La0.6Sr0.4CoO3-δ Research Articles

Strategy to Enhance Air Electrode Performance and Durability in Soe and Co-Soe Modes: Composite Electrode with a Gradually Changing Composition

Among the key challenges of the Solid Oxide Cell (SOC) is stable, long-term operation in electrolysis (SOE, Solid Oxide Electrolysis), and co-electrolysis (co-SOE) modes. Many factors impact the SOC’s lifespan, i.e., the chemical composition of the fuel and air electrode, the type of the cell, and working conditions (e.g., current density, temperature). Therefore, the development of high-performance and durable cells seems to be crucial, as SOE/co-SOE systems may play an important role in the ongoing transformation toward a climate-neutral economy (low-emission hydrogen production; efficient utilization of CO2and renewable energy) [1,2].One of the crucial degradation mechanisms of SOC in electrolysis/co-electrolysis mode is the delamination of the air electrode, caused by the accumulation of high oxygen partial pressure on the interphase of the electrolyte, the formation of additional phases, and/or reaction of voids/cracks in the electrolyte or buffer layer [2,3]. A strategy to mitigate the risk of air electrode delamination is to use composite electrode based on the buffer layer material (GDC- Gd0,1Ce0,9O2) and state-of-the-art electrode – LSC (La0,6Sr0,4CoO3-δ), as it will lower the effect of the thermal expansion mismatch between the electrode and buffer layer/electrolyte. Moreover, by manipulating the microstructure of the electrode, e.g., by introducing a pore-forming agent, it is possible to ensure fast and effective collection of oxygen generated during operation in the SOE/co-SOE mode on the air side (preventing potential differences leading to the stresses on the electrode-electrolyte interface).In this study, the electrochemical performance of solid oxide cells with a modified, gradually changing composite LSC-GDC air electrode was verified in electrolysis and co-electrolysis modes. The following air electrode compositions were proposed for cell preparation: type 1: 1st layer 50LSC:50CGO, 2nd layer: 75LSC: 25GDC, 3rd layer: LSC, type 2: 1st layer 75LSC:25CGO, 2nd and 3rd layers: LSC with PMMA as a pore former; type 3: 1st layer 75LSC:25CGO, 2nd and 3rd layers: 90LSC:10GDC, and type 4: 1st layer 85LSC:15CGO, 2nd layer: 90LSC:10GDC; 3rd layer: LSC with PMMA as a pore former. The proposed air electrode was tested at the single-cell level (cells size of 50 mm x 50 mm), and the most promising solutions were implemented in the SOC stack (a stack consisting of 3-5 cells with a size of 110 mm x 110 mm). The electrochemical analysis of the developed cells includes measurements of the j-V dependences and EIS spectra under different modes (SOE and co-SOE), various temperatures, current densities, and different gas flows delivered at the air side of the cell. The microstructure, morphology, and composition of the prepared cells and samples after testing were analyzed using SEM, SEM-EDS, and, for selected samples, the FIB-SEM method. The obtained results showed that by a gradually changing the electrode composition, specifically by reducing the GDC content in the electrode, it is possible to obtain a stable electrode (a strategy to prevent air electrode delamination) with high catalytic activity in both electrolysis and co-electrolysis modes. The composite GDC-LSC electrodes with various compositions seem to be promising air electrodes for SOE and co-SOE systems. The study achieves relatively high current densities compared to the SoA cells, with only negligible degradation changes observed after long-term testing (>300 h in single cell configuration). Acknowledgments The presented research was financially supported by: the National Centre for Research and Development, Poland, within project no. LIDER/1/0003/L-12/20/NCBR/2021, which focuses on research related to composite electrodes. Anna Niemczyk acknowledges support from the Foundation for Polish Science (FNP) through a scholarship from the START program. References B. Mogensen et al., Clean Energy 3 (2019) 175; DOI: 10.1093/ce/zkz023Hauch, P. Blennow, Solid State Ionics 391 (2023) 116127; DOI: 10.1016/j.ssi.2022.116127Subotić, C. Hochenauer, Progress in Energy and Combustion Science 93 (2022) 101011; DOI: 10.1016/j.pecs.2022.101011

Enhanced electrochemical performance of partially amorphous La0.6Sr0.4CoO3-δ oxygen electrode materials for low-temperature solid oxide cells operating at 400 °C

