High-performance Solid Oxide Research Articles

Facile synthesis of ceria-based composite oxide materials by combustion for high-performance solid oxide fuel cells

This article proposes the preparation of promising oxide materials with a broad range of applications as electrolytic materials for solid oxide fuel cells (SOFCs). The oxide materials, namely, samarium-doped ceria Sm0.2Ce0.8O (SDC), gadolinium-doped ceria Gd0.2Ce0.8O (GDC), and calcium-doped ceria Ca0.2Ce0.8O (CDC), were prepared through the conventional combustion method with glycerol as a complexing agent. The thermal behavior of the materials was examined through thermogravimetry-differential scanning calorimetry measurements, and their structural and morphological properties were analyzed via X-ray diffractometry (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy confirmed the presence of the metal oxide group in the range of 400–1500 cm−1. Two probe methods were used for electrical measurements. The XRD patterns obtained confirmed that the materials have cubic fluorite structures with an average crystallite size in the range of 26.8–44.7 nm. The ionic conductivities of the ceria samples were measured in the temperature between 300 and 700 °C. The samples consistently showed semiconducting behavior, with SDC exhibiting the highest ionic conductivity of 8.32 × 10−3 S/cm. A maximum power density of 265 mW/cm2 was recorded at 650 °C when SDC was used as an electrolyte.

Pr-Doping Motivating the Phase Transformation of the BaFeO3-δ Perovskite as a High-Performance Solid Oxide Fuel Cell Cathode.

Intermediate temperature solid oxide fuel cells (IT-SOFCs) have been extensively studied due to high efficiency, cleanliness, and fuel flexibility. To develop highly active and stable IT-SOFCs for the practical application, preparing an efficient cathode is necessary to address the challenges such as poor catalytic activity and CO2 poisoning. Herein, an efficient optimized strategy for designing a high-performance cathode is demonstrated. By motivating the phase transformation of BaFeO3-δ perovskites, achieved by doping Pr at the B site, remarkably enhanced electrochemical activity and CO2 resistance are thus achieved. The appropriate content of Pr substitution at Fe sites increases the oxygen vacancy concentration of the material, promotes the reaction on the oxygen electrode, and shows excellent electrochemical performance and efficient catalytic activity. The improved reaction kinetics of the BaFe0.95Pr0.05O3-δ (BFP05) cathode is also reflected by a lower electrochemical impedance value (0.061 Ω·cm2 at 750 °C) and activation energy, which is attributed to high surface oxygen exchange and chemical bulk diffusion. The single cells with the BFP05 cathode achieve a peak power density of 798.7 mW·cm-2 at 750 °C and a stability over 50 h with no observed performance degradation in CO2-containing gas. In conclusion, these results represent a promising optimized strategy in developing electrode materials of IT-SOFCs.

ALD CeO2-Coated Pt anode for thin-film solid oxide fuel cells

Surface modification of electrodes for realizing high electrochemical reactivity and thermal stability is an attractive strategy for high-performance low temperature solid oxide fuel cells (LT-SOFCs). Herein, the atomic-layer-deposited (ALD) CeO2-coated Pt anode structure is fabricated and applied to anodized aluminum oxide (AAO)-based thin-film LT-SOFC. The effect of Pt anode morphology on the infiltration of ALD CeO2 is elucidated. Anode kinetics are improved in the ALD CeO2-coated porous Pt anode cell possibly due to the larger Pt–CeO2 interface density, leading to a decrease in activation resistance by 86%. The maximum power density of the cell with the ALD CeO2-coated porous Pt anode shows 478 mW/cm2; a dramatic improvement by a factor of two compared to the bare porous Pt anode.

