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Article

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

by
Xiaoxing Yang
1,
He Miao
1,
Baowei Pan
1,
Ming Chen
2 and
Jinliang Yuan
1,*
1
Faculty of Maritime and Transportation, Ningbo University, Ningbo 315211, China
2
Department of Energy Conversion and Storage, Technical University of Denmark, 2800 Lyndby, Denmark
*
Author to whom correspondence should be addressed.
Energies 2022, 15(6), 2178; https://0-doi-org.brum.beds.ac.uk/10.3390/en15062178
Submission received: 4 January 2022 / Revised: 11 March 2022 / Accepted: 15 March 2022 / Published: 16 March 2022
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Versions Notes

Abstract

:
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.

1. Introduction

Reversible solid oxide cell (RSOC) is able to work as both a solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC), i.e., not only use fuel to generate electricity in SOFC mode, but also by using waste heat and renewable energy (such as solar energy and wind energy) to produce hydrogen through electrolysis of water for the purpose of energy storage with no by-products [1,2,3]. Therefore, RSOC is considered as one of the highest potential energy conversion devices for hydrogen production and power generation [4]. RSOC has attracted much more attention in recent years due to its high conversion efficiency and cleanliness in hydrogen production and power generation [5,6], and the RSOC system can constitute the core component connecting the existing and future energy networks [7], further to be applied in the field of energy storage [8].
Although RSOC technology has been developed for some years [9], the high decay rate appeared in the SOEC operating mode has always been a major obstacle hindering the development of RSOC. It is found that interfacial resistance in the oxygen electrode is much higher compared with that in fuel electrode, which is considered as one of the major reasons for resulting in performance decay. When the RSOC with the La0.8Sr0.2MnO3 (LSM)-YSZ oxygen electrode was electrolyzed at a high potential for a long time, delamination could occur at interface region between the electrode/electrolyte layers, which may result in a total performance failure [10,11].
Mixed ionic conductors, which are suitable for RSOC oxygen electrodes due to their excellent ionic and electronic conductivity [5], have been well developed in recent years. Sm0.5Sr0.5CoO3-δ (SSC) has attracted a lot of attention due to its excellent electrochemical performance and high mixed ion conductivity [12]. Sm0.5Sr0.5CoO3-δ-Ce0.8Sm0.2O1.9 (SSC-SDC) and SSC-GDC composite cathodes showed the improved performance in solid oxide fuel cell and electrolysis cell compared with LSM oxygen electrode [13,14,15,16,17,18]. Jiang et al. [19] prepared the SSC-SDC composite material as the RSOC oxygen electrode, and it is found that the oxygen electrode performance of SSC-SDC had a great advantage over LSM. Ping et al. [20] impregnated SSC and SDC nanoparticles into the LSM framework as the oxygen electrode of RSOC, and it was revealed that the maximum power density of the impregnated oxygen electrode reached 1.21 W·cm−2, while the current density reached 1.62 A·cm−2 at an applied voltage of 1.5 V, which is a great improvement compared to the LSM oxygen electrode. Jiang et al. [19] fabricated a NiO-GDC|YSZ|SSC-GDC single cell using SSC-GDC as the oxygen electrode, and it was revealed that in SOFC mode, the peak power density reached 0.244 W·cm−2 at 850 °C, while in SOEC mode, a current density of 0.1 A·cm−2 was obtained when a voltage of 1.3 V was applied. However, after 14 cycles of alternating runs in SOFC and SOEC modes, the oxygen electrode in the cell was delaminated from the electrolyte layer [19]. An important issue for the discharge and electrolysis operation of RSOC is the performance of the oxygen electrode, which is mainly determined by two factors, one is the characteristics of the material itself, and the other one is the structure of the oxygen electrode. Although intrinsic material properties (such as the electrochemical catalytic activity and electrical conductivity of electrode materials) are crucial [21], in practice, the oxygen electrode structure largely determines the overall cell performance [22]. SSC has a relatively large thermal expansion coefficient (TEC) (21.7~24 × 10−6 K−1) [23,24], while SDC has a lower value (12 × 10−6 K−1) [25]. Mixing of both SSC and SDC may obtain a proper value of TEC, which is essential for the oxygen electrode of RSOC [26]. Reducing the particle size of SSC-SDC composite may further improve the performance of RSOC. In order to explore the effect of the atomic particle diameter of SSC and SDC on the performance of oxygen electrode, the in-situ composite method is employed in the current study to prepare SSC and SDC composites.
In this work, the SSC@SDC powder is fabricated by an in-situ method and applied as the oxygen electrode for RSOC with SSZ electrolyte. The effects of the composition of 10-xSSC@xSDC (x = 3, 4, 5, 6) on the interfacial polarization resistance were studied using symmetrical half-cells. It is found that the electrolyte-supported cells with 5SSC@5SDC showed low interfacial resistances, high power density, and electrolysis performance with an improved stability.