This work evaluates partially amorphous La0.6Sr0.4CoO3-δ (LSC) as a potential oxygen electrode for low-temperature solid oxide cells. LSC was deposited using the spin-coating technique onto Ce0.8Gd0.2O2-δ (CGO) substrates. The optimal oxygen electrode thickness was determined as 500 nm. The electrochemical impedance spectroscopy (EIS) study showed a significant improvement in oxygen reduction/oxidation reaction kinetics when annealing temperatures below 600 °C. The lowest value of the polarisation resistance was observed for the sample annealed at 400 °C, followed by a temperature of 500 °C. EIS measurements at different pO2 content were performed at levels between 0.5 % and 20 %. A comprehensive equivalent circuit analysis was carried out for an explanation of the limiting factors of the catalytic reaction. X-ray absorption fine structure analysis allowed for the identification of differences between crystalline LSC and its partially amorphous form. X-ray absorption near-edge spectroscopy analysis indicated that cobalt adopts a lower oxidation state for the partially amorphous form. Moreover, extended X-ray absorption fine structure analysis indicated the decreased of cobalt oxidation state in partially amorphous LSC. It can be assumed that the increased activity of LSC at temperatures below the crystallization may be due to increased defects and oxygen vacancies in the material.

Revealing the Influence of Electron Migration Inside Polymer Electrolyte on Li+ Transport and Interphase Reconfiguration for Li Metal Batteries.

The development of highly producible and interfacial compatible in situ polymerized electrolytes for solid-state lithium metal batteries (SSLMBs) have been plagued by insufficient transport kinetics and uncontrollable dendrite propagation. Herein, we seek to explore a rationally designed nanofiber architecture to balance all the criteria of SSLMBs, in which La0.6Sr0.4CoO3-δ (LSC) enriched with high valence-state Co species and oxygen vacancies is developed as electronically conductive nanofillers embedded within ZnO/Zn3N2-functionalized polyimide (Zn-PI) nanofiber framework for the first time, to establish Li+ transport highways for poly vinylene carbonate (PVC) electrolyte and eliminate nonuniform Li deposits. Revealed by characterization and theoretical calculation under electric field, the positive-negative electrical dipole layer in LSC derived from electron migration between Co and O atoms aids in accelerating Li+ diffusion kinetics through densified electric field around filler particle, featuring a remarkable ionic conductivity of 1.50 mS cm-1 at 25 °C and a high Li+ transference number of 0.91 without the risk of electron leakage. Integrating with the preferential sacrifice of ZnO/Zn3N2 on PI nanofiber upon immediate detection of dendritic Li, which takes part in reconfiguring hierarchical SEI chemistry dominated by LixNy/Li-Zn alloy inner layer and LiF outer layer, SSLMBs are further endowed with prolonged cycling lifespan and exceptional rate capability.

Structural Characterization of La0.6Sr0.4CoO3-δ Thin Films Grown on (100)-, (110)-, and (111)-Oriented La0.95Sr0.05Ga0.95Mg0.05O3-δ.

In this study, a detailed structural characterization of epitaxial La0.6Sr0.4CoO3-δ (LSC) films grown in (100), (110), and (111) orientations was conducted. LSC is a model air electrode material in solid oxide fuel and electrolysis cells and understanding the correlation of bulk structure and catalytic activity is essential for the design of future electrode materials. Thin films were grown on single crystals of the perovskite material La0.95Sr0.05Ga0.95Mg0.05O3-δ cut in three different directions. This enabled an examination of structural details at the atomic scale for a realistic material combination in solid oxide cells. The investigation involved the application of atomic force microscopy, X-ray diffraction, and high-resolution transmission electron microscopy to explore the distinct properties of these thin films. Interestingly, ordering phenomena in both cationic as well as anionic sublattices were found, despite the fact that the thin films were never at higher temperatures than 600 °C. Cationic ordering was found in spherical precipitates, whereas the ordering of oxygen vacancies led to the partial transition to brownmillerite in all three orientations. Our results indicate a very high oxygen vacancy concentration in all three thin films. Lattice strains in-plane and out-of-plane was measured, and its implications for the structural modifications are discussed.

Controllable Technology for Thermal Expansion Coefficient of Commercial Materials for Solid Oxide Electrolytic Cells.

