Low-temperature Solid Oxide Fuel Cells Research Articles

Advances in low-temperature solid oxide fuel cells: An explanatory review

This review article explores recent advancements and potential advantages of low-temperature solid oxide fuel cells (LT-SOFCs), offering a comprehensive overview of critical developments in the field. It highlights the significance of utilizing oxygen ion conducting electrolytes such as La0.8Sr0.2Ga0.8Mg0.2O3–type (LSGM) perovskties and yttria-stabilized zirconia (YSZ) in LT-SOFCs, emphasizing their role in facilitating efficient oxygen transport at lower temperatures. Furthermore, the review discusses the importance of electrode tailoring at the nanoscale using techniques like sol-gel and pulsed laser deposition (PLD), which have been shown to enhance the oxygen reduction reaction (ORR) at the cathode, thereby improving overall cell performance. One of the key focal points of the review is the exploration of perovskite structures and their imperative characteristics in LT-SOFCs. Specifically, it elucidates how oxygen defects within perovskites contribute to the migration of oxygen ions, consequently augmenting electrical conductivity within the cell. This discussion underscores the significance of understanding the fundamental principles governing ion transport mechanisms in electrolyte materials, which is crucial for the development of next-generation LT-SOFCs with improved efficiency and performance. Moreover, the review highlights recent advancements in the fabrication of nanoscale electrolyte films, which have shown promising results in reducing series resistance and enhancing cell performance at lower temperatures. Techniques such as atomic layer deposition (ALD), and spark plasma sintering (SPS) are discussed in the context of fabricating these nanoscale membranes, underscoring their potential for revolutionizing LT-SOFC technology. Overall, this review consolidates recent research findings and technological advancements in the field of LT-SOFCs, shedding light on the novel approaches and strategies employed to overcome existing challenges and propel the development of more efficient and practical fuel cell systems. By synthesizing key insights and highlighting future research directions, this review serves as a valuable resource for researchers and engineers working towards the advancement of LT-SOFC technology.

Ni/GDC Fuel Electrode for Low-Temperature SOFC and its Aging Behavior Under Accelerated Stress

The microstructural integrity of Ni-based fuel electrodes is important for long-term solid oxide fuel cell (SOFC) operation. Degradation due to microstructural changes such as Ni-agglomeration, coarsening, and densification must be prevented by an appropriate microstructure. Here, the performance of four types of nickel-ceria-based fuel electrodes, which differ concerning layer sequence and manufacturing processes, was evaluated by electrochemical impedance spectroscopy at the nominal operating temperature of 600 °C. Electrodes produced through screen-printed GDC exhibited an acceptable polarization resistance (0.260 Ωcm2), whereas electrodes with an additional printed Ni/GDC layer demonstrated inferior performance (0.550 Ωcm2). Electrodes formed through infiltration of GDC into the printed GDC-layer displayed unreproducible performance values ranging from 0.16 to 1.20 Ωcm2 despite similar processing. Conversely, electrodes with an extra layer of GDC infiltrated into the Ni-backbone exhibited good performance (0.195 Ωcm2) and stability. Accelerated degradation tests under OCV at increased operating temperatures of 700 and 900 °C were performed on the sample based on a GDC infiltrated Ni-backbone that performed best among reproducible samples. The polarization resistance at 600 °C recorded at the beginning and the end of life increased by up to 100%. Microstructural analysis of the electrodes at different aging states revealed strong microstructural changes of fine-infiltrated GDC structures and Ni agglomeration at higher operating temperature.

Optimizing Bilayer Electrolyte Thickness Ratios for High-Performing Low-Temperature Solid Oxide Fuel Cells

