The development of alternative ceramic anodes for low-temperature solid oxide fuel cells (LT-SOFCs) is essential to overcome the inherent challenges such as redox instability and coking associated with Ni-based cermet anodes. Moreover, due to the large electrolyte ohmic loss at low temperature, it is critical to developing an electrode supported cell that allows electrolyte thickness reduction. Here we successfully demonstrated a high performance SrFe0.2Co0.4Mo0.4O3−δ (SFCM) ceramic anode supported LT-SOFC with a peak power density of 730 mW cm−2 and 300 mW cm−2 at ambitious low temperatures of 550 °C and 450 °C, respectively, in humidified H2. The new anode material SFCM exhibits exceptional conductivity of over 30 S cm−1 at 450 °C in humidified H2, providing essential current collection capability as an anode backbone appropriate for the infiltration of Ni-gadolinia doped ceria (GDC) electrocatalysts. Compared to conventional Ni-cermet anodes, the nano-sized Ni-GDC particles in our SFCM based electrode significantly improves the cell stability in hydrocarbon gases. We demonstrated a stable long-term operation over a period of 380 h in CH4–containing gas mixtures at 450 °C with a voltage degradation rate of 4% per 1000 h at a constant current of 0.2 A*cm−2. Our results demonstrate a high performance ceramic anode with high stability for low temperature operation.

Coatings play key roles in solid oxide fuel cell (SOFC) stack durability. For example, diffusion barrier coatings on Cr-containing interconnect and balance of plant (BOP) components protect electrodes from Cr poisoning over the long operational lifetimes (>10,000 hours) of the fuel cell stack. Common defects in coatings, such as cracks, pinholes, and porosity, result in a failure to protect the electrodes, resulting in shorter operational lifetime and thus higher cost. It is very unlikely, even in the best coating process, that all these defects can be mitigated, hence identifying critical defects in parts, and removing defective parts from production before they can damage the stack, becomes paramount. Furthermore, these quality control techniques must be operational in the production/assembly line (in-line), i.e., high throughput and non-destructive, and cost effective. Redox Power Systems, LLC (Redox) together with the National Renewable Energy Laboratory (NREL) developed much needed high throughput, in-line metrology techniques for protective coatings. The overall goal of the project is to lower cost while increasing robustness, reliability, and endurance of SOFC stacks. To accomplish this, we had several objectives, including: to identify key coating and substrate defects that lead to coating failure through the use of detailed characterization methods (e.g., microscopy, XRD, EDS, electrochemistry); to assess capabilities of in-line metrology techniques, e.g., optical profilometry (Redox) and thermography (NREL), to probe these defects, or evidence thereof; demonstrate long-term performance of “defect-free” protective coatings, as identified by in-line metrology, in solid oxide fuel cell (SOFC) stack operation. In the first part of this project, the ability to identify key defects expected to lead to coating and SOFC degradation using in-line metrology tools were evaluated. Coated interconnect samples with controlled defect types and populations were tested under conditions similar to SOFC operation, followed by detailed post-test analysis to reveal the defects responsible for observed degradation. In the second part of the project, the optimal in-line metrology techniques and methodologies were used to map the defect distribution in full-size interconnects with critical defects intentionally allowed to exist in some cases. These interconnects underwent SOFC testing for extended periods (up to ~3,000 hours) followed by post-test analysis to evaluate the effectiveness of in-line metrology techniques in mitigating MCO coating related degradation. Key accomplishments in this project included the following: Demonstrated ASR of < 0.05 ohm-cm2 at 650 °C for 1,000 hours with low defect (determined by in-line metrology) interconnect samples (average ASR=37 milliohms-cm2 after over 1,000 hours). Demonstrated that low defect coatings on interconnects (as screened using in-line metrology) have low volatilization of chromium at ~650 °C for 1,000 hours as detected using Cr-getter material (< 5 at% increase above baseline); 1022 hour duration tests under humidified, elevated temperature (750 °C rather than 650 °C) compared a base case against different coating thicknesses. Demonstrated capability to identify initial key defects of interest with in-line metrology techniques using up to 8 cm by 10 cm having coatings with and without intentional defects of interest using thermal imaging and optical profilometry. Correlated key defects identified using metrology techniques with observed coating performance (e.g., ASR and Cr volatility). Conducted several 4 cm by 4 cm cell tests using MCO-interconnects that were pre-screened using some of the metrology techniques developed in the project (e.g., optical profilometry). An analysis of ASR measurements were able to show that defect-free coatings resulted in the anticipated performance in the cell tests.

