Scandia-stabilized Zirconia Research Articles

In-Situ Observation of Temperature Distribution on a Planar Type SOEC During Start-Stop Cycle Operation

Introduction It is important to establish various analytical methods for solid oxide electrolysis cells (SOECs) under practical operating conditions in order to improve their performance and to analyze their degradation phenomena. In-situ observation of temperature distribution on a planar type SOEC enables to reveal the distributions of electrochemical reactions and the cell degradation. While there have been several reports on the internal visualization of solid oxide fuel cells (SOFCs)1, 2, there have been only a few reports on that of SOECs. Since the endothermic electrolysis reaction occurs in SOECs, comparing with SOFCs, a different temperature distribution will appear. Therefore, it should be necessary to evaluate the phenomena on the planar SOECs for analyzing the temperature distribution taking gas flow and current distribution into consideration.The purpose of this study is to evaluate the effect of cell degradation caused by the start-stop cycle operation on the temperature distribution using a 5 cm × 5 cm planar cell observed by infrared camera. Experimental In this study, a planar cell was fabricated using a scandia-stabilized zirconia electrolyte (ScSZ, 200 µm thick, 5 cm × 5 cm in area) as a substrate. LSM ((La0.8Sr0.2)0.98MnO3) and LSM-ScSZ composite materials were used for the air electrode, and nickel and ScSZ cermet were used for the fuel electrode. The electrode area was 4 cm × 4 cm (16 cm2). Each electrode material was screen-printed and sintered. A platinum mesh was used as the current collector.In this test, the cell was operated at 800 °C and 50%-humidified hydrogen (200 ml min-1) was supplied to the fuel electrode. The durability test was conducted under the accelerated degradation conditions of a start-stop cycle repeated in every 1 hour with 0.2 A cm-2 for 500 cycles (1000 hours). Electrochemical characteristics were measured by connecting Pt wires, spot-welded every 1 mm on one side of both electrode surfaces, to the voltage terminals of the electrochemical measurement setup and to the current terminals of the external power supply unit.Figure 1 shows a schematic view of the experimental setup and temperature change compared with the initial condition. The temperature distribution was observed by infrared camera (FLIR SC2500 - NIR, uncertainty ±0.02 oC) from the air electrode side open to the electric furnace. The difference between the temperatures before and during current loading was derived as the distribution of temperature changes. Results and discussion First, the electrochemical characteristics of the planar type SOECs during the start-stop cycle test were obtained. The cell voltage at 0.2 A cm-2 increased from 1.19 V to 1.29 V during the test up to 500 cycles. The cell voltage was 1.27 V even after the initial 50 cycles. This suggests that SOEC electrode degradation3,4 occurred in the early stage of the start-stop cycling.The temperature changes after 50 cycles showed that each temperature change was relatively small because the cell was operated near the thermoneutral potential (around 1.29 V at 800 °C). It was confirmed that the endothermic electrolysis reaction was predominant near the fuel inlet. In addition, heat generation due to Joule heating was also appeared near the current collecting Pt wire connected to the power supply. Therefore, in SOEC operation, it is suggested that the temperature distribution is affected by the shape of current collector, gas supply condition, and electrochemical reaction distribution. The detailed analysis on the SOEC electrochemical properties and temperature distribution observed by in-situ measurements during cycling tests is also presented. Acknowledgements A part of this research was supported by New Energy and Industrial Technology Development Organization (NEDO), project No. JPNP14026. References (1) S. Shinichi and H. Iwai, J. Power Sources, 482, 229070 (2021).(2) Y. Shiratori, T. Ogura, H. Nakajima, M. Sakamoto, Y. Takahashi, Y. Wakita, T. Kitaoka, and K. Sasaki, Int. J. Hydrogen Energy, 38 (25), 10542 (2013).(3) M. Keane, M. K. Mahapatra, A. Verma, and P. Singh, Int. J. Hydrogen Energy, 37 (22), 16776 (2012).(4) M. Hubert, J. Laurencin, P. Cloetens, B. Morel, D. Montinaro, and F. Lefebvre, J. Power Sources, 397, 240 (2018). Figure 1

Characteristic and challenges of scandia stabilized zirconia as solid oxide fuel cell material – In depth review

Scandia-stabilized zirconia (ScSZ) has 1.5–3 times superior conductivity owing to its crystal structure as compared to yttria stabilized zirconia (YSZ). However, also due to this, ScSZ experienced phase structure transition which affects its stability when used as an SOFC electrolyte material and as anode. The typically ceria-doped 10 mol%ScSZ (10Sc1CeSZ) experienced Ce4+ − Ce3+ transition in reduced environment led to lower fracture strength and instability. Alternative promising co-dopants to stabilized ScSZ phase, such as Nd, Sm and Gd are identified as a way forward in using ScSZ in reduced SOFC environment. The high affinity of the ScSZ oxide to Ni causes the dissolution of Ni in ScSZ grains and vice versa, thereby affecting the conductivity and material connectivity at the anode. The tolerance of Ni-ScSZ to hydrocarbon fuel and sulfur is significantly higher than that of Ni-YSZ and exhibited different behavior on carbon growth; graphitic carbon growth on Ni-ScSZ, and amorphous carbon on Ni-YSZ. The differences reflect the superior methane cracking catalytic ability of Ni-ScSZ and the effect of the crystal structure on the type of carbon formed. Doping is a suitable solution to enhance the reforming activity of the cell as well and resolve the Ni-ScSZ anode degradation issue.

