LaGaO3-based Electrolyte Research Articles

Recent Advances in High Temperature Electrolysis Cells using LaGaO3-based Electrolyte

High temperature electrolysis is a promising option for carbon-free hydrogen production and huge energy storage with high energy conversion efficiencies from renewable and nuclear resources. Over the past few decades, yttria-stabilized zirconia (YSZ) based ion conductor has been widely used as a solid electrolyte in solid oxide electrolysis cells (SOECs). However, its high operation temperature and lower conductivity in the appropriate temperature range for solid electrochemical devices were major drawbacks. Regarding improving ionic-conducting electrolytes, several groups have contributed significantly to developing and applying LaGaO3 based perovskite as a superior ionic conductor. La(Sr)Ga(Mg)O3 (LSGM) electrolyte was successfully validated for intermediate-temperature solid oxide fuel cells (SOFCs) but was rarely conducted on SOECs for its high efficient electrolysis performance. Their lower mechanical strengths or higher reactivity with electrode compared with the YSZ electrolysis cells, which make it difficult to choose compatible materials, remain major challenges. In this field, SOECs have attracted a great attention in the last few years, as they offer significant power and higher efficiencies compared to conventional YSZ based electrolysers. Herein, SOECs using LSGM based electrolyte, their applications, high performance, and their issues will be reviewed.

Recent Advances in High Temperature Electrolysis Cells using LaGaO3-based Electrolyte

High temperature electrolysis is a promising option for carbon-free hydrogen production and huge energy storage with high energy conversion efficiencies from renewable and nuclear resources. Over the past few decades, yttria-stabilized zirconia (YSZ) based ion conductor has been widely used as a solid electrolyte in solid oxide electrolysis cells (SOECs). However, its high operation temperature and lower conductivity in the appropriate temperature range for solid electrochemical devices were major drawbacks. Regarding improving ionic-conducting electrolytes, several groups have contributed significantly to developing and applying LaGaO3 based perovskite as a superior ionic conductor. La(Sr)Ga(Mg)O3 (LSGM) electrolyte was successfully validated for intermediate-temperature solid oxide fuel cells (SOFCs) but was rarely conducted on SOECs for its high efficient electrolysis performance. Their lower mechanical strengths or higher reactivity with electrode compared with the YSZ electrolysis cells, which make it difficult to choose compatible materials, remain major challenges. In this field, SOECs have attracted a great attention in the last few years, as they offer significant power and higher efficiencies compared to conventional YSZ based electrolysers. Herein, SOECs using LSGM based electrolyte, their applications, high performance, and their issues will be reviewed.

PrBaCo2O5+δ-Sm0.5Sr0.5CoO3 Composite Oxide as Active Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

From decreasing the cost and the reliability of solid oxide fuel cells (SOFCs), increase in power density is strongly required. In order to achieve these requirements, decrease in operating temperature is the most effective way. However, reduced operating temperature leads to significant decrease in electrode activity, particularly cathode. Therefore, the development of novel and highly active cathode is strongly required for intermediate temperature (873-1073 K). In this study, we studied cathodic performance of double perovskite oxide of PrBaCo2O5 as active cathode of SOFC. Because of delamination of PrBaCo2O5 cathode is easily occurred because of larger thermal expansion coefficient. Mixing effects of PrBaCo2O5 with another perovskite oxide were investigated using a LaGaO3-based electrolyte. The electrochemical performance of the cell was measured using electrolyte-supported single cell at 873, 973 and 1073 K and humidified H2 was used as fuel and O2 as oxidant.Among the oxides mixed with PrBaCo2O5 (PBCO), it was found that mixing Sm0.5Sr0.5CoO3 (SSC)shows the smallest cathodic overpotential and the most suitable for increase in cathodic activity. Therefore, composite oxide of PBCO with SSC is active as cathode for SOFC. However, the cells with composite cathodes show lower performance at 1073 K comparing with PBCO cathode and this could be explained by small cathodic internal resistance at 873 K. On the other hand, the cell with PBCO-SSC (1:1) shows small overpotential at 873 K and much larger power density. Therefore, it was found that mixing PBCO with SSC shows the positive effects on the oxygen dissociation on the cathode at decreased temperature and suitable for low temperature operation SOFC. The optimization of SSC content on the cathodic activity of PBCO-SSC mixed oxide was further studied. The cathodic overpotential at 50 mA/cm2 was decreased with increasing amount of SSC and the smallest overpotential was achieved at 1:1 composition at all temperature studied. Positive effects of mixing PBCO and SSC could be assigned to the increased three phase boundary and increased activity to oxygen dissociation. Since cathodic overpotential was decreased significantly by mixing PBCO-SSC, power density of the cell using PBCO-SSC cathode at 1:1 composition shows 232 mW/cm2 at 873 K which is two times larger than that of the cell using PBCO single oxide cathode. Application of PBCO-SSC composite oxide for anode of steam electrolyser was also studied and it was found that PBCO-SSC is also active to oxygen association under applied voltage. Therefore, this study reveals that PBCO-SSC composite is potential air electrode material for intermediate-temperature solid oxide cells.

