Fabrication of Lanthanum Strontium Cobalt FerriteâGadolinium-Doped

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Fabrication of lanthanum strontium cobalt ferrite-gadolinium doped ceria composite cathodes using a low-price inkjet printer Gwon Deok Han, Hyung Jong Choi, Kiho Bae, Hyeon Rak Choi, Dong Young Jang, and Joon Hyung Shim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b11462 • Publication Date (Web): 17 Oct 2017 Downloaded from http://pubs.acs.org on October 23, 2017

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ACS Applied Materials & Interfaces

Fabrication of lanthanum strontium cobalt ferritegadolinium doped ceria composite cathodes using a low-price inkjet printer Gwon Deok Han,† Hyung Jong Choi,† Kiho Bae,†,‡ Hyeon Rak Choi,† Dong Young Jang,† Joon Hyung Shim†,* †

School of Mechanical Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul

02841, South Korea ‡

High-Temperature Energy Materials Research Center, Korea Institute of Science and

Technology (KIST), 14-5 Hwarang-ro, Seongbuk-gu, Seoul 02792, South Korea

KEYWORDS: solid oxide fuel cells, inkjet printing, lanthanum strontium cobalt ferrite, gadolinium doped ceria, composite cathode 1 ACS Paragon Plus Environment


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ABSTRACT In this work, we have successfully fabricated lanthanum strontium cobalt ferrite (LSCF)gadolinium doped ceria (GDC) composite cathodes by inkjet printing and demonstrated their functioning in solid oxide fuel cells (SOFCs). The cathodes are printed using a low-cost HP inkjet printer and the LSCF and GDC source inks are synthesized with fluidic properties optimum for inkjet printing. The composition and microstructure of the LSCF and GDC layers are successfully controlled by controlling the color level in the printed images and the number of printing cycles, respectively. Anode-support type SOFCs with optimized LSCF-GDC composite cathodes synthesized by our inkjet printing method have achieved a power output of over 570 mW cm–2 at 650 °C, which is comparable to the performance of a commercial SOFC stack. Electrochemical impedance analysis is carried out to establish a relationship between the cell performance and the compositional and structural characteristics of the printed LSCF-GDC composite cathodes.

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1. INTRODUCTION Inkjet printing is attracting considerable attention as a technique capable of easily and rapidly producing functional thin film materials.1-3 Recent studies have demonstrated the easy patterning of ceramic films into desired shapes using commercial inkjet printers without the need for complicated lithographic processes or masks.4, 5 Ceramic films produced by inkjet printing have been found to exhibit the desired properites5, 6 and researchers have acknowledged this technique as a useful and versatile tool for the rapid prototyping of functional ceramic films. Successful applications of inkjet-printed ceramic films include solar cells,7, 8 batteries,9, 10 thin-film transistors,11, 12 and sensors.13, 14 The inkjet printing technique has also been successfully utilized for the fabrication of solid oxide fuel cell (SOFC) components.15-26 An SOFC is a thin film-based energy conversion system consisting of ceramic functional layers of electrodes and electrolytes.27 In SOFCs, the cathode (oxygen electrode), where significant energy loss occurs, is a key component that can dictate the cell performance. Of the various electrochemical reactions that occur in SOFCs, the oxygen reduction reaction (ORR) at the cathode is known to be the ratelimiting step; therefore, it is important to develop a high-performance cathode to improve the performance of the SOFCs.28-30 However, the development of high-performance cathodes must take into account the following conditions:31 i) a catalytic reaction in which oxygen gas is reduced to oxygen ion species, ii) an ion conduction pathway through which oxygen ions are transferred to the electrolyte, and iii) a highly porous structure through which oxygen gas can diffuse. Owing to these reasons, the fabrication of high-performance cathodes is a very difficult task. Functional composite materials can be effectively used to improve the cathode performance. At the cathode, the functional composite material includes an additional conducting path for the 3 ACS Paragon Plus Environment


