Synthesis and characterization of aluminum-doped perovskites as cathode materials for intermediate temperature solid oxide fuel cells

(Ba_0.5Sr_0.5)(Fe_1-xAl_x)O_3-δ (BSFAx, x = 0–0.2) oxides have been synthesized as novel cobalt-free cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) using a sol-gel method. The BSFAx (x = 0–0.2) materials have been characterized by X-ray diffraction and scanning electron microscopy. The electrical conductivities and electrochemical properties of the prepared samples have also been measured. At 800 °C, the conductivity drops from 15 S cm⁻¹ to 5 S cm⁻¹ when the doping level of aluminum is increased to 20%. The aluminum-doping concentration has important impacts on the electrochemical properties of BSFAx materials. The BSFA0.09 cathode shows a significantly lower polarization resistance (0.26 Ω cm²) and cathodic overpotential value (55 mV at the current density of 0.1 A cm⁻²) at 800 °C. Furthermore, an anode-supported single cell with BSFA0.09 cathode has been fabricated and operated at a temperature range from 650 to 800 °C with humidified hydrogen (∼3vol% H₂O) as the fuel and the static air as the oxidant. A maximum power density of 676 mWcm⁻² has been achieved at 800 °C for the single cell. We believe that BSFA0.09 is a promising cathode material for future IT-SOFCs application.     

A novel post-treatment to calcium cobaltite cathode for solid oxide fuel cells

The calcium cobaltite (CCO) cathodes are post-treated by dipping in the hydrogen peroxide (H₂O₂). The electrochemical properties are investigated by the electrochemical impedance spectra (EIS) and current-voltage test in the symmetrical cell and single cell, respectively. The phase structure and morphology of the cathodes are characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The experiment results show that the mesopores are created on the surface of the cathode particles and the pore channels of the cathode are cleaned up after leaching with 10 wt % H₂O₂, resulting in a remarkable decreasing of the area specific resistance (e.g. only 42.5% of that for the untreated cathode at 800 °C). The single cell with treated cathode is about 2 times the peak power density of the cell with untreated cathode, signifying the post-treating method may be promising.     

A novel core-shell LSCF perovskite structured electrocatalyst with local hetero-interface for solid oxide fuel cells

In this work, a La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF₁₁₃) perovskite core coated by Ruddlesden-Popper phase La_0.6Sr_1.4Co_0.2Fe_0.8O_4-δ (LSCF₂₁₄) thin film to form a LSCF_113-214 core-shell structure cathode is synthesized by Sr²⁺ solution coating method. Its phase composition, lattice structure, electrochemical catalytic activity and full cell performance are investigated. The electrocatalytic activity and stability of the LSCF₁₁₃ cathode are enhanced by in situ formation of LSCF₂₁₄ on the LSCF₁₁₃ surface. The electrochemical performance enhancement is due to the higher catalytic activity of the LSCF₂₁₄ Ruddlesden-Popper phase and the mismatch of the lattice parameters between the LSCF₂₁₄ and LSCF₁₁₃ regions leading to more favorable oxygen vacancy formation and oxygen molecule adsorption. The electrochemical impedance spectrum indicates that LSCF_113-214 electrode has a lower polarization resistance (0.17 Ωcm²) than the LSCF₁₁₃ electrode (0.32 Ωcm²) at 650 °C. And the long term stability of LSCF_113-214 is evaluated with no structure evolution in 400 h test at 600 °C. An anode-supported single cell with doped ceria as the electrolyte is used to evaluate the electrochemical performance of LSCF_113-214, which shows an open circuit voltage of 0.81 V and a maximum power density of 0.57 W cm⁻² at 650 °C.     