Offsetting the thermal expansion mismatch: a new way to high-performance solid oxide fuel cell cathodes

Offsetting the thermal expansion mismatch: a new way to high-performance solid oxide fuel cell cathodes

A simple but effective design to enhance the performance and durability of direct carbon solid oxide fuel cells

The development of high-performance and durable direct carbon solid oxide fuel cells requires that the rate of the Boudouard reaction is enhanced without significantly increasing the fuel cell temperature. Herein, a simple design is proposed to improve the performance of direct carbon solid oxide fuel cells by introducing a heat bar into the anode carbon compartment. This design is evaluated numerically using a 2D model. After model validation, parametric simulations are conducted to compare the performance of direct carbon solid oxide fuel cells with and without the heat bar. The heat bar improves the temperature uniformity of the fuel cell and enhances the local temperature in the carbon compartment. As a result, the Boudouard reaction rate is enhanced by 14% at a voltage of 0.6 V, leading to a performance enhancement of 4.1%. The heat bar significantly reduces the difference between the maximum and minimum temperatures in the fuel cell by 40%, leading to improved durability. This design becomes more effective when using a heat bar with a high thermal conductivity and at lower operating voltages. This study clearly demonstrates that this new design is a simple but effective method for enhancing the performance and durability of direct carbon solid oxide fuel cells.

Low-temperature processing technique of Ruddlesden-Popper cathode for high-performance solid oxide fuel cells

The Ruddlesden-Popper phase lanthanum nickelate, La2NiO4+δ (LNO), offers excellent material properties as a cathode for solid oxide fuel cells (SOFCs). However, taking full advantage of its intrinsic properties is difficult in realistic cells because of its high chemical reactivity with the electrolyte at elevated temperatures. Herein, we demonstrate high-performance SOFCs with an LNO-based cathode fabricated by a low-temperature processing route that suppresses harmful chemical reactions. The sintering capability of the composite cathode composed of LNO and gadolinia-doped ceria (GDC) was enhanced by mixing Fe-based sintering additive with GDC, which formed reliable interfacial bonding with the electrolyte at a temperature ~200 °C below the typical processing temperature. Because no interdiffusion between cathode and electrolyte occurs at such low temperatures, the cell is successfully fabricated without diffusion blocking layer, which simplifies the cell structure and manufacturing process. The cell with the LNO-based cathode outperformed state-of-the-art cells, particularly at lower operating temperatures. These results highlight that the processing parameters strongly affect the electrochemical performance of this LNO-based cathode and must be carefully engineered to fully exploit its superior intrinsic properties.

Tailored Sr-Co-free perovskite oxide as an air electrode for high-performance reversible solid oxide cells

Sr-Co containing perovskite oxides are prospective air electrode candidates for reversible solid oxide cells (RSOCs). However, their efficiencies are limited by Sr segregation and the high thermal expansion coefficient (TEC) of Co-based perovskites. Herein, La0.6Ca0.4Fe08Ni0.2O3−δ (LCaFN) is tailored as an Sr-Co-free perovskite air electrode for highperformance RSOCs. Compared with La0.6Sr0.4Fe0.8Ni0.2O3−δ (LSFN) and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCoF), LCaFN has a high electrical conductivity (297 S cm−1), TEC compatibility (11.2 × 10−6 K−1) and improved chemical stability. Moreover, LCaFN has high oxygen reduction reaction (ORR) activity with a low polarization resistance (0.06 Ω cm2) at 800°C. A single-cell Ni-YSZ/YSZ/gadolinium-doped ceria (GDC)/LCaFN-GDC operated at 800°C yields a maximum power density of 1.08 W cm−2 using H2 as fuel. In the solid oxide electrolysis cell (SOEC) mode, the cell can achieve a current density of approximately 1.2 A cm−2 at 1.3 V with 70% humidity at 800°C. The cell exhibits good reversibility and remains stable in continuous SOEC and solid oxide fuel cell (SOFC) modes. These findings indicate the potential application of LCaFN as an air electrode material for RSOCs.

Stability and activity controls of Cu nanoparticles for high-performance solid oxide fuel cells

Cu-based electrodes could advance solid oxide fuel cells (SOFC) technology due to good electric conductivity and relatively high electrochemical activity among transition metals. However, one of the main challenges for designing anode materials is thermal stability in SOFC operation condition. Herein, a promising anode material decorated with Cu nanoparticles (NPs) was synthesized via in-situ exsolution from La0.43Sr0.37Cu0.12Ti0.88O3-δ (LSCuT) perovskite. Compared to infiltration process, Cu NPs prepared by in-situ exsolution displayed homogeneous nano size distribution on the substrate and excellent thermal stability at 600 °C in H2 atmosphere, for ∼50 h. In addition, we employed electrochemical reduction (ER) at 2.3 V for a few seconds to demonstrate that NPs can be rapidly grown, and the substrate reduced. A single cell with LSCuT anode (10 μm)||ScSZ electrolyte (90 μm) ||LSM-ScSZ cathode (20 μm) exhibits maximum power density of 1.38 Wcm−2 at 900 °C under wet H2. The present study provides possibility of a broad application of thermally stable Cu-based electrodes.

