Highly Stable and Efficient Perovskite Ferrite Electrode for

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Highly Stable and Efficient Perovskite Ferrite Electrode for Symmetrical Solid Oxide Fuel Cells Weiwei Fan, Zhu Sun, Yu Bai, Kai Wu, and Yonghong Cheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b04286 • Publication Date (Web): 10 Jun 2019 Downloaded from http://pubs.acs.org on June 12, 2019

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ACS Applied Materials & Interfaces

Highly Stable and Efficient Perovskite Ferrite Electrode for Symmetrical Solid Oxide Fuel Cells Weiwei Fan,†,‡ Zhu Sun,*,§ Yu Bai,*,† Kai Wu,‖ and Yonghong Cheng‖ †State

Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an

710049, People’s Republic of China ‡Department

of Nuclear Science and Engineering, Massachusetts Institute of Technology,

Cambridge 02139, USA §State

Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an

710049, People’s Republic of China ‖ State

Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University,

Xi'an 710049, People’s Republic of China

ABSTRACT:

Here,

we

report

a

new

perovskite

oxide

with

formula

Sm0.8Sr0.2Fe0.8Ti0.15Ru0.05O3−δ (SSFTR), which exhibits great promise as symmetrical electrode material with satisfying stability in both reducing and oxidizing environments. Moreover, SSFTR exhibits good redox and thermal cycle stability. The electrolyte-supported (Sm0.2Ce0.8O1.9, SDC) symmetrical cell with SSFTR electrodes possesses peak power density of 271 mW cm−2 at 800 °C in wet H2. Moreover, the peak power density is remarkably improved to 417 mW cm−2 when applying A-site deficient perovskite oxide Sm0.7Sr0.2Fe0.8Ti0.15Ru0.05O3−δ as the symmetrical electrode, benifiting by the in situ exsolved Ru nanoparticles with excellent electrocatalytic activity, since A-site deficiency can provide additional driving force for the exsolution of B-site cations upon reduction. As an ingenious approach, this exsolution of electrocatalytically active nanoparticles on the surface of electrode may be applicable to the development of other excellent-performance electrodes for symmetrical SOFCs and other electrochemical systems. KEYWORDS: Symmetrical solid oxide fuel cell, in situ exsolution, nanoparticle catalyst, perovskite oxide, electrochemical performance

1. INTRODUCTION As a green and promising energy technology, solid oxide fuel cell (SOFC) is widely focused and utilized in the past few decades since their specific advantages, such as low pollution emission and high conversion efficiency.1–3 Besides, SOFCs not only 1

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can use hydrogen coming from the internal reforming of multifarious hydrocarbons as fuel, but also can directly work on hydrocarbon fuels.4–7 However, because of the stability and cost issues, SOFC has still not been realized for the widespread commercial application. Hence, to compete with today’s mature power generation technologies based on the combustion of fossil fuel, it is urgently needed to develop new materials and fabrication methods. A traditional SOFC consists of La0.8Sr0.2MnO3 (LSM) cathode, stabilized zirconia electrolyte and nickel-based anode. Due to their different functions and properties, the cathode and anode layers were generally fabricated by different procedures, leading to a relative high cost of the cell fabrication. Besides, two different interfaces (cathode/electrolyte and anode/electrolyte) can bring about more potential problems about the compatibility between the electrode material and the electrolyte material. Generally, nickel-based cermet anode exhibits excellent activity towards the fuel oxidation and good conductivity.8 However, carbon deposition and sulfur poisoning will occur when the nickel-based anode is operated in carbon- and sulfur-containing fuels, resulting in the deterioration of cell performance. Moreover, nickel cermet anode is liable to re-oxidation, which can affect remarkably the integrity of fuel cell.9– 11

Regarding to the commonly used LSM cathode, it is unstable in a strong reducing

environment. When the fuel cell is operated at lower voltage, the oxygen partial pressure at triple phase boundary is very low. That is to say, the cell performance will decrease under this condition since the poor redox stability of LSM cathode.12 Taking the above problems into consideration, a new configuration to replace the conventional SOFC was proposed, using the same material as cathode and anode simultaneously, and this new configuration is named as symmetrical SOFC (SSOFC).13,14 Compared to the traditional SOFC, this new configuration has a number of advantages. For example, SSOFC can provide an effective way to simplify the process of cell fabrication, minimize the compatibility problems about thermal stresses which come from the interfaces of different cell components, reduce potentially the processing costs and improve the stability and reliability. Furthermore, any performance degradation of anode caused by carbon deposition could be recovered by readily switching gas flow. Similarly, sulfur poisoning could also be effectively relieved. Notwithstanding these outstanding advantages, it is difficult to find competent materials which can be applied for SSOFC, because the requirements for symmetrical electrode materials are very strict. The eligible symmetrical electrode materials should possess enough electronic conductivity, favourable catalytic activities toward hydrogen oxidation as well as oxygen reduction, and good structural stability in both 2


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oxidizing and reducing environments. Hitherto, on account of these particular restrictions, the qualified symmetrical materials are limited, which are generally perovskite oxides. Recently, it was demonstrated that La0.8Sr0.2Sc0.2Mn0.8O3−δ (LSSM) possessed excellent structural and chemical stability under reducing and oxidizing environments.15 Bastidas et al. reported that the peak power density of LSCM (La0.75Sr0.25Cr0.5Mn0.5O3−δ) |yttria-stabilized zirconia (YSZ) |LSCM was 300 mW cm−2 when applying H2 as fuel at 900 °C.16 Yang et al. employed La0.7Sr0.3Fe0.7Ga0.3O3−δ (LSFG) as both anode and cathode, and found that the LSGM (La0.8Sr0.2Ga0.83Mg0.17O3−δ) electrolyte-supported symmetrical cell with LSFG electrode material possessed good stability in H2.17 Martínez-Coronado obtained that the electrical conductivity of symmetrical material La0.5Sr0.5Co0.5Ti0.5O3−δwas 29 S cm−1 at 850 °C in air, while a value of 0.11 S cm−1 was acquired at 900 °C in 5%H2/95%N2 atmosphere.18 In current research, aiming to develop new symmetrical electrode material, Sm0.8Sr0.2Fe0.8Ti0.15Ru0.05O3−δ

