Sulfur poisoning of cathode materials is one of the important factors to cause cathode performance degradation resulting in shortening lifetime of SOFC. The sulfur attacks alkali earth components of the rare earth-transition metal perovskite oxides, such as Ba, Ca, Sr, which reacts with SO2 to form sulfates. In this work, the La(Ni0.6Fe0.4)O-3 (LNF) cathode material without alkali earth elements was employed to investigate the sulfur poisoning behavior by flowing 30 ppm SO2 at different temperatures of 500 degrees C-800 degrees C. It was found that SO2 readily reacts with the La2O3 component in LNF to form La2O2SO4 at 700 degrees C and 800 degrees C. The extent of the chemical reaction is temperature dependent. These results confirm that sulfur poisoning also occurs in cathode materials free of alkali earth components. The study prompts the exploration of new materials and new strategies for the developing new cathode materials with high sulfur tolerance. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

We have examined the initial-stage degradation of a Ni-gadolinia-doped ceria (GDC) cermet hydrogen electrode prepared on a GDC buffer layer of a stabilized-zirconia electrolyte supported cell during steam electrolysis operation at 800 degrees C. With use of an air reference electrode, the IR-free electrode potential E and ohmic resistance of the hydrogen electrode side (RH2-side) were recorded. After a steam electrolysis operation at -1.0 A cm(-2) for 211 h, the RH2-side increased appreciably, by 36 %, while the value of E was nearly unchanged. It was found via a depth-direction analysis with use of focused ion beam-scanning ion microscopy that the remaining percentage of Ni decreased to ca. 60 % in the layer between 1 and 3 mu m from the top of the GDC buffer layer, followed by a further decrease to 42 % at 0.5 mu m. Since this suggests a significant cathodic polarization within the thin reaction zone, an enlargement of the reaction zone, together with a stabilization of Ni contacting with GDC, could be essential to mitigate such a degradation. (C) 2021 The Ceramic Society of Japan. All rights reserved.

ABSTRACT Intergranular glass phases can have a significant influence on the fracture resistance (R-curve behavior) of silicon nitride ceramics and appears to be related to the debonding of the β-Si 3 N 4 /oxynitride-glass interfaces. Applying the results from β-Si 3 N 4 -whisker/oxynitride-glass model systems, self-reinforced silicon nitrides with different sintering additive ratios were investigated. Silicon nitrides sintered with a lower Al 2 O 3 :Y 2 O 3 additive ratio exhibited higher steady-state fracture toughness together with a steeply-rising R -curve. Analytical electron microscopy studies suggested that the different fracture behavior is related to the Al content in the SiAlON growth band on the elongated grains, which could result in differences in interfacial bonding structures between the grains and the intergranular glass.

We have developed high-performance oxygen electrodes for reversible solid oxide cells. La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) center dot (CeO2)(0.8)(SmO1.5)(0.2) (SDC) composite scaffolds were infiltrated with SDC nanoparticles. The electrode with 30 vol% load of SDC nanoparticles exhibited very low overpotentials, eta <= 0.010 V for anodic and vertical bar eta vertical bar <= 0.030 V for cathodic reactions at 0.7 A cm(-2) and 800 degrees C, which was ascribed to a noticeable increase in the exchange current densities. The electrodes have shown very stable performance under anodic oxygen evolution operation at -0.5 A cm(-2) and 750 degrees C for 400 h. Such electrodes developed are extremely promising oxygen electrodes for R-SOC ever reported.

We have developed highly active and durable oxygen and hydrogen electrodes for reversible solid oxide cells (R-SOCs). The infiltration of samaria-doped ceria nanoparticles (i-SDC) in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)–SDC scaffolds enhanced performances for the oxygen evolution and oxygen reduction without noticeable degradation. The exchange current density j0 on 30 vol.% i-SDC/LSCF–SDC was about 3 to 4 times larger than that without i-SDC at 900 to 750 °C. Such an increase in the j0 values is ascribed, with certainty, predominantly to an increase in the transport rate of oxide ions through the SDC particles of the LSCF–SDC composite and i-SDC. The durability of a double-layer hydrogen electrode, consisting of SDC scaffold with highly dispersed Ni–Co nanoparticles as the catalyst layer and a thin current collecting layer of Ni–YSZ cermet, was found to be improved greatly by a reversible cycling operation between electrolysis and fuel cell-modes.

