Samaria-doped Ceria Interlayer Research Articles

Remarkably Improved Durability of Ni–Co Dispersed Samaria-Doped Ceria Hydrogen Electrodes by Reversible Cycling Operation of Solid Oxide Cells

We have examined the durability of a double-layer hydrogen electrode, consisting of a samaria-doped ceria (SDC) scaffold with highly dispersed Ni–Co nanoparticles as the catalyst layer and a thin current collecting layer of Ni–yttria-stabilized zirconia (YSZ) cermet for a reversible solid oxide cell (R-SOC). When steam electrolysis was performed continuously (solid oxide electrolysis cell, SOEC) at 800 °C, a rapid, large increase in the ohmic resistance of the hydrogen electrode side was observed. In contrast, the durability of the hydrogen electrode was found to be improved remarkably by reversible cycling operation between SOEC and solid oxide fuel cell (SOFC) modes, i.e., virtually no degradation over 1200 h. This could be ascribed to a stabilization of the microstructure of the hydrogen electrode. It was also found that the durability of the oxygen electrode, which was based on a composite of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and SDC with an SDC interlayer, was also improved by the reversible cycling operation, compared with a slight degradation in the continuous SOEC operation.

Performance and Properties of Suspension Plasma Sprayed Metal‐Supported Cu‐Co‐Ni‐SDC SOFC Anodes in Methane

AbstractIn this study, metal‐supported solid oxide fuel cell (SOFC) anodes containing Cu and samaria doped ceria (SDC) with additions of Ni and Co were evaluated in CH4. It was found that metal support oxidation and Fe diffusion from the metal support to the anode were the main factors affecting the cell behavior observed. Thus, strategies to prevent diffusion of Fe into the anode were also evaluated. It was found that the best performing method to prevent diffusion of Fe and Cr into the anode in this study consisted of a combination of all three evaluated strategies (i.e., pre‐oxidation of metal support prior to cell fabrication, application of a protective LaCrO3 coating to the metal supports prior to anode fabrication, and addition of an SDC interlayer between the metal support and anode coating). It was found that the most effective stand‐alone method to diminish the diffusion of Fe into the anode was the addition of a SDC interlayer between the anode and the metal support.

Ridge‐Valley Nanostructured Samaria‐Doped Ceria Interlayer for Thermally Stable Cathode Interface in Low‐Temperature Solid Oxide Fuel Cell

Agglomeration of the metal electrode decreases the performance of low‐temperature solid oxide fuel cells (LT‐SOFC) during operation at elevated temperatures. Here, we report a Pt electrode/ridge‐valley nanostructured samaria‐doped ceria (SDC) layer interface with extended lifetime. LT‐SOFCs with RF‐sputtered SDC interlayers with thicknesses in the range 65–260 nm show a >20 times lower degradation of performance as compared to cells without interlayer when operated at 450 °C (1.8% h−1 vs. 45% h−1). Micromorphological analysis reveals that the coarsening of the Pt electrode is significantly suppressed by the presence of the nanostructured SDC interlayer, possibly due to a stronger bonding between this layer and the Pt grains.

Effect of Microstructure on Performance of Double-Layer Hydrogen Electrodes for Reversible SOEC/SOFC

We have developed high-performance double-layer (DL) hydrogen electrodes for reversible solid oxide cells. The DL hydrogen electrode consisted of mixed conductor, samaria-doped ceria (SDC), with highly dispersed Ni or Ni-Co nanocatalysts as the catalyst layer (CL) and, on top of it, a thin Ni−SDC cermet as the current collecting layer (CCL). The performance of the DL hydrogen electrode was appreciably improved by controlling the microstructure. The use of a thin, porous CCL increased the electronic conducting path to and from the CL, while maintaining sufficient gas-diffusion rates of H2 and H2O, and enlarging the effective reaction zone at the CL. The optimum CCL thickness was found to be 5 μm. The IR-free overpotentials η at the optimized DL hydrogen electrode in humidified hydrogen (p[H2O] = 0.4 atm) and Tcell = 800°C were 0.20 and −0.20 V at j = 0.5 and −0.5 A cm−2, respectively, indicating a highly reversible operation. The use of a full cell with the configuration of Ni0.9Co0.1/SDC DL hydrogen electrode|YSZ electrolyte|SDC interlayer|LSCF−SDC O2 electrode led to very promising results for the SOEC operation in which an IR-free electrolytic cell potential of 1.21 V at j = −0.5 A cm−2 and 800°C was achieved.