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conduction of oxygen ion species as well as a catalyst for the ORR. In recent years, lanthanum strontium cobalt ferrite (LSCF)-gadolinium doped ceria (GDC) composites have attracted attention as alternative cathodes due to their high catalytic activity for ORR and their excellent thermal and chemical compatibility with GDC electrolytes.32-35 LSCF is a promising mixed ion electronic conductor capable of fast oxygen ion and electron conduction and promotes ORR as a highly active catalyst.36 GDC is a typical electrolyte material with high oxygen ion conductivity and transfers reduced oxygen ion species from the surface of the cathode to the electrolyte.37 As a composite cathode, an optimum composition using both LSCF and GDC can maximize the performance of SOFCs. In addition, the LSCF-GDC composite cathode needs to be optimized in terms of its microstructure as well, since the diffusion of reaction gases and ion and electron conduction occur at the same time. In this case, inkjet printing can be used efficiently to fabricate LSCF-GDC composite cathodes and identify the optimal composition and microstructure conditions. The composition and microstructure of composite ceramics can be easily controlled by adjusting the proportions of source materials in the ink and by varying the printing parameters. On the basis of these advantageous features, inkjet printing has recently been successfully used to optimize biomaterials as well as catalysts for direct methanol fuel cells and water splitting by a combination approach.38-41 In this study, we attempted to fabricate prototypes of LSCF-GDC cathodes with varying compositions and microstructures by inkjet printing. Our experiments were performed using a low-cost HP inkjet printer, which costs under USD 100. Using a commercial printer enables easy drawing of desired patterns via user friendly software such as Microsoft PowerPoint or 3D CAD programs. We fabricated LSCF-GDC composite cathodes using individually synthesized LSCF and GDC inks. The composition of the LSCF-GDC 4 ACS Paragon Plus Environment

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composite cathodes was varied by simply adjusting the two color levels. We evaluated the fuel cell performance of the LSCF-GDC composite cathodes in terms of the power output and electrochemical impedance and arrived at the optimum composition and structure. 2. EXPERIMENTAL SECTION Commercially available La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF, Fuelcellmaterials) and Gd0.1Ce0.9O2-δ (GDC, Rhodia) nanopowders were used as the raw materials. A mixture of 20 wt.% ethanol and 80 wt.% water was used as the solvent for LSCF and GDC inks. The LSCF and GDC powders were dispersed in pre-mixed solvents with DISPERBYK-2012 (BYK-Chemie GmbH) as the dispersing agent and 1,5-pentanediol (Sigma-Aldrich) as the surfactant. The LSCF and GDC inks were then ball-milled for 48 h at 110 rpm using 3, 5, and 10 mm zirconia beads. Anode-supported unit cells were used as the substrates for the evaluation of the LSCF cathode and LSCF-GDC composite cathode performance. A NiO/yttria-stabilized zirconia (NiO-YSZ) anode support was fabricated by uniaxial pressing followed by sintering at 1200 °C. An 8-µmthick NiO-YSZ anode functional layer and a 10-µm-thick YSZ electrolyte layer were sequentially deposited on the anode support by spin coating followed by co-sintering at 1400 °C. The detailed fabrication conditions are described in our previous report.42 A commercial HP inkjet printer (HP Deskjet 1010) with a HP61 black and tri-color cartridge was used for fabricating the LSCF cathodes and the LSCF-GDC composite cathodes. The HP Deskjet 1010 printer was modified to enable ceramic printing on thick and rigid substrates. The original ink cartridges were cleaned in an ultrasonicator with ethanol. To fabricate the LSCF and LSCF-GDC cathodes, the inkjet cyan-magenta-yellow-black (CMYK) color printing principle 5 ACS Paragon Plus Environment


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was used. The prepared LSCF and GDC inks were injected into the black ink and magenta ink cartridges, respectively. The compositional gradient between LSCF and GDC was accomplished by adjusting the black ratio from 60 to 100 % in the Microsoft Publisher software. The thickness variation in each cathode layer was controlled by adjusting the printing scan cycle based on the average deposition rate. The drying time for each printing scan cycle was about 20 s. As shown in Figure S1, the sintering condition was scheduled after taking the results of thermogravimetric analysis (TGA) of DISPERBYK-2012 and 1,5-pentanediol into consideration (Figure S1); all printed cathodes were sintered at 950 °C for 3 h in air. To prevent an interface reaction between the cathode and the electrolyte, a 900-nm-thick GDC buffer layer was printed on the YSZ electrolyte. Subsequently, the printed GDC buffer layer was sintered at 1250 °C. The crystallinity of the LSCF and GDC powders was analyzed using X-ray diffraction (XRD, SmartLab, Rigaku) in the 2 theta/theta scanning mode, as shown in Figure S2. The particle size distribution of the LSCF and GDC inks was evaluated using a particle size analyzer (ELSZ1000, Otsuka Electronics Co. Ltd.). The viscosities and surface tensions of the inks were measured using a viscometer (SV-10, A&D Company) and a tensiometer (K100, KRÜSS GmbH), respectively. The composition of the LSCF-GDC composite cathodes was analyzed using a field emission scanning electron microscope (FE-SEM, S-4800, Hitachi) equipped with an energy dispersive X-ray spectrometer (EDS) (Figure S3). The microstructures of the cathodes, including the thickness of the cathode layer, were observed using a SEM (F50, FEI). The electrochemical performance of the cells was evaluated using a custom-built SOFC test station in the temperature range of 500–650 °C. The current-voltage (I-V) characteristics and electrochemical impedance spectra (EIS) were analyzed using an electrochemical analyzer 6 ACS Paragon Plus Environment