Inkjet-printed Ag@SDC core-shell nanoparticles as a high-performance cathode for low-temperature solid oxide fuel cells

This work demonstrates the superior thermostability of silver-based nanoparticle cathodes under continuous solid oxide fuel cell operation by coating the samarium-doped ceria (SDC) thin shell over silver nanoparticles. The Ag-core/SDC-shell (Ag@SDC) nanoparticles prepared by solvothermal synthesis (Ag core diameter = 48 nm; average SDC shell thickness = 2–5 nm) is inkjet-printed on electrolyte substrates as a thin film cathode. The Ag@SDC film survives the 48-h thermal annealing and its most porosities remain visibly un-agglomerated. The results of fuel cell current stability test show that the cell using the Ag@SDC nanoparticle cathode have only 3% of current degradation after 25 h, which is remarkably lower than that of the cell using the bare Ag nanoparticle cathode (96.1%). In addition, the electrochemical performance of the bare silver cathode in oxygen reduction reaction has significantly improved because of the enhanced surface oxygen adsorption/dissociation process provided by the SDC thin shell.     

Transport properties of Ca-doped Ln2NiO4 for intermediate temperature solid oxide fuel cells cathodes and catalytic membranes for hydrogen production

Novel methods were applied in this work to elucidate the structure evolution of Ln_2-xCa_xNiO_4+δ oxides (Ln = La, Pr, Nd; x = 0, 0.3) and study their oxygen mobility. Relationship between cations state, structural, electrical, electrochemical and kinetic properties was revealed. In all doped materials the overall oxygen mobility characterized by Do declined by more than an order of magnitude due to decreasing the interstitial oxygen content and hampering cooperative mechanism of oxygen migration. For La nikelate additional slow diffusion channel appears with D_O 5.4·10⁻¹⁴ cm²/s at 700 K. Correlation of electrochemical and oxygen transport properties was demonstrated. A high electrical conductivity (up to 120 S/cm at 700 K) in Ln_1.7Ca_0.3NiO_4+δ (Ln = Pr, Nd) along with satisfactory oxygen mobility and electrochemical properties makes these materials promising for a wide row of electrochemical applications.     

Review on recent advancement in cathode material for lower and intermediate temperature solid oxide fuel cells application

Solid oxide fuel cell (SOFC) is known for its higher efficiency compared to the other types of fuel cells. Even so, the application of SOFC is hindered by the operational temperature of 800 °C–1000 °C. Lowering the operational temperature below 1000 °C of SOFC becomes the major concern to allow wider applications as well as to increase the durability of the system. Improving the electrochemical performance for SOFC requires further improvement on the main components of SOFC including the air/oxygen electrode namely, the cathode. The manganite, cobaltite, ferro-cobaltite, and ferrite-based materials are known to be used as SOFC cathode, alongside new candidates such as lithiated-based material. Nonetheless, the key challenges for SOFC cathode are to find a suitable material with high electrocatalytic property at lower operational temperature of 400 °C–800 °C. This review paper provides brief information that covered as-mentioned cathode categories, taking into account the microstructural modifications performed via composite, doping, infiltration technique, and synthesis method. Finally, electrolyte-layer free fuel cell (EFFC) is introduced as a new type of SOFC that use natural resources in the fuel cells as a process to reduce its cost.     

基于镧锶锰氧化物基阴极的中温固体氧化物燃料电池的性能优化研究

为了提高基于镧锶锰氧化物(LaxSr1-xMnO3,LSM)阴极的中温固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)的电化学性能,文章利用CuO清扫Ce0.85Sm0.15O2-δ(SDC)晶界的SiO2杂质以提高SDC的离子电导率,制备了复合电解质材料SDC-CuO,并将SDC-CuO和LSM结合成复合阴极材料,随后分别制备了以LSM和LSM/SDC-CuO作为阴极的SOFC,并研究了这两种SOFC的电化学性能。研究结果表明:在开路电压和工作温度为800℃的条件下,LSM/SDC-CuO基阴极的SOFC的极化电阻为0.14Ω·cm2,明显低于LSM基阴极SOFC的极化电阻(0.36Ω·cm2);LSM/SDC-CuO基阴极的SOFC的最大输出功率密度为237 mW/cm2,显著高于LSM基阴极的SOFC的最大输出功率密度(132 mW/cm2)。     

An anode-supported micro-tubular solid oxide fuel cell with redox stable composite cathode