A nanoarchitectured cermet composite with extremely low Ni content for stable high-performance solid oxide fuel cells

ABSTRACT A strategy for improving the stability of nickel-based solid oxide fuel cell (SOFC) anodes via compositional and microstructural engineering is presented. Ni content was reduced to 2 vol%, and nanosized Ni particles were uniformly dispersed in a mixed ionic-electronic conducting matrix comprising gadolinium-doped ceria (GDC) using a thin-film technique. Remarkable stability with no performance deterioration even after 100 reduction-oxidation cycles could be observed for the optimized nanostructured anodes. Cell performance at 500°C was enhanced, exceeding 650 mW/cm2. This study offers valuable insights for enhancing the durability, performance, and productivity of SOFCs.

Reducing d-p band coupling to enhance CO2 electrocatalytic activity by Mg-doping in Sr2FeMoO6-δ double perovskite for high performance solid oxide electrolysis cells

Solid oxide electrolysis cells (SOECs) could convert CO 2 greenhouse gas into valuable fuels and chemicals with high energy efficiency. Unfortunately, the lack of efficient cathode materials obstructs their practical applications. Herein, a promising cathode material with high activity and stability is developed, with the partial replacement of the transition metal Mo by the alkaline-earth metal Mg in the double perovskite structure of Sr 2 FeMoO 6-σ . The replacement of Mo by Mg could not only improve its redox stability, but also enhance the CO 2 electrolysis performance. In the same test environment, the electrolytic current of the LSGM electrolyte-supported single cell with Sr 2 FeMo 2/3 Mg 1/3 O 6−δ as the cathode is almost two times higher than that of the Sr 2 FeMoO 6-σ cathode. Density functional theory with Hubbard correlation reveals that the improved electrocatalytic performance results from the reduced d-p band coupling introduced by the dopant of Mg, which is short of d electrons, favoring the formation of oxygen vacancies for the Mg B -V O -Fe B′ and Fe B -V O -Fe B′ bonds. These newly formed oxygen vacancies have highly catalytic activity toward CO 2 activation and the subsequent dissociation process. Our strategy demonstrates a general method for the development of promising new catalysts for efficient CO 2 reutilization by modulating the electronic structures using d -electron-free elements. • A highly active and stable cathode material for SOECs is successfully obtained. • The formation energy of oxygen vacancy in SFM is obviously reduced by Mg doping. • Mg doping reduces the coupling between the d bands of metals and p bands of oxygen. • The CO 2 activation and the subsequent dissociation process are optimized by Mg doping. • It is a promising method for efficient CO 2 reutilization by using d -electron-free elements.

High-performance direct carbon dioxide-methane solid oxide fuel cell with a structure-engineered double-layer anode

Reduced La0.6Sr0.2Cr0.85Ni0.15O3 (LSCrN) contains exsolved Ni nanoparticles (LSCrN@Ni) and abundant oxygen vacancies. Thus, it is an excellent catalyst for CO2 dry reforming of CH4. To use CH4 directly in solid oxide fuel cells, Ni–Ce0.9Gd0.1O1.95 (GDC) anode-supported cells are fabricated with and without a layer of LSCrN@Ni-20 wt% GDC on top of the anode, which are defined as double anode supported cell (DASC) and conventional anode supported cell (CASC), respectively. They are investigated comparatively by X-ray diffraction, thermal expansion, thermogravimetry, scanning electron microscopy, and electrochemical performance measurement in H2 and 50%CO2–50%CH4 fuels. Both CASC and DASC demonstrate similarly high performance with H2 fuel, the maximum power density is 856 and 822 mW cm−2 at 750 °C, respectively. When 50%CO2–50%CH4 is used, DASC outperforms CASC significantly, showing a maximum power density of 758 mW cm−2 and an on-cell CH4 conversion of 85.5% at 750 °C. Also, DASC demonstrates a stable performance, and the cell voltage and CH4 conversion remain unchanged at 0.65 V and 84% without detectable carbon formation in the anode, while those of CASC decrease monotonously from the beginning with observable carbon formation during a test of 36 h under 400 mA cm−2 at 750 °C.

