La0.8Sr0.2Ga0.8Mg0.2O3-δ Research Articles

Electrolyte-supported solid oxide electrochemical cells for versatile operations

Electrolyte-supported solid oxide electrochemical cells (SOCs) offer advantages in terms of easier fabrication and enhanced mechanical properties, but achieving high performance and multifunctionality remains challenging. In this study, we develop high-performance and versatile electrolyte-supported SOCs using La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte materials through microstructural engineering of Sr2Fe1.5Mo0.5O6-δ (SFM)-based fuel electrodes. We evaluate the cells for power generation, hydrogen production, and carbon dioxide reduction, showcasing the diverse potential of various fuel electrode configurations. Among these, the impregnated SFM@LSGM electrode achieves the best overall performance, with a maximum power density of 739 mW cm−2 in fuel-cell mode, a current density of −0.81 A cm−2 at 1.3 V during steam electrolysis, and an unprecedented current density of −1.92 A cm−2 at 1.5 V in CO₂ electrolysis. Furthermore, it exhibits satisfactory stability across all operational modes. These findings provide valuable insights into the design of versatile electrolyte-supported SOCs and open new possibilities for their flexible applications in future low-carbon energy systems.

CO2-tolerant and cobalt-free La4Ni3-xCuxO10±δ (x = 0, 0.3, 0.5 and 0.7) cathodes for intermediate-temperature solid oxide fuel cells

Cu is doped to La4Ni3O10±δ to improve its electrochemical performance as a potential intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode material. A new higher-order Ruddlesden-Popper (R-P) phase composition La4Ni3-xCuxO10±δ, (L4N3-xCx, 0.0 ≤ x ≤ 0.7) is synthesized using an EDTA-citrate process. The L4N3-xCx cathode has a good chemical compatibility with the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. A thermodynamic stability test shows that L4N3-xCx is stable after 72 h exposure to 600, 700, and 800 °C in air. The L4N3-xCx cathode shows chemical stability against CO2, and a stable structure over 12 h in CO2 has been demonstrated. The thermal expansion coefficients (TECs) have been determined to be in the range of 14.1–14.6 × 10−6 K−1, close to that of the LSGM electrolyte. The Cu content (x) significantly affects the electrical conductivity and sinter density of L4N3-xCx. La4Ni2.7Cu0.3O10 (L4N2.7C0.3) displays the highest electrical conductivity value of which reaches about 383 to 319 S cm−1 at 600–800 °C. In addition, Cu doping improves the electrochemical performance of L4N3-xCx. The area specific resistance (ASR) of the La4Ni2.5Cu0.5O10 (L4N2.5C0.5) cathode was found to be 0.045 Ω cm2 at 800 °C, which is significantly better than that of L4N3. The peak power density of a single cell using the L4N2.5C0.5 cathode is 526 mW cm−2 at 800 °C, and a 200 h long-term test demonstrates good stability. These results indicate that La4Ni3-xCuxO10±δ cathode is a promising cathode material for IT-SOFCs.

CO2 conversion improvement of solid-oxide electrolysis cells by inserting buffer layers between MFe2O4 (M = Ni, Cu, Co, Fe) cathode and electrolyte

This study investigated the potential of spinel-structured materials (MFe2O4; M = Ni, Cu, Co, and Fe) as cathodes of solid oxide electrolysis cells (SOECs); at the same time, it revealed that the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) blocking layers would improve the performance of SOECs by interposing between MFe2O4 and the Sm0.2Ce0.8O2-δ (SDC) electrolytes. The fabricated SOECs were tested under 39% CO2-1% CO-60% He up to 800 °C. Our results showed that the Faradaic efficiency for CO2 reduction was significantly improved and approached the theoretical production rate after the insertion of LSGM blocking layers. In addition, the LSGM barrier layers effectively prevent the short-circuit effect between MFe2O4 and SDC, allowing the open-circuit voltage (OCV) to increase from ∼0.56 V to ∼0.77 V, which dramatically improved the gas generation efficiency of SOECs. According to our optimized SOEC structure, NiFe2O4 and CuFe2O4 exhibited superior electrolytic performance and maintained stable electrolysis after 10 h without degradation. In summary, the inserted LSGM layers would gently modify the interfacial contact and address the mismatch between the spinel-structured materials and SDC to avoid the performance degradation caused by electrode detachment and achieve higher durability than the SOECs without LSGM layers.