Solid oxide electrolysis cell (SOEC) industrialization has been developing for many years. Commercial materials such as 8 mol% Y2O3-stabilized zirconia (YSZ), Gd0.1Ce0.9O1.95 (GDC), La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), La0.6Sr0.4CoO3-δ (LSC), etc., have been used for many years, but the problem of mismatched thermal expansion coefficients of various materials between cells has not been fundamentally solved, which affects the lifetime of SOECs and restricts their industry development. Currently, various solutions have been reported, such as element doping, manufacturing defects, and introducing negative thermal expansion coefficient materials. To promote the development of the SOEC industry, a direct treatment method for commercial materials-quenching and doping-is reported to achieve the controllable preparation of the thermal expansion coefficient of commercial materials. The quenching process only involves the micro-treatment of raw materials and does not have any negative impact on preparation processes such as powder slurry and sintering. It is a simple, low-cost, and universal research strategy to achieve the controllable preparation of the thermal expansion coefficient of the commercial material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) through a quenching process by doping elements and increasing oxygen vacancies in the material. Commercial LSCF materials are heated to 800 °C in a muffle furnace, quickly removed, and cooled and quenched in 3.4 mol/L of prepared Y(NO3)3. The thermal expansion coefficient of the treated material can be reduced to 13.6 × 10-6 K-1, and the blank sample is 14.1 × 10-6 K-1. In the future, it may be possible to use the quenching process to select appropriate doping elements in order to achieve similar thermal expansion coefficients in SOECs.

Pr2Ni0.8Co0.2O4+δ impregnated La0.6Sr0.4CoO3-δ oxygen electrode for efficient CO2 electroreduction in solid oxide electrolysis cells.

The solid oxide electrolysis cell (SOEC) is an advanced electrochemical device with a promising future in reducing CO2 emissions. Currently, the insufficient oxygen evolution reaction activity in conventional anode materials severely restricts the development of electrolytic CO2. Herein, the PNCO-LSC composite oxygen electrode was exploited by impregnating Pr2Ni0.8Co0.2O4+δ (PNCO) on the surface of La0.6Sr0.4CoO3-δ (LSC) oxygen electrode. The results of electrochemical tests and various physicochemical characterizations indicate that the infiltration of PNCO can lead to a significant improvement in the performance of the cell for CO2 electroreduction by increasing the surface oxygen exchange. The current density of the PNCO-LSC oxygen electrode infiltrated twice at 800 °C and 1.5 V reaches 0.917 A cm-2, which is about 40% higher than that of the bare LSC oxygen electrode. In addition, the single cell did not show significant degradation in a long-term stability test at a current density of 0.4 A cm-2 for 100 h of electrolysis. Therefore, the PNCO-LSC composite oxygen electrode material is effective in enhancing electrolytic CO2 performance.

Nanostructured LSC Thin Film Electrodes with Improved Electrochemical Performance and Long-Term Stability

Nanostructured La0.6Sr0.4CoO3-δ (LSC) thin film electrodes exhibit exceptionally high oxygen surface exchange properties, surpassing those of conventional microscale electrode structures, which are desirable for application in solid oxide cells (SOC) [1-2]. On the other hand, the LSC nanostructures also tend to undergo significant morphological changes at typically high temperatures required for SOC operation, leading to rapid degradation in performance. Here, towards the goal of improving the long-term stability of electrochemical performance of nanostructured LSC thin films, a systematic investigation of the effect of processing temperatures on long-term stability was carried out [3]. By varying the deposition temperature (500 °C to room temperature), the as-grown characteristic nanostructures of LSC thin films prepared using pulsed laser deposition can be tuned from highly dense nanocolumnar grains to nanofibrous structures with high porosity. Variations in the deposition temperature also resulted to differences in the proportion of surface-bound/lattice-bound Sr and Co2+/Co3+ at the surfaces of the as-grown LSC thin films; however, prolonged annealing at 700 °C in air essentially transforms the surfaces to a final state with mostly lattice-bound Sr and Co3+. Nevertheless, LSC films with initially nanofibrous structures are found to be less prone to the grain sintering effect occurring at high temperatures and exhibit less degradation of the electrode polarization resistance as compared to well-dense films. Using lower deposition temperatures, cation interdiffusion occurring at LSC/GDC interfaces is also significantly suppressed, thus leading to better interfacial stability as compared to those prepared at higher deposition temperatures. These results highlight the relationship between characteristic nanostructures of thin film electrodes and electrochemical performance and provide guidance on designing electrodes with improved long-term stability.[1] J. Januschewsky, M. Ahrens, A. Opitz, F. Kubel and J. Fleig, Adv. Funct. Mater., 2009, 19, 3151–3156.[2] J. Hayd, L. Dieterle, U. Guntow, D. Gerthsen and E. Ivers-Tiffee, J. Power Sources, 2011, 196, 7263–7270.[3] K. Develos-Bagarinao, O. Celikbilek, R. A. Budiman, G. Kerherve, S. Fearn, S. J. Skinner and H. Kishimoto, J. Mater. Chem. A, 10, 2445-2459 (2022).