(SSFTR)

perovskite

oxide

was

successfully

synthesized. In principle, to obtain a good adherence between electrode and electrolyte, they should possess similar thermal expansion coefficient (TEC).19,20 Here, it was demonstrated that SSFTR electrode possessed similar TEC to that of Sm0.2Ce0.8O1.9 (SDC) electrolyte, and it exhibited promising electrochemical performance and durability under both oxidizing and reducing conditions. The SDC-supported symmetrical SOFC with the configuration of SSFTR|SDC|SSFTR showed satisfactory cell performance. These make SSFTR possible to be a potential candidate as symmetrical electrode material. Moreover, it was found that, when using A-site deficient oxide Sm0.7Sr0.2Fe0.8Ti0.15Ru0.05O3−δ as the symmetrical electrode, the cell performance could be significantly enhanced, which was mainly attributed to the in situ exsolved Ru nanoparticles with high electrocatalytic activity.

2. EXPERIMENTAL 2.1. Synthesis and Fabrication. A batch of samples Sm0.8Sr0.2Fe0.8Ti0.2−xRuxO3−δ (x = 0.00, 0.05, 0.10, 0.15), denoted as SSFTR00, SSFTR05, SSFTR10 and SSFTR15, respectively, were prepared via solid state reaction method. During the preparation, Sm2O3 (99.9%), SrCO3 (99.95%), Fe2O3 (99.99%), TiO2 (99.99%), and RuO2 (99.9%) were employed as raw materials. In order to remove carbonates and hydroxides of the highly hygroscopic oxides, Sm2O3 and RuO2 were calcined in air for 1 h at 600 °C. After weighing the respective oxides according to the stoichiometry, the mixture was ball-milled for 10 h and subsequently calcined for 4 h at 1200 °C. Sm0.2Ce0.8O1.9 3



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(SDC) powders were prepared via EDTA-citrate sol-gel method. Sm(NO3)3·6H2O (99.9%) and Ce(NO3)3·6H2O (AR) were applied as the raw materials. Briefly, adding stoichiometric amounts of the corresponding materials into the as-prepared deionized water and then EDTA and citric acid (citric acid : EDTA : total metal ions was 2:1:1) were added. After the vaporizing process at 70 °C, the obtained gel was subsequently calcined at 950 °C for 5 h in air at a heating rate of 5 °C min−1 to form the desired SDC phase. SDC pellets (~12.0 mm in diameter) were prepared by compressing the original powders using hydraulic press and sintered for 10 h at 1400 °C. For preparing SDC-supported SSOFCs, the electrode, well dispersed in the prepared reagent (volume ratio of terpilenol to turpentine was 5:95), was symmetrically screen-printed onto both sides of the SDC electrolyte, and then treated for 4 h at 900 °C. The active area and thickness of the electrode were about 0.5 cm2 and 30 µm, respectively. Gold mesh was used for current collection from both electrodes. Single cell was sealed to alumina tubes using ceramic adhesives (Cerama-bond 552, Aremco) and wet H2 (~3% H2O) was used as the fuel during the measurement of cell performance. 2.2. Characterization. The structure of as-synthesized powders was identified by Bruker D2 PHASER diffractometer. GSAS/EXPGUI software was used to perform the Rietveld refinements of the XRD patterns. The structural stability of SSFTR as a function of temperature was investigated by Bruker D8 Advance diffractometer, which was equipped with Anton Paar HTK 1200N chamber. Data were collected in the 2θ range 20–80° from room temperature (RT) or 100 °C to 800 °C. Netzsch DIL 402C dilatometer with an aluminium oxide reference was applied to inspect the thermal expansion coefficient (TEC) of SSFTR oxide. For the TEC measurement, the as-prepared SSFTR powders were pressed into cylinder-shaped sample (∅10 mm × 25 mm), which was then calcined in air at 1200 °C for 4 h. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Thermo Scientific iCAP 7000) was employed to verify the elemental compositions. Iodometric titration technique was used to estimate the room temperature’s oxygen nonstoichiometry (δ0). Powders with the weight of 0.1 g were dissolved in HCl (6 mol L−1), and the as-prepared thiosulfate (S2O32−) solution was used for titration. For credibility, three parallel experiments were carried out. The δ at high temperatures was measured by thermogravimetric analysis (TGA, Mettler Toledo TGA/DSC 1, Switzerland). To determine the chemical states of SSFTR samples, X-ray photoelectron spectroscopy (XPS) was characterized in situ using Thermo Scientific ESCALAB 250Xi spectrometer. The microstructure of the prepared samples was characterized by FEI Quanta 600F and KEYENCE VE-9800 scanning electron 4


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microscope (SEM). Investigation of transmission electron microscopy (TEM) was carried out on a Tecnai G2F20 S-Twin instrument. For conductivity test, the prepared SSFTR powders were pressed into rectangular bars under a pressure of 100 MPa, and then followed by sintering for 4 h at 1200 °C. The sintered bars were polished by using sandpaper to the dimension of approximately 10 mm × 10 mm × 3 mm. Additionally, the pO2 dependence of σ at 800 °C was also investigated. Before the measurement, a zirconia pO2 sensor was integrated into the conductivity test fixture. During the measurement, sensor was placed closely ( 600 °C).48,49 At 800 °C, a peak power density (PPD) of 271 mW cm−2 was acquired, suggesting that SSFTR was a promising symmetrical electrode material. Figure 7b displays the operation stability of SSFTR|SDC|SSFTR symmetrical cell using wet H2 as fuel at 800 °C. The results revealed that cell voltage maintained at ~0.67 V over a period of 240 h, implying SSFTR could be soundly operated in both cathode and anode environments. For SEM observation, the fuel cell was disassembled from the testing jig after measurement. It could be seen from Figure 7c and d, SSFTR electrodes adhered intimately to the SDC electrolyte without the occurrence of delamination, which further demonstrated the good thermal-mechanical compatibility between SSFTR electrode material and SDC electrolyte material. To further improve the electrochemical performance of SSFTR perovskite oxide, we tried to introduce cation deficiency at Sm-site, and the target material with 10