PrBaCo2O5+δ-Sm0.5Sr0.5CoO3 Composite Oxide as Active Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Cathodic performance of double perovskite oxide of PrBaCo2O5 as an active catalyst for SOFC was investigated. Because delamination of PrBaCo2O5 cathode is easily occurred by larger thermal expansion coefficient, mixing effects of PrBaCo2O5 with another perovskite oxide were investigated using a LaGaO3-based electrolyte. Among the oxides mixed with PrBaCo2O5 (PBCO), it was found that mixing Sm0.5Sr0.5CoO3 (SSC) with PBCO shows the smallest cathodic overpotential and the most suitable for increase in cathodic activity. Increase in cathodic performance can be assigned to the high activity of oxygen dissociation on SSC and the fast oxide ion diffusivity in PBCO. Therefore, composite oxide of PBCO with SSC is highly active as cathode for SOFC at intermediate temperature.

Development of Highly Efficient Composite Electrodes, CuFe2O4-La(Sr)Fe(Mn)O3, for High-Temperature Co-Electrolysis of CO2-Steam

La0.6Sr0.4Fe0.8Mn0.2O3-δ (LSFM) perovskite cathode has an advantage in product control for solid oxide electrolysis cell, while it limited by its insufficient electrolysis current density. To improve its electrochemical performance, we developed a highly efficient composite cathode by mixing LSFM with CuFe2O4 spinel. In this study, CO2/H2O co-electrolysis were investigated using CuFe2O4, LSFM, and their composites as cathodes on LaGaO3-based electrolyte. It was found that mixing LSFM and CuFe2O4 was effective for a significant increase in the electrolysis current density in co-electrolysis. Compared to the individual LSFM (0.60 A/cm2) and CuFe2O4 (1.00 A/cm2) cathode, a promising electrolysis current density of 1.43 A/cm2 was achieved at 1.6 V and 800oC with excellent Coulombic efficiency (> 95% of theoretical value), remarkable operation stability, and reversibility in co-electrolysis. In addition, a homogeneous and uniform surface morphology with a well-distributed porous structure was observed on the LSFM-CuFe2O4 composite layer after the operation.

Effective buffer layer thickness of La-doped CeO2 for high durability and performance on La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte supported type solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have been gaining increased attention in the energy sector. Commonly, yttria-stabilized zirconia is widely employed as commercial electrolyte, however, resulted in drawbacks such as high-temperature operating and low conductivity which negatively affect the durability and efficiency. Thus there are many efforts to find high-ionic conductors. From the point of manufacturing, the major difficulty of LaGaO3-based electrolyte as a high-ionic conductor is its incompatibility with commercial Ni-based anodes during high-temperature processes as well as operating. Several interlayers have been introduced to prevent the reaction between LaGaO3-based electrolyte and Ni-based anode. In this study, we investigate the optimal thickness of the La-doped CeO2 (LDC) interlayer by the screen-printing method using La0.9Sr0.1Ga0.8Mg0.2O3-δ for the commercial electrolyte supported SOFCs. As a result, the superior power performance of 2.2 W·cm−2 at 1123 K is achieved through the optimized LDC thickness of 20 μm through not lab-scaled but commercial ceramic manufacturing processing.

Effect of Ni-based cathodic layer on intermediate temperature tubular electrolysis cell using LaGaO3-based electrolyte thin film

NiO-YSZ tubular-type supported solid oxide electrolysis cell (SOEC) was prepared by dip-coating and co-sintering process for intermediate temperature steam electrolysis. To achieve a small overpotential, infiltration of Sm0.5Sr0.5CoO3−δ (SSC) powder into porous La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) layer on dense LSGM electrolyte film was performed for the air electrode. In this study, the effect of the Ni-Sm0.2Ce0.8O2−δ (Ni-SDC) and Ni-Fe2O3 (Ni-Fe) cathodic layer on steam electrolysis was further investigated. It was found that the Ni-based layer was effective for increasing electrolysis performance of the cell at low temperature in particular, but Ni-Fe layer was more effective. Impedance analysis suggests that this increased electrolysis performance of the cell using Ni-Fe layer was attributed to the decrease both in cathodic IR loss and overpotential. Electrolysis current density at 1.5 V was achieved to current density of 0.69, 0.47 and 0.28 A cm−2 at 873, 823 and 773 K, respectively. In addition, the overpotential was also decreased by the insertion of Ni-SDC layer, which shows the mixed conductivity. The long-term stability of the cell when using Ni-SDC layer was also measured up to 150 h and stable electrolysis performance was demonstrated (degradation rate: around 1.9%/100 h).