Subcontinuous 2D La0.6Sr0.4CoO3-δ nanosheet as an efficient charge conductor for boosting the cathodic activity of solid oxide fuel cells

The formation of La0.6Sr0.4CoO3-δ (LSC) nanoparticles on cathode surfaces enhances the charge conductivity, thus enabling high performance in solid oxide fuel cells. However, the 0D structure has limitations such as inefficient charge conducting paths and fading of reaction sites due to the excessive loading level needed to ensure continuity of the nanoparticles. In this study, we report a uniformly grown ultrathin 2D La0.6Sr0.4CoO3-δ nanosheet that can be used to enhance cathode performance. The continuous 2D form more efficiently enlarges the reaction site and has a low loading level compared to the conventional 0D form. The 2D nanosheet structure is ideal for enlarging the charge conducting path because it shows favorable networking within the cathode scaffold compared to other structures. A solid oxide fuel cell using a 2D La0.6Sr0.4CoO3-δ nanosheet exhibits an enhanced power density of 1.2 W cm−2 at 600 °C. This improvement occurs because the nanosheet facilitates charge conducting within the cathode. Our strategy provides a method to build high-performance solid oxide fuel cells using a cathode structure design.

Leveraging catalytic effects of heterointerfaces through multilayering for superior cathode performance

Cathode materials with high activity for oxygen surface exchange are required to achieve high-performance solid oxide fuel cells (SOFCs) at intermediate operating temperatures. LSC (La0.6Sr0.4CoO3-δ) and gadolinia-doped ceria (GDC, Ce0.9Gd0.1O1.95) thin films are alternately stacked to create multilayered cathode structures on yttria-stabilized zirconia (YSZ) electrolytes using pulsed laser deposition. Analysis of the electrochemical impedance spectra of symmetrical cells having varied number of LSC and GDC layers revealed that the existence of additional heterointerfaces leads to catalytic effects on the oxygen exchange properties. This is evidenced by a monotonic enhancement of the oxygen surface exchange coefficient (k*), commensurate with the increasing number of LSC-GDC interfaces. Due to the remarkable enhancement of the oxygen exchange properties, a significant lowering of the polarization resistance with increasing number of LSC-GDC interfaces is achieved. Furthermore, the LSC-GDC multilayers exhibited better long-term stability of the polarization resistance compared to a single-layer LSC in cell tests up to 600 h performed at 600 °C in air. These results highlight the important role of similar heterointerfaces in SOFC structures and provide guidance for the rational design of novel cathode materials with superior electrochemical performance at intermediate temperatures.

Multiple Effects of Iron and Nickel Additives on the Properties of Proton Conducting Yttrium-Doped Barium Cerate-Zirconate Electrolytes for High-Performance Solid Oxide Fuel Cells

Transition metal oxides have been used as sintering aids for proton-conducting barium cerate-zirconates, which are promising electrolyte materials for low-temperature solid oxide fuel cells (SOFCs) and high-performance electrochemical membrane reactors. However, the effects of the additives on properties other than the density of the electrolytes have been ignored. Here, we report our findings that transition metal additives also affect the electrical properties, stability, and even catalytic activity of proton-conducting ABO3-type perovskites. BaCe0.7Zr0.1Y0.2O3-δ (BCZY) is selected as the basic material, and 2 mol % of Ni1-xFex (x range: from 0 to 1.0) oxides and 4 mol % of FeO1.5 are, respectively, added into BCZY to prepare electrolytes of anode-supported SOFCs. All of the electrolytes with additives can be densified after sintering at 1400 °C for 5 h, while BCZY without additive is porous. X-ray diffraction (XRD) spectra show that Ni and Fe are doped into the lattice of BCZY. For the first time, we find a positive function of Fe additive in BCZY that it not only acts as a good sintering aid but also improves the electrical performance and stability of the BCZY electrolyte in CO2 and H2O at reduced temperatures. The cell with the 2 mol % Ni0.5Fe0.5-doped BCZY electrolyte, with an unoptimized cathode, gives a power density of 973 mW cm-2 at 700 °C, 120 mW cm-2 at 450 °C, and 45 mW cm-2 at 350 °C. It operates under a constant current of 800 mA cm-2 at 650 °C for over 200 h, during which the voltage decreases from 0.73 to 0.71 V. A newly discovered densified layer, formed in the cathode during the SOFC operation, may cause the degradation.