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chemical formula Sm0.7Sr0.2Fe0.8Ti0.15Ru0.05O3−δ (SSFTR72) was synthesized by the same route of SSFTR. As shown in Figure 8a, SSFTR72 exhibits similar XRD pattern with that of stoichiometric SSFTR, suggesting appropriate introduction of A-site deficiency has negligible effect on the perovskite structure. Similar result was also reported in other literature.50 Moreover, the HT-XRD patterns (Figures 8b and c) of SSFTR72 indicated that no structure change occurred during the measurement. Besides, the elemental compositions of SSFTR and SSFTR72 samples were examined by ICP-AES (Table S6), and the results verified that the actual compositions were close to the expected oxides. Exhilaratingly, when SSFTR72 was treated in 5% H2/Ar for 72 h at 800 °C, it was found that a lot of nanoparticles were uniformly distributed on the surface of SSFTR72 oxide, while SSFTR exhibited a clear and smooth surface (Figures 9a and b). This was mainly due to that A-site deficiency could provide extra driving force for the exsolution of B-site cations upon reduction.51 Furthermore, SSFTR72 powders were examined by transmission electron microscopy before and after the reduction treatment. As shown in Figure 9c, the un-reduced SSFTR72 powder displayed no unusual features. However, after the reduction treatment, nanoclusters were readily apparent on the surface of SSFTR72 particle in high-resolution TEM image (Figure 9d). Lattice fringes yielded atomic spacing in the (1 0 0) direction of 0.236 nm, which was close to the value 0.234 nm for hexagonal Ru [JCPDS card #65-1863], and this result was further confirmed by the following XRD and XPS (Figure 10) results52. To investigate both the stability of SSFTR72 under anode condition of SSOFC and the possible segregation of Ru from the SSFTR72 perovskite, the as-prepared sample was treated in wet H2 (~3%H2O) at 800 °C for 20 h. As displayed in Figure 11, a very weak signal (~44°) was detected in addition to the main phase of SSFTR72, associating with the metallic Ru phase. The experimental results strongly implied that similar effect would occur during the operation of full cell using SSFTR72 as anode. Thus, an enhanced cell performance could be predicted on account of the excellent catalytic activity of metallic Ru. Figure 12a displays the performance of SSFTR72|SDC|SSFTR72 symmetrical cell in humidified H2. As expected, the cell performance improved significantly, and a PPD of 417 mW cm-2 was obtained at 800 °C. This outstanding performance of SSFTR72 is mainly ascribed to two reasons. One is that the exsolved Ru nanoparticles have excellent catalytic activity toward the oxidation of H2, and the other is that the introduced A-site deficiency in perovskite oxide can promote the formation of oxygen vacancies, which contribute to the surface-exchange and migration processes of oxygen species.53–55 These synergetic effects lead to the enhancement of cell output. 11



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Moreover, the stability of SSFTR72|SDC|SSFTR72 symmetrical cell was evaluated. As shown in Figure 12b, SSFTR72 electrodes delivered a steady performance at 800 °C during the operation, suggesting the excellent structural stability of SSFTR72 oxide. After the test, SEM was carried out to investigate the microstructure of the single cell SSFTR72|SDC|SSFTR72 (Figures 12c and d). As expected, nanosized Ru particles were distributed uniformly on the surface of SSFTR72 anode (Figure S6). Additionally, the EIS of SDC electrolyte-supported fuel cells SSFTR|SDC|SSFTR and SSFTR72|SDC|SSFTR72 were measured with one side exposed to wet H2 and the other to ambient air (Figure S7). The polarization resistance was 0.46 Ω cm2 for SSFTR electrodes, while it decreased to 0.34 Ω cm2 for Sm-site deficiency SSFTR72 electrodes at 800 °C, and this result was consistent with the result of power density. The obtained results demonstrate that the exsolution of nanometer-sized particles with high catalytic activity from the parent oxide under working conditions was an ingenious way to improve the symmetrical SOFCs’ performance. In our near future research, we will systematically investigate the in situ exsolution process and the influence of exsolved Ru nanoparticles on the physical and chemical properties of SSFTR72. Finally, for comparison, some other symmetrical SOFCs’ performances are listed in Table 1. It reveals that our fuel cells exhibit simpatico performance, further demonstrating that SSFTR and SSFTR72 oxides can be applied as potential symmetrical electrode materials for SOFCs.

4. CONCLUSIONS In summary, we have developed a novel electrode material with excellent structure stability

under

both

oxidizing

and

reducing

conditions.