Abstract Bilayer electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs) offer the potential for higher power density by lowering the ohmic area specific resistance (ASR) and increasing the open circuit voltage (OCV) of mixed ionic/electronic conducting (MIEC) type electrolyte (e.g., GDC). However, optimizing the bilayer electrolyte thickness ratio is essential to achieve high power densities at low-temperatures (650-500℃). Herein we provide a systematic study of GDC/YCSB bilayer thickness ratios on anode-supported LT-SOFCs. In all cases the bilayer maximum power density (MPD) is higher than single-layer GDC based cells with reduced ohmic ASR values. Specifically, a high MPD of ~1 W/cm2 at 650℃ was achieved on a GDC(20 μm)/YCSB(12 μm) bilayer electrolyte based SOFC, which is 62% higher than single-layer GDC based SOFC (0.64 W/cm2) operating on humidified H2 as fuel. Such enhancement is due to the 9.3% improvement in OCV and 36% reduction in ohmic ASR values with the addition of the YCSB layer. The reduction in ohmic ASR of the bilayer electrolyte SOFCs is due to an increase of GDC electrical conductivity caused by the lower pO2 at the YCSB/GDC interface which must be considered in optimizing the thickness ratio of the bilayer electrolyte for achieving higher power density LT-SOFCs.

Semiconductor ionic Cu doped CeO2 membrane fuel cells

Operation of low-temperature solid oxide fuel cells (LT-SOFCs) in the range of 300–500 °C has emerged as a promising technology and desired operational temperature for clean and efficient energy conversion. However, the lack of suitable electrolyte materials for these temperatures presents a significant challenge. In this article, a novel approach is proposed to address the hurdle of operational temperature by tailoring copper-doped cerium oxide, Cu0.1Ce0.9O2 as a semiconductor ionic membrane (SIM) to act as an electrolyte in a cell. The Cu0.1Ce0.9O2 formed a single-phase cubic fluorite structure. As a SIM, it shows enhanced ionic conductivity and reduced electrolyte/electrode polarizations, therefore achieved good fuel cell performance and electro-kinetics, reaching a power density of 515 mW/cm2 at 500 °C, with an ionic conductivity exceeding 0.1 S/cm. The detailed investigation shows dominant protonic conduction (H+) behavior in the Cu0.1Ce0.9O2 membrane. Interesting phenomenon of coupling effect elaborated through the distribution of relaxation time (DRT) analysis depicted to understand the romance of protons and electrons conduction mechanism. These advancements lead to Cu0.1Ce0.9O2 as a new type of SIM in LT-SOFCs, emphasizing the need for further research and development in this promising field to unlock the SIM and fuel cell potential.

Na0.6Co3O4- La/Pr co-Doped Ceria as Semiconductor-Ionic Heterostructure Material for Fuel Cell Application

Functional Sodium-doped cobalt oxide (Na0.6Co3O4, NCO) was incorporated to regulate and improve the electrochemical performance of La/Pr co-doped ceria (LCP) electrolytic materials with good operative stability, forming an p-n heterostructure electrolyte (LCP-NCO) for low-temperature solid oxide fuel cell (LTSOFC) application. LCP-NCO is a new potential semiconductor-ionic material, achieving a maximum power density of 1075 mW cm−2 along with a high open-circuit voltage of 1.061 V at 520 °C. Scanning electron microscopy combined with transmission electron microscopy unveiled the crystallographic microstructure of heterostructure interface between LCP and NCO. Raman spectra and Fourier transform infrared spectroscopy spectra were analyzed to distinguish the functional groups and the vibrational properties. Ultraviolet–visible absorption and ultraviolet photoelectron spectroscopy have determined the accurate band edge positions of LCP and NCO and p-n heterojunction nature. Built-in electric field in semiconductor heterostructure and more oxygen vacancies created through the variation of Co3+/Co2+ ratio in LCP-NCO during the fuel cell test, contributed to the enhanced ionic transport. Characteristic of competent conductivity of 0.26–0.42 S cm−1 at 400 °C–520 °C, and the improved cell duration, revealed that the LCP-NCO as a hybrid oxygen ion and protonic conductor would be a potential electrolyte for LTSOFC.