A kinetic study of La0.75Sr0.25Cr0.5Mn0.5O3-δ nano-structured electrodes for intermediate temperature symmetric solid oxide fuel cells

La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) mixed conducting has been studied as nanostructured air and fuel electrode, for intermediate temperature symmetric Solid Oxide Fuel cell (S–SOFC). The possible mechanisms involved in the oxygen reduction and hydrogen oxidation reactions of these LSCM nanostructures porous electrodes deposited on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte, were analyzed by electrochemical impedance spectroscopy (EIS) at 700 °C varying the oxygen partial pressure (pO2) and the hydrogen partial pressure (pH2). This analysis was complemented by the study of the electrical conductivity by the four-probe DC technique in the range between 300 and 800 °C in flowing dry atmospheres of air or H2. Results suggested that the O2 reduction reaction mechanism involves the O2- dissociative adsorption and O- ion migration near the surface region, while the H2-oxidation reaction limiting-step is controlled by a slow charge transfer process, and H2- dissociative adsorption on the ultimate O-layer.

Study on Exsolution Process of Sr2FeMo0.6Ni0.4O6 via in Situ Cathodic Polarization

Solid oxide cells (SOCs) are nowadays one of the most promising energy conversion technologies, to accelerate and promote the ongoing energy transition1,2, based on the use of renewable resources. These devices in fact allow the development of valuable low carbon footprint power-to-X (X= power, fuels) chains of energy conversion and storage3. In this respect is crucial the design of innovative, cost-effective materials and processes for more and more versatile and reversible devices.In the last decade, simple perovskite (ABO3) and double perovskite (A2BBʹO6) oxide have been proved to be a valuable alternative to cermet SOC electrodes, thanks to their relative ease of functionalization via doping and exsolution and their mixed ionic-electron conduction4-6. Exsolution process is strongly dependent on the type of metal and perovskite and on methodology adopted to induce the reduction7. Cathodic electrochemical polarization has been demonstrated to be a valuable approach to boost the exsolution especially from titanate based structures, obtaining higher dispersions than that derived from thermal reduction8.In this work, we explored for the first time the behaviour of the double perovskite Sr2FeMo0.6Ni0.4O6-δ (SFMN) under cathodic polarization and we investigated the impact of the structural evolution on the electrochemical performances of a multi-functional electrode for H2-SOFC and CO2-SOEC applications.SFMN was prepared by sol gel method and used to prepare supported SFMN/ La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)/La0.6Sr0.4Fe0.8Co0.2O3-δ:Ce0.9Gd0.1O2-δ (LSFCo:GDC) cells that were tested either before and after thermal or electrochemical reduction at 850°C.As already reported the thermal reduction of SFMN leads to the exsolution of metal nanoparticles (of Ni or Ni-Fe alloys) and the in situ formation of Ruddlesden-Popper phase9 (RP). HRTEM, SEM and XRD characterizations of tested cells allowed to observe an acceleration of the structural transformation of perovskite under cathodic polarization in comparison to what observed under thermal reduction. This allows to gain insights on the role of entire transformation on the electrochemical behaviours of cells. Electrochemical properties of SFNM were investigated by EIS analysis. Distribution of relaxation times (DRT) analyses was also used to obtain further insights on the impedance of the different cell mechanisms according to their characteristic frequency.The exsolved metal nanoparticles contributed to improve the conductivity and activity of the electrode, however, also the formation of RP phase seems have a significant role, especially in the electroreduction of CO2. Further studies are in progress to better understand the mechanisms of interaction between the phases formed during the exsolution process and their role on SOC electrodes activity. References 1 Hauch et al., Science 370, eaba6118 (2020). 2 M.B. Mogensen et al. Clean Energy, 3 (2019) 175–2013 F. Salomone et.al Chem. Eng. Journal 377 (2019), 1202334.Irvine, J. T. S. Perovskite Oxide Anodes for SOFCs. In Perovskite Oxide for Solid Oxide Fuel Cells; Ishihara, T., Ed.; Springer US: Boston, MA, 2009; pp 167–182.5. W. Yin, et al. Energy Environ. Sci. 12 ( 2019) 442–4626. Q. Islam, et al. J. Power Sources 492 ( 2021) , 229626.7. O. Kwon et.al. J. Phys. Energy2, ( 2020), 0320018. Jh, Myung, Jh. et al. Nature 537, (2016) 528–5319. Z.; Du et.al ACS Nano 10, 2016, 8660–8669