A relationship of porosity and mechanical properties of spark plasma sintered scandia stabilized zirconia thermal barrier coating

Porous ceramic materials are popularly accepted as thermal barrier coatings (TBCs) in insulating gas turbine parts working at high temperatures. In this research, three different types of Scandia stabilized zirconia (ScSZ) systems, a nanometric 10 mol% ScSZ (10-ScSZ), a micrometric 8 mol% ScSZ (8-ScSZ) and a combination of these two powders (10-8-ScSZ) have been developed by Spark Plasma Sintering (SPS) process. Varying SPS parameters, for instance, temperature, pressure and dwell time were applied to develop the different volumes of porosity in the materials. Subsequently, the microstructure of the materials has been studied and mechanical properties have been evaluated. All three materials demonstrate a reduced porosity level at high sintering temperature and pressure. However, the nanometric 10-ScSZ material shows a higher reduction of porosity from 51.8% to 11.1% at 30 MPa pressure and 40.2%–8.5% at 60 MPa pressure within the temperature range of 1000–1200 °C. Besides, the 10-8-ScSZ composite exhibits substantially increased porosity in comparison to its constituent parts. The results also show that the nanometric 10-ScSZ material exhibits a greater mechanical strength including Vickers microhardness of 81 HV, flexural strength of 361 MPa and elastic modulus of 187 GPa at 5% porosity level, as compared to the other two materials. Additionally, it is observed that all the mechanical properties for all three materials consistently decrease with the increase in porosity levels. While compared with the traditional atmospheric plasma spray (APS) processed ceramic coating, the porous ScSZ coating materials exhibit a larger elastic modulus. Therefore, the porous ScSZ developed by the SPS process could be a prospective alternative thermal barrier coating (TBC).

Long-Term Conductivity Stability of Electrolytic Membranes of Scandia Stabilized Zirconia Co-Doped with Ytterbia.

The effect of high-temperature aging for 4800 h at a temperature of 1123 K on the crystal structure and the conductivity of (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 and (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 single-crystal membranes were studied. Such membrane lifetime testing is critical to the operation of solid oxide fuel cells (SOFCs). The crystals were obtained by the method of directional crystallization of the melt in a cold crucible. The phase composition and structure of the membranes before and after aging were studied using X-ray diffraction and Raman spectroscopy. The conductivities of the samples were measured using the impedance spectroscopy technique. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition showed long-term conductivity stability (conductivity degradation not more than 4%). Long-term high-temperature aging of the (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 composition initiates the t″ → t' phase transformation. In this case, a sharp decrease in conductivity of up to 55% was observed. The data obtained demonstrate a clear correlation between the specific conductivity and the change in the phase composition. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition can be considered a promising material for practical use as a solid electrolyte in SOFCs.

Development of Multiple Ceramic Coatings on Porous Tubular Metal Support

Dip coating was used to develop anodic half-cell for micro-tubular metal-supported solid oxide fuel cells (MS-SOFCs) economically. Ni–scandia-stabilized zirconia (SSZ) and SSZ were used as anode functional layer and electrolyte, respectively. Successive coatings of the SOFC functional layers were applied onto the porous metallic support using a dip coating technique. Additionally, to prevent delamination between the metal support and anode functional layer, an intermediate layer consisting of stainless steel powder, Ni, and yttria-stabilized zirconia (YSZ) was introduced. After coating, the individual layers were fired in a reducing atmosphere at 1000 °C followed by co-sintering of metal/anode/electrolyte multilayers at 1350°C. Microstructure of the sintered cells was characterized using scanning electron microscopy (SEM). General problems encountered during the fabrication of anodic half-cell for MS-SOFCs by a cost-effective dip coating followed by co-sintering route have been investigated. The sintering conditions and multilayer designs were studied to minimize the metal support oxidation and ceramic layer peeling during co-sintering.