Kinetics of CO oxidation and redox cycling of Sr2Fe1.5Mo0.5O6-δ electrode for symmetrical solid state electrochemical devices

Resultsof the redox cycling of the Sr2Fe1.5Mo0.5O6-δ electrode in contact with the LaGaO3-based electrolyte at 800°С in air - CO/CO2 - Ar/H2 are presented for the first time. The electrochemical impedance method was used to demonstrate that the electrode polarization resistance at fast gas cycling remained almost unchanged. In the long-term cycling from oxidizing to reducing atmospheres (and vice versa) the polarization resistance equilibrated rapidly (slowly). The kinetics of the CO oxidation in CO/CO2 gas mixtures at 800°С (pO2 ≈ 10−16 – 10−19 atm) near the equilibrium electrode potential was studied. By means of a complex approach to the impedance spectra analysis using the distribution of relaxation times and non-linear least squares methods, it was determined that the CO oxidation is limited by three steps: CO adsorption (CO2 desorption) at the electrode surface, oxygen hetero-exchange and the oxygen ion transport in the electrode bulk. We assume that the charge transfer and the gas diffusion do not limit the CO oxidation reaction on the Sr2Fe1.5Mo0.5O6-δ electrode.

Highly active oxide cathode of La(Sr)Fe(Mn)O3 for intermediate temperature CO2 and CO2-H2O co-electrolysis using LSGM electrolyte

Electrochemical conversion of carbon dioxide to carbon monoxide (CO2→CO) is a potential step in the desirable transformation of the greenhouse gas to fuel or useful chemicals. In this study, the electrochemical conversion of CO2 to CO and H2O to H2 on an oxide cathode was studied in a solid oxide electrolysis cell (SOEC) by using a LaGaO3-based electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) at elevated temperature (i.e. 973–1173K), which is a good candidate as electrolyte for electrolysis cell because of the high oxide ion conductivity at intermediate temperatures. Although metal, in particular, Ni is widely used as cathode of CO2 electrolysis cell, it was found that a LaFeO3−δ–based perovskite material as cathode (La0.6Sr0.4Fe0.8Mn0.2O3−δ, LSFM6482) shows much higher activity and selectivity to CO2 electrolysis and a current density of CO2 electrolysis is achieved with a value of 0.52A/cm2 at 1.6V and 1173K. In contrast, substitution of Co, Cu, and Ni decrease the anodic performance of LaFeO3 resulting in the decrease in electrolysis current. A cell using the LSFM6482 oxide cathode has a high selectivity for the electrolysis of CO2 to CO without carbon formation. In this study, application of LSGM6482 to CO2-H2O co-electrolysis was also studied and it was found that CO2-H2O co-electrolysis was successfully proceeded and CO/H2 syngas with ca. 1/1 ratio was obtained from CO2/H2O=1/1.

Ce0.6Mn0.3Fe0.1O2-δ as an Alternative Cathode Material for High Temperature Steam Electrolysis Using LaGaO3-based Oxide Electrolyte

Ce0.6Mn0.3Fe0.1O2-δ (CMF) has been used as a new oxide cathode of solid oxide electrolysis cell (SOEC) using LaGaO3-based electrolyte for H2 production under a feeding gas composition of 20%steam/1%H2/79%Ar. CMF cathode exhibits good electrolysis performance and well-performed hydrogen production rate with the Faraday’s law at 1173-973K. Through impedance measurement under a DC polarized condition, the studies show that polarization resistance and ohmic resistance decreased with increasing DC bias potential. Furthermore, CMF showed good stability, and no significant aggregation and delamination were noticed during the electrolysis measurement. These results suggest that CMF can be a promising oxide cathode candidate for intermediate temperature SOEC.