Unveiling the Electrocatalytic Activity of the GdBa0.5Sr0.5Co2-xCuxO5+δ (x ≥ 1) Oxygen Electrodes for Solid Oxide Cells.

The A-site cation-ordered GdBa0.5Sr0.5Co2-xCuxO5+δ (GBSCC) double perovskites are evaluated regarding the development of high-performance oxygen electrodes for reversible solid oxide cells (rSOCs). The aims are to maximally decrease the content of toxic and expensive cobalt by substitution with copper while at the same time improving or maintaining the required thermomechanical and electrocatalytic properties. Studies reveal that compositions with 1 ≤ x ≤ 1.15 are particularly interesting. Their thermal and chemical expansions are decreased, and sufficient transport properties are observed. Complementary density functional theory calculations give deeper insight into oxygen defect formation in the considered materials. Chemical compatibility with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) and Ce0.9Gd0.1O2-δ (GDC) solid electrolytes is evaluated. It is documented that the GdBa0.5Sr0.5Co0.9Cu1.1O5+δ oxygen electrode enables obtaining very low electrode polarization resistance (Rp) values of 0.017 Ω cm2 at 850 °C as well as 0.111 Ω cm2 at 700 °C, which is lower in comparison to that of GdBa0.5Sr0.5CoCuO5+δ (respectively, 0.026 and 0.204 Ω cm2). Systematic distribution of relaxation times analyses allows studies of the electrocatalytic activity and distinguishing elementary steps of the electrochemical reaction at different temperatures. The rate-limiting process is found to be oxygen atom reduction, while the charge transfer at the electrode/electrolyte interface is significantly better with LSGM. The studies also allow elaborating on the catalytic role of the Ag current collector as compared with Pt. The electrodes manufactured using materials with x = 1 and 1.1 permit reaching high power outputs, exceeding 1240 mW cm-2 at 850 °C and 1060 mW cm-2 at 800 °C, for the LSGM-supported cells, which can also work in the electrolysis mode.

Novel cobalt-free perovskite PrBaFe1.9Mo0.1O5+δ as a cathode material for solid oxide fuel cells

Fe-based perovskite PrBaFe2O5+δ is inactive toward the oxygen reduction reaction (ORR) due to the sluggish oxygen-ion transport kinetics. Herein, Mo doping is developed as a simple and effective strategy to improve the ORR activity of PrBaFe2O5+δ. Mo-doped PrBaFe1.9Mo0.1O5+δ (PBFMO) is comparatively studied with undoped PrBaFe2O5+δ (PBFO) to reveal the effect of Mo doping on its crystal structure, thermal expansion behavior, electrical and electrochemical properties. PBFMO sample has a tetragonal structure with P4/mmm space group. Pr, Fe, and Mo in PBFMO sample exist as Pr3+/Pr4+, Fe2+/Fe3+, and Mo5+/Mo6+ mixed valence states. Mo doping reduces the average thermal expansion coefficient (TEC) from 18.8 × 10−6 K−1 down to 14.5 × 10−6 K−1, which is closer to the TEC of La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. Moreover, Mo doping results in the increment of oxygen vacancy content and thus the enhancement of electrochemical performance. The polarization resistance (Rp) is 0.092 Ω·cm2 at 800 °C for PBFMO and is reduced by 27.0% after Mo doping. The peak power density is 0.68 W·cm−2 at 800 °C for PBFMO-based single cell. These obtained results indicate Mo doped PBFMO can be a good candidate for cathode material of intermediate temperature SOFC.