Novel PrBa0.9Ca0.1Co2-xZnxO5+δ double-perovskite as an active cathode material for high-performance proton-conducting solid oxide fuel cells

Zn-doped PrBa0.9Ca0.1Co2-xZnxO5+δ (PBCCZx) with x equaling 0, 0.05, 0.10, 0.15, and 0.2, designated as PBCCZ00, PBCCZ05, PBCCZ10, PBCCZ15, and PBCCZ20, respectively, are prepared and investigated in the aspects of crystal structure, thermal expansion behavior, defect chemistry, and electrochemical performance as the cathode of proton-conducting solid oxide fuel cells (H–SOFCs). With the increase of the content of doped Zn, the thermal expansion coefficient of PBCCZx remains unchanged essentially. But the bulk and surface concentrations of oxygen vacancy are increased, and the maximum power density (MPD) of the cells at 750 °C with PBCCZx-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) composite cathodes are improved from 335 (x = 0) to 876 (x = 0.15) mW cm−2. With the PBCCZ15-BZCYYb cathode, the MPD of the cell increases with temperature from 299 mW cm−2 at 600 °C to 876 mW cm−2 at 750 °C with a reduction of cell polarization resistance from 0.68 to 0.04 Ω cm2 accordingly.

Application of a Triple-Conducting Heterostructure Electrolyte of Ba0.5Sr0.5Co0.1Fe0.7Zr0.1Y0.1O3-δ and Ca0.04Ce0.80Sm0.16O2-δ in a High-Performance Low-Temperature Solid Oxide Fuel Cell.

Dual-ion electrolytes with oxygen ion and proton-conducting properties are among the innovative solid oxide electrolytes, which exhibit a low Ohmic resistance at temperatures below 550 °C. BaCo0.4Fe0.4Zr0.1Y0.1O3-δ with a perovskite-phase cathode has demonstrated efficient triple-charge conduction (H+/O2-/e-) in a high-performance low-temperature solid oxide fuel cell (LT-SOFC). Here, we designed another type of triple-charge conducting perovskite oxide based on Ba0.5Sr0.5Co0.1Fe0.7Zr0.1Y0.1O3-δ (BSCFZY), which formed a heterostructure with ionic conductor Ca0.04Ce0.80Sm0.16O2-δ (SCDC), showing both a high ionic conductivity of 0.22 S cm-1 and an excellent power output of 900 mW cm-2 in a hybrid-ion LT-SOFC. In addition to demonstrating that a heterostructure BSCFZY-SCDC can be a good functional electrolyte, the existence of hybrid H+/O2- conducting species in BSCFZY-SCDC was confirmed. The heterointerface formation between BSCFZY and SCDC can be explained by energy band alignment, which was verified through UV-vis spectroscopy and UV photoelectron spectroscopy (UPS). The interface may help in providing a pathway to enhance the ionic conductivities and to avoid short-circuiting. Various characterization techniques are used to probe the electrochemical and physical properties of the material containing dual-ion characteristics. The results indicate that the triple-charge conducting electrolyte is a potential candidate to further reduce the operating temperature of SOFC while simultaneously maintaining high performance.