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(Gamry Reference 3000 Potentiostat/Galvanostat/ZRA). Au and Ni meshes were used as the current collectors at the cathode and anode, respectively. The EIS data was collected at frequencies in the range of 106–0.1 Hz with an AC amplitude of 10 mV and a cell voltage of 0.95 V in an open circuit condition. The I-V characteristics were measured by linear sweep voltammetry from the open circuit voltage (OCV) to 0.2 V. Humidified hydrogen and air (PO2 = 0.2 atm) were supplied to the anode and cathode, respectively, at a flow rate of 150 sccm. 3. RESULTS AND DISCUSSION Figure 1 shows the dispersion and fluid properties of the synthesized LSCF and GDC inks. From Figure 1a, the particle-size distribution peaks of the LSCF and GDC inks are seen to be 0.27 and 0.17 µm, respectively. The distribution peaks of the two inks are smaller than the nozzle diameters of the HP61 ink cartridges. The dispersion stability of the LSCF and GDC inks was evaluated by analyzing the particle distribution on the 17th day after ink production, as shown in Figure 1b. Both inks exhibited a narrow particle-size distribution without any secondary peaks that are associated with sedimentation or aggregation. This confirms that the added dispersant was effective in stabilizing the LSCF and GDC nanoparticles.43 Figure 1c illustrates the surface tension and viscosity measurement results of the LSCF and GDC inks. It was confirmed that the fluidic properties of the synthesized inks were similar, regardless of the particle type. The surface tension values of the LSCF and GDC inks were measured to be 36.1 and 36.5 mN m–1, respectively, and the viscosities of the LSCF and GDC inks were 2.6 and 2.5 cP, respectively. The printability of the ink can be assessed by evaluating the dimensionless Z value calculated from the analyzed surface tension and viscosity.44 The Z value, which is the reciprocal of the Ohnesorge number (Oh), is obtained as follows (Eq. 1) 7 ACS Paragon Plus Environment


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Z

⋅ ⋅

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(1)

where σ is the surface tension, ρ is the density, a is the characteristic length, and η is the viscosity. The cartridge nozzle diameter (20 µm) is typically chosen as the characteristic length of the ink fluid. The Z values of the LSCF and GDC inks were calculated to be 10.57 and 10.98, respectively (Figure 1d). It has been reported that inks with Z values in the range of 4 to 14 are in the optimum printable range.45 Therefore, our results indicate that the synthesized LSCF and GDC inks are suitable for inkjet printing.

Figure 1. Properties of the LSCF and GDC inks. Analysis of the particle size distribution at (a) 3 days and (b) 17 days after synthesis, (c) surface tension and viscosity measurement results, and 8 ACS Paragon Plus Environment

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(d) printability of the synthetic inks expressed in terms of the Z values in a Weber-Reynolds number diagram. Reproduced with permission from reference 2. Copyright 2003 Cambridge University Press. Figures 2 and S4 show the test images and texts printed using the “black” and “magenta” colors, which represent the LSCF and GDC inks, respectively. The printed characters could be clearly identified. No faults caused by nozzle clogging or faulty ink ejection could be detected by visual examination. In Figure 2a, we have demonstrated that a gradual change in the composition between LSCF and GDC is possible by mixing the two color levels during inkjet printing. The inset image in Figure 2a is the input image drawn using Microsoft Publisher. The patterns and characters were printed clearly on various substrates, including PET films and glass (Figure 2a, b). Figure 2c shows that LSCF and GDC inks can be used to print large-scale complex images with no significant flaws. These results confirm that our LSCF and GDC inks can be used for the fabrication of LSCF-GDC composite cathodes and enable a precise control of composition and pattern.