We have evaluated double-layer hydrogen electrodes with catalyst layers (CLs) and current-collecting layers (CCLs) in order to apply them in proton-conducting solid oxide cells. The scaffolds of the CLs were fabricated from a composite of mixed protonically-electronically conductive (MPEC) perovskite oxide BaCe0.50Zr0.27Y0.20Ni0.03O3-delta (BCZYN) and Ni on a BaCe0.50Zr0.30Y0.20O3-delta electrolyte. Both powders were synthesized via a flame oxide-synthesis method and both had a unique microstructure, i.e., a fused-aggregate network structure [BCZYN(fans), Ni(fans)]. This unique structure was constructed from both a network of particles fused with their nearest neighbors and pores surrounded by the fused particles. This structure was found to be favorable for constructing both electronically conductive pathways and gas diffusion pathways in the CLs. Highly dispersed Ni nanoparticles [Ni(np)] were also loaded on the MPEC of BCZYN(fans) in the CLs. Composite CCLs of micrometer-sized BaCe0.50Zr0.30Y0.20O3-delta and Ni were also fabricated on the CLs. The catalytic activity of a hydrogen electrode using a CL comprising a composite of BCZYN(fans) and Ni(fans) was higher than that of a CL comprising BCZYN(fans) at a Ni(np) loading amount of 30 vol.% due to the improvement of the electronic conductivity in CLs by Ni(fans). The catalytic activity of the hydrogen electrode using the CLs increased with increases in the Ni(np) loading amount, moreover, and reached saturation at around 30 vol.% due to relief from the effect of the depletion layer on the outer surface of BCZYN(fans). (C) 2018 The Ceramic Society of Japan. All rights reserved.

