Lanthanum Gallate Electrolyte Research Articles

Development of a tubular direct carbon solid oxide fuel cell stack based on lanthanum gallate electrolyte

The direct carbon solid oxide fuel cell (DC-SOFC) is a new-type energy conversion device that converts chemical energy stored in solid carbon into electricity efficiently with environmental benignity and low cost for abundant carbon resources, which reveals upward impetus recently. To accelerate the practical application of DC-SOFC, here, we report a high-performance La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte-supported tubular DC-SOFC stack for portable applications, in which Ag– Ce0.8Gd0.2O1.9 (Ag-GDC) is used as symmetrical electrodes and camellia oleifera shell char as fuel. The performance of the 3-cell-stack stands out, with an open circuit voltage (OCV) of 3.18 V, an output power of 2.65 W, and a maximum volumetric power density of 605 mW cm−3 at 800 °C. In addition, the stack can survive for 5.82 and 1.12 h under the constant discharging currents of 200 and 800 mA, respectively, exhibiting discharge capacities of 3492 and 2688 mA h. Furthermore, adopting the external anode design can sextuple the fuel load and lead to remarkably improved output performance, discharge time, and discharge capacity of the stack (3.71 W, 9.2 h, 22080 mA h). The above results indicate that LSGM electrolyte-supported tubular DC-SOFC stacks show great potential for developing into high-performing, efficient, and environmentally friendly portable power sources for distributed applications.

Effect of grain size on the electrical properties of strontium and magnesium doped lanthanum gallate electrolytes

The aim of this research is to investigate the effect of average grain size on electrical and electrochemical performances of La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM). For this purpose, the glycine-nitrate method is used to synthesize the LSGM electrolytes and subsequently sintered at 1350, 1400, 1450 and 1500 °C in a muffle furnace with temperature holding for 10 h. XRD study reveals that all of the sintered LSGM ceramic electrolytes crystallize to a single phase of orthorhombic perovskite structure without any impurity phases. Results from scanning electron microscopy (SEM) study demonstrate that increasing sintering temperature from 1350 to 1500 °C leads to increase in average grain size from 1.02 to 4.87 μm. Electrochemical AC impedance tests show that the bulk resistance is nearly independent on the average grain size, and the grain boundary resistance changes because of the difference in the average grain size. The LSGM sample sintered at 1500 °C achieves the maximum electrical conductivity 9.19 × 10−2 S cm−1 at 800 °C. The maximum power density of assembled cell with LSGM sintered at 1500 °C as an electrolyte is 0.76 W cm−2 at 800 °C in air atmosphere.

High performance solid-state iron-air rechargeable ceramic battery operating at intermediate temperatures (500–650 °C)

An efficient, reliable and cost-effective energy storage is necessary to increase the use of renewables and to contribute in reducing the carbon footprint of the electricity grid. A novel iron-air battery characterized by high performance, safety and reliability for operation at intermediate temperatures (500–650 °C) is demonstrated. The iron-air rechargeable battery is based on a new configuration where both the nickel-electrode and the hydrogen/water redox processes, generally utilized in high temperature ceramic batteries, are avoided in this system completely operating in the solid state. This can increase the durability and reliability of the battery while providing excellent performance (specific energy of 0.46 Wh g−1, specific capacity of 0.5 Ah g−1, faradaic efficiency 80%). These characteristics favourably compare to low temperature iron-air batteries. Excellent performance and cyclability are achieved at 650 °C for the iron-air solid-state battery showing no relevant degradation after more than 100 cycles. The concept is based on a composite iron-ceria anode in contact with an oxygen anion-conducting lanthanum gallate electrolyte and a mixed conductivity lanthanum ferrite perovskite-based cathode. This combines both simplicity of operation and intrinsic safety with high energy density and durability. The excellent dynamic behaviour, the absence of influence of external environmental conditions and the use of cost-effective ceramic materials, with the possibility to produce high quality heat to cover the chain of electrical and thermal energy, make such systems largely appealing for applications related to renewable power sources.