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Figure 2. Test images and text printed using LSCF and GDC inks. (a) A variety of logo patterns printed on a PET film (the inset image shows the original image), (b) Newton’s quotation printed on a glass substrate, and (c) Kim Hong-do’s “Tiger under a pine tree” printed on Korean traditional paper (the inset image shows the original image) Figure 3a shows the composition of the LSCF-GDC composite layer printed by controlling the black level (corresponding to LSCF) in the printing patterns. EDS was used to analyze the elemental composition of the composite layers and the results confirmed that the composition was reproducible. The GDC content tends to increase with a decrease in the black level of the printing ink while the LSCF content decreases as anticipated. It was interesting to note that the deposition rate increases with an increase in the black level or the LSCF content, as shown in Figure 3b, implying that GDC negatively affects the deposition rate. This observation can be explained as follows. The LSCF particle size is larger than that of GDC, resulting in the deposition of a thicker layer in each LSCF printing cycle as compared to the GDC cycle and therefore, we observe an enhanced overall deposition rate at higher LSCF contents. However, when the ink ejection amount becomes large, evaporation of the solvent in the printed ink requires more time and the resulting morphology of the printed layer can be rough and irregular.46, 47 Due to this reason, even though pure LSCF printed layers exhibit the highest deposition rates, they experience significantly large thickness deviations, as shown in Figure 3b. The average deposition rates of the cathode layers corresponding to 60, 75, 80, and 100 % black levels were 0.21, 0.11, 0.09, and 0.06 µm cycle-1, respectively (Figure 3b). In the following sections, we evaluated the compositions of the LSCF-GDC composite cathodes corresponding to black levels of 60, 75, 80, and 100 %. These cathodes are termed as LG37, LG55, LG73, and LSCF, respectively. 10 ACS Paragon Plus Environment

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Figure 3. (a) Composition and (b) deposition rate of the LSCF-GDC composite cathodes, according to the black color level. The composition and deposition rate were analyzed by EDS and SEM, respectively. The microstructures of the printed LSCF and LSCF-GDC composite layers were analyzed by SEM and the results are shown in Figures 4 and S5. The LG73 and LG55 surfaces exhibited uniformly distributed pores and less particle agglomeration as compared to the LSCF layer (Figure 4a–c). In addition, the cross-sectional images of the LG73 and LG55 samples show that a 11 ACS Paragon Plus Environment


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properly connected particle structure is well attached to the GDC buffer layer (Figure S5). On the other hand, as can be seen in Figure 4d, the excess GDC content in LG37 resulted in a microstructure with nonuniform pore structure and particle agglomeration. The average grain size of the tested films was analyzed using ImageJ software; the results (Figure S6) confirmed that the average grain size increases with an increase in the LSCF content.

Figure 4. SEM observations of the surface morphologies of (a) LSCF, (b) LG73, (c) LG55, and (d) LG37 cathodes. The average grain size of each cathode was analyzed using ImageJ software. For the fuel cell test, 8- and 14-µm-thick LSCF and LSCF-GDC cathodes were printed on anode-supported SOFC cells. The LSCF, LG73, LG55, and LG37 cathodes having a thickness of 12 ACS Paragon Plus Environment

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8 µm were designated as LSCF(8), LG73(8), LG55(8), and LG37(8), respectively. In a similar manner, 14-µm-thick LSCF, LG73, LG55, and LG37 cathodes were named LSCF(14), LG73(14), LG55(14), and LG37(14), respectively. The I-V results of SOFCs with LSCF and LSCF-GDC composite cathodes are shown in Figures 5 and S7. The open circuit voltage (OCV) of the tested samples was found to be in the range of 1.12–1.15 V, which agrees with the theoretical values.48 The cell with the LG73(8) cathode exhibited the highest fuel cell performance among the cells with 8-µm-thick cathodes, in terms of the peak power output. In the case of the 14-µm-thick cathodes, we found that the LG55(14) cell produced the highest peak power output. The SOFC with the LG73(8) cathode achieved peak power densities of 349, 240, 143, and 67 mW cm–2 at 650, 600, 550, and 500 °C, respectively. At the same temperatures, the peak power densities achieved by the cell with the LG55(14) cathode were 574, 333, 164, and 70 mW cm–2, respectively. It is clear that a proper composition of LSCF and GDC enhances the fuel cell performance. On the other hand, an excess of GDC (LG37) can degrade the fuel cell performance. Overall, cells with 14-µm-thick cathodes appeared to outperform those with 8-µmthick cathodes, as shown in Figure 5c, which implies that a thickness of 8 µm is not sufficient for a good current collection at the cathode. This result is also confirmed in the EIS analysis, which will be discussed in the following sections.