2. Materials and Methods

2.1. Fabrication of Oxygen Electrodes

Figure 1a shows the preparation diagram of different proportions of SSC and SDC (marked as 10-xSSC@xSDC, x = 3, 4, 5, 6 stands for SDC ratio) to be applied for the oxygen electrode of RSOC, (I) refers to the SSC and SDC solution, (II) refers to the mixing solution of 10-xSSC@xSDC (x = 3, 4, 5, 6), (III) refers to the 10-xSSC@xSDC (x = 3, 4, 5, 6) powder. The 10-xSSC@xSDC powders were successfully fabricated from the following steps. Stoichiometric amounts of Sm(NO3)2·6H2O, Sr(NO3)2·6H2O, Co(NO3)2·6H2O and Sm(NO3)2·6H2O, and Ce(NO3)2·6H2O were dissolved in 50 mL of deionized water, respectively (marked as solution A and B). EDTA and citric acid with the ratio of metal ion, EDTA, citric acid being 1:1.5:1.2 were dissolved in 200 mL deionized water, respectively. Then, ammonia is added until it is completely dissolved (marked as solution C and D). The solutions of A and C, B and D are mixed and stirred completely, and then the mixed solution is heated in water at 80 °C accompanied with stirring until the gel was formed. the gel is dried at 180 °C for 10 h and sintered at 850 °C for 5 h to fabricate 10-xSSC@xSDC (x = 3, 4, 5, 6).
The SSC, SDC powders were fabricated with the same preparation method of 10-xSSC@xSDC (x = 3, 4, 5, 6) except for the different stoichiometric ratio of the metal ions. For comparison, SSC and SDC with a weight ratio of 1:1 is prepared by the physical mixing under ball milling (marked as SSC-SDC). Figure 1b shows particle model of SSC@SDC, where (IV) represents the particles of SSC and SDC after in-situ synthesis procedure, and (V) and (VI) are the microstructure models of SSC and SDC, respectively. Figure 1c shows the single cell model and its microstructure schematics of the oxygen electrode, in which (VII) refers to the structure of the single cell, including the fuel electrode, electrolyte, and oxygen electrode layer, while (VIII) and (IX) represent the oxygen electrodes with traditional SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6).

2.2. Fabrications of Symmetrical Cells and Single Cells

Symmetrical cells were successfully fabricated with a commercial SSZ electrolyte layer (thickness 200 μm, diameter 200 μm from Ningbo SOFCMAN energy technology Co, Ltd., Ningbo, Zhejiang, China). The mixed slurries of SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC were prepared by mixing with ethyl cellulose and terpineol under ball milling. The slurries were screen-printed on the both sides of the electrolyte layers, and then sintered at 1250 °C for 5 h. The thickness of the electrode was kept about 20 μm, while the cathode active area is controlled at around 0.79 cm2. For fabrication of the full electrode, NiO and YSZ physically mixing slurry (NiO-YSZ from Ningbo SOFCMAN energy technology Co, Ltd., Ningbo, China) was screen-printed on one side of the SSZ electrolyte layer as the fuel electrode, while SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) slurries were screen-printed on the other side of the electrolyte layer, respectively, while the obtained cells were further sintered at 1250 °C for 5 h.