Electricity generation in dry methane by a durable ceramic fuel cell with high-performing and coking-resistant layered perovskite anode

A novel A-site deficient ceramic oxide (PrBa)0.95(Fe0.9Nb0.1)2O5+δ with layered perovskite structure has been investigated as an anode material for a direct-hydrocarbon fueled solid oxide fuel cell. Promising performance of this anode is achieved by stabilizing the material with Nb doping at B sites, which shows excellent chemical stability and high catalytic activity in the reducing fuel condition. The button cell based on lanthanum gallate electrolyte exhibits peak power density of 1.05 W cm−2 in H2, 0.64 W cm−2 in CH4 (∼3% H2O) and 0.57 W cm−2 in dry CH4 at 800 °C, respectively. When the temperature is decreased to as low as 600 °C, the cell still reaches 0.18 W cm−2 in hydrogen. The anode is highly resistant against redox cycling with capability of rapid recovery from oxidizing condition. Based on a series of performance durability tests under various fuel conditions, this anode material has been demonstrated to be feasible for long-term operation in dry CH4 without observable degradation. The results demonstrate a new technical route to develop highly active and stable ceramic anode by doping high-valence rare-earth elements into B sites of perovskite material.

Development of tubular anode-supported solid oxide fuel cell cell and 4-cell-stack based on lanthanum gallate electrolyte membrane for mobile application

Anode-supported tubular solid oxide fuel cells and 4-cell-stack with lanthanum-doped ceria barrier layer and strontium, magnesium doped lanthanum gallate tri-layer electrolytes membrane are investigated. The single cell exhibits peak power densities of 1061 mW cm−2 and 917 mW cm−2 at 800 °C fueled with bubbled hydrogen and methane (3 vol % water), respectively. Energy dispersive X-ray detector result demonstrates that no measurable carbon is detected in the anode directly operated in methane during the whole testing process.The 4-cell-stack assembled with single cells provides maximum output power of 1.66 W and open circuit voltage of 3.13 V at 800 °C with hydrogen as fuel. While the 4-cell-stack presents maximum output power of 1.38 W and open circuit voltage of 3.88 V at 800 °C fueled with methane. A stability test of each cell in 4-cell-stack is developed at constant current densities (J = 0 A cm−2, J = 0.1 A cm−2, J = 0.4 A cm−2) directly fueled with 75 ml min−1 methane at 800 °C. The results show that the voltages of each cell in 4-cell-stack stabilize during the whole durability test. The results demonstrate that the stability and dependability of 4-cell-stack is good, and it is promising for mobile application of intermediate temperature solid oxide fuel cells.

Lanthanum gallate based amperometric electrochemical sensor for detecting ammonia in ppm level: Optimization of electrode compositions

Fabrication of a highly sensitive amperometric electrochemical gas sensor would require optimisation of the electrode materials and rigorous testing of device performance under different processing conditions. An ammonia sensor based on lanthanum gallate electrolyte having the composition La0.8Sr0.2Ga0.8Mg0.1Ni0.1O3 (LSGMN) has been investigated for its detecting at ppm level. A single phase solid solution of 30 mol% Zr4+ in CeO2 (CZ73) as an active (sensing) electrode yielded optimum results. Similarly, La0.5Sr0.5Mn0.8Ni0.2O3 (LSMN5582) was found to be the best composition for the inactive (reference) electrode. All the devices were found to have maximum sensitivity at 400 °C and a typical response and recovery times of 40 s and 110 s respectively. Moreover, they exhibited better efficiency in amperometric mode as compared to potentiometric mode and were stable up to several cycles of operation. It was established through mechanistic studies that even though both the electrodes were simultaneously exposed to both the gases, higher sensitivity was obtained when CZ73 was biased at +1 V with respect to LSMN5582 as against −1 V, implying that NH3 oxidation took place preferentially at CZ73 whereas oxygen reduction took place at the inactive electrode. Step by step sensitivity at 400 °C improved from 28.2 to 35 μA/decade. Further, the electrolyte thickness was decreased to 0.4 mm in view of reducing the internal resistance and a prototype device was fabricated that yielded enhanced sensitivity of 49 μA/decade under optimized conditions.

Dominant Factors Influencing the Electrochemical Performance of Plasma-Sprayed LSGM Electrolyte

Atmospheric plasma spraying (APS) is promising to fabricate functional layers for solid oxide fuel cells (SOFCs). In this article, the factors dominating the performance of APS Mg/Sr-doped lanthanum gallate (LSGM) electrolyte for intermediate-temperature SOFCs will be introduced based on our recent systematic investigation. It is found that the evaporation of Ga during plasma spraying is significantly influenced by spray particle size, which remarkably affects the properties of plasma-sprayed LSGM deposit. Moreover, it is revealed that the application of the critical deposition temperature concept to the deposition of LSGM results in the fabrication of a dense LSGM with excellent lamellar bonding. The dense LSGM electrolyte exhibits an ionic conductivity of ~80% sintered bulk LSGM. The electrochemical performance test confirms that the SOFC cell assembled with APS LSGM electrolyte shows high performance with a maximum output power density of 710 mW/cm2 at 800oC using H2/air. Thus, it is possible to prepare superior LSGM electrolyte membranes by APS.