Solid oxide fuel cells (SOFCs) are, in principle, able to be operated in reverse as solid oxide electrolysis cells (SOECs) to generate pure hydrogen from water vapor with the highest efficiency. Since the pioneering work in late 1960s (1) and HOT-ELLY (hot-electrolysis) project in 1980s (2), the materials and system for the SOECs have been extensively investigated (3). We have engaged in the research and development of high-performance electrodes with novel architecture for the SOEC/SOFC reversible system (4-9). The essential factors to improve the electrode performance are a high electrocatalytic activity and an extended effective reaction zone (ERZ: effective transport of gas, ions, and electrons). In the present work, we demonstrate that the microstructure of both hydrogen and oxygen electrodes plays an important role in reducing the ohmic and polarization losses under reversible SOFC/SOEC operations. Figure 1 shows cross-sectional SEM images of double-layer (DL) hydrogen electrodes (6) prepared on YSZ electrolyte. The DL electrodes consisted of a mixed conducting samaria-doped ceria, (CeO2)0.8(SmO1.5)0.2 (SDC), with highly dispersed Ni0.9Co0.1 catalysts (8 vol%-Ni0.9Co0.1) as a catalyst layer (CL, thickness = 14 to 16 μm), on top of which a Ni-SDC cermet (60 vol%-Ni) was attached as a current collecting layer (CCL) with a thickness of 5 to 20 μm. A SEM image of the single CL without CCL is also shown for comparison in Fig. 1 (a). The porosity of the CCL has to be high to increase the gas-diffusion rate. The CCLs formed on the CL were found to be uniform in the thickness and the apparent porosity was 69 to 70%, irrespective of the thickness. A test cell was prepared with the following configuration: DL H2 electrode│YSZ (0.5 mm)│SDC interlayer│O2electrode The oxygen electrode employed was a composite of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) with 40 vol% SDC. A detailed analysis of the oxygen electrode microstructure is given elsewhere (8). As a Pt/air reference electrode, a Pt wire was wrapped along the lateral of the YSZ electrolyte disk and fixed with Pt paste. Figure 2 shows steady-state IR-free I−E curves of the DL hydrogen electrodes, which were measured by the current interruption method, in the reversible SOFC/SOEC operation mode with H2 + H2O (p[H2O] = 0.4 atm) at 800ºC. The thickness of the CCL showed a significant effect in reducing the polarization loss. The test cell with 5 μm-CCL exhibited the highest performance in both SOFC/SOEC operations, i.e., the IR-free cathode potential at j = −0.5 A cm−2(SOEC operation) was −1.16 V vs. air reference electrode, which corresponds to an overpotential of −0.20 V. We also expect that the thin CCL with high electronic conductivity can act as a micrometer-size current collector to minimize the ohmic loss between the separator (interconnect) and the CL in stacks. The ohmic resistance of the test cells R cell was indeed smaller than that without the CCL, and reached the minimum value with the 5 μm-CCL. This suggests that the whole Ni0.9Co0.1/SDC of the catalyst layer can work effectively. A further increase in the CCL thickness (≥ 10 μm) increased the R cell (additional ohmic resistance of the cermet). The gas diffusion rate through the CCL is presumably slowed down with increasing the CCL thickness. In summary, the 5 μm-CCL provides the best balance in enlarging the ERZ by an effective transport of gases (H2O and H2) and an effective conductive network for electrons and oxide ions. This work was supported by the funds for “Advanced Low Carbon Technology Research and Development Program” (ALCA) from Japan Science and Technology Agency (JST). References 1. H. S. Spacil and C. S. Tedmon, Jr., J. Electrochem. Soc., 116, 1618 (1969). 2. W. Donitz and E. Erdle, Int. J. Hydrogen Energy, 10, 291 (1985). 3. S. D. Ebbesen, S. H. Jensen, A. Hauch, and M. B. Mogensen, Chem. Rev., 114, 10697 (2014). 4. H. Uchida, N. Osada, and M. Watanabe, Electrochem. Solid-State Lett., 7, A500 (2004). 5. N. Osada, H. Uchida, and M. Watanabe, J. Electrochem. Soc., 153, A816 (2006). 6. H. Uchida, S. Watanabe, Y. Tao, N. Osada, and M. Watanabe, ECS Trans., 7(1), 365 (2007). 7. H. Uchida and M. Watanabe, “High-Performance Electrodes for Solid Oxide Fuel Cells” in Modern Aspects of Electrochemistry(R. E. White and M. E. Gamboa-Aldeco Eds.), Springer (New York), Vol. 42, pp.53-87 (2008). 8. Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta, 54, 3309 (2009). 9. R. Nishida, P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, RSC Adv., 4, 16260 (2014). Figure 1

In order to establish clear criteria for designing highly active and highly durable oxygen electrode for reversible solid oxide fuel cells, we have focused on the effect of samaria-doped ceria (SDC) interlayers prepared on YSZ solid electrolyte surface on the performances of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-SDC composite oxygen electrode. Symmetrical cells with the configuration, LSCF-SDC|SDC interlayer|YSZ|SDC interlayer|LSCF-SDC, were constructed. We prepared two kinds of SDC interlayers, one from a mixed solution of cerium 2-ethylhexanoate (denoted as octoate) and samarium octoates (o-interlayer) and another from a mixed solution of cerium and samarium nitrates (n-interlayer). The LSCF-SDC electrodes with o-interlayer and n-interlayer exhibited very similar performances in both the anodic and cathodic reactions at 900 °C. When temperature was decreased to 800 °C, an increase in overpotentials was observed. However, the LSCF-SDC electrode with o-interlayer exhibited superior performance to that with n-interlayer. It was found that the entire surface of the YSZ electrolyte disk was well covered with a dense o-interlayer of uniform thickness. Such an interlayer enables uniform transport of oxide ions to and from the LSCF-SDC electrode, resulting in an enlarged effective reaction zone (ERZ). The I-E performance of the LSCF-SDC|o-interlayer|YSZ cell was found to be comparable to that of the identical electrode prepared on a dense SDC sintered electrolyte disk (as a reference). This observation supports our views regarding the essential role of a dense interlayer with uniform thickness in enhancing the performance of reversible solid oxide cells.