2.3. Microstructure Characterizations

The phase structures of the obtained powders were investigated by X-ray Diffraction (XRD) with Bruker D8 Advance X-ray diffractometer (Cu Kα = 1.5418 Å). The diffraction patterns were collected at a temperature in the range of 20~80° with the step width of 0.02° and scan rate of 0.5 s·step−1. The microstructures of the powders and porous oxygen electrodes were observed using a scanning electron microscope (FESEM, Hitachi S4800, 5 kV). The distribution of the elements was observed by energy dispersive X-ray spectrometry (EDS) mapping.

2.4. Electrochemical and Cell Performance Measurements

The thermal expansion coefficients were measured with a thermal expansion tester (Thermal dilatometer, NETZSCH DIL402C), and the oxygen electrode powders were pressed into a 2 × 0.66 × 0.23 cm long bar. The polarization resistances and area specific resistances (ASR) of 10-xSSC@xSDC (x = 3, 4, 5, 6) oxygen electrodes were characterized by the electrochemical impedance spectra (EIS) (Zahner Electrochemical Workstation) in the frequency range of 100 mHz to 100 KHz at AC amplitude of 50 mV.
The schematic diagram of the testing device for RSOCs is shown in Figure 2. The silver paste was coated on the fuel electrode and oxygen electrode of the RSOC as a current collecting layer, and then the silver wires were used as the current collecting line. In the SOFC mode, the H2-H2O mixture with 8% absolute humidity (A.H) was introduced into the fuel electrode, while air was introduced into the oxygen electrode. I-V curves of RSOCs were obtained at 700, 750, and 800 °C. In the SOEC mode, the water vapor containing 10% H2 was heated at 300 °C and introduced into the fuel electrode, and the electrolysis performances at 800 °C was evaluated by I-V curves. The electrolytic stability of SOEC was tested under the condition of a constant current density of 0.40 A·cm−2 at 800 °C.

3. Results and Discussion

3.1. Characterization of Phase Structure and Microstructure

The Figure 3 shows the X-ray diffraction (XRD) patterns of the synthesized SSC, SDC, SSC-SDC, and 10-xSSC@xSDC (x = 3 ,4, 5, 6) by sol-gel and in-situ synthesis methods after the sintering at 850 °C for 2 h. The results demonstrate that the prepared powders are consistent with the characteristic peaks of the cubic perovskite structure SSC (PDF#53-0112) and fluorite structure SDC (PDF#75-0158) without any other impurity peaks, as also presented in Chang [27] and Lee et al. [28]. It means that all powders have been successfully prepared with good chemical compatibility.
Figure 4 shows the micromorphologies of SSC-SDC and 5SSC@5SDC composite powders characterized by SEM. The SDC phase and SSC phase have been marked in the diagrams of the presented microstructure. Figure 4a indicates that the particle diameters of SSC and SDC in SSC-SDC are equivalent, about 800~1000 nm. The 5SSC@5SDC was composed of a skeleton with the large particles in the diameter range of 200~300 nm, while many 10~20 nm fine particles were coated on the skeleton (Figure 4b). Whereas, almost no such fine particles can be found in SSC-SDC composite powders (Figure 4a), obtaining the fine particles coated on the SDC skeleton is the key for the high-performance oxygen electrode of RSOC, which can provide more catalytic active sites performing the oxygen catalytic reactions [28]. Besides, using the oxygen ion conductor material (SDC) to construct a dense skeleton structure with evenly dispersed nano-size oxygen catalysts is beneficial to form the large TPB length and well-connected networks in the resulted oxygen electrodes.