(Invited) Performance and Durability of Solid Oxide Cells for Energy Storage

The first part of this talk will discuss the application of reversible solid oxide cells (SOCs) for grid-scale energy storage, focusing on pressurized reduced-temperature cell conditions where co-electrolysis yields methane-rich fuel. A full analysis of a storage system utilizing low-resistance thin Lanthanum Gallate electrolyte cells and large-scale underground caverns for gas storage indicates that round-trip storage efficiency > 70% can be achieved, along with storage capacity and operating cost values that are comparable or better than pumped hydroelectric storage. The second part of the talk will describe results on degradation mechanisms, important for SOC storage technologies to achieve sufficient long-term durability for economic viability. LSM-YSZ and LSCF oxygen electrodes have been studied in both dc electrolysis and reversing-current (alternating between electrolysis and fuel cell operation) modes; similar delamination mechanisms are observed in both cases, although stability is improved by current cycling. A critical current density and overpotential is observed below which degradation is too slow to measure over ~ 1000 h, but above which degradation rate increases rapidly. High efficiency storage requires SOCs characterized by low resistance at intermediate temperatures. This makes it desirable to utilize nano-scale electrodes, but these may be susceptible to degradation by particle coarsening. Accelerated life test results for impregnated oxygen electrode materials are presented and fitted using a combined electrochemical/coarsening model, and the resulting expressions are used to predict long-term performance degradation. Life test results on Ni-based fuel electrodes are also discussed.

(La,Ba)CoO3 and Pr1.9(Ni,Cu,Ga)O4 Composite Oxide as Active Cathode for Intermediate Temperature Solid Oxide Fuel Cells Using Doped LaGaO3 Electrolyte Films

Ba0.5La0.5CoO3 (BLC) and Pr1.9(Ni,Cu,Ga)O4 (PNCG) composite cathode were investigated to enhance electrochemical performance in solid oxide fuel cells using Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte films at intermediate temperatures (773–973 K). Effect of the calcination temperature of the composite cathode was studied on chemical compatibility, area specific resistance (ASR), and power generation property. ASR of the composite cathode was smaller than that of SSC but increased with increasing calcination temperature by chemical reaction. Improved maximum power density of 1.270 and 0.146 Wcm-2 at 973 K and 773 K was achieved on a single cell using BLC-PNCG composite as cathode on LSGM film.

A solid oxide cell yielding high power density below 600 °C

Here we report solid oxide cells with thin strontium- and magnesium-doped lanthanum gallate electrolytes that yield power densities of 1.06 W cm−2 at 550 °C and 0.81 W cm−2 at 500 °C when operated on humidified hydrogen and ambient air. Cost-effective ceramic processing and chemical solution impregnation methods were utilized, yielding a dual micron- and nano-scale architecture that is essential for achieving good low-temperature performance.

Improved sintering and electrical properties of La-doped CeO2 buffer layer for intermediate temperature solid oxide fuel cells using doped LaGaO3 film prepared by screen printing process

Effects of a sintering agent for La-doped ceria (LDC) as a buffer layer to prevent a chemical reaction between Ni in anode and Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte during sintering were studied for improving sintering and electrical properties. Electrochemical performance of anode-supported solid oxide fuel cells (SOFCs) using LDC and LSGM films prepared by screen printing and co-sintering (1,350 °C) was also investigated. The prepared cell with dense LDC (ca. 17 μm) and LSGM electrolyte (ca. 60 μm) films showed an open circuit voltage close to the theoretical value of 1.10 V and a high maximum power density (0.831 W cm–2) at 700 °C. The addition of 1 wt.% LSGM to porous LDC buffer layer was effective for improving the sintering density and electrical conductivity, resulting in the high power density due to the decreased internal resistance loss.