Effect of samaria-doped ceria (SDC) interlayer on the performance of La0.6Sr0.4Co0.2Fe0.8O3-δ/SDC composite oxygen electrode for reversible solid oxide fuel cells

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.

Optimization of SDC Interlayer for YSZ-Based IT-SOFCs

Inserting a porous samaria-doped ceria (SDC) interlayer between yttria-stabilized zirconia (YSZ) electrolyte and anode is an effective method to enhancing the performance of intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this work, the microstructure and morphology of the SDC interlayer were optimized by varying its thickness and sintering temperature. Results show that the SDC interlayer fabricated by utilizing once screen printing method and then sintered at 1300 °C for 2 h obtains the best electrochemical performance. The resulting polarization resistance and anodic overpotential (at a current density of 0.05 Acm-2) were 0.84 Ωcm2and 0.07 V at 800 °C in H2, reduced by factors of 4.7 and 5.6, respectively, when compared with the LSCM anode without the SDC interlayer.

Influence of the grain size of samaria-doped ceria cathodic interlayer for enhanced surface oxygen kinetics of low-temperature solid oxide fuel cell

The catalytic role and grain boundary effect of samaria-doped ceria (SDC) interlayers were investigated. To see the catalytic role, an SDC interlayer was deposited on a single crystalline YSZ (100) substrate by using the pulsed laser deposition (PLD) for an epitaxial film. The grain boundary effects were analyzed with SDC interlayers with various grain sizes on polycrystalline YSZ substrates. As a result, the membrane electrode assembly (MEA) with an epitaxial SDC interlayer exhibited a peak power density that was twice that of a YSZ controlled MEA. More detailed experiments were conducted with MEAs with various grain sizes. In the electrochemical analysis, the MEA with a nano grain SDC interlayer showed an increased maximum power density and lower cathodic impedance. This result suggests that the performance of low temperature solid oxide fuel cells (LT-SOFCs) could be enhanced by applying an SDC interlayer with nano grains for the enhanced oxygen reduction reaction.

Enhancing the performance of doped ceria interlayer for tubular solid oxide fuel cells

Doped ceria interlayer fabricated by conventional wet ceramic process such as dip-coating often suffers from high resistance due to either low density or solid-state reaction with yttria-stabilized zirconia (YSZ) electrolyte in solid oxide fuel cells (SOFCs). This work presents a new route to reduce the resistance by increasing the density while minimizing the solid-state reaction through impregnating samaria-doped ceria (SDC) nano-particles to porous SDC interlayer of anode-supported tubular SOFCs. Results show that impregnated fine structure can substantially reduce the ohmic resistance, from 0.140 to 0.087 Ω cm2 at 750 °C, and consequently significantly improve the fuel cell performance, peak power density from 1.01 to 1.50 W cm−2 at 750 °C. The significant improvements demonstrate that impregnation is an effective method to improve the interlayer performance.

Reaction Sites of Mixed Conductor Anodes in Solid Oxide Fuel Cells

Pt pattern anodes with defined TPB length were prepared on the surface of YSZ or SDC (Samaria-doped ceria) interlayer deposited on an YSZ disk, in order to investigate the reaction sites of SOFC anodes consisting of mixed conductor oxides. The electrode resistance was measured by AC impedance method under different conditions and assigned to reaction resistances by fitting to an equivalent circuit. The dependence of the reaction resistances was investigated by varying operation temperature, hydrogen partial pressure, and the number of the Pt electrode patterns. The impedance in the Nyquist plots was fitted by two semicircles at low and high frequency, and the high frequency arc was assigned to the anodic reactions nearby the TPB. For the same TPB length, the conductivity determined from the high frequency arc for the Pt electrodes on the SDC layer was almost ten times as large as that on the YSZ layer.

Polarization Behavior of SDC Cathode with Highly Dispersed Ni Catalysts for Solid Oxide Electrolysis Cells

We have developed a mixed conducting samaria-doped ceria (SDC) cathode with highly dispersed Ni catalysts in a solid oxide electrolysis cell (SOEC) for efficient hydrogen production. The Ni-dispersed SDC cathode exhibited the highest performance at 17 vol %-Ni loading due to the effective enhancement of the reaction rate by increasing the active reaction sites and lowering the electronic resistance. The cathode activity was found to increase with an increase in the ionic conductivity of zirconia electrolyte, similar to the case of SOFC electrodes. An SOEC comprised of Ni-dispersed SDC cathode, ScSZ electrolyte, and anode (with SDC interlayer) exhibited high performance for the short-term test; IR-free cell at and under the atmosphere of and .