Experimental Demonstration of the Electric Efficiency with BZYb based Protonic Ceramic Fuel Cell

Protonic Ceramic Fuel Cell (PCFC) is expected to be the next-generation fuel cell for its higher energy conversion efficiency and lower operation temperature. BaZrO3 based oxide are potential materials as PCFC electrolyte because they have a high chemical stability under CO2 condition and high proton conductivity. We have developed PCFC using BaZr0.8Yb0.2Ox (BZYb) as the electrolyte and performed max power density 0.49 W cm–2 at 873 K. For practical use of PCFC, it is needed to conduct the higher electric efficiency and to improve the durability. Especially, improving the electric efficiency of PCFC might be difficult due to the internal current leakage by the hole creation.In this work, we have evaluated the electric efficiency using a Φ60mm anode supported PCFC (active electrode area: Φ45mm, 15.9 cm2). Thin and dense BZYb electrolyte is supported on porous Ni-BZYb cermet anode and La0.6Sr0.4CoOx cathode. The effect of fuel utilization on PCFC cell was examined and the electric efficiency of PCFC was calculated as follows:η = V / (-ΔH / nF) × Ufwhere the n and F are the mole number and the Faraday constant, respectively. ΔH is the standard combustion enthalpy of hydrogen or methane. The value of -ΔH / nF is 1.24 V or 1.04 V in the case of hydrogen supply or methane supply respectively. V is the cell voltage and Uf is the fuel utilization.Φ60mm anode supported PCFC was fabricated by tape-casting process used for the industrial production of ceramic electronic devices. NiO-BZYb anode slurry and BZYb electrolyte slurry were prepared by mixing the powder, binder, solvents and plasticizer. And then, these slurries were tape-casted respectively. The anode green sheets and the electrolyte green sheets were stacked and pressed. The anode electrolyte half-cell was obtained by firing this laminate at 1673–1773 K for 2 h. La0.6Sr0.4CoO3-δ (LSC) paste was applied to the surface of the half-cell by screen–printing, and then, fired at 1223 K for 2 h to form a cathode.The electrochemical performance of the Φ60mm anode supported PCFC was investigated at 873 K under the conditions of a humid fuel gas (i.e., 3% H2O, 48.5% N2 and 48.5% H2) and a humid air (i.e. 3% H2O and 97% air). Fuel flow rate were determined by the operational current and the fuel utilization (Uf), and air flow rate were constant at 264 cc min–1, which the air utilization (Uair) was 30% at the current of 0.3 A cm–2.Figure 1 shows the comparison of the current-voltage (I-V) and current-power (I-P) characteristics of Φ60mm and Φ20mm BZYb cell. Fuel flow rate was 100 cc min–1 at this experiment. The same electrochemical performance was observed, and the maximum power reached 7 W at 12.9 A in the case of the Φ60mm cell.Figure 2 shows the cell performance of 0.3 A cm–2 current density under the various Uf condition. The theoretical voltage line was also drawn in the figure, which was calculated by Nernst equation used the PH2 in the anode outlet gas, PO2 and PH2O in the cathode outlet gas. Cell voltage followed the same path as the theoretical voltage in the low Uf condition (Uf≦70%). On the other hand, the gap between the cell voltage and theoretical one was larger in the higher Uf condition (Uf≧80%). Anode gas diffusion overvoltage might be increased by PH2 decreasing in anode gas or the imbalanced gas flow due to decreasing the anode gas flow rate. We demonstrated that BZYb based PCFC could be operated at high Uf condition (i.e., Uf=90%) and the maximum electric efficiency was 55% (DC). This presentation is partially based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Electrochemical Performance and Durability of a Solid Oxide Cell with Nanoparticles-Modified Electrodes for CO2 Electrolysis