Fuel flexibility is a unique feature of solid oxide fuel cells (SOFCs), the instability of Ni-based cermet anodes in hydrocarbon fuels impede the advancement of low-temperature solid oxide fuel cells (LT-SOFCs). Here we demonstrate highly stable LT-SOFCs prepared by catalytically modifying the surface of a conductive ceramic oxide, SrFe0.2Co0.4Mo0.4O3 (SFCM), using Ni-GDC nanoparticles (<100 nm). The nano-sized Ni-GDC electrocatalysts, resulting from careful optimization of Ni-to-GDC ratio, and subsequent low-temperature calcination process, enhance the fuel oxidation kinetics and stability of SFCM anode significantly. An optimized Ni-to-GDC ratio of 1:10 on SFCM-supported SOFC delivered peak power density of 0.75, 0.65 and 0.36 W cm(-2) at 650 degrees C, 600 degrees C and 550 degrees C, respectively, in humidified H-2 and 0.62, 0.39 and 0.22 W cm(-2) at 650 degrees C, 600 degrees C and 550 degrees C, respectively, in CH4/H-2 gas mixtures, nearly 4x higher than GDC as electrocatalyst. Remarkably, for the same Ni-to-GDC ratio, a stable cell voltage of 0.82 V is maintained over 200 h of operations (under current) at 600 degrees C in CH4/H-2 gas mixtures. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

A critical factor hampering the deployment of fuel-flexible, low-temperature solid oxide fuel cells (LT-SOFCs) is the long-term stability of the electrode in different gas environments. Specifically, for state-of-the-art Ni-cermet anodes, reduction/oxidation (redox) cycles during fuel-rich and fuel-starved conditions cause a huge volume change, eventually leading to cell failure. Here, we report a robust redox-stable SrFe0.2Co0.4Mo0.4O3 (SFCM)/Ce0.9Gd0.1O2 ceramic anode-supported LT-SOFC with high performance and remarkable redox stability. The anode-supported configuration tackles the high ohmic loss associated with conventional ceramic anodes, achieving a high open circuit voltage of ∼0.9 V and a peak power density of 500 mW/cm2 at 600 °C in hydrogen. In addition, ceramic anode-supported SOFCs are stable over tens of redox cycles under harsh operating conditions. Our study reveals that oxygen nonstoichiometry of SFCM compensates for the dimensional changes that occur during redox cycles. Our results demonstrate the potential of all ceramic cells for the next generation of LT-SOFCs.

Sputtering of thin electrolyte layers has been demonstrated to increase solid oxide fuel cell (SOFC) performance in very small-scale, e.g., button cells. The few cases where thin film techniques were brought in to early stages of commercialization (e.g., Lilliputian and SiEnergy) showed remarkable low temperature SOFC performance, but required sophisticated cell designs processed with Si and MEMs type technologies. This work takes advantage of low cost, conventional ceramic processing to build large format (10 cm x 10 cm) half-cells upon which the sputtered layers above are added to dramatically increase SOFC performance. In this work, an electron-blocking layer which increases the open circuit cell voltage of the GDC electrolyte based cell and a Gd doped ceria (GDC) buffer layer which mitigates reactions between the cathode and electron blocking layer are deposited by sputtering. This presentation will present progress towards developing increased SOFC performance using this sputtering technology at the commercial-scale. Challenges encountered or expected with thin film development for SOFC commercialization will be discussed.

While there have been significant breakthroughs in new functional cathodes facilitating the oxygen reduction reaction (ORR) for low-temperature solid oxide fuel cells (LT-SOFCs), sluggish oxygen charge transfer across the cathode/electrolyte heterogeneous interface also hinders overall performance. To promote oxygen ion exchange at the interface, a thin layer of cerium oxide decorated by an amorphous cobalt oxide overcoating was introduced to function as a fast oxygen ion transport pathway at the interface. The peak power density (PPD) of the modified cell achieved 767 mW/cm(2) at a low operation temperature of 550 degrees C, which is almost 3 times the power output of the unmodified cell. Oxygen isotope exchange confirmed that the oxygen reduction active cobalt oxide nanolayer drastically reduced the energy barrier for oxygen transport across the solid-solid interface. Such interface modification successfully demonstrates an effective route to enable fast ORR and oxygen transport across the cathode/electrolyte interface at low temperature.