Meanwhile,

Sm0.8Sr0.2Fe0.8Ti0.15Ru0.05O3−δ (SSFTR) perovskite oxide exhibited favourable redox stability between reduction and re-oxidation cycles, making this material a candidate for symmetrical SOFCs. SSFTR|SDC|SSFTR symmetrical cell showed a peak power density of 271 mW cm−2 and good stability at 800 °C. Encouragingly, it was found that modest A-site deficiency led to the exsolution of electrocatalytically active Ru nanoparticles in reducing atmosphere, bringing about a significant enhancement in the cell performance. More importantly, further improvements are anticipated due to the possibility to make the exsolution of other single-metal or multi-metal (multicomponent alloy) happen by virtue of prudent selection of other active transition metals and defect chemistries. Hence, this masterly method provides a promising way to remarkably improve the catalytic properties of electrode materials which can be applied in the fields of energy conversion and energy storage. 12


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 ASSOCIATED CONTENT Supporting Information Powder XRD patterns of Sm0.8Sr0.2Fe0.8Ti0.2−xRuxO3−δ (x = 0.00 (SSFTR00), 0.05 (SSFTR05), 0.10 (SSFTR10), 0.15 (SSFTR15)) compositions, XRD profile and SEM image of SSFTR after reduction in humidified H2, SEM images of fresh SSFTR and SSFTR after reduction in 5%H2/N2. HR-TEM images of SSFTR and H-SSFTR, XRD profiles of the mixture of SSFTR and SDC, Nyquist plots of electrochemical impedance spectra for the symmetrical half cell SSFTR|SDC|SSFTR, SEM image of SSFTR72 anode after stability test, Nyquist plots of electrochemical impedance spectra for the symmetrical fuel cells SSFTR|SDC|SSFTR and SSFTR72|SDC|SSFTR72, refined structural parameters for SSFTR and H-SSFTR, binding energies of SSFTR and H-SSFTR samples, percentage contribution from core electrons for Fe, Ti and Ru, parameters obtained from the data fitting of the equivalent circuit LRs(Q1R1)(Q2R2), chemical composition of the as-prepared SSFTR and SSFTR72 samples

 AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. *E-mail: [email protected]. ORCID Yu Bai: 0000-0001-7632-1722 Zhu Sun: 0000-0001-6881-8720

Notes The authors declare no competing financial interest.

 ACKNOWLEDGEMENTS This work is financially supported by the National Natural Science Foundation of China (Grant No: 51507133). W. W. Fan and Z. Sun contribute equally to this work.

 REFERENCES (1) Shao, Z. P.; Haile, S. M. A High-Performance Cathode for the Next Generation of Solid-Oxide Fuel Cells. Nature 2004, 431, 170–173. (2) Chan, K. Y.; Ding, J.; Ren, J. W.; Cheng, S. A.; Tsang, K. Y. Supported Mixed Metal Nanoparticles as Electrocatalysts in Low Temperature Fuel Cells. J. Mater. Chem. 2004, 14, 505– 516. (3) Wachsman, E. D.; Lee, K. T. Lowering the Temperature of Solid Oxide Fuel Cells. Science 13



Page 14 of 34

2011, 334, 935–939. (4) Park, S.; Vohs, J. M.; Gorte, R. J. Direct Oxidation of Hydrocarbons in a Solid-Oxide Fuel Cell. Nature 2000, 404, 265–267. (5) Gross, M. D.; Vohs, J. M.; Gorte, R. J. Recent Progress in SOFC Anodes for Direct Utilization of Hydrocarbons. J. Mater. Chem. 2007, 17, 3071–3077. (6) Mclntosh, S.; Gorte, R. J. Direct Hydrocarbon Solid Oxide Fuel Cells. Chem. Rev. 2004, 104, 4845–4866. (7) Steele, B. C. H.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414, 345– 352. (8) Jiang, S. P.; Chan, S. H. A Review of Anode Materials Development in Solid Oxide Fuel Cells. J. Mater. Sci. 2004, 39, 4405–4439. (9) Atkinson, A.; Barnett, S. A.; Gorte, R. J.; Irvine, J. T. S.; Mcevoy, A. J.; Mogensen, M.; Singhal, S. C.; Vohs, J. Advanced Anodes for High-Temperature Fuel Cells. Nat. Mater. 2004, 3, 17–27. (10) Goodenough, J. B.; Huang, Y. H. Alternative Anode Materials for Solid Oxide Fuel Cells. J. Power Sources 2007, 173, 1–10. (11) Klemenso, T.; Mogensen, M. Ni–YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical Characterization. J. Am. Ceram. Soc. 2007, 90, 3582–3588. (12) Minh, N. Q. Ceramic Fuel Cells. J. Am. Ceram. Soc. 1993, 76, 563–588. (13) Ruiz-Morales, J. C.; Canales-Vázquez, J.; Peña-Martínez, J.; Marrero-López, D.; Núñez, P. On the Simultaneous Use of La0.75Sr0.25Cr0.5Mn0.5O3−δ as Both Anode and Cathode Material with Improved Microstructure in Solid Oxide Fuel Cells. Electrochim. Acta. 2006, 52, 278–284. (14) Ruiz-Morales, J. C.; Marrero-López, D.; Canales-Vázquez, J.; Irvine, J. T. S. Symmetric and Reversible Solid Oxide Fuel Cells. RSC Adv. 2011, 1, 1403–1414. (15) Zheng, Y.; Zhang, C. M.; Ran, R.; Cai, R.; Shao, Z. P.; Farrusseng, D. A New Symmetric Solid-Oxide Fuel Cell with La0.8Sr0.2Sc0.2Mn0.8O3−δ Perovskite Oxide as Both the Anode and Cathode. Acta Materialia 2009, 57, 1165–1175. (16) Bastidas, D. M.; Tao, S.; Irvine, J. T. S. A symmetrical Solid Oxide Fuel Cell Demonstrating Redox Stable Perovskite Electrodes. J. Mater. Chem. 2006, 16, 1603–1605. (17) Yang, Z. B.; Chen, Y.; Jin, C.; Xiao, G. L.; Han, M. F.; Chen, F. L. La0.7Sr0.3Fe0.7Ga0.3O3−δ as Electrode Material for a Symmetrical Solid Oxide Fuel Cell. RSC Adv. 2015, 5, 2702–2705. (18) Martínez-Coronado, R.; Aguadero, A.; Pérez-Coll, D.; Troncoso, L.; Alonso, J. A.; Fernández-Díaz, M. T. Characterization of La0.5Sr0.5Co0.5Ti0.5O3−δ as Symmetrical Electrode Material for Intermediate-Temperature Solid-Oxide Fuel Cells. Int. J. Hydrog. Energy 2012, 37, 18310–18318. (19) Ullmann, H.; Trofimenko, N.; Tietz, F.; Stöver, D.; Ahmad-Khanlou, A. Correlation Between Thermal Expansion and Oxide Ion Transport in Mixed Conducting Perovskite-Type 14


Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Oxides for SOFC Cathodes. Solid State Ionics 2000, 138, 79–90. (20) Tietz, F. Thermal Expansion of SOFC Materials. Ionics 1999, 5, 129–139. (21) Pikalova, E. Y.; Maragou, V. I.; Demina, A. N.; Demin, A. K.; Tsiakaras, P. E. The Effect of Co-Dopant Addition on the Properties of Ln0.2Ce0.8O2−δ (Ln = Gd, Sm, La) Solid-State Electrolyte. Journal of Power Sources 2008, 181, 199–206. (22) Sameshima, S.; Ichikawa, T.; Kawaminami, M.; Hirata, Y. Thermal and Mechanical Properties of Rare Earth-Doped Ceria Ceramics. Mater. Chem. Phys. 1999, 61, 31–35. (23) Mazzieria, V.; Coloma-Pascual, F.; Arcoya, A.; L′Argentière, P. C.; Fígoli, N. S. XPS, FTIR and TPR Characterization of Ru/Al2O3 Catalysts. Appl. Surf. Sci. 2003, 201, 222–230. (24) Christie, A. B.; Lee, J.; Sutherland, I.; Walls, J. M. An XPS Study of Ion-Induced Compositional Changes with Group II and Group IV Compounds. Appl. Surf. Sci. 1983, 15, 224– 237. (25) Bu, Y. F.; Zhong, Q.; Xu, D. D.; Tan, W. Y. Redox Stability and Sulfur Resistance of Sm0.9Sr0.1CrxFe1−xO3−δ Perovskite Materials. J. Alloys Compd. 2013, 578, 60–66. (26) Jin, F. J.; Shen, Y.; Wang, R.; He, T. M. Double-Perovskite PrBaCo2/3Fe2/3Cu2/3O5+δ as Cathode Material for Intermediate-Temperature Solid-Oxide Fuel Cells. J. Power Sources 2013, 234, 244–251. (27) Yang, L. M.; Xie, K.; Xu, S. S.; Wu, T. S.; Zhou, Q.; Xie T.; Wu, Y. C. Redox-Reversible Niobium-Doped Strontium Titanate Decorated with in situ Grown Nickel Nanocatalyst for High-Temperature Direct Steam Electrolysis. Dalton Trans. 2014, 43, 14147–14157. (28) Elmasides, C.; Kondarides, D. I.; Gru1nert, W.; Verykios, X. E. XPS and FTIR Study of Ru/Al2O3 and Ru/TiO2 Catalysts: Reduction Characteristics and Interaction with a Methane−Oxygen Mixture. J. Phys. Chem. B 1999, 103, 5227–5239. (29) Ghaffari, M.; Shannon, M.; Hui, H.; Tan, O. K.; Irannejad, A. Preparation, Surface State and Band Structure Studies of SrTi(1−x)Fe(x)O(3−δ) (x = 0–1) Perovskite-Type Nano Structure by X-Ray and Ultraviolet Photoelectron Spectroscopy. Surf. Sci. 2012, 606, 670–677. (30) Lee, K. T.; Manthiram, A. Synthesis and Characterization of Nd0.6Sr0.4Co1−yMnyO3−δ (0 ≤ y ≤ 1.0) Cathodes for Intermediate Temperature Solid Oxide Fuel Cells. J. Power Sources 2006, 158, 1202–1208. (31) Chen, M.; Paulson, S.; Thangadurai, V.; Briss, V. Cr-Substituted La0.3Sr0.7FeO3−δ Mixed Conducting Materials as Potential Electrodes for Symmetrical SOFCs. ECS Trans 2012, 45, 343– 348. (32) Xiao, G. L.; Liu, Q.; Komvokis, V. G.; Amiridis, M. D.; Heyden, A.; Ma, S. G.; Chen, F. L. Synthesis and Characterization of Mo-doped SrFeO3−δ as Cathode Materials for Solid Oxide Fuel Cells. Journal of Power Sources 2012, 202, 63–69. (33) Zhou, W.; Ran, R.; Shao, Z. P.; Zhuang, W.; Jia, J.; Gu, H. X.; Jin, W. Q.; Xu, N. P. Barium- and Strontium-Enriched (Ba0.5Sr0.5)1+xCo0.8Fe0.2O3−δ Oxides as High-Performance 15