Ni-Alloy Fuel Electrodes for Reversible Solid Oxide Cells

Introduction Reversible solid oxide cells (r-SOCs, or solid oxide reversible cells) are devices that can efficiently operate in both fuel cell and electrolysis operating modes. It is expected that they can serve as a technology for green, flexible, and efficient energy systems coupled with renewable energy (1). However, a fuel electrode of r-SOCs might be degraded due to redox cycles in switching operation modes. In our research group, we have fabricated redox-resistant anodes with Ni-Co alloy cermet (2). Here in this study, we apply such alloy-based cermet to the fuel electrode, and evaluate electrochemical performance, reverse cycling durability, and the effect of Co addition. Moreover, we compare the cell performance of Ni-Co alloy cermet with conventional Ni-ScSZ fuel electrode. Experimental In this study, scandia-stabilized zirconia (ScSZ, 10mol% Sc2O3-1mol% CeO2-89mol% ZrO2) was used as the solid electrolyte. The powder prepared by mixing Ni-Co-based oxide powder prepared by ammonia co-precipitation with Ce0.9Gd0.1O2 (GDC) in a weight ratio of 48.1:51.9, was used as the fuel electrode material. Ni-Co-GDC fuel electrode with x mol% of Co added to Ni, is denoted as Ni(100 – x)Cox -GDC fuel electrode. The fuel electrodes of x = 0, 5, 10, and 20 were fabricated. Two types of Ni-GDC cermet were prepared. One was fabricated by using NiO powder by ammonia co-precipitation, and the other was by using commercial NiO powder (Kanto Chemical, Japan). We prepared the Ni-Co alloy cermet by mixing powder and binder, preparing and printing electrode paste on the electrolyte plate, followed by heat treatment. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode material. The electrochemical characteristics and r-SOC reversible cycle durability of the fuel electrodes were evaluated under the condition at an operating temperature of 800℃, while 100 ml/min of 50%-humidified hydrogen fuel was supplied to the fuel electrode, and 150 ml/min of air was supplied to the air electrode. Electrochemical characteristics were evaluated by electrochemical impedance measurements (1255WB, Solartron, UK), which separate ohmic and non-ohmic resistances. The durability in reverse r-SOC operation was evaluated by repeatedly varying current density within ± 0.2 A cm-2 at a current sweep rate of 1.56 mA cm-2 s-1 up to 1,000 cycles. The degradation was evaluated by averaging the percentage change in fuel electrode potential at ± 0.2 A cm-2. Results and discussion Figure 1 shows the initial performance of the cells with each fuel electrode. Figure 2 shows the degradation of each fuel electrode within 1,000 cycles after the r-SOC reverse durability test. The initial performance of Ni-Co-GDC was superior to Ni-ScSZ, and it increased with decreasing Co content. Two types of Ni-GDC exhibited identical performance. Similarly, the r-SOC reverse durability of Ni-Co-GDC was superior to Ni-ScSZ, and it increased with decreasing Co content. Furthermore, two types of Ni-GDC exhibited almost the same durability. These results indicate that GDC contributes to the increased cell performance and durability rather than alloying or the feature of original NiO powder. It appears that Co is not essential for r-SOC fuel electrodes in terms of r-SOC durability. However, fuel electrode materials should be selected by comprehensively considering the performance and the durability at both SOFC and SOEC modes. As Ni-Co alloy shows higher redox cycle durability compared with Ni-GDC (3), Ni-Co alloy is still one of the promising materials for r-SOC fuel electrodes. Acknowledgements A part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO). References N. Q. Minh and M. B. Mogensen, Electrochem. Soc. Interface, 22, 55 (2013).Y. Ishibashi, S. Futamura, Y. Tachikawa, J. Matsuda, Y. Shiratori, S. Taniguchi, and K. Sasaki, J. Electrochem. Soc., 167, 124517 (2020).K. Matsumoto, Y. Tachikawa, J. Matsuda, S. Taniguchi, and K. Sasaki, ECS Trans., 103, 1549 (2021). Figure 1

Performance and Durability of Solid Oxide Electrolysis Cell Air Electrodes Prepared By Various Conditions