Improved power generation performance of solid oxide fuel cells using doped LaGaO3 electrolyte films prepared by screen printing method II. Optimization of Ni–Ce0.8Sm0.2O1.9 cermet anode support

A Ni and Sm-doped ceria (Ce0.8Sm0.2O1.9, SDC) cermet anode as a porous support of doped LaGaO3 film prepared by a wet coating and co-firing process was investigated. Different preparation methods and compositions were used to improve the power density of intermediate temperature solid oxide fuel cells. NiO–SDC precursor powder with fine particles and a porous microstructure with high surface area was synthesized by a modified impregnation method and compared with that synthesized by a ball milling method. In addition, an open circuit voltage, which is almost equal to the theoretical value of 1.1 V, and maximum power densities of 835, 277, and 67 mW cm−2 at 700, 600, and 500 °C, respectively, were achieved on a single cell supported by a 75 wt% Ni–SDC cermet anode when a 60 μm thick Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was used. The improved power density was explained by the enlarged reaction area for the anode as a result of the low polarization resistance of the anode by high porosity and uniform distribution of Ni and SDC particles. Although a small amount of Ni diffused to the interface between the La-doped ceria (LDC) buffer layer and the LSGM electrolyte film, an adverse reaction that deteriorates cell performance seemed to be suppressed, and thus, reasonably high power density was achieved on the cell using the LSGM film prepared by the screen printing method with optimization of the anode substrate structure and composition.

A reduced temperature solid oxide fuel cell with nanostructured anodes

Reduced-temperature solid oxide fuel cells (SOFCs), featuring thin strontium- and magnesium-doped lanthanum gallate (LSGM) electrolytes and nano-scale Ni anodes, showed high power densities of 1.20 W cm−2 at 650 °C and 0.39 W cm−2 at 550 °C when operated on humidified hydrogen fuel and air oxidant.

Effects of anode firing temperature on the performance of the lanthanum-gallate thick-film-supported SOFC

The reaction between lanthanum-gallate electrolyte and Ni in the anode often occurs during the co-firing of an anode-supported cell and results in the degradation of cell performance. In this study, a thick-film LSGM (La 0.9Sr 0.1 Ga 0.8 Mg 0.2O 3-δ) electrolyte-supported micro-cell was fabricated and electrochemically tested to see the effects of the anode-firing temperature on the SOFC performance. The LSGM tape (~ 20 μm-thick) was sintered and then mounted on a LSGM cylindrical-ring (~ 400 μm-thick) by sintering two pieces together at 1500 °C. NiO-GDC (Gd-doped ceria) slurries were brush painted for the anode on the bottom surface of the supporting LSGM electrolyte and the electrolyte/anode layers were subsequently fired at 1300, 1350, 1375 or 1400 °C, respectively. SSC (Sm 0.5Sr 0.5CoO 3− δ ) slurries were also brush painted for cathode on the opposite side and the cathode/electrolyte/anode layers were fired at 900 °C. The cell with the anode sintered at 1300 °C showed the highest performance (OCV ~ 1.1 V, P max or maximum power density ~ 0.93 W/cm 2 at 700 °C). The increase of the anode-firing temperature reduced the cell performance. Although the anode fired at 1375 °C showed a reduced OCV (~ 0.90 V at 700 °C), the cell performance was still high (P max: ~ 0.55 W/cm 2 at 700 °C). The cell with the anode fired at 1400 °C showed the lowest OCV (~ 0.27 V). The open-circuit voltage (OCV) and thus the performance of the cells were largely dependent upon the anode-firing temperature since the reaction of Ni with the LSGM electrolyte induces an electronic conduction in the LSGM electrolyte which then decreases the OCV.

Progress in Development of IT-SOFC Based on Lanthanum Gallate Electrolyte

Mitsubishi Materials Corporation and The Kansai Electric Power Co., Inc. are developing highly efficient units based on intermediate-temperature solid oxide fuel cells for stationary power generation applications. The use of high oxide ion conducting electrolyte made up of strontium, magnesium and cobalt doped lanthanum gallate (LSGMC) help realize the intermediate-temperature operation between 600{degree sign}C and 800{degree sign}C. An improved 10 kW-class CHP system based on LSGMC electrolyte was subjected to a second time long term stability test for over 3,000 hrs. No significant voltage degradation was observed when the output power was slightly reduced during the second long term stability test of the 10kW CHP system. In addition, scale-up of cells were achieved by doubling the active surface area. 170mm diameter cells were manufactured and successfully tested in high power density modules.

