xuefeng Wang , Nakajima Hironori , Ito Kohei
Published: July 2021

The spatial distribution of current and temperature plays important role in the electrochemical performance of Solid Oxide Electrolysis Cells (SOECs). Many numerical predictions of current and temperature distribution have been reported, whereas experimental investigations were rare. In this research, we are applying a electrode-segmentation [1] method to investigate the spatial current and temperature variation in a cathode-supported microtubular SOEC. The electrode-segmentation method shows a remarkable current variation among the segments. The current densities of the midstream and downstream segments are smaller than the upstream segment with an increased cell voltage, implying that the cell suffers from water starvation. Besides, the temperature at each segment increases with the voltage increase. The largest current in the upstream segment is observed, which agrees with the largest temperature rise there. The largest temperature gradient happens between the upstream and midstream segments.

References

Aydin, T. Koshiyama, H. Nakajima, T. Kitahara, Journal of Power Sources, 279, 218-223 (2015).
The Effect of the Current Collector Type on the Performance and Durability of the SOFCs
Authors: Joh Dong Woo , Masaud Zubair , Song Rak-Hyun , Hong Jong-Eun , Lee Seung-Bok , Lim Tak-Hyoung
Published: July 2021

SOFC cathode current collector is necessary to lower the resistance and ensure long-term stability. SOFC current collection is performed on both the anode and cathode to collect the charge generated as a result of the electrochemical reaction of the fuel cell. Most of the research work carried out on current collection is related to the contact established on the cathode side of SOFC, and most of the research on current collecting material, contact area between cathode and current collector, and so on. The contact material on the cathode side of the SOFC may or may not bond. The bonding material is usually a paste of conductive precious metal or other ceramic material. Combined materials include metal mesh, felt, foam, and expanded metal. The shape of the current collector is not only related to the contact resistance, but also to damage due to the stress concentration caused by the local pressure applied to the electrodes of the stack under load. In this study, we tried to determine the effect of the shape of the current collector on the performance and durability of the cell or stack.
Interface Contribution on Conductivity Enhancement in Doped Ceria−Carbonates Composite Electrolyte
Authors: Fung Kuan-Zong , Chang Ting-You , Tang Jhih Yu , Tsai Shu-Yi
Published: July 2021

To simultaneously improve both ionic/electronic conduction in many electrochemical devices have received great attention. For example, (Ba,Sr)(Co,Fe)O3 perovskite exhibiting unique hole/oxygen ion mixed conduction behavior becomes important membrane materials for oxygen separation application. In additions, composite electrolytes consisting of multiple ionic conductors have received great attention for high temperature fuel cell application. For instance, enhanced conduction was observed when the oxygen ion conductor, doped ceria, was directly mixed with Li/K carbonates. The electrical conduction of composite electrolyte was contributed by the migration of oxygen ions in solid state and carbonate ions in liquid state. It is believed that ions tend to be highly mobile at the interface between doped ceria and carbonates. As a result, higher conductivity of the composite electrolyte was observed. In other words, the super-ionic conduction path/domain might exist at the interface between doped ceria and carbonates. However, to optimize the mixed conduction, the materials/microstructure designs play an important role. Thus, the objective of this study is to conduct (1) fabrication/design of composite electrolytes (2) microstructure development, (3) characterization of conduction/interfacial kinetics for composite electrolytes in high-temperature fuel cells. High-resolution SEM, XRD, and electrochemical Impedance Spectroscopy are employed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrolytes will be rationalized based on the pore size, pore distribution and interfacial area.
Enhancing the Catalytic Activity of Lanthanum-Ceria Fluorite for Methane Conversion in SOFC
Authors: Vilela Vanessa Bezerra , Thyssen Vivian Vazquez , Rodrigues Lays Nunes , Fonseca Fabio Coral
Published: July 2021