We have examined the long-term durability of a La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF)-samaria-doped ceria (SDC) composite oxygen electrode with SDC interlayer for reversible solid oxide cells (R-SOCs). A symmetrical cell with the configuration: LSCF-SDC vertical bar SDC interlayer vertical bar yttria-stabilized zirconia (YSZ) electrolyte vertical bar SDC interlayer vertical bar LSCF-SDC, was operated at 900 degrees C and a constant current density of 0.5 A cm(-2) with the top electrode as the anode (O-2 evolution). The IR-free overpotentials at both the anode and cathode were virtually constant during 5500 h of operation. The value of ohmic resistance at the anode side (R-A) increased slightly, whereas that at the cathode side (R-C) increased markedly. The I-E performance of the bottom electrode (operated as the cathode), that was measured from -1.0 to 1.0 A cm(-2) every 1000 h, degraded specifically at high current densities. It was found that the thickness, pore size, and porosity in both electrodes were unchanged, but the distribution of the Sr component changed markedly at both the LSCF-SDC/SDC interlayer and SDC interlayer/YSZ interfaces. While the diffusion of the Sr component from the anode was limited within the SDC interlayer, the Sr component from the cathode reached the SDC interlayer/YSZ interface, which could increase the R-C, likely due to the formation of SrZrO3. However, the diffusion rates of Sr were found to be noticeably slowed down at dense portions of the SDC interlayer. Hence, it is essential to prepare a dense, uniform SDC interlayer to improve both the durability and performance of R-SOCs. (C) 2017 The Ceramic Society of Japan. All rights reserved.

Nickel nanoparticles loaded on the electron–proton mixed conductor BaCe0.5Zr0.3−xY0.2NixO3−δ (Ni/BCZYN, x = 0 and 0.03) were synthesized for use in the hydrogen electrode of a proton-conducting solid oxide electrolysis cell (SOEC). The Ni nanoparticles, synthesized by an impregnation method, were from 45.8 nm to 84.1 nm in diameter, and were highly dispersed on the BCZYN. The BCZYN nanoparticles, fabricated by the flame oxide synthesis method, constructed a unique microstructure, the so-called “fused-aggregate network structure”. The BCZYN nanoparticles have capability of constructing a scaffold for the hydrogen electrode with both electronically conducting pathways and gas diffusion pathways. The catalytic activity on Ni/BCZYN (x = 0 and 0.03) catalyst layers (CLs) improved with the circumference length of the Ni nanoparticles. Moreover, the catalytic activity on the Ni/BCZYN (x = 0.03) CL was higher than that of the Ni/BCZYN (x = 0) CL. BCZYN (x = 0.03) possesses higher electronic conductivity than BCZYN (x = 0) due to the Ni doping, resulting in an enlarged effective reaction zone (ERZ). We conclude that the proton reduction reaction in the ERZ was the rate-determining step on the hydrogen electrode, and the reaction was enhanced by improving the electronic conductivity of the electron–proton mixed conductor BCZYN.