3.2. Characterization of Thermal Expansion Coefficients and Symmetrical Cells

Figure 5a shows the results of the TEC of the compressed long samples using the powders in the air between 200 and 800 °C. The specific TEC values are shown in Table 1. As shown in the table, compared with the TEC of SSC (21.7~24 × 10−6 K−1) [23,24], the TEC of SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) is smaller, with the average values between 16.1~19.82 × 10−6 K−1. In addition, the TEC of 10-xSSC@xSDC (x = 3, 4, 5, 6) prepared by in-situ composite materials has reached the minimum value of 13.62 × 10−6 K−1 when x = 5. However, when x = 6, the thermal expansion coefficient increases. This is because the thermal expansion coefficient of the combination of SSC and SDC reaches the threshold when the in-situ composite preparation is performed, which is similar to the results obtained by Zhu et al. [29].
In order to further explore the performance of 10-xSSC@xSDC (x = 3, 4, 5, 6) composite powders, the symmetrical cells with SSZ electrolyte layer are fabricated to measure the polarization resistance by the electrochemical impedance spectroscopy (EIS) (Figure 5b). EIS is a useful technique for examining the electrochemical properties of oxygen electrodes [30]. Polarization resistance (Rp) of the oxygen electrode can be estimated by fitting the results of the equivalent circuit (inset in Figure 5b). The polarization resistance (Rp) values of the composite oxygen electrodes SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC are shown in Table 2. It is found that the case of 5SSC@5SDC has the lowest polarization resistance of 0.17 Ω·cm2, which is much smaller than that of SSC-SDC (0.45 Ω·cm2 from the EIS curves).

3.3. Performance and Electrochemical Testing

The RSOC with various composite materials (SSC-SDC, 7SSC@3SDC, 6SDC@4SDC, and 5SSC@5SDC) are operated using 8% H2O-H2 mixture fuel gas fed into the fuel electrode and air into the oxygen electrode, respectively. Figure 6a shows the I-V curves under the H2O-H2 mixture gas in both fuel cell and electrolysis mode at 800 °C. In the fuel cell mode, the H2O mass ratio in the mixture gas is 8%, and the open circuit voltages (OCVs) of the four cells are higher than 1.00 V, which indicates that the SSZ electrolyte layers are fully dense, and a good sealing is also achieved for the testing cells.
Table 3 lists the electrochemical performance of SOFC with SSC-based oxygen electrodes. The performances of the RSOC with SSC-SDC composite is the worst among those with all the composite electrodes. In both the electrolysis and fuel cell modes, the RSOC with 5SSC@5SDC composite oxygen electrode shows the best electrochemical performances, and the electrolysis current density and peak power density can reach 0.40 A·cm−2 at 1.30 V and 0.49 W·cm−2, respectively. Figure 6b shows the EIS plots of different composite electrodes at the open circuit voltage. Each curve is collected after the cell reaches a steady state at 800 °C. As shown in Figure 6b, the polarization resistance of RSOC decreases from 0.89 Ω·cm2 (7SSC@3SDC) to 0.69 Ω·cm2 (5SSC@5SDC) with the increase of SDC content in the different SSC@SDC oxygen electrodes. While the SSC-SDC oxygen electrode has the largest polarization resistance of 1.27 Ω·cm2 among all the tested RSOC with the composite oxygen electrodes, compared with RSOC using SSC-SDC oxygen electrode, the smaller polarization resistance of RSOC with 5SSC@5SDC can be ascribed to the smaller SSC particles coated on SDC skeleton surfaces, which can dramatically improve the oxygen catalytic activities and increase the TPB lengths of the oxygen electrodes.
Figure 6c,d show the electrochemical performances of RSOC with 5SSC@5SDC as the oxygen electrode operated at the fuel cell mode. All the measurements are performed with 8% H2O-H2 as the fuel and air as the oxidant. The I-V/I-P curves of RSOC with 5SSC@5SDC as the oxygen electrode are obtained at the different temperatures. The OCV of RSOC decreases with the increasing of the operating temperature. The peak power density increases from 0.20 to 0.49 W·cm−2 with the operating temperature increasing from 700 to 800 °C. Figure 6d shows the EIS curves of RSOC with 5SSC@5SDC in the temperature range of 700~800 °C. The polarization resistances of the 5SSC@5SDC increase from 0.69 to 2.26 Ω·cm2 with decreasing the temperature from 800 to 700 °C.