A NiO–YSZ anode-supported hollow fiber solid oxide fuel cell (HF-SOFC) has been fabricated with redox stable (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3−δ–Sm_0.2Ce_0.8O_1.9–YSZ (LSCM–SDC–YSZ) composite cathode. The characterization of NiO–YSZ hollow fibers prepared by the phase inversion method is focused on the microstructure, porosity, bending strength and electrical conductivity. A thin YSZ electrolyte membrane (about 10 μm) can be prepared by a vacuum-assisted dip-coating process and is characterized in terms of microstructure and gas-tightness. The performance of the as-prepared HF-SOFC is investigated at 750–850 °C with humidified H₂ as fuel and ambient air as the oxidant. The peak power densities of 513, 408 and 278 mW cm⁻² can be obtained at 850, 800 and 750 °C, respectively, and the corresponding interfacial polarization resistances are 0.14, 0.29 and 0.59 Ω cm². The high performance at intermediate-to-high temperatures could be attributed to thin electrolyte and proper composite cathode with low interfacial polarization resistance. The low interfacial polarization resistance suggests potential applications of LSCM–SDC–YSZ composite oxides as the redox stable cathode. This investigation indicates that the redox stable LSCM–SDC–YSZ is a promising cathode material system for the next generation YSZ-based HF-SOFC. The results will be expected to open up a new phase of the research on the micro-tubular SOFCs.     

High performance yttria-stabilized zirconia based intermediate temperature solid oxide fuel cells with double nano layer composite cathode

A composite double layer cathode of La_0.6Sr_0.4Co_0.8Fe_0.2O_3?δ/La_0.8Sr_0.2FeO_3?δ (LSCF/LSF) was successfully fabricated by infiltration method to accelerate the sluggish oxygen reduction reaction (ORR) processes. In this composite cathode, both LSF and LSCF layers are uniformly distributed on Yttria-stabilized Zirconia (YSZ) scaffold by optimizing the infiltrating solution components. LSF serves as a protective layer between LSCF and YSZ. The introduction of the LSCF exterior layer has greatly improved cell performance compared with the cell with sole LSF cathode. At 600 °C, the maximum power density of the cell with LSCF/LSF/YSZ composite cathode reaches up to 0.559 W cm^?2. The evolution of the cathode polarization resistance verifies that the ORR activity has been greatly enhanced. Therefore, the results indicate that the high cell performance at intermediate temperatures can be obtained by adopting the LSCF cathode into YSZ-based SOFCs using protective layer and that the infiltration method is a practical way for constructing electrode.     

Electrochemical performances of spinel oxides as cathodes for intermediate temperature solid oxide fuel cells

The spinel-type oxides of (Mn, Co, Cu)₃O₄ prepared via a citric–EDTA acid process were investigated as candidate cathodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). (Mn, Co)₃O₄ spinel oxide shows a phase transition from tetragonal to cubic when the doping amount of cobalt element increases. Their electric conductivities increase with the cobalt content and are enough high for them used as cathodes of IT-SOFCs. A fuel cell with (Mn, Co)₃O₄ spinel cathode was successfully evaluated based on YSZ electrolyte. (Mn, Co)₃O₄ spinel cathodes show good electrochemical activities, demonstrating the feasibility of the spinel oxide being a cathode of IT-SOFC. As copper doped into (Mn, Co)₃O₄ spinel, the P_peak for Cu_0.5MnCo_1.5O₄ cathode rise to 343, 474 and 506 mW cm⁻² at 700, 750 and 800 °C, respectively. The results reveal that the spinel-type oxides are promising cathodes for IT-SOFCs, especially for Cu_0.5MnCo_1.5O₄.     

Novel gradient porous cathode for intermediate temperature solid oxide fuel cell

As a mixed ion electronic conducting oxide, PrBaCo₂O_5+δ is regarded as a promising solid oxide fuel cell cathode. To further improve PrBaCo₂O_5+δ cathode's oxygen reduction reaction activity, porosity graded PrBaCo₂O_5+δ-based cathode is prepared by screen printing technology. With a porous top and a comparative denser base, oxygen ions concentration and oxygen gas concentration in the cathode can be graded distributed. This concentration gradient works as driven force which can enhance the cathode catalytic activity. And distribution of relaxation time analysis is carried out to investigate cathodes performance optimization mechanism, the result shows that gradient porous PrBaCo₂O_5+δ cathode's area specific resistance value is much lower than the traditional homogeneous porosity PrBaCo₂O_5+δ cathode. The scaffold porosity modification promotes the cathode oxygen ions transfer processes without obvious impact on the cathode oxygen surface processes.     