Solid oxide electrolysis cell (SOEC) is one of the most effective technologies for converting carbon dioxide to carbon monoxide using renewable energy sources. Improving the electrode performance of an SOC by manufacturing nanocomposite electrodes via infiltration has attracted growing interest in recent years. This work investigated the electrochemical performance and long-term durability of a Ni/yttria-stabilized zirconia (YSZ)-supported planar-type SOEC cell (CGO@Ni/YSZ|YSZ|CGO|LSC/CGPO@CGO) infiltrated with nano-catalysts for CO2 electrolysis. The Ni/YSZ fuel electrode was infiltrated with Ce0.8Gd0.2O2−δ (CGO) solution, and the porous CGO scaffold was co-infiltrated with La0.6Sr0.4CoO3-δ (LSC) and Gd, Pr co-doped CeO2 (CGPO) nano-sized electrocatalysts. The cells were operated at 800 °C and -1 A/cm2 for 1548 h with a mixture of 24 L/h CO2/CO (83/17) supplied to the Ni/YSZ fuel electrode and pure O2 to the oxygen electrode. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis were conducted. Cell activation occurred at ⁓400 h of the durability testing due to the gas resupply from an unexpected power outage at ⁓360 h. During the durability testing period, the cell voltage increased from 1246 mV to 1400 mV with a degradation rate of 99.1 mV/kh (7.95%/kh). Furthermore, the cell showed a much lower degradation of ohmic resistance R s (7.14 mΩ cm2/kh) compared to that of polarization resistance R p (129.05 mΩ cm2/kh) after the gas resupply. DRT reveals that the degradation originates mainly from the Ni/YSZ fuel electrode during durability testing. Results from the current work demonstrate the potential of modifying SOECs for CO2 electrolysis at a high current density through the infiltration technique.

Investigation of atomic-scale decorations on mixed conducting oxides via time-of-flight secondary ion mass spectrometry (ToF-SIMS)

Sub-nanometer modifications of mixed ionic electronic conducting (MIEC) materials, like the perovskite La0.6Sr0.4CoO3-δ (LSC), represent a promising approach to improving their oxygen exchange kinetics and degradation stability. The complex interactions between decoration layers and the host material are still not fully understood and are a subject of current research. Under these circumstances, a novel approach using time-of-flight secondary ion mass spectrometry (ToF-SIMS) was developed to gain deeper insight into the electronic and chemical interactions of LSC with different oxidic decorations. The investigated samples were prepared by pulsed laser deposition (PLD) on YSZ single crystals, starting with a 100 nm thin LSC layer, which was then modified by sub-nm decorations of CaO, TiO2, and SnO2 (nominally 0.05–0.5 nm) on top. By using ToF-SIMS with a sampling depth of 1–2 nm, it was possible to extract information simultaneously on the decoration layer and the host oxide. Significant differences in secondary ion (SI) intensities of the host material LSC were found that can be attributed to the formation of surface-near dipoles as a consequence of the acidic or basic nature of the decoration oxide. Further, relative stoichiometric variations of the La+, Sr+, and Co+ signals depending on the decoration oxide were observed, suggesting different preferential decoration sites on the LSC surface.

Tuning the surface chemistry of La0.6Sr0.4CoO3-δ perovskite via in-situ anchored chemical bonds for enhanced overall water splitting

Perovskites have garnered huge interest as electrocatalysts in water–oxidation. Despite their salient features, chemical instability of the perovskite oxide surfaces still limits their durability in electrochemical water–splitting. Here, we propose a simple strategy to increase the overall activity and stability of La0.6Sr0.4CoO3-δ (LSC) perovskite just by reconstructing its surface. Preeminent oxygen evolution (OER) and hydrogen evolution reaction (HER) catalysts, namely, nickel–iron oxyhydroxide (NiFe(OH)2 denoted as NiFe) and nickel–manganese hydroxide (NiMn(OH)2 denoted as NiMn) are in–situ anchored on LSC surface, respectively. The resulting composites greatly facilitate the electron mobility and deliver excellent activity towards OER and HER with low overpotentials of η = 250 mV at 10 mA cm−2 and η = 63 mV at 50 mA cm−2, respectively. The (LSC@NiFe‖LSC@NiMn) electrolyzer reached 10 mA cm−2 at a cell voltage of 1.57 V. We also validated the redistribution of electrons and oxygen, and the abundance of exposed active sites by incorporation of active hydroxides.