3.4. Stability Testing

The short-term stabilities of RSOC with SSC-SDC and 5SSC@5SDC oxygen electrodes are measured in the electrolysis mode under the constant operating current density. The mixed gas of 90% H2O-10%H2 is supplied into the fuel electrode as the reactant gas. Figure 7a depicts the stability testing performance of the two cells with 5SSC@5SDC and SSC-SDC oxygen electrodes under the operating electrolysis current density of 0.20 and 0.40 A·cm−2 at 800 °C, respectively. It can be found that the voltage of RSOC with SSC-SDC rapidly increases from 1.40 to 3.00 V due to the high oxygen partial pressure of the oxygen electrode, which causes the delamination of the oxygen electrode layer from the SSZ electrolyte layer (Figure 7c). Whereas, the operating electrolysis voltage of RSOC with SSC@SDC slightly decreases from 1.28 to 1.17 V at the early stage and then keeps almost stable. The decrease of the electrolysis voltage can be related to the activation of the oxygen electrode [32,33]. After the stability testing stage, the oxygen electrode and electrolyte layer are closely connected without any delamination appeared (Figure 7d).

4. Conclusions

In this work, a novel 5SSC@5SDC composite material was synthesized by a facile in-situ sol-gel method, and further used as the oxygen electrode of RSOC. 5SSC@5SDC was composed of an SDC skeleton and many fine SSC nanoparticles coated on the SDC skeleton. Such a structure leads to a high catalytic activity, large TPB length, and well-connected network in the oxygen electrode. It is found that the polarization resistance of 5SSC@5SDC was as low as 0.69 Ω·cm2, and the peak power density of RSOC with 5SSC@5SDC could reach 0.49 W·cm−2 at 800 °C. More importantly, compared with RSOC employing SSC-SDC, the case with 5SSC@5SDC materials demonstrates a greatly improved stability under SOEC operating model.