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Figure 5. Representative I-V curves measured at 650 °C – SOFCs with (a) 8-µm-thick cathodes and (b) 14-µm-thick cathodes. (c) Peak power densities obtained from all the cells used in this study, measured in the range of 500–650 °C. Figures 6, S8, and S9 illustrate the EIS results of the cells with LSCF and LSCF-GDC composite cathodes. In the Nyquist plot, the ohmic impedance, determined by the real axis intercept, is mainly related to charge transport through the electrolyte and current collectors. On the other hand, the arc shape varies with the type of electrode and the arc spectrum represents the polarization impedance of the electrode. It can be observed in Figure 6 that changes in cell 14 ACS Paragon Plus Environment

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voltage and cathode type caused a significant variation in the shape of the arc but no appreciable change in the real axis intercept, except in the case of the LG37 cell. The Arrhenius plots show that this tendency is maintained at all test temperatures (Figures 7 and S10). This also confirmed that the spectrum arcs represent polarization impedance at the electrodes while the real axis intercept values represent the ohmic resistance. As the test cells use the same anode and electrolyte, the polarization process is considered to be led by the cathodic reaction. It is noteworthy that the LG37 cell exhibits significantly high ohmic resistance, as shown in Figure S10, presumably because the excess GDC interferes with electron transport through the cathode. Furthermore, the EIS analysis confirmed that the ohmic impedance increases at the thinner cathode (8-µm thickness), as previously anticipated with the I-V data. In our work, it was identified that the LG73 and LG55 cathodes exhibit the lowest polarization resistances, as shown in Figures 6 and 7. It has been reported that the LSCF-GDC composite cathodes have the lowest polarization resistance.32-35 As shown in Figure 7, LG73 exhibited the lowest polarization resistance among the 8-µm-thick cathodes while LG55 exhibited the smallest polarization impedance among the 14-µm-thick cathodes. This corresponds to the power tendency observed in Figure 5.



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Figure 6. Representative EIS spectra at 650 °C – SOFCs with 8-µm-thick cathodes at cell voltages of (a) OCV and (b) 0.95 V. SOFCs with 14-µm-thick cathodes at cell voltages of (c) OCV and (d) 0.95 V


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Figure 7. Arrhenius plots of the polarization area specific resistance (ASRpolarization) measured in the range of 500–650 °C – SOFCs with 8-µm-thick cathodes at cell voltages of (a) OCV and (b) 0.95 V. SOFCs with 14-µm-thick cathodes at cell voltages of (c) OCV and (d) 0.95 V The Bode plots were analyzed to investigate the characteristics of the cathodic processes in detail. The results of the analysis are shown in Figures 8, S11, and S12. In the Bode spectra, impedances in the intermediate frequency range of 10 Hz–10 kHz represent resistances from electrochemical ORRs, including oxygen surface exchange and oxygen ion diffusion, while low frequency (f ≤ 10 Hz) impedances are considered associated with gas-phase diffusion.49-52 From our measurements, it is clear that polarization enhancement in the LG73 and LG55 cathodes is due to a decrease in the gas-diffusion impedance. It is in turn related to the



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microstructures identified in Figures 4 and S5; the LG73 and LG55 cathodes exhibited relatively uniform porous structures with minimal agglomeration of particles. In the case of the LSCF-GDC composite, Esquirol et al. reported that the oxygen diffusion coefficient of the composite was much higher than that of the non-composite LSCF, but the oxygen surface exchange coefficient did not increase.53 From Figure 8, it is clear that the LG73(8) and LG55(14) cells have lower impedances at intermediate and low frequencies than other cells. These results indicate that the LG73 and LG55 cathodes have optimal compositions, which can enhance oxygen ion conduction, and have porous structures that allow for the diffusion of O2 gas. Taken together, it can be concluded that an optimum amount of GDC in the composite cathode improves the rate of oxygen reduction. Finally, we evaluated the long-term stability of the best performing cathode (LG55(14)) among all the cathodes tested in this investigation. The potentio-static current measurements (Figure 9) confirm the improved power output and stability of LG55(14) in comparison to LSCF(14). This phenomenon is attributed to the high content of GDC in LG55. Addition of GDC to a porous structure can alleviate the thermal expansion stress at the cathode-electrolyte interface and thus improve the thermal stability of the cell.29