A2B2O7 compounds have unique properties, such as good thermal stability, oxygen mobility, ionic conductivity, etc. Such compounds with tailored compositions exhibit good catalytic properties in a variety of high-temperature reactions, such as reform and oxidative coupling of methane (OCM). An effective catalyst for OCM must have electrophilic oxygen mobility and alkalinity on its surface. A typical A2B2O7 compound that contains a trivalent rare earth metal at site A, such as La, can provide the necessary surface alkalinity for a good OCM catalyst. Previous studies show that La2Ce2O7 (LCO) catalysts perform well in OCM due to the selective mobile oxygen sites, suitable alkaline sites, and high thermal stability. Doping LCO with Ca increases the alkalinity, which can considerably increase selectivity for ethylene in the OCM reaction. We have studied calcium-doped lanthanum ceria materials as a catalytic layer in solid oxide fuel cells reactors for methane conversion to ethylene. We have explored the combustion synthesis to obtain homogeneous La2-xCaxCe2O7 powders with x = 0, 0.25, and 0.50 (LCO, LCa25, and LCa50, respectively). X-ray diffraction (XRD) showed that the calcium addition in LCO formed a single-phase solid solution. The crystalline structure of the synthesized materials is the disordered fluorite-type, as indicated by both XRD and Raman analysis. Raman spectroscopy data evidenced the presence of surface oxygen vacancies on all materials, which may benefit the OCM reaction. SEM images of as-prepared powders obtained evidenced a similar microstructure composed of porous sponge-like agglomerated particles with irregular shape, expected from the combustion synthesis (Fig. 1). Ca-doping changed the sintering behavior by reducing the onset of shrinkage during the sintering process. Impedance spectroscopy data showed increased ionic conductivity with increasing Ca-doping. Such an increase is more evident at high measuring temperature (800 oC) and indicates enhanced oxygen mobility that are expected to contribute to OCM reaction.

Figure 1: Scanning electron microscope micrographs of La2-xCaxCe2O7 (x = 0, 0.25, and 0.50) as-prepared powders obtained by combustion method.

Figure 1
Phase Field Modeling of Cubic to Tetragonal Transformation in YSZ and its Effect on Ionic Conductivity Degradation and Mechanical Damages
Authors: Da Yule , Jiao Zhenjun , Zhong Zheng
Published: July 2021

During the high-temperature operation of solid oxide fuel cells (SOFCs), the degradations of electrolyte material yttria-stabilized zirconia (YSZ) in both ionic conductivity and mechanical strength can be caused by the cubic to tetragonal phase transformation. In this work, microelasticity phase field model is built to simulate the YSZ phase transformation considering the effects of grain boundary and solid morphology. The YSZ skeleton in real SOFC anode is reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The ionic conductivity degradation and the mechanical damages under external mechanical loads of brittle YSZ phase in anode are investigated based on the phase field simulation results. The simulation results may provide theoretical guidelines for improving the SOFC anode during fabrication.
Dry Surface Treatment Technology for the Design of the Anode Side of the Metal Support Solid Oxide Fuel Cell (MS-SOFC)
Authors: Ye Xiaolei , Luo Huan , Bertrand Pierre , Billard Alain , Briois Pascal
Published: July 2021

As an electrochemical energy conversion device, solid oxide fuel cell (SOFC) has many advantages in energy conversion efficiency, fuel flexibility and environmental benefits. A typical high temperature SOFC possesses the advantages of high power density and high-grade waste heat production. However, high-temperature SOFC faces challenges in cost and long-term durability. Once the operating temperature of SOFC is effectively reduced, the fuel cell configuration anode supported can be changed to metal-supported SOFC (MS-SOFC). Alternative MS-SOFC designs have the advantages of low-cost material, robustness and convenient manufacturing.

In the present work, the metal supported half-cell with ITM / protective layer / Ni-YSZ / YSZ / GDC configurations were elaborated. Three protective layers of Co, Ce/Co and GDC were compared in terms of preventing Cr diffusion. Reactive magnetron sputtering (RMS) was used to deposit the electrolyte and the barrier layer because it can easily achieve a dense adherent and thin film. Atmospheric plasma spraying (APS) was used to deposit the cermet Ni-YSZ anode layer to facilitate the formation of porous structures. The morphology, microstructure and chemical composition of MS-SOFC were characterized by SEM, XRD and EDX, respectively. Finally, its electrical characteristics were measurements by four probe electrical and electrochemical impedance spectroscopy measurements.