Author Contributions

Experiment—X.Y.; Writing—original draft preparation, X.Y.; Writing—review and editing, H.M., M.C. and J.Y.; Formal analysis, B.P.; Supervision, H.M. and J.Y.; Project administration, J.Y.; Funding acquisition, J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Key Research and Development Project of China (2018YFB1502204), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2019B10043).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Schematics of fabricating process of 10-xSSC@xSDC (x = 3, 4, 5, 6) by in-situ sol-gel synthesis, (I) SSC and SDC solution, (II) mixing solution of 10-xSSC@xSDC (x = 3, 4, 5, 6), (III) 10-xSSC@xSDC (x = 3, 4, 5, 6) powder. (b) Schematics of the 10-xSSC@xSDC (x = 3, 4, 5, 6) particles, (IV) 10-xSSC@xSDC (x = 3, 4, 5, 6) procedure particles, (V) SSC microstructure model (VI) SDC microstructure model. (c) Single cell structure and schematics of oxygen electrode layer composing of SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) particles, (VII) single cell structure, (VIII) traditional oxygen electrodes with SSC-SDC, (IX) in-situ composite oxygen electrodes with 10-xSSC@xSDC (x = 3, 4, 5, 6).
Figure 1. (a) Schematics of fabricating process of 10-xSSC@xSDC (x = 3, 4, 5, 6) by in-situ sol-gel synthesis, (I) SSC and SDC solution, (II) mixing solution of 10-xSSC@xSDC (x = 3, 4, 5, 6), (III) 10-xSSC@xSDC (x = 3, 4, 5, 6) powder. (b) Schematics of the 10-xSSC@xSDC (x = 3, 4, 5, 6) particles, (IV) 10-xSSC@xSDC (x = 3, 4, 5, 6) procedure particles, (V) SSC microstructure model (VI) SDC microstructure model. (c) Single cell structure and schematics of oxygen electrode layer composing of SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) particles, (VII) single cell structure, (VIII) traditional oxygen electrodes with SSC-SDC, (IX) in-situ composite oxygen electrodes with 10-xSSC@xSDC (x = 3, 4, 5, 6).
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Figure 2. Schematic diagram of single cell testing equipment.
Figure 2. Schematic diagram of single cell testing equipment.
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Figure 3. XRD patterns of pure SSC, pure SDC, physically mixed SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) after firing at 850 °C for 2 h.
Figure 3. XRD patterns of pure SSC, pure SDC, physically mixed SSC-SDC and 10-xSSC@xSDC (x = 3, 4, 5, 6) after firing at 850 °C for 2 h.
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Figure 4. (a) SEM micrograph of SSC-SDC. (b) SEM micrograph of 5SSC@5SDC.
Figure 4. (a) SEM micrograph of SSC-SDC. (b) SEM micrograph of 5SSC@5SDC.
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Figure 5. (a) TEC curves for SSC-SDC, 7SSC@3SDC, 6SDC@4SDC, 5SSC@5SDC, and 4SSC@6SDC samples. (b) EIS curves of the symmetric cells with SSC-SDC, 7SSC@3SDC, 6SDC@4SDC, 5SSC@5SDC, and 4SSC@6SDC electrodes measured at 800 °C.
Figure 5. (a) TEC curves for SSC-SDC, 7SSC@3SDC, 6SDC@4SDC, 5SSC@5SDC, and 4SSC@6SDC samples. (b) EIS curves of the symmetric cells with SSC-SDC, 7SSC@3SDC, 6SDC@4SDC, 5SSC@5SDC, and 4SSC@6SDC electrodes measured at 800 °C.
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Figure 6. Electrochemical performances of RSOC with the SSC-SDC and SSC@SDC oxygen electrodes. (a) I-V (a,b) EIS curves of RSOCs with SSC-SDC, 7SSC@3SDC, 5SSC@5SDC, and 4SSC@6SDC in fuel cell and electrolysis modes at 800 °C. (c) I-V curves and (d) EIS curves of RSOCs with 5SSC@5SDC in fuel cell model at 700, 750, and 800 °C.
Figure 6. Electrochemical performances of RSOC with the SSC-SDC and SSC@SDC oxygen electrodes. (a) I-V (a,b) EIS curves of RSOCs with SSC-SDC, 7SSC@3SDC, 5SSC@5SDC, and 4SSC@6SDC in fuel cell and electrolysis modes at 800 °C. (c) I-V curves and (d) EIS curves of RSOCs with 5SSC@5SDC in fuel cell model at 700, 750, and 800 °C.