High Performance Electrodes for Reversible Solid Oxide Fuel Cells

We have developed high performance electrodes for reversible SOFCs. In an SOFC mode, mixed conducting samaria-doped ceria (SDC) anode was activated effectively by highly dispersed Ni electrocatalysts, A porous LaCoO 3 -based cathode prepared on a thin and dense SDC interlayer exhibited a low overpotential of -0.05 V at 0.4 A cm -2 and 800°C in air. A solid oxide electrolysis cell (SOEC) using the same component materials as the SOFC produced hydrogen with a small IR-free cell voltage = 1.15 V at 0.5 A cm -2 and 900°C under the atmosphere of H 2 + H 2 O (p[H 2 O] =0.6 atm p[H 2 ] = 0.4 atm) and O 2 (1 atm).

High-Performance Electrode for Steam Electrolysis

We have developed a high-performance cathode for solid oxide electrolysis cells (SOECs) for hydrogen production. Mixed conducting samaria-doped ceria (SDC) particles were employed in combination with highly dispersed Ni electrocatalysts. The Ni (8 vol %) dispersed SDC cathode exhibited very high performance at a water vapor pressure >0.4 atm at 900°C. An SOEC, comprised of Ni-dispersed SDC cathode, La(Sr)CoO 3 anode with SDC interlayer, and YSZ electrolyte, exhibited fairly high performance; IR-free cell voltage = 1.20 V at 0.50 A cm - 2 and 900°C under the atmosphere of H 2 + H 2 O (p[H 2 ] = 0.6 atm, p[H 2 O] = 0.4 atm), and O 2 (1 atm).

Electrochemical properties of reduced-temperature SOFCs with mixed ionic–electronic conductors in electrodes and/or interlayers

We have investigated the electrochemical properties of two types of reduced-temperature solid oxide fuel cells (SOFCs) in which the mixed ionic–electronic conductors are used to improve their performances. Electrolyte-supported cells, in which doped LaGaO 3 strengthened by Al 2O 3 dispersion is used as the electrolyte, were prepared and tested. Samaria-doped ceria (SDC) interlayers of 0.3-μm thickness were fired onto both surfaces of the electrolyte of 0.2-mm thickness at 1523 K, before firing the Ni–Sm 0.1Ce 0.9O 1.95–(CeO 2) 0.1[(Y 2O 3) 0.08(ZrO 2) 0.92] 0.9 (Ni–SDC–CeYSZ) (10 mol% ceria-doped yttria-stabilized zirconia [YSZ]) cermet anode at 1723 K and La 0.7Sr 0.3Co 0.2Fe 0.8O 3–Sm 0.2Ce 0.8O 1.9 (LSCF–SDC) composite cathode at 1373 K. The cells have a nominal size of 60×60 mm 2 with an effective electrode area of 4 cm 2. The single cell thus prepared showed a high power density of 0.67 W cm −2 at 1073 K and long-term stability during the operation time of 1000 h. Anode-supported cells with a thin YSZ electrolyte film approximately 30 μm thick were also prepared by co-sintering of screen-printed YSZ paste on a compacted anode substrate. The cells have a nominal size of 50×50 mm 2 with an effective electrode area of 4 cm 2. The single cell with the LSCF–SDC composite cathode having SDC interlayer showed the maximum power density of 0.648 W cm −2 at 1023 K. The bilayer cathode also showed high resistance against degradation by Cr-poisoning.

High performance electrodes for medium-temperature solid oxide fuel cells: Activation of La(Sr)CoO 3 cathode with highly dispersed Pt metal electrocatalysts

In order to apply La(Sr)CoO 3 (LSC) as a cathode for medium-temperature solid oxide fuel cells without causing unfavorable solid-state reactions between LSC and yttria-stabilized zirconia electrolyte, the use of samaria-doped ceria (SDC) interlayer was examined. A porous LSC cathode prepared on a thin and dense SDC interlayer exhibited very high performance even at 800°C. The performance was enhanced further by dispersing a small amount of nm-sized Pt catalysts on the LSC surface. The current density on the Pt–LSC cathode at an overpotential of −0.05 V was 0.6 A/cm 2 at 800°C in O 2.