Electrochemical and microstructural characterization of the high‐entropy perovskite La0.2Pr0.2Nd0.2Sm0.2Sr0.2CoO3‐δ for solid oxide cell air electrodes

AbstractStrontium segregation (coupled to phase decomposition and impurity poisoning) and electrode delamination are two of the most important degradation mechanisms currently limiting the long‐term stability of solid oxide fuel cell and electrolysis cell (SOFC and SOEC) air electrodes. The present study aims to demonstrate that air electrodes made of entropy‐stabilized multi‐component oxides can mitigate these degradation mechanisms while providing excellent cell performance. A SOEC utilizing La0.2Pr0.2Nd0.2Sm0.2Sr0.2CoO3‐δ (LPNSSC) as an air electrode delivers −1.56 A/cm2 at 1.2 V at 800°C. This performance exceeds that of a commercial cell with La0.6Sr0.4CoO3‐δ (LSC) air electrode, which reaches −1.43 A/cm2. In a long‐term electrolysis test, the LPNSSC cell shows stable performance during 700 h, while the LSC cell degrades continuously. Post‐mortem analyses by scanning electron microscopy‐energy dispersive X‐ray spectroscopy indicate complete delamination of the LSC electrode, while LPNSSC shows excellent adhesion. The amount of secondary phases formed (esp. SrSO4) is also much lower in LPNSSC compared to LSC. In conclusion, the high‐entropy perovskite LPNSSC is a promising option for air electrodes of solid oxide cells. While LPNSSC can compete with ‒ or even outperform ‒ LSC air electrodes in terms of electrochemical performance, it could be particularly advantageous in terms of long‐term stability in SOEC mode.

Hydrogen-Rich Gas Production by Steam Reforming and Oxidative Steam Reforming of Methanol over La0.6Sr0.4CoO3-δ: Effects of Preparation, Operation Conditions, and Redox Cycles.

La0.6Sr0.4CoO3-δ (LSC) perovskite, as a potential catalyst precursor for hydrogen (H2)-rich production by steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM), was investigated. For this purpose, LSC was synthesized by the citrate sol-gel method and characterized by complementary analytical techniques. The catalytic activity was studied for the as-prepared and prereduced LSC and compared with the undoped LaCoO3-δ (LCO) at several feed gas compositions. Furthermore, the degradation and regeneration of LSC under repeated redox cycles were studied. The results evidenced that the increase in the water/methanol ratio under SRM, and the O2 addition under OSRM, increased the CO2 formation and decreased both the H2 selectivity and catalyst deactivation caused by carbon deposition. Methanol conversion of the prereduced LSC was significantly enhanced at a lower temperature than that of as-prepared LSC and undoped LCO. This was attributed to the performance of metallic cobalt nanoparticles highly dispersed under reducing atmospheres. The reoxidation program in repetitive redox cycles played a crucial role in the regeneration of catalysts, which could be regenerated to the initial perovskite structure under a specific thermal treatment, minimizing the degradation of the catalytic activity and surface.

Crystal-Orientation-Dependent Oxygen Exchange Kinetics on Mixed Conducting Thin-Film Surfaces Investigated by In Situ Studies.

The oxygen exchange kinetics and the surface chemistry of epitaxially grown, dense La0.6Sr0.4CoO3-δ (LSC) thin films in three different orientations, (001), (110), and (111), were investigated by means of in situ impedance spectroscopy during pulsed laser deposition (i-PLD) and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). i-PLD measurements showed that pristine LSC surfaces exhibit very fast surface exchange kinetics but revealed no significant differences between the specific orientations. However, as soon as the surfaces were in contact with acidic, gaseous impurities, such as S-containing compounds in nominally pure measurement atmospheres, NAP-XPS measurements revealed that the (001) orientation is substantially more susceptible to the formation of sulfate adsorbates and a concomitant performance decrease. This result is further substantiated by a stronger increase of the work function on (001)-oriented LSC surfaces upon sulfate adsorbate formation and by a faster performance degradation of these surfaces in ex situ measurement setups. This phenomenon has potentially gone unnoticed in the discussion of the interplay between the crystal orientation and the oxygen exchange kinetics and might have far-reaching implications for real solid oxide cell electrodes, where porous materials exhibit a wide variety of differently oriented and reconstructed surfaces.