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Figure 8. Representative Bode plots measured at 650 °C – SOFCs with 8-µm-thick cathodes at cell voltages of (a) OCV and (b) 0.95 V. SOFCs with 14-µm-thick cathodes at cell voltages of (c) OCV and (d) 0.95 V



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Figure 9. Potentio-static currents measured over 40 h using SOFCs with LSCF(14) and LG55(14) cathodes at a cell voltage of 0.75 V and an operating temperature of 600 °C 4. CONCLUSIONS In this study, we fabricated LSCF-GDC composite cathodes by inkjet printing using a low-cost HP inkjet printer. LSCF and GDC inks were synthesized with fluidic properties appropriate for inkjet printing. The LSCF and GDC inks exhibited a single distribution peak of less than 0.3 µm and maintained good dispersion stability without any secondary peaks. Furthermore, based on the calculated Z values, the two inks were found to be in the optimum printable range; they were successfully used to print large and complex images with no errors. The content and porosity of the printed LSCF and GDC layers were adjusted by controlling the color level in the printed images and the number of printing cycles. SEM analysis confirmed that the LG73 and LG55 cathodes exhibit the most desirable structures with uniformly distributed pores, minimal particle agglomeration, proper particle connection, and good adhesion with the underlying GDC buffer layer. Based on these features, cells with LG73 and LG55 cathodes outperformed cells with 20 ACS Paragon Plus Environment

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cathodes of other compositions. Among the test samples with a thickness of 8 µm, the LG73 cathode exhibited the best fuel cell performance with a peak power density of 349 mW cm–2 at 650 °C. On the other hand, the LG55(14) cathode exhibited the highest power output of 574 mW cm–2 at 650 °C. An increase in the cathode thickness was found to enhance the power output, indicating that an improved current collection enhanced fuel cell operation even at low LSCF contents. EIS analysis confirmed that polarization impedances are reduced in the cells with LG73 and LG55 cathodes, in accordance with the cell power output trend. Among the polarization processes, mass diffusion-related impedance appears to be critical in determining the overall fuel cell performance. The potentio-static current measurement results indicate that the stability of the LSCF-GDC cathode printed at the optimum composition is much higher than that of the reference LSCF cell.

ASSOCIATED CONTENT Supporting Information Details on the following topics: TGA analysis of polymeric additives; XRD spectra of LSCF and GDC powders; EDS results of the LSCF and LSCF-GDC cathodes; test images and text printed using LSCF and GDC inks; cross-sectional SEM images of the LSCF and LSCF-GDC cathodes; average particle size of the cathode samples; I-V curves, EIS spectra, and Bode plots measured in the range of 500–600 °C; Arrhenius plots of the ohmic area specific resistance measured in the range of 500–600 °C. This material is available free of charge via the Internet at http://pubs.acs.org.



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AUTHOR INFORMATION Corresponding Authors *J. H. Shim (E-mail: [email protected], Tel.: +82-2-3290-3353, Fax: +82-2-926-9290) Notes The authors declare that there are no competing financial interests.

ACKNOWLEDGMENT This work was supported by the Korea Ministry of Environment (MOE) as a “Public Technology Program based on Environmental Policy” [grant number E416-00070-0604-0] and the Global Ph.D. Fellowship Program through the National Research Foundation of Korea, funded by the Ministry of Education [grant number NRF-2014H1A2A1020561]. The Brain Korea 21 Plus program (21A20131712520) is also acknowledged for its support.


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Esquirol,

A.;

Kilner,

J.;

Brandon,

N.

Oxygen

Transport

in

La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.8Ge0.2O2−x composite cathode for IT-SOFCs. Solid State Ionics 2004, 175, 63–67.


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Fabrication of Lanthanum Strontium Cobalt FerriteâGadolinium-Doped

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