Nanofiber Sr2Fe1.5Mo0.5O6-δ Electrodes Fabricated by the Electrospinning Method for Solid-Oxide Cells

Solid oxide cells (SOCs) are attracting much more attention as promising energy conversion and storage devices. One of the challenges of optimizing of solid-oxide cells’ performance is that there are not enough triple-phase boundaries (TPB) in the electrode bulk. To enhance the reaction area for SOCs, Sr2Fe1.5Mo0.5O6-δ nanofibers are synthesized by electrospinning with metal nitrate precursors and used for SOC electrodes operated in both humidified air and a hydrogen atmosphere. SFMO nanofibers display a highly porous and crystallized perovskite structure and continuous pathways by XRD analysis and SEM observation. The average diameter of the SFMO nanofibers after sintering is about 100 nm. The La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) electrolyte-supported symmetrical cell with the SFMO nanofiber electrode exhibits enhanced electrochemical performance in humidified air and an H2 atmosphere. Moreover, a distribution of the relaxation time method is used to analyze the impedance spectra, and the polarization peaks observed are assigned to correspond different electrochemical processes. The results indicate that the SFMO nanofiber with an improved nanostructure can be the potential material for the SOC electrode.

Further optimization of the properties of Pr0.6Sr0.4Fe0.9W0.1O3-δ by Cu-doping as symmetric electrodes for solid oxide fuel cells

Copper-doped Pr0.6Sr0.4Fe0.8Cu0.1W0.1O3-δ (PSFCuW) as a symmetric electrode material is investigated for La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)-based symmetric solid oxide fuel cells (SSOFCs). The effect of Cu-doping on stability and mechanism of hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) is investigated and analyzed. Fe partially replaced by Cu on the B-site could also keep the phase structure stable after treatment under reducing conditions and improve the electrical conductivity, which reaches 30.3 and 0.78-1 under oxidizing and reducing conditions at 800 oC, respectively. The distribution of relaxation times (DRT) indicates that the rate-limiting step processes under oxidation conditions are oxygen adsorption and diffusion, while hydrogen adsorption and charge transfer have important influences on the rate-limiting step under reduced atmospheres, respectively. Finally, the LSGM-supported SSOFC (PSFCuW|LSGM|PSFCuW) shows excellent stability and reversibility. These results imply that PSFCuW is an up-to-coming symmetric electrode material for application in SSOFCs.

Coke-resistant ferrite anode decorated with in-situ exsolved ceria for carbonaceous fuel oxidation

In this work, the perovskite-type La0.8Ce0.2FeO3 (LCF) is employed as a host oxide for the exsolution of ceria in air and the further doping on La site using Pr3+ (La0.7Pr0.1Ce0.2FeO3, LPCF) or Gd3+ (La0.7Gd0.1Ce0.2FeO3, LGCF) is used to achieve the exsolution of PrOx- and Gd2O3- doped ceria (PDC and GDC). The exsolution of (doped) ceria is accompanied by the segregation of Fe2O3 that can promote fuel oxidation. The resulting perovskites are used as potential anode materials for solid oxide fuel cells. At 800 °C, the LPCF with 1 wt% Ni infiltration cell on a LSGM (La0.9Sr0.1Ga0.8Mg0.2O3-δ) electrolyte yields the lowest Rp (polarization resistance) value (0.11 Ω cm2) and the highest cell performance (808 mW cm−2) in H2 fuel, but the cells with LCF and LGCF anode show a stable performance under hydrocarbon fuel conditions if Ni is infiltrated into the anode to assist the deprotonation. The parameters controlling the exsolution of the doped ceria and the catalysis for the hydrocarbon reforming are analyzed, proposing an intriguing path to achieving the exsolution of complex oxide on the surface of perovskite for the construct of a hierarchical electrode/catalyst for the applications in fuel conversion.