Introduction Fuel electrode materials are important for achieving higher performance and durability of Solid Oxide Fuel Cell (SOFC), Solid Oxide Electrolysis Cell (SOEC), and Reversible Solid Oxide Cells (r-SOCs). On the other hand, the air electrode also faces performance and durability issues. For example, the diffusion of Sr ions from the air electrode materials has been reported.1, 2 In SOECs, if electrolysis can be performed at a thermoneutral potential balancing heat absorption by electrolysis and heat generation by the internal resistance of the electrolysis cell, hydrogen can be generated theoretically without heat supply. The purpose of this study is to evaluate the electrochemical performance and durability of the SOECs by conducting electrolysis performance tests of LSCF-based air electrodes with different preparation conditions, and electrolysis durability tests at the thermoneutral potential. Experimental Each test was conducted using a cell with a scandia-stabilized zirconia electrolyte (ScSZ, 200 µm thick) as a substrate. For the fuel electrode, Ni-GDC co-impregnated fuel electrode was used3. A mixture of Ni(NO3)2･6H2O, Gd(NO3)3･6H2O, and Ce(NO3)3･6H2O was impregnated into the porous LST-GDC framework, a mixture of LST powder (La0.1Sr0.9TiO3) and GDC powder (Gd0.9Ce0.1O₃). LSCF, (La0.6Sr0.4)(Co0.2Fe0.8)O3, was used for the air electrodes. GDC was inserted between the LSCF layer and the electrolyte plate as a buffer layer. In fabricating air electrodes, four types of air electrodes were applied, at shown in Table 1. For the electrochemical measurements of the air electrodes, Pt reference electrode was attached to the electrolyte on the fuel electrode side, and the voltage terminals of the electrochemical measurement system were connected between the reference electrode and the air electrode to measure air electrode voltage.In the performance tests, the voltage (potential) and impedance of the air electrode were measured at operating temperatures of 800°C, 750°C, and 700°C. In the durability tests, the air electrode was maintained at thermoneutral potentials at 800°C and 700°C (1.286 V and 1.283 V, respectively), and the voltage and impedance of the air electrodes were measured before and after the durability tests to evaluate the degradation of the air electrodes. Results and discussion Figure 1 shows the air electrode voltage obtained from the performance tests at each operating temperature for the four types of air electrodes shown in Table 1. First, regarding the dependence of the electrolysis performance on operating temperature, an increase in air electrode voltage (degradation of the air electrode) was found at 800°C.The increase in air electrode voltage with current density was almost linear, but at lower operating temperatures, the increase in air electrode voltage at lower current densities becomes larger. In other words, the I-V curve was rather ohmic at 800°C, but non-ohmic at 700°C.Figure 2 shows the results of an 80-hour durability test at different temperatures. The current density of the cell corresponding to the thermoneutral potential was -0.298 Acm-2 when operated at 800°C and -0.018 Acm-2 when operated at 700°C.The degradation rate was calculated from the difference in air electrode voltage before and after the performance and durability test at these current densities: 0.172% at 800°C and 0.792% at 700℃. The degradation rate increased as the operating temperature decreased in the SOEC mode, despite the low current density. Microstructural observation of the air electrode after the durability test showed that Sr diffused to the LSCF/GDC interface similar to SOFCs mode4, and that the diffusion of Sr was accelerated at 700°C. In addition, Co diffusion was also observed. Such diffusion may occur during LSCF firing process and/or during SOEC operation. More detailed investigation is in progress. Acknowledgements This research was supported in part by NEDO (New Energy and Industrial Technology Development Organization). We thank all parties involved. References (1) V. Subotić, S. Futamura, G. F. Harrington, J. Matsuda, K. Natsukoshi, and K. Sasaki, J. Power Sources, 492, 229600 (2021).(2) S. P. Simner, M. D. Anderson, M. H. Engelhard, and J. W. Stevenson, Electrochem. Solid-State Lett., 9 A478 (2006).(3) K. Natsukoshi, K. Miyara, Y. Tachikawa, J. Matsuda, S. Taniguchi, G. F. Harrington, and K. Sasaki, ECS Trans., 03, 203 (2021).(4) S. Kanae, Y. Toyofuku, T. Kawabata, Y. Inoue, T. Daio, J. Matsuda, J,-T. Chou, Y. Shiratori, S. Taniguchi, and K. Sasaki, ECS Trans., 68, 2463 (2015). Figure 1

Atmospheric plasma spraying to fabricate metal‐supported solid oxide fuel cells with open‐channel porous metal support

AbstractMetal‐supported solid oxide fuel cells (MS‐SOFCs) have been fabricated by applying phase‐inversion tape‐casting and atmospheric plasma spraying (APS). The effect of the binder amount of the phase‐inversion slurries on the microstructure development of the 430L stainless steel metal support was investigated. The pore structures, the viscosity of the slurry, porosity and permeability of the as‐prepared metal supports are significantly influenced by the amount of the binder. NiO–scandia‐stabilized zirconia (ScSZ) anode, ScSZ electrolyte and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode layers were consecutively deposited on the metal support with an ideal microstructure by APS process. The effect of plasma power of the APS on the microstructure of the electrolyte and cathode was investigated. A dense electrolyte layer and a porous cathode layer were successfully obtained at 40 and 6 kW of the APS plasma power, respectively. MS‐SOFCs, with a cell configuration of 430L/Ni‐ScSZ/ScSZ/LSCF, achieved a maximum cell power density of 1079 mW cm−2 at 700°C using humidified H2 as fuel and ambient air as oxidant. The corresponding ohmic resistance and total resistance of MS‐SOFCs was 0.14 and 0.32 Ω cm2, respectively. This work demonstrates the feasibility of fabricating high‐performance MS‐SOFCs with economical and scalable techniques.