Enhancement of Performance and Sulfur Tolerance of Ceria-Based Fuel Electrodes in Low Temperature SOFC

The trend of operating the solid oxide fuel cell at significantly lower operation temperatures enables the application of electrodes with finer microstructure or even nanostructured electrodes with increased active surface and enhanced performance. To maintain the high performance in hydrocarbon fuels commonly impurified with sulfur compounds, a required sulfur tolerance has to be maintained. In this study we compare performance and H2S-poisoning of four ceria-based electrodes: conventional Ni/Ce0.9Gd0.1O2−δ cermets and sub-μm scaled Ce0.8Gd0.2O2−δ -electrodes with and without infiltrated nickel. Symmetrical cells were operated in a hydrogen/steam/nitrogen gas mixture with and without minor amounts of H2S at 600 °C. The performance is analyzed by electrochemical impedance spectroscopy. The distribution of relaxation times is applied to deconvolute the electrochemical processes followed by a complex nonlinear least square fit to quantify the loss processes and the impact of sulfur. Whereas two different Ni/Ce0.9Gd0.1O2−δ cermet electrodes exhibit polarization resistances at 600 °C without/with 0.1 ppm H2S of 2.89/5.56 Ωcm2 and 2.15/2.75 Ωcm2, the single phase Ce0.8Gd0.2O2−δ electrode reaches 0.98/2.37 Ωcm2. With an infiltration of Ni-nitrate forming nickel nanoparticles on the gadolinia-doped ceria-surfaces, the ASR could be drastically reduced to 0.32/0.37 Ωcm2.

In Situ Phase-Transformation Forming a Bicontinuous (Ni, Co, Ti, and Al)-Oxide/Li2CO3 Interpenetrating Network Electrolyte for Solid Oxide Fuel Cells.

Designing heterogeneous electrolytes with superior interface charge transfer is promising for low-temperature solid oxide fuel cells (LT-SOFCs). However, a rational construction with optimal interfaces to maximize ionic conduction remains a challenge. Here an in situ phase-transformation strategy is demonstrated to prepare a highly conductive heterogeneous electrolyte. A pristine LiNiO2-TiO2 nanocomposite precursor undergoes chemical reactions and phase-transformation upon heating and feeding H2, destroying the original phases, and forming new species, including an amorphous Li2CO3 scaffold within a (Ni, Co, Al, and Ti)-oxide (NCAT) matrix. It creates an intertwining and continuous network inside the electrolyte with plentiful interfaces. The in situ formed NCAT/Li2CO3 heterogeneous electrolyte displays superior ionic conductivity and impressive fuel cell performance. This work emphasizes the potential of rational heterogeneous structure design and interface engineering for LT-SOFC electrolyte through an in situ phase-transform approach. The generated interfaces enhance ion transport, presenting an opportunity for further optimizing electrolyte candidates, and lowering the operating temperatures of SOFCs.

Thermally Stable Silver Cathode Covered by Samaria-Doped Ceria for Low-Temperature Solid Oxide Fuel Cells.

Samaria-doped ceria (SDC) overlayers were deposited on Ag cathodes by sputtering. The SDC sputtering time was varied to investigate the properties of the Ag-SDC overlayer cathode-coated fuel cells depending on the thickness of the SDC overlayers. Among the fabricated fuel cells, Ag with a 10-nm-thick SDC overlayer (Ag-SDC10) cathode-coated fuel cell exhibited the highest peak power density of 6.587 mW/cm2 at 450 °C, showing higher performance than a pristine Pt-coated fuel cell. Moreover, electrochemical impedance spectroscopy revealed that the Ag-SDC10 cathode-coated fuel cell significantly mitigated polarization loss originating from enhanced oxygen reduction reaction kinetics compared to the pristine Ag-coated fuel cell.

Structural and ionic conduction study of Sm–Pr co-doped ceria electrolyte materials for LT-SOFC applications

Samarium praseodymium (Sm–Pr) co-doped ceria was synthesized by the co-precipitation technique as an electrolyte for low-temperature solid oxide fuel cell (LT-SOFC) applications. The structural, morphological, compositional, and electrical characterization of the synthesized samples were evaluated via x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and impedance spectroscopy. The generation of a single-phase fluorite structure of co-doped ceria without any secondary phases has been verified by XRD analysis, exhibiting the successful incorporation of Sm and Pr ions into the ceria lattice. Vegard's law is utilized for Pr redox behavior explaining the variation in lattice constant values. SEM pictures show that the co-doped ceria powder has a homogeneous and well-dispersed microstructure, and has enhanced particle size. The impedance spectroscopy results indicate that Sm–Pr co-doped ceria has much higher ionic conductivity than single-doped ceria. The highest amount of ionic conductivity (σionic) for the composition Ce0.80Sm0.10Pr0.10O2−δ recorded as 2.12×10−2S/cm at 500°C, and 6.19×10−2S/cm at 750°C with the lowest activation energy Ea=0.48eV, which has been not reported earlier. Sm and Pr are chosen as dopants because of their capacity to generate oxygen vacancies and improve ceria's ionic conductivity. This study contributes to the enhancement in the ionic conductivity of co-doped ceria by co-precipitation technique and the temperature-dependent frequency exponent factor "s" is also explored to comprehend the conduction mechanism of the prepared samples.