A reversible solid oxide cell (R-SOC) is a reciprocal direct energy converter between hydrogen and electricity (1). We have engaged in the research and development of high-performance electrodes with novel architecture for the R-SOC (2-9). A mixed conducting samaria-doped ceria (CeO2)0.8(SmO1.5)0.2 (denoted as SDC) has been used in both hydrogen and oxygen electrodes. A double-layer (DL) hydrogen electrodes consisting of SDC with highly dispersed Ni0.9Co0.1 catalysts as a catalyst layer and a Ni-SDC cermet attached as a current collecting layer (4, 7) was proposed and tested as a hydrogen electrode. We used an oxygen electrode consisting of a composite of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and SDC with SDC interlayer (5), in which SDC acted as a high oxide ionic conductor in oxygen atmosphere. In the present work, we demonstrate that the SDC is a key material in increasing the durability of both electrodes under reversible operations. We examined the durability of the LSCF-SDC electrode with SDC interlayer by using a symmetrical cell: LSCF‒SDC|SDC interlayer|YSZ electrolyte|SDC interlayer|LSCF‒SDC (8, 9). Pure oxygen gas at ambient pressure was supplied to both electrodes. The anodic overpotential (η A) and cathodic overpotential (η C), together with the ohmic resistances of the anode side R A and the cathode side R C, were measured by the current-interruption method with the use of a Pt/air reference electrode. The symmetrical cell was operated at 900 °C and a constant current density of 0.5 A cm−2. It was found that the values of η A and η C were virtually constant over whole operation of 5500 h. In contrast, the value of R C increased somewhat markedly, although the change in the R A was very small. Figure 1 shows the elemental distribution of Ce, Sr, and Zr for a cross-section of the LSCF‒SDC/SDC interlayer/YSZ region observed by SEM equipped with EDX. For the pristine electrode (Fig. 1(A)), we confirmed negligible inter-diffusion of Sr and Zr components at the LSCF‒SDC/SDC interlayer/YSZ. This is ascribed, with certainty, to a low fabrication temperature (1050 °C for 1 h). On the anode side after 5500 h of operation (Fig. 1(B)), the Sr component penetrated into the SDC interlayer with a layer-like distribution, which could be ascribed to rapid diffusion along the sub-layer of the SDC. It is noteworthy that the presence of Sr was limited within the SDC interlayer on the anode side, whereas the Sr component from the cathode reached the YSZ surface just below the SDC interlayer. It was suggested that a rapid diffusion of Sr over the YSZ surface could form SrZrO3, leading to the increase in R C. Because the concentration of Sr was found to be high in the vicinity of defects (dips or voids) of the SDC interlayer, the formation of a dense, uniform SDC interlayer is very important to obtain high durability with high performance in R-SOCs. We are performing the durability test of a full cell with the configuration: DL H2 electrode│YSZ or ScSZ│SDC interlayer│O2 electrode. The initial IR-free applied voltage at 0.5 A cm−2 was 1.16 V at 800 °C and 1.24 V at 750 °C. Effects of microstructure of DL hydrogen electrodes on the durability will be discussed. This work was supported by the funds for “Advanced Low Carbon Technology Research and Development Program” (ALCA) from the Japan Science and Technology Agency (JST). References 1. S. D. Ebbesen, S. H. Jensen, A. Hauch, and M. B. Mogensen, Chem. Rev., 114, 10697 (2014). 2. H. Uchida, N. Osada, and M. Watanabe, Electrochem. Solid-State Lett., 7, A500 (2004). 3. N. Osada, H. Uchida, and M. Watanabe, J. Electrochem. Soc., 153, A816 (2006). 4. H. Uchida, S. Watanabe, Y. Tao, N. Osada, and M. Watanabe, ECS Trans., 7 (1), 365 (2007). 5. Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta, 54, 3309 (2009). 6. R. Nishida, P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, RSC Adv., 4, 16260 (2014). 7. H. Uchida, P. Puengjinda, K. Miyano, K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and M. Watanabe, ECS Trans., 68 (1), 3307 (2015). 8. K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, Electrochim. Acta, 225, 114 (2017). 9. K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, J. Ceram. Soc. Jpn., in press. Figure 1