A brief review of the bilayer electrolyte strategy to achieve high performance solid oxide fuel cells

A brief review of the bilayer electrolyte strategy to achieve high performance solid oxide fuel cells

Barium-doped nickelates Nd2–xBaxNiO4+δ as promising electrode materials for protonic ceramic electrochemical cells

One of the main directions for the attainment of high-performance solid oxide electrochemical cells, including those based on proton-conducting electrolytes, consists in the rational engineering of functional materials. Herein, we examine the use of Nd2–xBaxNiO4+δ (NBNx, 0 ≤ x ≤ 0.4) materials as potential oxygen electrodes for protonic ceramic fuel cells (PCFCs) based on conventional Ba(Ce,Zr)O3-electrolytes. A Ba-doping strategy is proposed for Nd2NiO4+δ for reducing chemical interdiffusion of barium-ions from electrolyte to electrode during long-term operation. It is experimentally confirmed that a moderate Ba-content is beneficial in terms of reducing the quantity of impurity phases formed at the NBNx/Ba(Ce,Zr)O3 interface during deliberately-imposed extreme temperature conditions (1250 °C for 20 h). In addition, materials with x = 0.1 and 0.2 exhibit the highest electrical conductivity with no adverse effects on their thermomechanical properties. Thus, when characterising symmetrical cells in wet air conditions, NBN0.1 and NBN0.2 electrodes demonstrates lower polarisation resistances (down to 1.7 Ω cm2 at 700 °C) compared with NBN0, NBN0.3 and NBN0.4 electrodes. Based on these findings, the Ba-doping of nickelates can be recommended as a promising modification for the design of electrodes having good performance and chemical compatibility.

Lanthanum strontium cobaltite-infiltrated lanthanum strontium cobalt ferrite cathodes fabricated by inkjet printing for high-performance solid oxide fuel cells

Abstract In this study, lanthanum strontium cobalt ferrite cathodes surface-treated with lanthanum strontium cobaltite nanoparticles are synthesized using inkjet printing and their performances are evaluated using intermediate-temperature solid oxide fuel cells. The porous lanthanum strontium cobalt ferrite cathode of an anode-support solid oxide fuel cell is prepared under optimized inkjet printing conditions. The surface treatment is performed by infiltrating a lanthanum strontium cobaltite ink followed by calcination. The lanthanum strontium cobalt ferrite cathode is evenly surface-covered with lanthanum strontium cobaltite nanoparticles, confirming the effectiveness of the inkjet printing for the cathode surface modification. The fuel cell performances are evaluated in the intermediate temperature range of 550–650 °C. The power is significantly improved even with a small addition of the surface lanthanum strontium cobaltite; the enhancement factor reaches the value of five. An electrochemical impedance analysis confirms that the enhanced fuel cell performance is attributed to the reduced polarization impedance, significantly activating the surface catalysis. The addition of lanthanum strontium cobaltite retained the stability of the lanthanum strontium cobalt ferrite cell. However, an excessive amount of lanthanum strontium cobaltite significantly reduces the cell performance.

Energy storage and hydrogen production by proton conducting solid oxide electrolysis cells with a novel heterogeneous design

The proton-conducting solid oxide electrolysis cell is a promising technology for energy storage and hydrogen production. However, because of the aggressive humid condition in the air electrode side, the stability of electrolysis cells is still a concern. In addition, the energy efficiency needs further improvement before its practical application. In this work, considering both stability and energy efficiency, a novel heterogeneous design is proposed for proton-conducting solid oxide electrolysis cells. In this heterogeneous design, the merits of proton-conducting materials can be taken advantage of and the drawbacks of proton-conducting materials can be circumvented synchronously, resulting in better stability and higher efficiency of electrolysis cells. The feasibility and advantages of the heterogeneous design are demonstrated in electrolysis cells with yttrium and zirconium co-doped barium cerate-nickel as the fuel electrode material and yttrium-doped barium zirconate as the electrolyte material by experiment and modeling. The experimental results demonstrate that compared with the conventional homogeneous design, this novel design can efficiently improve the proton conductivity of the yttrium-doped barium zirconate electrolyte (from 0.88 × 10−3 S cm−1 to 2.13 × 10−3 S cm−1 at 873 K) and slightly improve the ionic transport number of the electrolyte (from 0.941 to 0.964 at 873 K), resulting in better electrochemical performance. The electrolysis cells with this design also show good stability. Moreover, the simulation results show that the faradaic efficiency and energy efficiency of electrolysis cells are improved by applying this novel design. These impressive results demonstrate that heterogeneous design is a rational design for high-performance and efficient proton-conducting solid oxide electrolysis cell.