Solution combustion-based synthesis of NiO-GDC and NiO-SDC nanocomposites for low-temperature SOFC

In the last decades, NiO-GDC and NiO-SDC composites have emerged as interesting anodic materials for low and intermediate-temperature Solid Oxide Fuel Cells (SOFC) due to their high electrical conductivities and low activation energies. In this work, we report a simple and efficient Solution Combustion Synthesis (SCS) procedure for fabricating NiO-GDC and NiO-SDC nanocomposites with attractive physical properties for applications in low-temperature SOFC. The nitrate-fuel combustion method using citric acid as organic fuel was chosen due to its relatively low cost and good efficiency. Their potential electrical and mechanical performance for competitive SOFC anode technologies was assessed by characterizing disk-like compacted powders obtained by SCS. Two structurally optimized NiO-GDC and NiO-SDC disks were considered for the study of these properties, which presented good porosity and compaction degree. Vickers hardness tests show the good mechanical properties of both samples, achieving maximum hardness values of 4.7–6.7 [GPa] and validating the efficiency of the used compaction process. Electrical conductivity studies suggest an insulating-like behavior for both samples, evidenced by an increase in conductivity as the temperature increases. Good conductivities and low activation energies about of 10−2 [S/cm] and 0.18 [eV] were estimated for a low-temperature operation regime (400–600 °C), respectively, representing a highly competitive performance concerning similar composites typically reported in the literature. Results show the efficiency of our fabrication procedures to produce efficient and competitive NiO-GDC and NiO-SDC composites with projections for future large-scale manufacturing of low-temperature SOFC anodes.

Preparation and Characterization of Nanocomposite Perovskite Cathode Materials La0.3Sr0.7Fe0.4Ti0.6O3‐δ (LSFT) for Low‐Temperature SOFCs with Incorporation of Graphene Oxide (GO)

AbstractThe porous and mixed ionic electronic cathode conductor plays a vital role in the efficient working of low‐temperature solid oxide fuel cells. Perovskite composite cathode material La0.3Sr0.7Fe0.4Ti0.6O3‐δ (LSFT) is synthesized using the sol–gel method. Graphene oxide (GO) is integrated in 1 and 1.5 wt.% into the perovskite LSFT cathode to use as a cathode for low‐temperature solid oxide fuel cell (LT‐SOFC). Crystal structure analysis is studied by XRD and the crystalline size of samples is determined in the range of 103–73 nm. SEM analysis is used to characterize homogeneous and porous morphology. The FTIR spectral analysis is examined for proposed nanocomposite cathode materials. The electrical conductivities are carried out by four probe method in air atmosphere in the temperature range 300–600 °C and enhanced conductivity is obtained 7 Scm−1 for LSFT‐1.5 wt.% GO sample. For the same sample, a minimum value of area‐specific resistance (ASR) of 0.02 Ωcm2 is obtained. The performance of three‐layer fuel cells is tested by supplying H2 fueled at the anode and oxygen at the cathode terminal of the cell and peak power density is determined to be 362 mWcm−2 for GO incorporated fuel cell. The prepared cathode can be proposed as a potential candidate for low‐temperature solid oxide fuel cells.