A novel electrolyte for intermediate solid oxide fuel cells

Scheelite-type, La_xCa_1−xMoO_4+δ electrolyte powders, are prepared by the sol-gel process. The crystal structure of the samples is determined by employing the technique of X-ray diffraction (XRD). According to XRD analysis, the continuous series of La_xCa_1−xMoO_4+δ (0 ≤ x ≤ 0.3) solid solutions have the structure of tetragonal scheelite. Their lattice parameters are greater than that of the original sample, and increase with increasing values of x in the La-substituted system. Results of sinterability and electrochemical testing reveal that the performances of La-doped calcium molybdate are superior to that of pure CaMoO₄. La_xCa_1−xMoO_4+δ ceramics demonstrate higher sinterability. The La_0.2Ca_0.8MoO_4+δ sample that achieved 96.5% of the theoretical density was obtained after being sintered at 1250 °C for 4 h. The conductivity increases with increasing lanthanum content, and a total conductivity of 7.3 × 10⁻³ S cm⁻¹ at 800 °C could be obtained in the La_0.2Ca_0.8MoO_4+δ compound sintered at 1250 °C for 4 h.     

Electrochemical performance of novel NGCO-LSCF composite cathode for intermediate temperature solid oxide fuel cells

In this study, a co-dopant CGO was synthesized to produce more efficient cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Neodymium (Nd) was doped into CGO in four different weight ratios in the formula Nd_xGd_0.15Ce_0.85-xO_2-δ (NGCO); the selected percentages for x were 1%, 3%, 5% and 7%. XRD patterns showed pure phase for all synthesized compositions and good compatibility at high temperature under static air with the most common ceramic cathode material in IT-SOFC (La_0·60Sr_0·40Co_0·20Fe_0·80O_2-ä, LSCF). Impedance spectroscopic characterization of symmetrical cells of the composite NGCO-LSCF at different temperatures (650–800 °C in steps of 50 °C) and a frequency range of 0.1–1 MHz in synthetic air revealed interesting results. The lowest polarization resistance (R_p) was achieved for Nd_0.05Gd_0.15Ce_0·80O_2-δ (0.06 Ω cm² at 800 °C, 0.17 Ω cm² at 750 °C, 0.31 Ω cm² at 700 °C, and 0.59 Ω cm² at 650 °C). The expected decrease in R_p was not observed for the sample with higher Nd content (7% Nd). Thus, it can be said that there is a distinction between the compositions Nd_0.05Gd_0.15Ce_0·80O_2-δ and Nd_0.07Gd_0.15Ce_0·78O_2-δ; the co-doping of Nd in NGCO incremented the oxygen ion diffusion path, thereby optimization in the triple phase boundary (TPB) sites was obtained. Furthermore, SEM and TGA measurements were conducted to clarify the reasons of such improvements. This work showed that an NGCO-LSCF composite can be considered as a potential candidate for cathode material for future IT-SOFC applications.     

Novel structured gadolinium doped ceria based electrolytes for intermediate temperature solid oxide fuel cells

Novel three-layered intermediate temperature solid oxide fuel cell (SOFC) electrolytes based on gadolinium doped ceria (GDC) are developed to suppress the electronic conductivity of GDC, to improve the mechanical properties of the cell and to minimize power loss due to mixed conductive nature of GDC. Three different electrolytes are fabricated by sandwiching thin YSZ, ScSZ and ScCeSZ between two relatively thick GDC layers. An electrolyte composed of pure GDC is also manufactured for comparison. NiO/GDC and LSCF/GDC electrodes are then coated on the electrolytes by a screen printing route. SEM results show that it is possible to obtain dense and crack free thin layers of YSZ, ScSZ and ScCeSZ between two GDC layers without delamination. Performance measurements indicate that interlayered thin electrolytes act as an electronic conduction barrier and improve open circuit voltages (OCVs) of GDC based cells.     