In-Situ Synthesis of Sm0.5Sr0.5Co0.5O3-δ@Sm0.2Ce0.8O1.9 Composite Oxygen Electrode for Electrolyte-Supported Reversible Solid Oxide Cells (RSOC)

Oxygen electrode has a crucial impact on the performance of reversible solid oxide cells (RSOC), especially in solid oxide electrolysis cell (SOEC) mode. Herein, Sm0.5Sr0.5Co0.5O3-δ@Sm0.2Ce0.8O1.9 (5SSC@5SDC) composite material has been fabricated by the in-situ synthesis method and applied as the oxygen electrode for RSOCs with scandium stabilized zirconia (SSZ) electrolyte. The phase structures, thermal expansion coefficients, and micromorphologies of 5SSC@5SDC have all been further analyzed and discussed. 5SSC@5SDC is composed of a skeleton with large SDC particles in the diameter range of 200~300 nm and many fine SSC nanoparticles coated on the skeleton. Thanks to the special microstructure of 5SSC@5SDC, the electrolyte-supported RSOC with SSC@SDC oxygen electrode shows a polarization resistance of only 0.69 Ω·cm2 and a peak power density of 0.49 W·cm−2 at 800 °C with hydrogen as the fuel in solid oxide fuel cell (SOFC) mode. In addition, the electrolysis current density of RSOC with SSC@SDC can reach 0.40 A·cm−2 at 1.30 V in SOEC model, being much higher than that with the SSC-SDC (SSC and SDC composite prepared by physical mixing). RSOC with 5SSC@5SDC shows an improved stability in SOEC model comparing with that with SSC-SDC. The improved performance indicates that 5SSC@5SDC prepared by the in-situ synthesis may be a promising candidate for RSOC oxygen electrode.

High-conductivity electrolyte with a low sintering temperature for solid oxide fuel cells

Bismuth oxide and scandia co-doped zirconia (Sc2O3)0.06(Bi2O3)x(ZrO2)0.94–x (ScSZB, x = 0, 0.01, 0.03, 0.05, 0.07, 0.1) powders are prepared via a citrate sol-gel method. Bi2O3 promotes the sintering process of scandia stabilized zirconia (ScSZ) and increases electrical conductivity of system. A high conductivity of ∼0.094 S/cm at 800 °C is achieved on 5 mol% Bi2O3 doped ScSZ (ScSZB05). X-ray Rietveld refinement and transmission electron microscope (TEM) analysis of the ScSZB05 reveal the formation of cubic phase and rhombohedral phase at room temperature. The electrolyte-supported cell constructed by the ScSZ electrolyte gives the maximum power density of 258.3 mW/cm2 at 800 °C, while the cell with ScSZB05 electrolyte shows a higher value of 387.6 mW/cm2. The performance obtained by theoretical simulation of the two electrolyte-supported cells is in good agreement with the experimental results.

On the mechanism of Mn(II)-doping in Scandia stabilized zirconia electrolytes

Cubic Scandia-stabilized zirconia (ScSZ) is an attractive electrolyte material for solid oxide cells due to its significant ionic conductivity, provided that the phase transition to its rhombohedral polymorph upon cooling is suppressed. The latter is achieved with addition of a secondary co-dopant, albeit it may be at the detriment of its ionic conductivity Here, we thoroughly investigate how MnO2 (0.5–10 mol%) as a co-dopant impacts on the sinterability, thermal expansion, crystal structure and ionic conductivity of ZrO2 doped with 10 mol% Scandia (10ScSZ), and we provide new insight on the chemistry of dissolved manganese in the fluorite lattice. Reactive sintering of 2 mol% MnO2 mixed with 10ScSZ enables to produce dense electrolyte with significant reduction of the peak sintering temperature and stabilisation of the cubic structure down to room temperature. Combined density functional theory and X-ray photoelectron spectroscopy analyses reveal that manganese predominantly enters the structure as Mn2+ during reactive sintering, with a prevalence of higher valence states at the surface and grain boundaries. The highest oxide ion conductivity is achieved for 2 mol% doped 10ScSZ (120 mScm−1 at 800 °C) and it decreases with increasing Mn concentration. For all compositions, the bulk conductivity remains independent of pO2 – corroborating a limited electronic conductivity contribution from Mn-doping. The grain boundary conductivity is found to decrease with sintering time and pO2, which is attributed to the chemistry and concentration of segregated manganese at the surface and grain boundaries, yielding depletion of oxygen vacancies in the space charge layer.