(Digital Presentation) Study of Structural and Ionic Conductivity Property in Gd3+ and Sm3+ Co-Doped Ceria for Low Temperature SOFC Electrolyte Application

In recent years, fuel cells have become one of the most efficient and clean energy conversion devices. Due to their use in stationary as well as mobile power applications, they have also gained a lot of attention in this field. From all other fuel cells, SOFC has several advantages such as absence of liquid component, vibration free working, fuel and many more. However, two most crucial aspects of SOFC are operating temperature and the choice of electrolyte materials. It is the most efficient fuel cell with a setback in its elevated operating temperature, as high as around 800℃ -1000℃. To achieve high ionic conductivity in a SOFC, it is very important to tailor the electrolyte properties, simultaneously reducing the operating temperature.Conventionally, Yttria Stabilized Zirconia (YSZ) has been the most studied electrolyte material with a limiting factor of its high operating temperature. Doped Ceria has been one of the most explored alternatives of YSZ, which not only reduces the operating temperature but also enhances the ionic efficiency due to its electro-catalytic property. The double valency property of CeO2 occurring due to oxygen non-stoichiometry (CeO2-δ), generates oxygen vacancies making it a potential electrolyte material. Rare Earth (RE) dopants like Gd3+ and Sm3+ have reported to have high ionic conductivity at low temperatures. In the present study, synthesis of Sm-Gd- co-doped CeO2 by wet chemical route to ensure homogenous distribution, with the stoichiometry Ce1-a Gda-y Smy O2-0.5δ where a=0.20 and 0≤y≤a. It was prepared by modified co-precipitation method wherein, no additional water has been utilized during the co-precipitation process in order to minimize the particle agglomeration. Phase pure particles were obtained by calcining the precipitants at 650℃ in air and the green body made from it were sintered in air at elevated temperature of 1450 °C to achieve high density pellet. XRD and Raman spectroscopy confirmed successful substitution of both dopants and presence of single-phase cubic structure of the nanoparticles. The surface morphology was studied using FESEM which showed highly dense structure with more than 97% density. The electrochemical impedance spectroscopy (EIS) of the sintered pellets in the temperature range of 400-700℃, showed much higher conductivity then singly doped Ceria . Figure 1

Effects of alumina addition on electrical properties of alumina-toughened zirconia for application in low- and intermediate-temperature solid oxide fuel cells

One of the priorities in the field of hydrogen energy is the development of intermediate-temperature (IT-SOFCs) and low-temperature solid oxide fuel cells (LT-SOFCs), which are capable of highly efficient operation in the range of 500–800 °C. The currently applied 8-YSZ electrolytes are expected to be replaced by one based on tetragonal zirconia (3Y-TZP), which is characterized not only by high ionic conductivity below 700 °C, but also significantly higher mechanical strength. One of the candidates is alumina-toughened zirconia (ATZ) with extraordinary mechanical properties (flexural strength of up to 1 GPa and outstanding fracture toughness (KIc) in excess of 10 MPa m0.5). A series of composites with a nanometric alumina content of 2.3, 10, and 20 vol% were obtained and investigated to evaluate the effects of aluminum addition on the electrical properties of the materials in relation to their microstructure, chemical and phase composition. Measurements performed by means of electrochemical impedance spectroscopy over the range of 300–650 °C showed that the total electrical conductivity of the obtained ATZ samples decreased slightly with increasing content of alumina inclusions and it was around one-third of an order of magnitude lower than that of the reference 3Y-TZP sinter prepared from the commercially available oxide powder containing 3 mol% of yttrium oxide (TOSOH). This is a consequence of the fact that ATZ sinters exhibited a lower specific conductivity of grain boundaries than 3Y-TZP whilst having comparable electrical conductivity of grain interiors. The total electrical conductivity values determined for the ATZ sinters at 700 and 800 °C are approximately the same as the electrical conductivity of 3Y-TZP, and they can therefore be considered a viable alternative to 8-YSZ electrolytes in applications such as IT-SOFCs or LT-SOFCs.