Development of Intermediate-Temperature Solid Oxide Fuel Cells Using Doped Lanthanum Gallate Electrolyte

Intermediate-temperature(IT) solid oxide fuel cells(SOFCs) were developed using lanthanum gallate electrolyte, samarium cobaltite cathode and the cermet anode of nickel and ceria. High efficiency operation below 800°C was enabled using planar disk type cells with unique seal less stack design. The first 10 kW-class combined heat and power (CHP) system provided AC output power of 10 kW with electrical and overall efficiency of 41 and 82 %HHV, respectively. Optimization of cell-stack components to increase the output power density is in progress.

Development of La-doped Ni-SDC Anode for High Performance IT-SOFC of Ni-SDC/LSGM/SSC

Sr and Mg co-doped lanthanum gallate electrolyte (LSGM) shows high oxide ion conductivity at temperatures of 650-800oC. However, LSGM has rather high chemical reactivity with anode materials; reaction compounds at the anode/electrolyte would lead to the degradation of the SOFC performance. In order to develop the optimum cermet anode for LSGM, La and Sm co-doped ceria (SLDC) was synthesized and investigated in connection with reactivity between SLDC and LSGM. The NiO-SLDC composite particles synthesized by spray pyrolysis were applied for cermet anodes in order to prevent the anode/electrolyte interface from undesirable interfacial reaction. The power density of the cells with Ni-SLDC anode was found to be higher than that with Ni-SDC anode. Current interruption measurements revealed that La addition to SDC has an effect of the decrease in ohmic loss.

Development of IT-SOFC Based on Lanthanum Gallate Electrolyte

The Kansai Electric Power Company, Inc. and Mitsubishi Materials Corporation started a joint research project for developing intermediate temperature (600{degree sign}C to 800{degree sign}C) solid oxide fuel cells (IT-SOFC) in 2001. High performance disk-type cells with lanthanum gallate-based electrolyte and a seal-less cell-stack design enable high efficiency operation at temperatures below 800{degree sign}C. The development of 10 kW-class CHP system under a project supported by NEDO (New Energy and Industrial Technology Development Organization) was started in FY2004. In 2007, the performance test of the 10 kW-class system using town gas as fuel has been undertaken. In this test, the electrical efficiency of 41%HHV on AC power output of 10 kW and the overall efficiency of 82%HHV by recovering 60åC hot water have been achieved. And the voltage degradation rate per 1,000 hours was 1.08% after 3,000 hours operation has been observed during the field test of the 10 kW-class system. Furthermore, after making some refinements to enhance the performance of 10 kW-class module, the second long-term stability test for 3,000 hours were carried out in 2008. Efforts to enhance cell and module durability have been made with 1 kW-class modules operated for 5,000 hours, and with the cell-stack units operated for 15,000 hours. The voltage degradation rates per 1,000 hours were 0.51 % for the 1 kW-class modules, and 0.23 - 0.48% for the cell-stack units.

Promising Ni–Fe–LSGMC anode compatible with lanthanum gallate electrolyte

A number of composite materials in the Ni–Fe–LSGMC family have been studied as potential anodes for solid oxide fuel cells (SOFCs) based on strontium, magnesium, and cobalt doped lanthanum gallate electrolyte (LSGMC). The results show that Ni reacts with LSGMC especially under reducing conditions at high temperatures, resulting in high contact resistance, large electrode polarization, and poor performance. The reaction between Ni and LSGMC depends strongly on the composition and pre-sintering temperature of LSGMC, the concentration of iron in the electrode, and the processing and operating temperatures. Under proper conditions, Ni–Fe–LSGMC5 could be a promising high-performance anode with good compatibility with LSGMC5 electrolyte.

Thick-Film Electrolyte-Supported SOFC Based on Lanthanum-Gallate Electrolyte Without Using Buffer Layer

A type of micro-solid oxide fuel cell (SOFC) was designed and fabricated that uses self-supporting thin (∼20 μm thick) lanthanum-gallate-based electrolyte. With this configuration, the cofiring of electrolyte and anode was avoided, and high power density was obtained without using a buffer layer, which prevents the reaction between the electrolyte and Ni in the anode. The maximum power densities were 0.29, 0.56, and 0.93 W/cm 2 at 600, 650, and 700°C, respectively, comparable to those of the anode-supported SOFCs that use lanthanum-gallate electrolyte and a buffer layer. This structure has the advantages of both electrolyte and electrode-support types.