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Figure 7. (a) Short-term durability testing of RSOC with SSC-SDC and SSC@SDC oxygen electrodes under electrolysis mode at 800 °C (90%H2O-10%H2 humidity condition, the constant current densities of 0.20 A·cm−2 for SSC-SDC oxygen electrode and 0.40 A·cm−2 for SSC@SDC oxygen electrode). (b) Button cell with electrolyte-support structure employing 5SSC@5SDC oxygen electrode, SSZ electrolyte, and NiO-YSZ anode electrode (c) SEM image of interface between electrolyte and oxygen electrode of SSC-SDC after 2 h electrolysis operation, and (d) SEM image of 5SSC@5SDC oxygen electrode after 10 h electrolysis operation.
Figure 7. (a) Short-term durability testing of RSOC with SSC-SDC and SSC@SDC oxygen electrodes under electrolysis mode at 800 °C (90%H2O-10%H2 humidity condition, the constant current densities of 0.20 A·cm−2 for SSC-SDC oxygen electrode and 0.40 A·cm−2 for SSC@SDC oxygen electrode). (b) Button cell with electrolyte-support structure employing 5SSC@5SDC oxygen electrode, SSZ electrolyte, and NiO-YSZ anode electrode (c) SEM image of interface between electrolyte and oxygen electrode of SSC-SDC after 2 h electrolysis operation, and (d) SEM image of 5SSC@5SDC oxygen electrode after 10 h electrolysis operation.
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Table
Table 1. Specific average TEC values for SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, 4SSC@6SDC composites between 200 and 800 °C in air.
Table 1. Specific average TEC values for SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, 4SSC@6SDC composites between 200 and 800 °C in air.
SampleTEC (10−6 K−1)
SSC21.7~24 [23,24]
SSC-SDC19.78
7SSC@3SDC19.82
6SSC@4SDC18.25
5SSC@5SDC13.62
4SSC@6SDC16.10
Table
Table 2. The polarization resistance (Rp) values of symmetric cells with composite oxygen electrodes SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC in air at 800 °C.
Table 2. The polarization resistance (Rp) values of symmetric cells with composite oxygen electrodes SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC in air at 800 °C.
SamplePolarization Resistance (Rp) (Ω·cm2)
SSC-SDC0.45
7SSC@3SDC0.32
6SSC@4SDC0.24
5SSC@5SDC0.17
4SSC@6SDC0.28
Table
Table 3. Electrochemical performance of the composite oxygen electrodes SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC in air at 800 °C.
Table 3. Electrochemical performance of the composite oxygen electrodes SSC-SDC, 7SSC@3SDC, 6SSC@4SDC, 5SSC@5SDC, and 4SSC@6SDC in air at 800 °C.
Oxygen ElectrodeElectrolyteFuel
Electrode		T
(°C)		OCV
(V)		Rp
(Ω·cm2)		MPD
(W·cm−2)		Ref.
SSC-SDCSSZNi/YSZ8001.0331.2710.247-
7SSC@3SDCSSZNi/YSZ8001.0440.8930.294-
6SSC@4SDCSSZNi/YSZ8001.0370.7210.338-
5SSC@5SDCSSZNi/YSZ8001.0490.6910.489-
4SSC@6SDCSSZNi/YSZ8001.0340.7570.308-
SSC-BCZYBCZYNi-BCZY700-0.370.24[31]
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Yang, X.; Miao, H.; Pan, B.; Chen, M.; Yuan, J. In-Situ Synthesis of Sm0.5Sr0.5Co0.5O3-δ@Sm0.2Ce0.8O1.9 Composite Oxygen Electrode for Electrolyte-Supported Reversible Solid Oxide Cells (RSOC). Energies 2022, 15, 2178. https://0-doi-org.brum.beds.ac.uk/10.3390/en15062178

AMA Style

Yang X, Miao H, Pan B, Chen M, Yuan J. In-Situ Synthesis of Sm0.5Sr0.5Co0.5O3-δ@Sm0.2Ce0.8O1.9 Composite Oxygen Electrode for Electrolyte-Supported Reversible Solid Oxide Cells (RSOC). Energies. 2022; 15(6):2178. https://0-doi-org.brum.beds.ac.uk/10.3390/en15062178

Chicago/Turabian Style

Yang, Xiaoxing, He Miao, Baowei Pan, Ming Chen, and Jinliang Yuan. 2022. "In-Situ Synthesis of Sm0.5Sr0.5Co0.5O3-δ@Sm0.2Ce0.8O1.9 Composite Oxygen Electrode for Electrolyte-Supported Reversible Solid Oxide Cells (RSOC)" Energies 15, no. 6: 2178. https://0-doi-org.brum.beds.ac.uk/10.3390/en15062178

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