Investigation on Reaction Mechanism in an SOFC Composite Cathode by Using Patterned Thin Film Electrodes

The reaction mechanism in an SOFC composite cathode was investigated by using patterned thin film model electrodes. In this work, we proposed new types of model electrodes, which could reproduce SOFCs cathodic reactions in a composite electrode of a mixed conducting electrode and an electrolyte. Then the model electrode was fabricated by choosing La0.6Sr0.4CoO3-δ (LSC) and Ce0.9Gd0.1O1.95 (GDC) as the electrode and the electrolyte, respectively. From the DC polarization measurements of the model electrode, it was found that making a composite of LSC and GDC can improve the cathodic performance especially at lower temperatures, possibly due to higher oxide ion conduction in GDC than LSC.

Electrochemical Performance and Durability of a Solid Oxide Cell with Nanoparticles-Modified Electrodes for CO2 Electrolysis

Solid oxide electrolysis cell (SOEC) is one of the most effective technologies for converting carbon dioxide to carbon monoxide using renewable energy sources. This work investigated the electrochemical performance and long-term durability of a Ni/yttria-stabilized zirconia (YSZ)-supported planar-type SOEC cell (CGO@Ni/YSZ|YSZ|CGO|LSC/CGPO@CGO) infiltrated with nano-catalysts for CO2 electrolysis. The Ni/YSZ fuel electrode was infiltrated with Ce0.8Gd0.2O2−δ (CGO) solution, and the porous CGO scaffold was co-infiltrated with La0.6Sr0.4CoO3-δ (LSC) and Gd, Pr co-doped CeO2 (CGPO) nano-sized electrocatalysts. The cells were operated at 800 °C and -1 A/cm2 for 1548 h with a mixture of 24 L/h CO2/CO (83/17) supplied to the fuel electrode and pure O2 to the oxygen electrode. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis were conducted. During the entire durability testing period, the cell voltage increased from 1246 mV to 1400 mV with a degradation rate of 99.1 mV/kh (7.95%/kh). Following the recovery after an unexpected power outage, the cell demonstrated an activation process over ⁓110 h, with a voltage decrease from 1337 mV to 1263.9 mV. Furthermore, the cell showed a much lower degradation of ohmic resistance R s (7.14 mΩ cm2/kh) compared to that of polarization resistance R p (129.05 mΩ cm2/kh). DRT reveals that the degradation originates from both electrodes. The present study reveals that it is crucial to carefully select the appropriate electrocatalyst candidate considering the specific operating conditions.

A novel symmetrical bi-electrode supported ceramic oxygen pump for efficient oxygen production

Based upon the solid oxide electrolysis cell (SOEC) technology, ceramic oxygen pumps (COPs) show great promise owing to their distinctive advantage of continuous and in situ production of high-purity oxygen with control easiness. Here we report on the fabrication of novel ceramic oxygen pumps by the phase-inversion tape casting, lamination and co-firing methods, featuring thin yttria-stabilized zirconia (YSZ) electrolytes supported on symmetrical La0.8Sr0.2 MnO3-δ (LSM)-YSZ electrodes with straight open pores. A current density of 0.33 A•cm−2 is obtained at 750°C and 0.6 V for the ceramic pumps to separate oxygen out of air. Impregnating nano-scale La0.6Sr0.4CoO3-δ (LSC) catalysts into both LSM-YSZ electrodes yields a sharp increase in the performance. For example, the pumping current density at 750°C and 0.6 V increases by a factor of 8 to 2.56 A•cm−2. The total interfacial polarization resistance decreases from 1.17 Ω•cm2 by a factor of 20 to 0.06 Ω•cm2. Analysis of impedance data in the homogeneous environments of air and oxygen indicates that the oxygen separation capability is predominantly limited by the surface oxygen exchange kinetics, which is substantially promoted by the added LSC catalysts. Preliminary short-term measurements show good stability in oxygen separation, indicating excellent resistance of the nano-scale LSC catalysts against coarsening at elevated temperatures. Furthermore, the present symmetrical ceramic oxygen pumps also demonstrate excellent thermal cycling durability.