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Cathodes for Intermediate-Temperature Solid-Oxide Fuel Cells. Acta Materialia 2008, 56, 2687– 2698. (34) Tao, S. W.; Irvine, J. T. S. Synthesis and Characterization of (La0.75Sr0.25) Cr0.5Mn0.5O3−δ, a Redox-Stable, Efficient Perovskite Anode for SOFCs. J. Electrochem. Soc. 2004, 151, 252–259. (35) Niu, Y.; Sunarso, J.; Liang, F.; Zhou, W.; Zhu, Z.; Shao, Z. A Comparative Study of Oxygen Reduction Reaction on Bi- and La-Doped SrFeO3−δ Perovskite Cathodes. J. Electrochem. Soc. 2011, 158, 132–138. (36) Markov, A. A.; Patrakeev, M. V.; Savinskaya, O. A.; Nemudry, A. P.; Leonidov, I. A.; Leonidova, O. N.; Kozhevnikov, V. L. Oxygen Nonstoichiometry and High-Temperature Transport in SrFe1−xWxO3–δ. Solid State Ionics 2008, 179, 99–103. (37) Rampling, M. J.; Mather, G. C.; Marques, F. M. B.; Sinclair, D. C. Electrical Conductivity of Hexagonal Ba(Ti0.94Ga0.06)O2.97 Ceramics. J. Eur. Ceram. Soc. 2003, 23, 1911–1917. (38) Sunarso, J.; Baumann, S.; Serra, J. M.; Meulenberg, W. A.; Liu, S.; Lin Y. S.; Costa, J. C. D. Mixed Ionic–Electronic Conducting (MIEC) Ceramic-Based Membranes for Oxygen Separation. J. Membr. Sci. 2008, 320, 13–41. (39) Lv, H.; Tu, H. Y.; Zhao, B. Y.; Wu, Y. J.; Hu, K. A. Synthesis and Electrochemical Behavior of Ce1−xFexO2−δ as a Possible SOFC Anode Materials. Solid State Ionics 2007, 177, 3467–3472. (40) Stefan, E.; Tsekouras, G.; Irvine, J. T. S. Development and Performance of MnFeCrO4-Based Electrodes for Solid Oxide Fuel Cells. Adv. Energy Mater. 2013, 3, 1454−1462. (41) Takeda, Y.; Kanno, R.; Noda, M.; Tomida, Y.; Yamamoto, O. Cathodic Polarization Phenomena of Perovskite Oxide Electrodes with Stabilized Zirconia. J. Electrochem. Soc. 1987, 11, 2656–2661. (42) Siebert, E.; Hammouche, A.; Kleitz, M. Impedance Spectroscopy Analysis of La1−xSrxMnO3-Yttria-Stabilized Zirconia Electrode Kinetics. Electrochim. Acta 1995, 40, 1741– 1753. (43) Ye, L.; Zhou, W.; Jaka, S.; Ran, R.; Shao, Z. P. Characterization and Evaluation of BaCo0.7Fe0.2Nb0.1O3−δ as a Cathode for Proton-Conducting Solid Oxide Fuel Cells. Int. J. Hydrog. Energy 2012, 37, 484−497. (44) Chen, D.; Ran, R.; Zhang, K.; Wang, J.; Shao, Z. P. Intermediate-Temperature Electrochemical Performance of a Polycrystalline PrBaCo2O5+δ Cathode on Samarium-Doped Ceria Electrolyte. J. Power Sources 2009, 188, 96–105. (45) Leonide, A.; Sonn, V.; Weber, A.; Ivers-Tiffée, E. Evaluation and Modeling of the Cell Resistance in Anode-Supported Solid Oxide Fuel Cells. J. Electrochem. Soc. 2008, 155, 36−41. (46) Bierschenk, D. M.; Haag, J. M.; Poeppelmeier, K. R.; Barnett, S. A. Performance and Stability of LaSr2Fe2CrO9−δ-Based Solid Oxide Fuel Cell Anodes in Hydrogen and Carbon Monoxide. J. Electrochem. Soc. 2013, 160, 90−93. 16


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(47) Zhou, W.; Shao, Z. P.; Ran, R.; Jin, W. Q.; Xu, N. P. A Novel Efficient Oxide Electrode for Electrocatalytic Oxygen Reduction at 400–600 °C. Chem. Commun. 2008, 44, 5791–5793. (48) Daisuke, H.; Atsuko, T.; Takashi, H.; Masahiro, N.; Mitsuru, S. Design of a Reduction-Resistant Ce0.8Sm0.2O1.9 Electrolyte Through Growth of a Thin BaCe1−xSmxO3−α Layer over Electrolyte Surface. Electrochem. Solid-State Lett. 2004, 7, 318–320. (49) Yang, G. M.; Su, C.; Chen, Y. B.; Tadé, M. O.; Shao, Z. P. Nano La0.6Ca0.4Fe0.8Ni0.2O3−δ Decorated Porous Doped Ceria as A Novel Cobalt-Free Electrode for “Symmetrical” Solid Oxide Fuel Cells. J. Mater. Chem. A 2014, 2, 19526–19535. (50) Sun, Y. F.; Li, J. H.; Zeng, Y. M.; Amirkhiz, B. S.; Wang, M. N.; Behnamiana, Y.; Luo, J. L. A-Site Deficient Perovskite: The Parent for in situ Exsolution of Highly Active, Regenerable Nanoparticles as SOFC Anodes. J. Mater. Chem. A, 2015, 3, 11048-11056. (51) George, T.; Dragos, N.; Irvine, J. T. S. Step-Change in High Temperature Steam Electrolysis Performance of Perovskite Oxide Cathodes with Exsolution of B-site Dopants. Energy Environ. Sci. 2013, 6, 256–266. (52) Mazzieria, V.; Coloma-Pascual, F.; Arcoya, A.; L'Argentieàea, P. C.; Fígoli, N. S. XPS, FTIR and TPR Characterization of Ru/Al2O3 Catalysts. Appl. Surf. Sci. 2003, 201, 222–230. (53) Hansen, K. K.; Hansen, K. V. A-Site Deficient (La0.6Sr0.4)1-sFe0.8Co0.2O3-δ perovskites as SOFC Cathodes. Solid State Ionics 2007, 178, 1379–1384. (54) Liu, Z.; Cheng, L. Z.; Han, M. F. A-Site Deficient Ba1-xCo0.7Fe0.2Ni0.1O3-δ Cathode for Intermediate Temperature SOFC. Journal of Power Sources 2011, 196, 868–871. (55) Su, C.; Wang, W.; Liu, M. L.; Tadé, M. O.; Shao, Z. P. Progress and Prospects in Symmetrical Solid Oxide Fuel Cells with Two Identical Electrodes. Adv. Energy Mater. 2015, 5, 1500188. (56) Azad, A. K.; Irvine, J. T. S. Characterization of YSr2Fe3O8–δ as Electrode Materials for SOFC. Solid State Ionics 2011, 192, 225–228. (57) Peña-Martínez, J.; Marrero-López, D.; Pérez-Coll, D.; Ruiz-Morales, J. C.; Núñez, P. Performance of XSCoF (X = Ba, La and Sm) and LSCrX ′