Mo-doped Ba0.5Sr0.5Co0.8Fe0.2O3-δ as a high-performance symmetric electrode for solid oxide fuel cells

The perovskite oxide Ba0.5Sr0.5(Co0.8Fe0.2)0.8Mo0.2O3-δ (BSCFM) is used as both an anode and cathode in symmetrical solid oxide fuel cells (SSOFCs) because of its high electrocatalytic activity for both oxygen reduction reaction and fuel oxidation. Doping with Molybdenum (Mo) not only stabilizes the structure of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) to improve the redox stability, it also dramatically enhances its electrochemical performance and thermal expansion compatibility. At 800 °C, the area specific polarization resistance (ASRp) for the BSCFM symmetric cell with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte is 0.064 Ω cm2 and the maximum power density can reach 1225 mW cm−2 with wet H2 (3 % H2O) as fuel.

A highly stable of tungsten doped Pr0.6Sr0.4Fe0.9W0.1O3-δ electrode for symmetric solid oxide fuel cells

In this work, a single perovskite Pr0.6Sr0.4Fe0.9W0.1O3-δ (PSFW) for the electrode of SSOFCs is designed and successfully synthesized. The PSFW exhibits excellent structure stability in both reducing and oxidizing atmospheres and thermal compatibility with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The area specific polarization resistances (ASRs) of PSFW under oxidizing and reducing atmospheres are only 0.086 and 0.215 Ω cm2 at 800 °C, respectively. The symmetric electrode shows excellent electro-catalytic activity toward oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) and the corresponding impedance spectra under different hydrogen and oxygen partial pressures are further explored by distribution of relaxation times (DRT), which reveals that rate-limiting steps of HOR and ORR are the hydrogen adsorption/diffusion and oxygen diffusion, respectively. A LSGM electrolyte-supported cell with PSFW as symmetric electrodes displays the outstanding power density, considerable stability and reversibility, proving that the PSFW is a promising electrode material for symmetric solid oxide fuel cells.

Highly efficient direct carbon solid oxide fuel cells operated with camellia oleifera biomass

Direct carbon solid oxide fuel cells (DC-SOFCs), energy conversion devices with an all-solid-state structure, utilize solid carbon as a fuel to generate electricity in a green and efficient manner. Recently, the use of biomass-derived carbon as a DC-SOFC fuel has become a key research topic owing to the abundance and renewability of biomass. Thus far, for the majority of studies, an anaerobic pyrolysis process is usually needed for converting the biomass to biochar prior to applying DC-SOFCs. In this study, DC-SOFCs were assembled with perovskite-type La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) and Ag-Gd0.2Ce0.8O2-δ as the electrolyte and electrodes, respectively. The electrochemical performance and stability were evaluated for two types of DC-SOFCs: those filled with Camellia oleifera shell biomass as the fuel and those filled with biochar derived from the biomass. The biomass-filled DC-SOFC achieved a maximum power density of 306 mW cm−2 at 800°C, which is close to that of the biochar-filled DC-SOFC (317 mW cm−2). Moreover, discharge test results of constant current indicate that biomass-filled DC-SOFCs have higher fuel utilization. This study verifies the feasibility and potential of loading biomass directly into DC-SOFCs as a carbon source, and reveals that, compared with DC-SOFCs operated with biochar, biomass-filled DC-SOFCs can deliver remarkable electrochemical performance and stability. Thus, a simpler and more convenient way to generate electricity through efficient and clean utilization of biomass energy is identified.

Co-free triple perovskite La1.5Ba1.5Cu3O7±δ as a promising air electrode material for solid oxide fuel cells

La1.5Ba1.5Cu3O7±δ (LBCu) complex oxide is evaluated as a Co-free candidate air electrode material for reversible Solid Oxide Cells (rSOC). LBCu is structurally and thermomechanically compatible with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte, maintains the layered (tripled along the c-axis) perovskite-related crystal structure at high temperatures, and shows reduced chemical expansion with the faster elongation ongoing perpendicular to the a-b plane. Its total thermal expansion is found to be moderate comparing to the Co-based perovskites. The onset temperature of the oxygen release from the material is low, ca. 300 °C in air, however, up to 800 °C the average oxidation state of copper remains above +2 in the oxidative atmospheres. The total electrical conductivity of LBCu correlates with the oxygen content, with the maximum of about 55–75 S cm−1 at ca. 350 °C in air. Functional LBCu air electrodes can be manufactured at temperatures as low as 750–800 °C, with exceptionally low (for Co-free material) polarization resistance values of 0.019 Ω cm2 at 750 °C, 0.041 Ω cm2 at 700 °C, and 0.090 Ω cm2 at 650 °C. Relatively high power output, ca. 162 mW cm−2 at 600 °C, and above 458 mW cm−2 at 750 °C is obtained for the laboratory-scale LSGM-supported cell.