Synthesis and characterization of carbon nanotubes and activated carbon assisted sol-gel derived La0.6Sr0.4CoO3-δ material

A pure perovskite-type oxide ceramic nanomaterial can be produced at a lower processing temperature than 1000 °C via sol-gel method. However, it is influenced by the nature of chemical agents such as chelating agent, surfactant and dispersant added during the synthesis process. Among them, dispersant is regarded as an important chemical agent as it can prevent the formation of hard agglomerated particles which is the main drawback of sol-gel method. In the present work, ceramic powder of lanthanum strontium cobaltite, La0.6Sr0.4CoO3-δ (LSCO) was prepared via sol-gel method with the aid of carbon nanotubes (CNTs) and activated carbon (AC) as dispersant. The prepared powder was characterized by thermal gravimetric analyser (TGA), X-ray diffractometer (XRD) and scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) spectrometer to evaluate its thermal decomposition, structural and microstructure properties, respectively. Thermal decomposition of the as-synthesized CNTs-based and AC-based powders completed at temperature 750 °C and pure perovskite phase of LSCO was formed at temperature 900 °C. Both CNTs-based and AC-based calcined powders consist of homogeneous and almost identical shape of particles. However, the CNTs-based calcined powder has higher agglomeration index value than the AC-based calcined powder as revealed in SEM images.

Closed-Pore Formation in Oxygen Electrodes for Solid Oxide Electrolysis Cells Investigated by Impedance Spectroscopy.

Electrochemical impedance spectroscopy was used to investigate the chemical capacitance of La0.6Sr0.4CoO3-δ (LSC) thin-film electrodes under anodic polarization (i.e., in the electrolysis mode). For this purpose, electrodes with different microstructures were prepared via pulsed-laser deposition. Analysis of dense electrodes and electrodes with open porosity revealed decreasing chemical capacitances with increasing anodic overpotentials, as expected from defect chemical considerations. However, extremely high chemical capacitance peaks with values in the range of 104 F/cm3 at overpotentials of >140 mV were obtained after annealing for several hours in synthetic air and/or after applying high anodic bias voltages of >750 mV. From the results of several surface analysis techniques and transmission electron microscopy, it is concluded that closed pores develop upon both of these treatments: (i) During annealing, initially open pores get closed by SrSO4, which forms due to strontium segregation in measurement gases with minute traces of sulfur. (ii) The bias treatment causes mechanical failure and morphological changes including closed pores in the bulk of dense films. Under anodic polarization, high-pressure oxygen accumulates in those closed pores, and this causes the capacitance peak. Model calculations based on a real-gas equation allow us to properly predict the experimentally obtained capacitance increase. We demonstrate that analysis of the chemical capacitance of oxygen electrodes in solid oxide electrolysis cells can thus be used as a nondestructive observation tool to detect and quantify closed porosity with a lower detection limit between 10-4 and 10-3.

Preparation of Pr2NiO4+δ-La0.6Sr0.4CoO3-δ as a high-performance cathode material for SOFC by an impregnation method

As a Ruddlesden-Popper (RP) phase solid oxide fuel cell (SOFC) cathode material, Pr2NiO4+δ (PNO) is a critical challenge for SOFC commercialization due to the lack of oxygen vacancies and insufficient redox reaction (ORR) activity. In this paper, various concentrations of La0.6Sr0.4CoO3-δ (LSC) nanoparticles are coated on the surface of PNO by an impregnation method, and the ORR kinetics of PNO is found to be improved by constructing a composite cathode with heterointerfaces. The formation of the heterointerface effectively enhances the transfer of interstitial oxygen in the PNO and the oxygen vacancies in LSC, which can promote the conduction of O2− in the cathode and thus improves the ORR activity of the material. When the impregnation concentration of LSC reached CLSC = 0.2 mol L−1, the ORR activity can reach the highest level. At 700 °C, the area-specific resistance of PNO-LSC reaches 0.024 Ω cm2, which is 83.4% lower than that of PNO (0.145 Ω cm2). And the peak power density of PNO-LSC reaches 0.618 W cm−2, which is 1.89 times larger than that of PNO (0.327 W cm−2). Therefore, the construction of composite cathodes with heterointerfaces via impregnation provides an alternative strategy for enhancing the ORR activity of the cathode materials in SOFC.