(Invited) High Temperature CO2 Electrolysis on La(Sr)Fe(Mn)O3 Oxide Cathode by Using LaGaO3 Based Electrolyte

Solid oxide electrolysis cells (SOECs) for converting CO2 to more useful chemical species are attracting considerable attention because of their high electrolytic efficiency, offering the possibility of direct conversion of CO2 to CO (CO2 → CO + 1/2O2). Heat energy supplied to SOECs can maximize electrolysis efficiency, offering both thermodynamic and kinetic advantages. The generated CO can be used as a fuel gas, converted into syngas via reaction with H2, or to reduce iron oxide to pure iron in the iron-making process. The application of SOECs and related technologies can contribute to a more sustainable economy. For the electrolyte in SOECs, ZrO2 doped with 8 mol% of Y2O3 (YSZ) has always been used because of its chemical stability and mechanical strength. However, an electrolyte for CO2 electrolysis with lower internal resistance and increased efficiency is highly desirable. LaGaO3-based electrolytes have higher oxide-ion conductivities and transport numbers, which can lead to higher energy conversion efficiency; hence, a doped-LaGaO3 electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) has been tested in this study. For CO2 electrolysis, another drawbacks is formation of C since electrolysis potential is close to that of CO formation. Although metals, particularly Ni, are widely used as cathodes in CO2 electrolysis cells, we found that a LaFeO3−δ-based perovskite cathode (La0.6Sr0.4Fe0.8Mn0.2O3−δ, LSFM6482) showed the highest activity for CO2 electrolysis among the examined oxides with a current density for CO2 electrolysis of 0.52 A/cm2 at 1.6 V and 1173 K. Among the cells using a La0.6Sr0.4Fe0.9M0.1O3−δ-based oxide cathode (M = Mn, Co, Ni, or Cu) for CO2 electrolysis at 1073K. Mn was the most effective Fe replacement on the B site, and the La0.6Sr0.4Fe0.9Mn0.1O3−δ cathode showed the highest activity and current density for CO2 electrolysis of this set of cathodes. Among the tested dopants, Mn and Co have ionic sizes most similar to Fe and a smaller size mismatch between the host and dopant cations in the perovskite structure, which should suppress dopant segregation and minimize detrimental effects of cation segregation. Overall, among the examined cations, Mn was the best dopant for the B site of the LaFeO3 cathode. A cell consisting of BLC64/LSGM/LSFM6482 exhibited the highest CO2 electrolysis activity (a current density of 0.52 A/cm2 at 1.6 V and 1173 K) of all cathodes investigated in this study and reduced CO2 at a rate of 153 μmol/cm2•min at 1173 K and 1.6 V with negligible carbon formation. The observed electrolysis current density was close to that of a Ni cathode but smaller than that of a Ni–Fe cathode, which is one of the most active cathodes for CO2 electrolysis. An LSFM6482 oxide cathode seems to be effective for improving not only initial cathodic performance but also long-term stability. LSFM6482 could be a potential candidate for high-temperature CO2 electrolysis. Further details of electrode reaction will be discussed based on impedance analysis and CO2 partial pressure.

(Invited) High Temperature CO2 Electrolysis on La(Sr)Fe(Mn)O3 Oxide Cathode by Using LaGaO3 Based Electrolyte

Electrochemical conversion of carbon dioxide to carbon monoxide (CO2→CO) is a potential useful step in the desirable transformation of the greenhouse gas to fuels or useful chemicals. In this study, the electrochemical conversion of CO2 to CO on oxide cathode was studied in a solid oxide electrolysis cell (SOEC) by using a LaGaO3-based electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) at elevated temperature (i.e. 973 - 1173 K), which is a good candidate as electrolyte for electrolysis cell because of the high oxide ion conductivity at intermediate temperatures. It was found that a LaFeO3-δ–based perovskite material as cathode (La0.6Sr0.4Fe0.8Mn0.2O3-δ, LSFM6482) shows much higher activity for CO2 electrolysis among the examined oxide and a current density of CO2 electrolysis is achieved with a value of 0.52 A/cm2 at 1.6 V and 1173 K. Doping Sr and Mn to LaFeO3 is highly effective for increasing the cathode activity for CO2 electrolysis under the feed gas condition, which is consisted of 50%CO2, 1%CO, and 49%Ar. Porous structure with fine particle (0.5 μm) and main phase stability of LSFM6482 cathode can be sustained under CO2 electrolysis condition.