Solid oxide electrolysis cells (SOECs) are promising candidates for highly efficient hydrogen generation. In particular, proton-conducting SOECs have the advantage of producing high-purity dry hydrogen. For the practical application of proton-conducting SOECs, the development of highly efficient hydrogen electrodes with gas diffusion pathways and proton-electron mixed conducting pathways is required. In this research, we propose a new design concept of a current collecting / catalyst double layer (CCL/CL) hydrogen electrode using a proton-electron mixed conductor, BaCe0.8-xZrxY0.2O3-δ (BCZY), with a unique fused-aggregate network structure (Fig. 1) for proton-conducting SOECs. We also evaluated the performance of the hydrogen electrode as a function of the Ni loading amount. The proton-electron mixed conductor (BCZY (x = 0.3)) powder was synthesized by the flame oxide-synthesis method. The BCZY (x = 0.7) electrolyte was prepared by solid state reaction. The BCZY (x = 0.3) scaffold was synthesized on the BCZY (x = 0.7) electrolyte by sintering at 1000°C for 4 h in air. The CCL of Ni-BCZY (x = 0.3) composite was formed on the BCZY (x = 0.3) scaffold at 1050°C after 4 h. The Ni nanoparticle catalysts were loaded on the BCZY (x = 0.3) scaffold by an infiltration method to obtain the CL. The counter electrode was a Pt-BCZY (x = 0.3) composite. The crystal phases were characterized by XRD, ICP-MS and STEM-EDX. The performance of the double-layer electrode was evaluated under hydrogen flow at 700°C. The XRD patterns for BCZY (x = 0.3) and BCZY (x = 0.7) were consistent with a single perovskite phase. BCZY (x = 0.3) had a unique microstructure, with a fused-aggregated network structure, which was able to provide a gas diffusion pathways and proton-electron mixed conducting pathways while maintaining the high surface area (Fig. 2(a)). The STEM-EDX image of a cross-section of the CL showed that the Ni nanoparticles (diameter 70 ± 12 nm) were highly dispersed on the fused-aggregated BCZY (x = 0.3) scaffold (Fig. 2(b)). The polarization curves of the double-layer electrode showed that the electrode performance improved with increasing Ni loading amount up to 20 vol.%. The Ni particles maintained a highly dispersed state on the BCZY (x = 0.3) scaffold, indicating that the increased effective reaction zone (ERZ) was able to enhance the performance of the double-layer electrode. At Ni content ≥ 20 vol.%, the electrode performance decreased significantly. This was ascribed with certainty to a decrease in the extent of the ERZ, because the aggregation of Ni particles was observed by STEM. Reference K. Katahira, Y. Kohchi, T. Shimura and H. Iwahara Solid State Ionics, 138, 91 (2000). Figure 1