Boosting oxygen reduction activity and CO2 resistance on bismuth ferrite-based perovskite cathode for low-temperature solid oxide fuel cells below 600 °C

Developing efficient and stable cathodes for low-temperature solid oxide fuel cells (LT-SOFCs) is of great importance for the practical commercialization. Herein, we propose a series of Sm-modified Bi0.7−xSmxSr0.3FeO3−δ perovskites as highly-active catalysts for LT-SOFCs. Sm doping can significantly enhance the electrocatalytic activity and chemical stability of cathode. At 600 °C, Bi0.675Sm0.025Sr0.3FeO3−δ (BSSF25) cathode has been found to be the optimum composition with a polarization resistance of 0.098 Ω cm2, which is only around 22.8% of Bi0.7Sr0.3FeO3−δ (BSF). A full cell utilizing BSSF25 displays an exceptional output density of 790 mW cm−2, which can operate continuously over 100 h without obvious degradation. The remarkable electrochemical performance observed can be attributed to the improved O2 transport kinetics, superior surface oxygen adsorption capacity, as well as O 2p band centers in close proximity to the Fermi level. Moreover, larger average bonding energy (ABE) and the presence of highly acidic Bi, Sm, and Fe ions restrict the adsorption of CO2 on the cathode surface, resulting in excellent CO2 resistivity. This work provides valuable guidance for systematic design of efficient and durable catalysts for LT-SOFCs.

PEALD Ru-decorated Ni-SDC cermet anode for utilizing methane fuel in low-temperature SOFCs

Highly active catalytic anodes with high thermal stability and carbon tolerance are essential for high performance and stable operation of hydrocarbon-fueled solid oxide fuel cells (SOFCs). In this study, we report on the design and fabrication of ruthenium (Ru) nanoparticles deposited through the plasma-enhanced atomic layer deposition (PEALD) onto Ni-SDC anode for the methane-fueled low-temperature SOFCs. A decoration of ∼ 4 nm-thick Ru to the Ni-SDC anode reduced the activation resistance by 31 %, and promoted the carbon removal process, mitigating carbon coking at the anode. Such an improvement seems to be due to the facilitation of methane reforming and/or oxidation reactions at intimate Ni-Ru and SDC-Ru interfaces by plasma-based process, which is of practical importance considering the use of cermet anode for SOFCs.

Enhancing densification and electrical properties of Sm-doped ceria with Ca and Zn as sintering aids

Ca and Zn were incorporated as sintering aids in Sm-doped ceria resulting in materials of general formula A0.02Sm0.08Ce0.9O1.94 for their use as solid electrolytes in Low Temperature-SOFCs. The synthesis was performed with 20 hours of mechanochemical ball-milling and XRD analyses revealed a cubic fluorite-like structure of the ceria and a promoted crystallinity with heat treatments up to 1500 °C. SEM images showed microstructures with larger grain sizes and less remnant porosity in the Zn-containing systems. Zn improved the relative density (92.95 %) of SDC when sintered at low temperatures such as 1200 °C, however, both Ca and Zn increased the electrical conductivity, with the highest value of 8.39 × 10−2 S/cm at 650 °C for the Zn-SDC system. Pure SDC and Ca-SDC resulted in lower relative densities and enhanced thermal insulation properties when sintered at 1200 °C.

Medium-entropy oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ as promising electrolyte for low-temperature solid oxide fuel cells

The development of high-performance electrolyte is crucial for low-temperature solid oxide fuel cells (LT-SOFCs). Traditional ceria-based materials such as Gd0.1Ce0.9O2-δ (GDC) are promising electrolytes in intermediate-temperature range but their performance drop rapidly with decreasing temperature. Recent advances proposed a new concept for SOFC materials design in terms of entropy, indicative of enormous potential. Herein, a medium-entropy ceria-based oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ (CSLG25) is developed via entropy engineering and evaluated as potential electrolyte for LT-SOFCs by comparing with low-entropy electrolyte GDC. The effects of configuration entropy on crystal structure, oxygen vacancy, electrochemical performance, and proton transport characteristic of the materials are systematically investigated. It is found the CSLG25 cell device exhibits a remarkable power density of 747 mW cm−2 at 520 °C, along with a superionic conductivity of 0.1534 S cm−1. Further study via XPS and Raman technology reveals that the higher entropy of CSLG25 creates more oxygen vacancies and contributes to fast proton transport, which leads to promising fuel cell performance at 430–520 °C. The CSLG25 cell device also delivers the 55.5 h durability performance at 520 °C. This study thus provides a novel electrolyte material for LT-SOFCs and points out a feasible entropy engineering strategy for developing ionic conductors.