Behavior of strontium- and magnesium-doped gallate electrolyte in direct carbon solid oxide fuel cells

Perovskite-type La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) is synthesized by conventional solid state reaction. Its phase composition, microstructure, relative density, and oxygen-ionic conductivity are investigated. Tubular electrolyte-supported solid oxide fuel cells (SOFCs) are prepared with the LSGM as electrolyte and gadolinia doped ceria (GDC) mixed with silver as anode. The SOFCs are operated with Fe-loaded activated carbon as fuel and ambient air as oxidant. A typical single cell gives a maximum power density of 383mWcm−2 at 850°C, which is nearly 1.3times higher than that of the similar cell with YSZ as electrolyte. A stability test of 72min is carried out at a constant current density of 210mAcm−2, with a fuel utilization of 60%, indicating that LaGaO3-based electrolyte is promising to be applied in direct carbon SOFCs (DC-SOFCs).

Ni–Fe bimetallic cathodes for intermediate temperature CO2 electrolyzers using a La0.9Sr0.1Ga0.8Mg0.2O3 electrolyte

A solid oxide electrolysis cell for reducing CO2 to CO was studied using a LaGaO3-based electrolyte at intermediate temperatures (973–1173 K). Various metals were examined as cathodes for CO2 reduction, and it was found that Ni shows high activity. However, coke formation was observed during the initial period. Furthermore, we found that the electrolysis current could be greatly improved by adding Fe to Ni, resulting in a current density of 1.84 A cm−2 at 1.6 V and 1073 K on a Ni–Fe (9 : 1) cathode. SEM observation suggests that improved cathodic activity can be explained by stabilizing Ni fine particles with the addition of Fe. Therefore, diffusion resistance can be decreased by adding Fe to Ni. The formation rate of CO is slightly lower than the consumption rate of CO2, suggesting coke formation during the initial period. However, stable CO2 electrolysis can be performed for at least 12 h, and Fe addition is effective for increasing long-term stability of electrolysis.

Intermediate temperature steam electrolysis using LaGaO 3-based electrolyte

Steam electrolysis was studied by using La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) oxide electrolyte and it was found that H 2 formation rate obeys the Faraday's law suggesting that the transport number of oxide ion in LSGM under electrolysis condition is unity. Ni–Fe alloy cathode is highly active to electrolysis of steam, however, insertion of Ni-SDC (1:9) layer between Ni–Fe cathode and LSGM electrolyte is further effective for improving the electrolysis performance of the cell. The current density at 1.8 V was achieved values of 314 and 254 mA/cm 2 at 1073 and 873 K, respectively. The improved current density by Ni-SDC is mainly assigned to a decreased cathodic overpotential. The electrolysis efficiency which ignored the inserted heat energy, was calculated based on the formed H 2 amount and the consumed electric energy, and it is found that the estimated efficiency was higher than 70%.

Solid-state amperometric CH 4 sensor using, LaGaO 3-based electrolyte

A solid-state amperometric CH 4 sensor using a LaGaO 3-based electrolyte was studied. For this sensor, a combination of active (anode) and inactive (cathode) electrodes for CH 4 oxidation was applied. Among the various active electrode materials studied, Pd mixed with tin-doped In 2O 3 (ITO) was found to be the most active electrode and RuO 2 the most inactive one. The sensitivities of the sensor using La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) electrolyte to CH 4 were approximately 797 µA/decade at 673 K and 188 µA/decade at 873 K. The changes in oxygen pumping current upon exposure to CH 4 could be attributed to the mixed potential generated by the difference in oxidation activity between the active and inactive electrodes.

The effect of mixed conductivity on the cathodic overpotential of LaGaO 3-based fuel cell

Cathodic performance of La 0.9Sr 0.1MnO 3 (LSM) electrode on LaGaO 3-based electrolyte was examined. The LSM was also mixed with La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) electrolyte to form a composite electrode. The electrodes with different preparation methods were tested to study the effects of the degree of chemical reaction between electrode and electrolyte, the microstructure, and the mixed-ionic and electronic conductivity on cathodic overpotential. To lower the cathodic overpotential, either reducing the reaction between electrode and electrolyte or enhancing the mixed-ionic and electronic conductivity was more important than controlling the microstructure.

Some Characteristics for Fabrication of LaGaO3-Based Electrolyte

Some Characteristics for Fabrication of LaGaO3-Based Electrolyte

Oxidative reforming of methane using solid oxide fuel cell with LaGaO 3-based electrolyte

Simultaneous production of thermal energy, electric power, and gaseous mixture of CO and H 2, suitable for the methanol synthesis was possible by the application of a solid oxide fuel cell to the catalytic reactor. In particular, large electric power as well as high yields of CO and H 2 were obtained upon the fuel cell reactor where La 0.9Sr 0.8Ga 0.8Mg 0.2O 3 perovskite-type oxide was used as solid electrolyte. The high electrical power density as well as the high yield of CO and H 2 were stably sustained over the examined 30 h.