(X ′

= Mn, Fe and Al)

Perovskite-Structure Materials on LSGM Electrolyte for IT-SOFC. Electrochim. Acta 2007, 52, 2950–2958. (58) El-Himri, A.; Marrero-López, D.; Ruiz-Morales, J. C.; Peña-Martínez, J.; Núñez, P. Structural and Electrochemical Characterization of Pr0.7Ca0.3Cr1–yMnyO3–δ as Symmetrical Solid Oxide Fuel Cell Electrodes. J. Power Sources 2009, 188, 230–237. (59) Chen, M.; Paulson, S.; Thangadurai, V.; Birss, V. Sr-Rich Chromium Ferrites as Symmetrical SOFC Electrodes. J. Power Sources 2013, 236, 68–79. (60) Zhou, Q.; Yuan, C.; Han, D.; Luo, T.; Li, J. L.; Zhan, Z. L. Evaluation of LaSr2Fe2CrO9–δ as a Potential Electrode for Symmetrical Solid Oxide Fuel Cells. Electrochimica Acta 2014, 133, 453–458. 17



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(61) Manasa, K. R.; Lee, K. T. Investigation of Aliovalent Transition Metal Doped La0.7Ca0.3Cr0.8X0.2O3−δ (X=Ti, Mn, Fe, Co, and Ni) as Electrode Materials for Symmetric Solid Oxide Fuel Cells. Ceramics International 2015, 41, 10878–10890. (62) Ruiz-Morales, J. C.; Canales-Vázquez, J.; Lincke, H.; Pena-Martínez, J.; Marrero-López, D.; Pérez-Coll, D.; Irvine, J.T.S.; Núnez, P. Potential Electrode Materials for Symmetrical Solid Oxide Fuel Cells. Bol. Soc. Esp. Ceram. V 2008, 47, 183–188. (63) Cao, Z. Q.; Zhang, Y. H.; Miao, J. P.; Wang, Z. L.; Lu, Z.; Sui, Y.; Huang, X. Q.; Jiang, W. Titanium-Substituted Lanthanum Strontium Ferrite as a Novel Electrode Material for Symmetrical Solid Oxide Fuel Cell. Int. J. Hydrog. Energy 2015, 40, 16572–16577.

18


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Table 1. Summary of Peak Power Densities (PPD) of Some Symmetrical Cells with Different Electrodes and Electrolytes Under Hydrogen Fuel Condition Thickness

PPD

Electrode

Electrolyte

SSFTR

SDC

600

800

271

This work

SSFTR72

SDC

600

800

417

This work

La0.8Sr0.2Sc0.2Mn0.8O3–δ

ScSZ

300

850

220

15

La0.75Sr0.25Cr0.5Mn0.5O3–δ

YSZ

20

900

300

16

La0.5Sr0.5Co0.5Ti0.5O3–δ

LSGM

300

800

110

18

YSr2Fe3O8–δ

YSZ

70

900

35

56

La0.75Sr0.25Cr0.5Al0.5O3–δ

LSGM

1500

800

45

57

Pr0.7Ca0.3Cr0.6Mn0.4O3–δ

YSZ

370

950

250

58

La0.3Sr0.7Fe0.7Cr0.3O3–δ

LSGM

500

800

300

59

LaSr2Fe2CrO9–δ

LSGM

500

800

224

60

La0.7Ca0.3Cr0.8Mn0.2O3–δ

LSGM

400

800

220

61

La0.7Ca0.3CrO3–δ

YSZ

1000

950

110

62

La0.3Sr0.7Ti0.3Fe0.7O3–δ

YSZ

400

800

215

63

(µm)

Temperature (℃)

(mW cm-2)

Reference

19



Page 20 of 34

Figure captions Figure 1. Rietveld-refined XRD profiles of (a) SSFTR and (b) H-SSFTR collected at RT. HT-XRD patterns of SSFTR measured in (c) air and (d) 5%H2/N2. Inset shows the orthorhombic structure of SSFTR, which can be represented as a three-dimensional network of MO6 (M = Fe/Ti/Ru) octahedral with the Sm/Sr atoms occupying the interstitial spaces between them. Figure 2. (a) The thermal expansion curves of SSFTR measured in air and 5% H2/N2 atmospheres. (b) Thermogravimetric analysis (TGA) weight loss and oxygen nonstoichiometry (δ) of SSFTR as a function of temperature in air. (c) TGA curve of SSFTR measured in 5% H2/N2. Figure 3. XPS spectra of SSFTR and H-SSFTR: (a) Fe 2p, (b) Ti 2p, (c) Ru 3d, and (d) O 1s. Figure 4. (a) Temperature dependence of the electrical conductivity for SSFTR in air and 5% H2/N2. (b) Oxygen partial pressure dependence of the electrical conductivity for SSFTR at 800 °C. (c) Electrical conductivity stability of SSFTR at different temperatures in air. Figure 5. Nyquist plots of electrochemical impedance spectra measured from 600 °C to 800 °C in (a) air and (b) 5% H2/N2 for SSFTR electrode. Figure 6. (a) R1 and (b) R2 of SSFTR versus the oxygen partial pressure (pO2) for a symmetrical electrode at different temperatures. (c) ASR of SSFTR versus the hydrogen partial pressure (pH2) for a symmetrical electrode at different temperatures. Linear fits to data are shown as lines. Values for ASR were obtained by fitting EIS data to equivalent circuits. (d) The variation in ASR measured in different atmospheres. Figure 7. (a) Voltage and power density versus current density curves of SDC electrolyte-supported symmetrical cell SSFTR|SDC|SSFTR operated in humidified H2 (3 vol % H2O). (b) Cell voltage as a function of testing time for symmetrical cell SSFTR|SDC|SSFTR operated under a constant current density of 0.25 A cm−2 at 800 °C. The interface views of (c) SSFTR anode /SDC electrolyte and (d) SSFTR cathode/SDC electrolyte. Figure 8. (a) Rietveld-refined XRD profile of SSFTR72 collected at RT. HT-XRD patterns of SSFTR72 measured in (b) air and (c) 5%H2/N2. Figure 9. The typical SEM images of (a) SSFTR and (b) SSFTR72 samples after the reduction treatment in 5%H2/Ar for 72 h at 800 °C. HR-TEM images of SSFTR72 (c) before and (d) after the reduction treatment in 5%H2/Ar for 72 h at 800 °C. Figure 10. XPS spectra of SSFTR72 and H-SSFTR72: (a) Fe 2p, (b) Ti 2p, (c) Ru 3d, and (d) O 1s. Figure 11. Rietveld-refined XRD profile of SSFTR72 after reduction at 800 °C for 20 h in wet H2 (3 vol % H2O). Blue vertical line corresponds to Ru. Figure 12. (a) Voltage and power density versus current density curves of SDC electrolyte-supported symmetrical cell SSFTR72|SDC|SSFTR72 operated in humidified H2 (3 20