Highly Active and Stable a-Site Deficient La0.4Sr0.4Ti0.94Ni0.06O3-δ SOFC Anode Material with in-Situ Exsolved of Ni Nanoparticles

La-doped strontium titanates with a perovskite structure are promising candidates of the anode materials for solid oxide fuel cells (SOFCs) owing to their good chemical compatibility with other components and superior redox-stability. Among these La-doped SrTiO3 (LST), A-site deficient LST materials have attracted much interest due to their improved electrochemical characteristics. Recently, exsolution in A-site deficient LST has been intensively studied, because catalytic active and durable metal nanoparticles can be exsolved on the LST surface. In this study, we developed the A-site deficient Ni-doped La0.4Sr0.4TiO3 (LSTN)-Ce0.9Gd0.1O1.95 (GDC) composite anodes, and investigate their electrochemical performance and redox stability on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte-based SOFCs. The maximum power density(MPD) of LSTN44-GDC anode based cell was 0.698 mW cm-2 at 900℃ in wet H2 fuel (3% H2O). Also, during redox cyclic tests combined with long-term stability test, The LSTN44-GDC cell maintained its performance without any degradation. All these results demonstrate that the A-site deficient LSTN-GDC is a promising material for an efficient and stable SOFC anode.

Redox-stable symmetrical solid oxide fuel cells with exceptionally high performance enabled by electrode/electrolyte diffuse interface

In this study, we report a high performance and redox-stable symmetrical solid oxide fuel cell (SOFC) based on (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ (BSMF) electrode and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. BSMF is able to operate both as anode and cathode. Excellent electrocatalytic activity has been achieved on BSMF towards hydrogen oxidation and oxygen reduction. Due to its closely matched lattice parameter to LSGM electrolyte, a unique diffuse interface is formed between BSMF and LSGM. Compared to a clean interface, e.g. BSMF/gadolinium doped ceria interface, this diffuse interface promotes the performance of BSMF electrode 1–1.8 times in 600–800 °C. Polarization resistance of the BSMF/LSGM specimen is as low as 0.047 and 0.007 Ωcm2 in humidified H2 and in air at 800 °C, respectively. On the BSMF/LSGM/BSMF symmetrical cell, a maximum power density of 2.28 W/cm2 is achieved at 800 °C, the highest among with redox-stable ceramic electrodes to the best of our knowledge. Redox stability of this cell is confirmed. The role of anode and cathode is reversed back and forth in different operation modes. No apparent degradation is observed through 4 cycles within a 110 h operation period. These findings demonstrate that (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ coupled with LSGM electrolyte is an excellent choice to build a high performance, redox-stable SOFC.

An efficient and prospective self-assembled hybrid electrocatalyst for symmetrical and reversible solid oxide cells

In view of the high catalytic activity, enhanced oxygen-ion transport and good stability, the self-assembled hybrid electrocatalyst can be used for symmetrical and reversible solid oxide cells (RSOCs). Herein, a new Ni-free ceramic fuel electrode can be obtained by in situ annealing the orthorhombic perovskite Pr0.6Sr0.4FeO3-δ (PSF) in H2 at 850 °C for 2 h, consisting of orthorhombic perovskite matrix with nano Ruddlesden–Popper oxide (RP/O-PSF). Symmetrical RSOCs consisting of RP/O-PSF fuel electrode, La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte and PSF air electrode (PSF|LSGM|PSF) were fabricated and the electrochemical performance was evaluated. The maximum power density of the cell under solid oxide fuel cell (SOFC) mode is 591 mW/cm2 at 800 °C, and the current density of the cell under solid oxide electrolysis cell (SOEC) mode is -1388 mA/cm2 at 800 °C with an applied electrolysis voltage of 1.6 V. The polarization resistances of cell under SOFC mode and SOEC mode are 0.152 Ω cm2 (OCV-0.2 V) and 0.126 Ω cm2 (OCV + 0.2 V), respectively, demonstrating an excellent catalytic activity of RP/O-PSF towards the water electrolysis process compared with hydrogen oxidation reaction (HOR) owing to the accelerated transfer rate of oxygen ions. In addition, the desirable long-term stability indicates the fact that RP/O-PSF hybrid electrode is such a suitable and prospective candidate for symmetrical and reversible solid oxide cells.