Highly conductive and stable ErxCe0.05Bi0.95-xO1.5+δ solid electrolytes for low-temperature solid-oxide fuel cells

Low-temperature solid oxide fuel cells (LT-SOFCs) are key to meeting China's dual-carbon goal, but existing solid electrolytes suffer from low conductivity. Here, a highly conductive Er/Ce co-doped bismuth oxide (ErxCe5SB, x = mol%) electrolyte is reported. Synthesis is achieved by reverse coprecipitation, and ErxCe5SB has a cubic fluorite structure with a uniform particle size of 100–200 nm, although Er5Ce5SB and Er10CeSB contain a minor rhombohedral phase. Dense pellets (relative density: 93 %) are formed after sintering at 800 °C for 6 h, and the lattice constants decrease with the increase in erbium dopant concentration. Er20Ce5SB had an impressive ionic conductivity of 0.016 S cm-1 at 450 °C. Notably, after being annealed at 600 °C for 4032 h, Er20Ce5SB showcased a commendable stability in conductivity, measuring approximately 0.09 S cm−1, with only a minor drop in its conductivity value. Even after such extended annealing, Er20Ce5SB retained its pure cubic phase structure, devoid of any impurities. Oxygen-ion ordering yields a superstructure, as observed by HR-TEM. Because of its high conductivity and long-term stability, Er20Ce5SB is a promising LT-SOFC electrolyte material.

Superionic conduction of self-assembled heterostructural LSCrF-CeO2 electrolyte for solid oxide fuel cell at 375–550 °C

Insufficient ionic conductivity of electrolyte materials and high manufacturing costs create bottlenecks in the commercialization of low-temperature solid oxide fuel cells (LT-SOFCs). Developing the semiconductor-ionic electrolyte represents a new research strategy for high-performance LT-SOFCs because of their attractive ion conduction and associated low polarization loss. In this study, a self-assembly approach is demonstrated by incorporating ABO3 perovskite La0.7Sr0.3Cr0.5Fe0.5O3-δ (LSCrF) into the fluorite structure CeO2, for developing 1LSCrF-xCeO2 composite as semiconductor-ionic heterostructure for LT-SOFCs with superior electrochemical efficiency at the temperature below 550 °C and even down to 370 °C over unmodified and mechanically mixed samples. Self-assembly enables abundant nanoscale hetero-interfaces accompanied by widely distributed oxygen vacancies, which leads to the superior ionic conductivity of 0.018–0.112 S cm−1, lower activation energy of 0.54 eV and better peak power density of 136–735 mW cm−2 over control samples at 370–550 °C, and stable operation for 50 h of resultant LT-SOFCs under a galvanostatic mode. This work highlights the important role of self-assembly in designing heterostructural semiconductor based electrolytes for high-performance LT-SOFCs.

A dual-layer electrolyte of CuFeO2–ZnO for low-temperature solid oxide fuel cells

Semiconductor-based heterostructure composites with high ionic conductivity have gained considerable attentions as potential electrolytes for low temperature solid oxide fuel cells (LT-SOFCs). Thereinto, the p-n junction is designed for the built-in electric field, thus avoiding short-circuiting occurrence and implementing fuel cell functionality. Herein, a novel strategy to construct the dual-layer electrolyte using p-type CuFeO2 (CFO) and n-type ZnO respectively as individual layer is proposed. Electrochemical studies find that the fuel cell performance is significantly correlated with the weight ratios of CFO and ZnO phases. The device based on 3CFO-7ZnO (CFO in 30 wt% and ZnO in 70 wt%) electrolyte exhibits an open circuit voltage (OCV) of 1.06 V and a peak power density (PPD) of 557 mW cm−2 at 550 °C, apparently superior to both of the direct mixture of CFO-ZnO nanocomposite (468 mW cm−2) and single-phase ZnO electrolytes (300 mW cm−2) at the same operating temperature. Further investigations on energy band structure and rectifying characteristics related to the CFO and n-type ZnO indicate the existence of p-n junction. This work proposed a new method to design effective dual-layer semiconductor-based electrolytes for LT-SOFC.