In this project, we improved the power output and voltage efficiency of our intermediate temperature solid oxide fuel cells (IT-SOFCs) with a focus on ~600 °C operation. At these temperatures and with the increased power density (i.e., fewer cells for same power output), the stack cost should be greatly reduced while extending durability. Most SOFC stacks operate at temperatures greater than 800 °C. This can greatly increase the cost of the system (stacks and BOP) as well as maintenance costs since the most common degradation mechanisms are thermally driven. Our approach uses no platinum group metal (PGM) materials and the lower operating temperature allows use of simple stainless steel interconnects and commercial off-the-shelf gaskets in the stack. Furthermore, for combined heating and power (CHP) applications the stack exhaust still provides “high quality” waste heat that can be recovered and used in a chiller or boiler. The anticipated performance, durability, and resulting cost improvements (< $700/kWe) will also move us closer to reaching the full potential of this technology for distributed generation (DG) and residential/commercial CHP. This includes eventual extension to cleaner, more efficient portable generators, auxiliary power units (APUs), and range extenders for transportation. The research added to the understanding of the area investigated by exploring various methods for increasing power density (Watts/square centimeter of active area in each cell) and increasing cell efficiency (increasing the open circuit voltage, or cell voltage with zero external electrical current). The results from this work demonstrated an optimized cell that had greater than 1 W/cm2 at 600 °C and greater than 1.6 W/cm2 at 650 °C. This was demonstrated in large format sizes using both 5 cm by 5 cm and 10 cm by 10 cm cells. Furthermore, this work demonstrated that high stability (no degradation over > 500 hours) can be achieved together with high performance in large format cells as large as 10 cm by 10 cm when operated at ~600 °C. The project culminated in the demonstration of a 12-cell stack using the porous anode-based SOFC technology.

Exploitation of alternative anode materials for low-temperature solid oxide fuel cells (LT-SOFCs, 350-650 °C) is technologically important but remains a major challenge. Here we report a potential ceramic anode Y0.7Ca0.3Cr1- xCu xO3-δ ( x = 0, 0.05, 0.12, and 0.20) (YCC) exhibiting relatively high conductivity at low temperatures (≤650 °C) in both fuel and oxidant gas conditions. Additionally, the newly developed composition (YCC12) is structurally stable in reducing and oxidizing gas conditions, indicating its suitability for SOFC anodes. The I- V characteristics and performance of the ceramic anode infiltrated with Ni-(Ce0.9Gd0.1O2-δ)(GDC) were determined using GDC/(La0.6Sr0.4CoO3-δ)(LSC)-based cathode supported SOFCs. High peak power densities of ∼1.2 W/cm2 (2.2A/cm2), 1 W/cm2 (2.0A/cm2), and 0.6 W/cm2 (1.3 A/cm2) were obtained at 600, 550, and 500 °C, respectively, in H2/3% H2O as fuel and air as oxidant. SOFCs showed excellent stability with a low degradation rate of 0.015 V kh-1 under 0.2 A/cm2. YCC-based ceramic anodes are therefore critical for the advancement of LT-SOFC technology.

Doped-YCrO3 ceramic oxides were investigated as potential anode materials for low-temperature solid oxide fuel cells (LT-SOFC, 400-650°C). This material has shown orthorhombic symmetry with the space group pmmm. Electrical conductivity >1 S/cm at 650°C was measured under reducing gas conditions. The anode-supported SOFCs were prepared by laminating GDC and doped-YCrO3 tapes. A fired half-cell assembly was further deposited with a dense barrier layer made of electrolyte material. The function of the barrier layer at the interface of GDC electrolyte and anode was to prevent the interdiffusion of elements. Furthermore, the LSM/bismuth-based composite low-temperature cathode was deposited on the barrier layer and Ni-GDC precursor was infiltrated on the anode (to introduce catalytic activity for hydrogen oxidation). Peak power density of 700 mW/cm2 (at 2 A/cm2) was obtained at 650°C in H2/3% H2O.