Solid oxide cells (SOCs) are high-temperature electrochemical energy conversion and storage devices, which can be operated under solid oxide electrolysis cell (SOEC) mode to produce pure hydrogen from water vapor with high efficiency. SOCs can also be operated in reverse under solid oxide fuel cell (SOFC) mode, providing high-energy conversion efficiency to convert hydrogen fuel to electricity. Similar to SOFCs, cost-effective metallic (alloy) can be used as interconnects for planar-type SOCs operated at reduced temperatures (≤ 800 °C). However, without an effective protective coating on the Cr-containing alloy, volatile Cr-containing species are generated at high temperatures in oxidizing atmosphere. It has been recognized that several oxygen electrodes such as Sr-doped LaMnO 3 (LSM) or La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 - δ (LSCF) suffer from a serious Cr-poisoning. 1–3 We have recently succeeded in improving the reversible performances of the single-layer LSCF-Ce 0.8 Sm 0.2 O 1.9 (SDC) composite O 2 electrode with SDC interlayer at 800 and 900 °C, 4–6 compared with those of an identical-type electrode in our previous work. 7 Though the degradation of the LSM or LSCF electrodes by Cr-poisoning has been studied under either SOFC or SOEC operation mode, separately, to the best of our knowledge, the Cr-poisoning have not been investigated on SOCs under simultaneously reversible operation of SOFC/SOEC modes. Here, we examined for the first time the effect of Cr-poisoning on the performances of LSCF-SDC oxygen electrodes under simultaneously cathodic and anodic polarization conditions in the presence of Fe-Cr alloy. A symmetrical cell [LSCF-SDC ǀSDC interlayerǀ ScSZ electrolyte ǀSDC interlayerǀ LSCF-SDC] was prepared. 4,5 Here, we briefly describe the protocol. The SDC interlayer was deposited on both sides of the scandia-stabilized zirconia (ScSZ, (ZrO 2 ) 0.89 (Sc 2 O 3 ) 0.10 (CeO 2 ) 0.01 ) electrolyte by spin coating of Ce(III) 2-ethylhexanoate and Sm(III) 2-ethylhexanoate mixed solution, followed by heat-treatment at 1050 o C for 2 h. The LSCF-SDC paste (60:40 volume ratio) was tape-casted onto the SDC interlayer and heat-treated at 1050 o C for 1 h. The air reference electrode consisted of a Pt wire wound around the ScSZ disk. A commercial Fe-Cr alloy (RA446, 23–27 wt% Cr, Rolled Alloy, Canada) was used as the metallic interconnect without any protective coating. The interconnect plate (12 × 12 × 4 mm) was machined with gas channels on one side. Air was supplied to both electrodes at a flow rate of 100 mL min −1 . The as-prepared symmetrical cell was sandwiched with two Fe-Cr interconnect plates, which were also acting as the current collectors. After a constant current density operation at 0.5 A cm −2 and 800 o C for 100 h, the IR-free polarization curves of both electrodes were measured. Hereinafter, the electrodes polarized anodically (O 2 evolution) and cathodically (O 2 reduction) for 100 h will be denoted as electrode A and electrode C, respectively. Figure 1 shows the polarization curves of electrode A and electrode C with and without Fe-Cr interconnect plate at 800 o C. When operated with Pt current collectors (without any Fe-Cr alloy), very high performance of both electrode A and electrode C was observed even after 100 h (negligibly small degradation). In contrast, after operation with Fe-Cr alloy interconnects, the overpotential at both electrodes significantly increased due to Cr-poisoning. While the difference in the anodic overpotential between electrode A and C was relatively small in the O 2 evolution reaction, electrode A showed much larger overpotential than that of electrode C in the O 2 reduction, specifically at high current densities. This could suggest that Cr-containing oxides deposited in the pores 2 might block the O 2 diffusion path. Analyses of the electrode morphology are under progress. This work was supported by the funds for “ALCA” from Japan Science and Technology Agency. References 1. C. C. Wang, T. Becker, K. Chen, L. Zhao, B. Wei, and S. P. Jiang, Electrochim. Acta , 139 , 173 (2014). 2. B. Wei, K. Chen, L. Zhao, Z. Lu, and S. P. Jiang, Phys. Chem. Chem. Phys. , 17 , 1601 (2015). 3. T. Horita, D. Cho, F. Wang, T. Shimonosono, H. Kishimoto, K. Yamaji, M. E. Brito, and H. Yokokawa, Solid State Ionics, 225 , 151 (2012). 4. K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, 23rd Annual Meeting of MRS-J , A-P11-009 (Dec. 9-11, 2013, Yokohama, Japan). 5. K. Shimura, H. Nishino K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, Proc. 81 st Annual Meeting of the Electrochemical Society of Japan , 1G17 (2014). 6. H. Uchida, P. Puengjinda, K. Miyano, K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and M. Watanabe, ECS Trans. , 68 (1), 3307 (2015). 7. Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta , 54 , 3309 (2009). Figure 1

Nanofiber-structured Sm0.5Sr0.5CoO3−δ–Gd0.2Ce0.8O1.9 (SSC–GDC) composite cathodes prepared by infiltration of Gd0.2Ce0.8O1.9 (GDC) precursor solution into a porous Sm0.5Sr0.5CoO3−δ (SSC) nanofiber scaffold are investigated. The SSC–GDC composite cathode with the optimum infiltration load of GDC achieves interfacial polarization resistances of 1.609, 0.595, 0.209, 0.081 and 0.038Ωcm2 at 600, 650, 700, 750 and 800°C, respectively. These polarization resistances are lower than those reported for comparable materials. Stable performance of the cathode is confirmed by testing at a constant current of 0.2A/cm2 for up to 100h. Furthermore, the peak power density of a cell using the nanofiber-structured SSC–GDC cathode in combination with a 650-μm-thick La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte is found to be 0.134W/cm2 at 800°C. All of these results make of the nanofiber-structured SSC−GDC composite cathodes a potential high-performance component for use in intermediate temperature solid oxide fuel cells.