Manufacturing method of BSCF cathode for low-temperature solid oxide fuel cell-A review

The fuel cell is a device used to convert chemical energy to electrical energy through the electrochemical process. It does not involve any intermediate step of direct combustion and gives higher conversion efficiency when compared to a conventional system. Solid oxide fuel cell is a type of fuel cell which involves oxide-ion conducting electrolytes. It has several advantages in higher efficiency, lower sensitivity to fuel impurities, and inexpensive materials. Nowadays, Low-Temperature Solid Oxide (LT-SOFC) Fuel Cell is attracted due to its lower operating temperature range of 500–800 °C. The various advantages of LT-SOFC are reducing the degradation of components involved, cell durability improvement, and reducing the cost involved. In solid oxide fuel cells, cathode plays an essential role in the electrochemical reduction. Common cathode materials are yttria-stabilized zirconia, scandia-stabilized zirconia, Samaria-doped ceria (SDC), gadolinia-doped ceria (GDC), and lanthanum strontium gallium magnesium oxide (LSGM). These cathodes have a high value of ionic conductivity at low temperatures. Recently, BSCF type cathode is attempted by researchers due to its attractive performance in LT-SOFC. The main objective of this article reviews the manufacturing method of BSCF cathode and its fabrication route on LTSO fuel cells. The result of this review article is observed to acquire knowledge of various manufacturing method of BSCF cathode in LT-SOFC fuel cell.

Effect of nanostructured grains in co-sputtered Ni-GDC thin-film anode on methane conversion kinetics for low temperature solid oxide fuel cells operating on nearly dry methane

Direct-methane solid oxide fuel cells (DMSOFCs) have recently attracted substantial attention due to their simplified system, reduced cost, and the direct availability of methane fuel obtained from natural gas. Among oxygen-ion conductive materials, doped-ceria such as gadolinium-doped ceria (GDC) or samarium-doped ceria can be incorporated into Ni-based anodes to reinforce their coking resistance, enlarge their electrochemical reaction area, and improve the kinetics of the internal reforming/electrochemical oxidation of methane. To reduce the range of operating temperatures of DMSOFCs while maintaining their performance, the thin film deposition technique of magnetron sputtering was adopted in this work. An Ni-GDC thin-film anode and a Pt thin-film cathode were deposited on scandia-stabilized zirconia (ScSZ) electrolyte supports. This fuel cell was tested with directly supplied methane fuel (3% H2O) at 500 °C. The results demonstrated the effects of the GDC volume fraction in the anode—which was controlled by co-sputtering power—on open circuit voltage and electrochemical performance. The co-sputtered Ni-GDC anode was able to survive through 36-h operation, although there was some performance degradation. Field-emission scanning electron microscopy results revealed no formation of filamentous carbon on the Ni catalysts, despite the fact that both X-ray photoelectron spectroscopy and Raman spectroscopy analyses detected carbon coking. The relatively high performance and resistance to carbon coking of co-sputtered thin-film anode were attributed to its intrinsic small grain size.

Effect of Microstructure of the Anode Support Tubes Towards SOFC Performance

Reversible solid-oxide fuel cells (rSOFC) attract enormous attentions because of their capability to operate in both fuel cell and electrolysis modes. rSOFC with a tubular cell design has multiple advantages over a planar design for example allowing faster startup and shutdown. Successful fabrication of tubular cells needs to overcome numerous technological challenges, including control of its mechanical stress and high interlayer electrode resistance. The scope of the present work involves fabrication and testing of anode supported rSOFC single cells using both ionic conducting electrolyte and protonic conducting electrolyte. For the ionic conducting cells, the rSOFCs constituted Ni + yttria-stabilized zirconia (YSZ) anode support tube, Ni + scandia-stabilized zirconia (ScSZ) anode functional layer, scandia-stabilized zirconia (ScSZ) electrolyte, samarium doped ceria (SDC) protective layer, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) + SDC cathode functional layer, and LSCF cathode current collector layer, respectively. For the protonic conducting cells, BaZr0.1Ce0.7Y0.1Yb0.1O3-d (BZCYb) was used as electrolyte.In this work, sequential dip-coating coupled with co-firing technique was implemented over the thin film cell structure fabrication. The nickel based tubular anode supports were made from various methods, including extrusion, freeze-casting and dipping processes. To achieve low interlayer resistance and dense electrolyte layer, we have optimized the ceramic slurry (ink) formulation parameters. Cell performance and microstructure of the rSOFC will be discussed and compared with the available data.

Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing

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.