Production of electricity by directly utilizing abundantly available fuels such as natural gas can meet the energy demands in various sectors. To make a robust, reliable and cost effective SOFC technology, the operating temperature of SOFCs has to be lowered down to 500°C. Albeit low ionic conductivity of electrolytes and hampered electrode kinetics at such low temperatures significantly affect the efficiency. Reducing the thickness of fast oxide-ion conducting electrolytes (e.g. Ce 0.9 Gd 0.1 O 2- δ ) and by using highly electrically conducing electrodes can lower the ohmic losses; however sluggish electrode reaction rates at low-temperatures remains a difficult problem causing huge non-ohmic losses. Nanostructuring of electrocatalyst on an electrically conducting electrode can significantly improve the reaction rate for hydrogen oxidation and oxygen reduction, thereby enhancing the efficiency of SOFCs. Additionally, operating SOFCs at a low temperature range would reduce particle growth and extend cell life-time compared to high-temperature SOFCs. In this study, the effect of nanostructured infiltrates on both catalytically active and inactive porous electrodes will be analyzed in detail. Improvement in electrode reaction rate will be quantified using electrochemical impedance spectroscopy (EIS). The main focus of the study will be on understanding how nanostructured electrodes could improve the efficiency and long-term stability of LT-SOFCs.

Variants of SNNV (Sr0.2Na0.8Nb1-xVxO3, X = 0.1-03) ceramic oxides were synthesized via wet chemical method. SNNVs show high electronic conductivity of > 100 S/cm when reduced in hydrogen at a relatively low temperature of 650 degrees C. In particular, 30% V-doped SNNV exhibited the highest conductivity of 300 S/cm at 450 degrees C. In order to investigate the fuel cell performance, Gd0.1Ce0.9O2-delta (GDC) based electrolyte-supported fuel cells were prepared to study the anode characteristics. Sr0.2Na0.8Nb0.9V0.1O3 (SNNV10)-GDC composite was used as an anode and La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF)-GDC as a cathode. Both electrodes were porous and sintered at 1050 degrees C for 2 h in air. The anode side of the fuel cell was infiltrated with 10 wt% GDC/Ni-GDC precursor to activate the anode for fuel oxidation. I-V characteristics were determined in gas conditions such as dry/humidified hydrogen and methane at 650 degrees C. With the infiltration Ni-GDC, peak power density (PPD) of 280 mW/cm(2) and 220 mW/cm(2) in dry H-2 and CH4, respectively, were obtained at 650 degrees C, which is higher than GDC alone as infiltrate. The high resistances in the humidified conditions are attributed to the lower conductivity of SNNV10 in high P-O2 atmospheres. (C) 2017 Elsevier B.V. All rights reserved.

Lanthanum-doped barium stannate, Ba0.98La0.02SnO3 (LBS) ceramic oxide was developed as an alternative redox stable anode material for oxide-ion conducting, low-temperature solid oxide fuel cells (350-650 degrees C). LBS with ZnO as a sintering aid exhibited a high electronic conductivity of 216 S/cm at 650 degrees C under reducing gas conditions. A flexural strength of similar to 66 MPa at 550 degrees C was obtained for ZnO-doped LBS; further investigation revealed that it can withstand 10 reduction-oxidation and thermal cycles. The performance of ZnO-doped LBS as an anode was determined with a GDC based electrolyte-supported SOFC. The catalytic activity for hydrogen oxidation and oxide conductivity was introduced by infiltration of Ni-GDC precursor. The maximum power densities of 0.28 W/cm(2) (at 0.6 A/cm(2)) and 0.17 W/cm(2) (at 0.36 A/cm(2)) was achieved at 650 and 600 degrees C, respectively, in humidified hydrogen as fuel for 2 wt% ZnO-doped LBS. (C) 2016 The Electrochemical Society. All rights reserved.

Barium stannate doped with 2 at.% of lanthanum was synthesized and investigated as a potential anode material for low temperature solid oxide fuel cells (LT-SOFCs). Ba 0.98 La 0.02 SnO 3-δ ceramic was calcined at 1200-1300°C in air to obtain the cubic perovskite phase and then sintered at 1550°C for 12h. The sintered sample has shown approx. 7% shrinkage and 70% density. For the 30% porous sample, electrical conductivity values of 8.7 S/cm and 9.3 S/cm, respectively was achieved, at 600°C and 400°C, respectively in 10% H 2 /3%H 2 O/N 2 .The preliminary results has shown a decent redox stability, approx. 7 % loss in conductivity at 600°C when cycled 3 times between air and reducing conditions over a period of 60 h. Post-test XRD analysis on Ba 0.98 La 0.02 SnO 3-δ samples show structural stability by retaining the cubic perovskite phase. The material was also stable in dry and humidified H 2 . Interestingly, the material has shown semi-conductor like behavior in the presence of methane. The conductivity values of the materials in 97%CH 4 /3%H 2 O gas were 6.4 and 2.2 S/cm at 600 and 500°C, respectively. This material has promising performance for integration into an LT-SOFC anode, but processing challenges remain.