In this work we attempt to give solution to apparently inconsistent results on grain boundary diffusion of Sr in 10GDC that we have found in our earlier diffusion experiments. The emphasis is placed on using of diffusion triplets: LSCF(porous)/10GDC(dense)/8YSZ(dense) that reproduce the driving forces for Sr diffusion found in solid oxide fuel cell (SOFC) real systems. The diffusion triplets were annealed at 1100 and 1200°C for one week. Detailed analyses of the microstructure and elemental distributions unequivocally demonstrate the SrZrO3 formation along both the LSCF/10GDC and the 10GDC/8YSZ interfaces as the result of strontium and zirconium counter directional grain boundary diffusion through the 10GDC interlayer. Furthermore, micro-cracks in the 10GDC interlayer, formed during pre-annealing of the 10GDC/8YSZ layers, were also found to contribute to the SrZrO3 formation via surface diffusion. Thermodynamic considerations taking in account these microstructural features successfully explain, in terms of the chemical potential gradients developed across the 10GDC layer, why SrZrO3 is formed along both interfaces when grain boundary diffusion, or surface diffusion (along crack walls), become dominant compared to bulk diffusion through the 10GDC.

Within the framework of developing reversible solid oxide fuel cells/solid oxide electrolysis cells (SOFCs/SOECs), we have engaged in the design of high-performance electrodes. Facile production of hollow spherical particles of samaria-doped ceria (SDC) decorated with Ni–Co alloy catalysts (Ni100−XCoX/SDC, X = 0–50 atom%), nanometers in size, was adopted. A distinctive microstructure was observed in the hydrogen electrode fabricated with this composite powder. The cobalt addition played a significant role in evolution of the microstructure and effectively enlarged the electrochemical reaction zone. Under SOFC/SOEC reversible operation, the optimal performance characterized by a comparatively low ohmic resistance and high electrocatalytic activity was achieved with the Ni80Co20/SDC composition. At 900 °C and an overpotential of 0.1 V, the current density reached remarkably high values of 0.18 and 0.37 A cm−2 in SOFC and SOEC operation, respectively.

Effects of the oxide substrate on the nickel (Ni) particle properties are examined by using a Ni agglomeration behavior analysis and Kelvin Force Microscope (KFM) technique. Agglomerated Ni particles are formed after annealing a Ni thin film on oxide substrates of yttria stabilized zirconia (YSZ) and gadolinia doped ceria (GDC). Nickel agglomeration is suppressed for the Ni particles on the GDC substrate compared to those particles on the YSZ substrate. Although evaluated at room temperature, the surface potential of GDC is more positive than that of YSZ, while Ni particle surface potential is about the same for both the Ni/YSZ and the Ni/GDC systems.

Graphene nanosheets (GN) are modified by electrodeposition of Prussian blue (PB) followed by shape-regulated depositing of small Pt nanoparticles via the interaction between PB and PtCl62- to form a novel catalyst Pt/PB/GN. The Pt/PB/GN composite exhibits significantly enhanced electrocatalytic activity with a mass activity of 445 mAmg(pt)(-1) (at 0.68 V vs. SCE) and high stability towards methanol oxidation. The high catalytic activity can be attributed to the unique porous architecture and peculiar electrical property of Prussian blue integrated with graphene layers which can not only well accommodate Pt nanoparticles but also provide multidimensional pathways to facilitate the mass and electron transport for methanol oxidation. This strategy can be readily extended to fabrication of other graphene-based hybrid supports for precious metal catalysts in fuel cell applications. (C) Crown Copyright 2014 Published by Elsevier Ltd. All rights reserved.

To accurately evaluate the role as diffusion barrier of gadolinia-doped ceria (GDC) interlayer, often used in real stacks of solid oxide fuel cells, the cation diffusion behavior in a LSCF/GDC/YSZ system was investigated. Diffusion under open circuit voltage (OCV) and cathodic polarization conditions was evaluated using pellet-type cells in which a dense GDC interlayer, about 1 pm in thickness, was prepared by pulse laser deposition (PLD). Results clearly show that under polarization, SrZrO3 formation along both LSCF/GDC and GDC/YSZ interfaces is accelerated. The enhancement of Sr diffusion during cathodic polarization is explained by a shift to higher values of the thermodynamic activity of Sr at the LSCF/GDC interface that also leads to a decrease in oxygen potential. (C) 2014 Elsevier B.V. All rights reserved.