Examine Operando Generated Ni-Based Alloy Nanomaterials as Fuel Electrode in Solid Oxide Cells

Solid oxide cells are highly efficient electrochemical device for energy conversion. They can convert chemical energy to electrical energy in solid oxide fuel cells (SOFCs) mode and vice versa in solid oxide electrolysis cells (SOECs) mode. Constructing nanostructured electrodes have been demonstrated as an effective approach to enhance performance and durability for solid oxide cells, primarily due to significantly extended triple phase boundaries, where the active sites for electrochemical reactions locate. [1, 2] Exsolution, an innovative method of generating uniformly distributed fine particles through redox treatment, is of particular interest in recent years, as it offers well embedded nanoparticles bringing greatly boosted catalytic properties, thermal stability, and coking resistance. A wide range of nanomaterials have been fabricated by this manner, including metals [3, 4] , alloys [5, 6] and oxides [7, 8] .Through exsolution processing, catalytically active materials can be produced either in-situ by exposing to a H2-containing atmosphere in which nanoparticles form on the surface upon reduction, or operando in an SOEC through electrochemical reduction when a high potential is applied. It was reported that exsolution happened almost instantly at 2.0 V in steam electrolysis operation, generating sufficiently high amount of nanocatalysts pinned on the surface of perovskite. [9] In contrast, it takes hours even days by chemical reduction, yet with less impressive performance. This indicates that electrochemical reduction by applying suitable potential or current can serve as an efficient method to produce electrocatalysts in nanoscale. However, potential-driven exsolution has not been extensively studied, especially in CO2 electrolysis via SOEC.In this work, we have been focusing on examine titanate perovskites with exsolved Ni-based alloy nanocatalysts as fuel electrode of solid oxide cells, particularly on generating nanocatalysts via electrochemical reduction in CO2 electrolysis conditions. A series of titanate perovskites were prepared, including La0.43Ca0.37Ni0.06Ti0.94O3-δ, La0.43Ca0.37Ni0.03Fe0.03Ti0.94O3-δ, and La0.43Ca0.37Ni0.03Co0.03Ti0.94O3-δ. These compositions represent metallic Ni, Ni-Fe alloy, and Ni-Co alloy as nanocatalysts to be exsolved respectively. X-ray diffraction (XRD) and DC conductivity measurement were conducted to determine material crystal structure and conductivity properties, respectively. SOCs with scandium stabilized zirconia (ScSZ) electrolyte, standard (La, Sr)MnO3 (LSM)/ScSZ air electrode and the above prepared titanates fuel electrodes were fabricated for electrochemical characterisation. The fuel electrodes were firstly activated by applying varying potential/current in pure CO2 gas, prior to performance evaluation. In-situ impedance spectroscopy and polarization curves were recorded, and post-mortem microstructure analysis was carried out to investigate the exsolution behaviour on different electrodes. Results obtained so far showed that nanoparticles induced by electrochemical reduction formed at potentials higher than 2V in CO2 electrolysis conditions, leading to improved cell performance towards CO2 reduction as well as H2 oxidation. Higher performance was observed on the cells with alloy nanocatalysts compared to that with sole Ni nanoparticles. P. A. Connor, X. Yue, C. D. Savaniu, R. Price, G. Triantafyllou, M. Cassidy, G. Kerherve, D. J. Payne, R. C. Maher, L. F. Cohen, R. I. Tomov, B. A. Glowacki, R. V. Kumar, J. T. S. Irvine, Adv. Energy Mater., 8, 1800120 (2018).J. T. S. Irvine, D. Neagu, M. C. Verbraeken, C. Chatzichristodoulou, C. Graves, M. B. Mogensen, Nat. Energy, 1, 15014 (2016).D. Neagu, G. Tsekouras, D. N. Miller, H. Menard, J. T. S. Irvine, Nat. Chem., 6, 916 (2013).D. Neagu, T. S. Ou, D. N. Miller, H. Me ́nard, S. M. Bukhari, S. R. Gamble, R. J. Gorte, J. M. Vohs, J. T. S. Irvine, Nat. Comm., 6, 8120 (2015).T. Zhu, H. E. Troiani, L. V. Mogni, M. Han, S. A. Barnett, Joule, 2, 478 (2018).D. Neagu, E. I. Papaioannou, W. K. W. Ramli, D. N. Miller, B. J. Murdoch, H. Ménard, A. Umar, A. J. Barlow, P. J. Cumpson, J. T. S. Irvine, I. S. Metcalfe, Nat. Comm., 8, 1855 (2017).J. Wang, J. Zhou, J. Yang, D. Neagu, L. Fu, Z. Lian, T. Shin, K. Wu, Adv. Mater. Interfaces, 7, 2000828 (2020).L. Ye, M. Zhang, P. Huang, G. Guo, M. Hong, C. Li, J. T. S. Irvine, K. Xie, Nat. Comm., 8, 14785 (2017).J. Myung, D. Neagu, D. N. Miller, J. T. S. Irvine, Nature, 537, 528 (2016).