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vol % H2O). (b) Cell voltage as a function of testing time for symmetrical cell SSFTR72|SDC|SSFTR72 operated under a constant current density of 0.3 A cm−2 at 800 °C. The interface views of (c) SSFTR72 anode/SDC electrolyte and (d) SSFTR72 cathode/SDC electrolyte.

21



Page 22 of 34

Table of Contents

22


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Figure 1. Rietveld-refined XRD profiles of (a) SSFTR and (b) H-SSFTR collected at RT. HT-XRD patterns of SSFTR measured in (c) air and (d) 5%H2/N2. Inset shows the orthorhombic structure of SSFTR, which can be represented as a three-dimensional network of MO6 (M = Fe/Ti/Ru) octahedral with the Sm/Sr atoms occupying the interstitial spaces between them. 220x148mm (144 x 144 DPI)



Figure 2. (a) The thermal expansion curves of SSFTR measured in air and 5% H2/N2 atmospheres. (b) Thermogravimetric analysis (TGA) weight loss and oxygen nonstoichiometry (δ) of SSFTR as a function of temperature in air. (c) TGA curve of SSFTR measured in 5% H2/N2. 279x71mm (144 x 144 DPI)


Page 24 of 34

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Figure 3. XPS spectra of SSFTR and H-SSFTR: (a) Fe 2p, (b) Ti 2p, (c) Ru 3d, and (d) O 1s. 164x122mm (144 x 144 DPI)



Figure 4. (a) Temperature dependence of the electrical conductivity for SSFTR in air and 5% H2/N2. (b) Oxygen partial pressure dependence of the electrical conductivity for SSFTR at 800 °C. (c) Electrical conductivity stability of SSFTR at different temperatures in air. 271x71mm (144 x 144 DPI)


Page 26 of 34

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Figure 5. Nyquist plots of electrochemical impedance spectra measured from 600 °C to 800 °C in (a) air and (b) 5% H2/N2 for SSFTR electrode. 214x101mm (144 x 144 DPI)



Figure 6. (a) R1 and (b) R2 of SSFTR versus the oxygen partial pressure (pO2) for a symmetrical electrode at different temperatures. (c) ASR of SSFTR versus the hydrogen partial pressure (pH2) for a symmetrical electrode at different temperatures. Linear fits to data are shown as lines. Values for ASR were obtained by fitting EIS data to equivalent circuits. (d) The variation in ASR measured in different atmospheres. 191x145mm (144 x 144 DPI)


Page 28 of 34

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Figure 7. (a) Voltage and power density versus current density curves of SDC electrolyte-supported symmetrical cell SSFTR|SDC|SSFTR operated in humidified H2 (3 vol % H2O). (b) Cell voltage as a function of testing time for symmetrical cell SSFTR|SDC|SSFTR operated under a constant current density of 0.25 A cm−2 at 800 °C. The interface views of (c) SSFTR anode /SDC electrolyte and (d) SSFTR cathode/SDC electrolyte. 183x141mm (144 x 144 DPI)



Figure 8. (a) Rietveld-refined XRD profile of SSFTR72 collected at RT. HT-XRD patterns of SSFTR72 measured in (b) air and (c) 5%H2/N2. 257x55mm (144 x 144 DPI)


Page 30 of 34

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Figure 9. The typical SEM images of (a) SSFTR and (b) SSFTR72 samples after the reduction treatment in 5%H2/Ar for 72 h at 800 °C. HR-TEM images of SSFTR72 (c) before and (d) after the reduction treatment in 5%H2/Ar for 72 h at 800 °C. 211x148mm (144 x 144 DPI)



Figure 10. XPS spectra of SSFTR72 and H-SSFTR72: (a) Fe 2p, (b) Ti 2p, (c) Ru 3d, and (d) O 1s. 154x116mm (144 x 144 DPI)


Page 32 of 34

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Figure 11. Rietveld-refined XRD profile of SSFTR72 after reduction at 800 °C for 20 h in wet H2 (3 vol % H2O). Blue vertical line corresponds to Ru. 189x150mm (150 x 150 DPI)



Figure 12. (a) Voltage and power density versus current density curves of SDC electrolyte-supported symmetrical cell SSFTR72|SDC|SSFTR72 operated in humidified H2 (3 vol % H2O). (b) Cell voltage as a function of testing time for symmetrical cell SSFTR72|SDC|SSFTR72 operated under a constant current density of 0.3 A cm−2 at 800 °C. The interface views of (c) SSFTR72 anode/SDC electrolyte and (d) SSFTR72 cathode/SDC electrolyte. 188x142mm (144 x 144 DPI)


Page 34 of 34

Highly Stable and Efficient Perovskite Ferrite Electrode for

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