Effect of tungsten doping on strontium ferrite electrode for symmetrical solid oxide electrochemical cell

Tungsten-doped strontium ferrite (SrFe1-xWxO3-δ, SFW) is prepared and characterized as the electrode materials for symmetrical solid oxide electrochemical cell. X-ray diffraction refinement reveals the symmetrical structure transform from cubic (pm3¯m) for x = 0.1 to tetragonal (I4/m) when x = 0.2. According to the analysis including electrical conductivity, Hydrogen temperature-programmed reduction (H2-TPR), thermal expansion and X-ray photoelectron spectra (XPS), it suggests that the decrease in conductivity, content of Fe2+ and oxygen vacancy concentration with the increase of W content is attributed to the stronger lattice framework. The oxygen vacancy can be dramatically activated around 600 °C. Using SrFe0.8W0.2O3-δ as the electrodes, symmetrical single cells supported on doped ceria electrolytes can achieve acceptable power density (0.19 W cm−2 at 750 °C) and considerable stability. Meanwhile symmetrical cells with La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte substrates can achieve 0.75 A cm−2 at 800 °C under the voltage of OCV (open circuit voltage) +0.5 V when it is operated in electrolysis mode. SrFe0.8W0.2O3-δ can gain a considerable stability and electrochemical activity under both oxide and reductive atmospheres. Oxygen vacancy formation energy (Evac) and electron density distribution are computed to verify the enhancement on crystal structure stability by doping W. The Evac critically depends on the distance from the W atom.

Electrochemical performance and structural durability of Mg-doped SmBaMn2O5+δ layered perovskite electrode for symmetrical solid oxide fuel cell

Symmetrical solid oxide fuel cells (SSOFCs), in which the same material serves as anode and cathode simultaneously, have attracted substantial attention because of the simplified electrode/electrolyte interface issue and cell fabrication process. The exploration of suitable electrode material for SSOFC is a great challenge. In this work, Mg-doped SmBaMn1.9Mg0.1O5+δ (SBMM) with Sm-Ba layered ordering is proposed as SSOFC electrode material. The SBMM shows high structure reversibility upon thermal and redox cycling, with orthorhombic Pmmm symmetry in air and tetragonal P4/nmm structure in reducing atmosphere. It exhibits similar thermal expansion coefficients of 15.14(1) × 10−6 K-1, 14.72(6) × 10−6 K-1 in 5% H2/Ar and air, respectively. Mg-doping decreases the chemical-induced expansion of SBMM remarkably, which ensures good thermomechanical compatibility of SBMM with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte and thus leads to a lower polarization resistance. The LSGM electrolyte (300 μm) supported symmetrical cell with SBMM electrodes delivers a maximum power density of 596 mW cm-2 at 900 °C. These results demonstrate that SmBaMn1.9Mg0.1O5+δ is a highly promising electrode material for SSOFCs.

An easily controllable flash sintering process for densification of electrolyte for application in solid oxide fuel cells

A step-wise current-limiting flash sintering process (SCFS process) was proposed to densify La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. Well-densified microstructures of LSGM samples were obtained at 690 °C under an electric field of 100 V cm−1. Compared with the current-limiting flash sintering process, the spike in power dissipation was avoided, the shrinkage rate of LSGM samples was moderate, and the microstructures of LSGM samples were uniform. The conductivity of LSGM samples sintered via SCFS process at 0.9 A for 30 min reached 0.072 S cm−1 at 850 °C, and this was approximately the same as the value of conventionally sintered LSGM samples at 1400 °C for 10 h. These results proved that SCFS process achieved easy controllability, and it is expected that SCFS process can be applied in industry.