Redox Durability of Ni-Co Alloy Cermet Anodes for SOFCs

Introduction Nickel (Ni) is commonly used as the anode material of SOFCs. However, in the power generation, as the oxygen partial pressure in the downstream of the SOFC systems increases, the metallic Ni can be oxidized to nickel oxide (NiO), causing volume expansion (1) This volume expansion and shrinkage in redox cycles cause irreversible degradation, by breaking electrode microstructure. Highly durable SOFC anodes using Ni-based alloy are therefore desirable (2). Here in this study, we focus on the Ni-Co alloy, by preparing a new Ni-Co-GDC cermet anode using the Ni-Co alloy, and evaluate the effects of cobalt addition on their redox durability. Experimental The cells were fabricated by screen-printing electrode paste on the electrolyte plate, followed by heat treatment. Scandia-Stabilized Zirconia (ScSZ, 10mol% Sc2O3-1mol% CeO2-89mol% ZrO2) was used as the solid electrolyte. Ni-Co-GDC cermet anodes were prepared by mixing Ni-Co-based oxide powder by ammonia co-precipitation with Ce0.9Gd0.1O2 (GDC) in a specific ratio by weight. La1-xSrxMnO3 (LSM) powder was used as the cathode material. The electrochemical characteristics of the cells, with the Ni-Co cermet anodes, were evaluated by measuring I-V measurements coupled with the current interruption method under the condition at 800oC, where 3%-humidified hydrogen fuel was supplied to the anode. Furthermore, the redox stability was evaluated using the durability test protocol simulating the fuel interruption (3). Anode microstructure was observed by a focused-ion beam system coupled with a scanning electron microscope (FIB-SEM). Results and discussion Figure 1 shows the I-V characteristics and overvoltages of the Ni-Co-GDC anode with various Co concentrations at 800oC with 3%-humidified hydrogen fuel. With increasing the Co content, the electrochemical performance decreased due to an increase in overvoltages. However, when the Co content was as low as 5 mol%, performance decrease was negligible. Figure 2 shows the redox stability of the Ni-Co-GDC anode evaluated by using the durability test protocol simulating the fuel interruption. With increasing the Co content, the redox stability was improved, associated with relatively-low ohmic losses. The microstructure of Ni-Co-GDC anodes will be reported and discussed. References Q. Fang et al., Int. J. Hydrogen Energy, 40, 1128 (2015).Y. Ishibashi et al., J. Electrochem. Soc., 167, 124517 (2020).M. Hanasaki et al., J. Electrochem. Soc., 161 (9), F850-60 (2014). Figure 1

Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing

The tubular solid oxide fuel cells (SOFCs) with one closed-end configuration have high thermal-cycling tolerance owing to the capability of expanding and shrinking freely in response to thermal stresses. The 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 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 were comprised of Ni-yttria-stabilized zirconia, Ni–scandia-stabilized zirconia (SSZ), 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 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.

Crystal phase, electrical properties, and solid oxide fuel cell electrolyte application of scandia-stabilized zirconia doped with rare earth elements

ZrO2–10 ​mol% Sc2O3 (10ScSZ) has attracted attention as an electrolyte material for solid oxide fuel cells owing to its high conductivity. However, the phase transition between cubic and rhombohedral occurs in the range 500–600 ​°C, resulting in its rapid decrease in conductivity below 500 ​°C. In this study, we determined the elements that can eliminate phase transition in the range 500–600 ​°C for 10ScSZ to realize high conductivity for all temperature regions. Rare elements were incorporated to 10ScSZ. X-ray diffraction and conductivity measurements were used to confirm the occurrence of phase transition. The results noted that the addition of La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb improved the conductivity of 10ScSZ below 500 ​°C, unlike that with the addition of Dy, Y, Ho, Er, Tm, Yb, Lu, and Sc. Further, although the addition of Ce to 10ScSZ was considered a solution, Nd and Sm were also noted to be effective additives.

Comparison of electrochemical impedance spectra for electrolyte-supported solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs)

Protonic ceramic fuel cells (PCFCs) are expected to achieve high power generation efficiency at intermediate temperature around 400–600 °C. In the present work, the distribution of relaxation times (DRT) analysis was investigated in order to deconvolute the anode and cathode polarization resistances for PCFCs supported on yttria-doped barium cerate (BCY) electrolyte in comparison with solid oxide fuel cells (SOFCs) supported on scandia-stabilized zirconia (ScSZ) electrolyte. Four DRT peaks were detected from the impedance spectra measured at 700 °C excluding the gas diffusion process for ScSZ and BCY. The DRT peaks at 5 × 102–1 × 104 Hz and 1 × 100–2 × 102 Hz were related to the hydrogen oxidation reaction at the anode and the oxygen reduction reaction at the cathode, respectively, for both cells. The DRT peak at 2 × 101–1 × 103 Hz depended on the hydrogen concentration at the anode for ScSZ, while it was dependent on the oxygen concentration at the cathode for BCY. Compared to ScSZ, steam was produced at the opposite electrode in the case of BCY, which enhanced the cathode polarization resistance for PCFCs.