Electrochemical performance and stability of nano-structured Co/PdO-co-impregnated Y2O3 stabilized ZrO2 cathode for intermediate temperature solid oxide fuel cells

Palladium (Pd) is an attractive cathode catalyst component for solid oxide fuel cells (SOFCs) that has high tendency to agglomerate during operation at around 800 °C. This work shows that such agglomeration can be inhibited by alloying Co into Pd. PdO, Pd_0.95Co_0.05O, Pd_0.90Co_0.10O, and Pd_0.80Co_0.20O were synthesized and characterized. Powder X-ray diffraction patterns at 750 and 900 °C confirmed that PdO decomposition to Pd which normally occurred at 840 °C was suppressed for Co containing Pd alloys while thermal gravimetric analyses indicated improved redox reversibility of PdO ? Pd conversion for alloys during the thermal cycling between 600 and 900 °C. Scanning electron microscopy images supported these arguments. Pd_0.90Co_0.10+yttria stabilized zirconia (YSZ) electrode (i.e., 10 mol % Co containing PdO-impregnated YSZ electrode) displayed the highest oxygen reduction reaction (ORR) performance and stability. The polarization resistance for ORR on Pd_0.90Co_0.10+YSZ cathode is only 0.088 Ω cm² at 750 °C. During polarization test at 750 °C, Pd_0.90Co_0.10+YSZ cathode showed stable performance for 30 h while the performance of Pd+YSZ cathode degraded after 10 h.     

Functionally-graded composite cathodes for durable and high performance solid oxide fuel cells

A double-layer dual-composite cathode is fabricated and has an ideal cathode microstructure with large electrochemical active sites and enhanced the durability in solid oxide fuel cells (SOFCs). The insertion of a yttria-stabilized zirconia (YSZ)-rich functional layer between the electrolyte and the electrode allows for a graded transition of the YSZ phase, which enhances ionic percolation and minimizes the thermal expansion coefficient mismatch. Electrochemical measurements reveal that the double-layer composite cathode exhibits improved cathodic performance and long-term stability compared with a single-layer composite cathode. A cell with a well-controlled cathode maintains nearly constant interfacial polarization resistance during an 80 h accelerated lifetime test.     

Effect of reduced graphene oxide addition on cathode functional layer performance in solid oxide fuel cells

Solid oxide fuel cells (SOFCs) operating at high temperatures are highly efficient electrochemical devices since they convert the chemical energy of a fuel directly into heat and electrical energy. The electrochemical performance of an SOFC is significantly influenced by the materials and microstructure of the electrodes since the electrochemical reactions in SOFCs take place at three/triple phase boundaries (TPBs) within the electrodes. In this study, graphene in the form of reduced graphene oxide (rGO) is added to cathode functional layer (CFL) to improve the cell performance by utilizing the high electrical properties of graphene. Various cells are prepared by varying the rGO content in CFL slurry (1–5 wt %), the number of screen printing (1–3) and the cathode sintering temperature (900–1100 °C). The electrochemical behavior of the cells is evaluated by electrochemical performance and impedance tests. It is observed that there is a ∼26% increase in the peak performance of the cell coated with single layer CFL having 1 wt % graphene and 1050 °C sintering temperature, compared to that of the reference cell.     

Porous YFe0.5Co0.5O3 thin sheets as cathode for intermediate-temperature solid oxide fuel cells

In this work, porous YFe_0.5Co_0.5O₃ (YFC) thin sheets were synthesized by citric acid method. The crystal structure, morphology, thermal expansion, electrical conductivity, and electrochemical properties of YFC were investigated to evaluate it as a possible cathode on BaZr_0.1Ce_0.7Y_0.2O₃ (BZCY) electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). An orthorhombic perovskite structure was observed in YFC. The conductivity of YFC is 183 S cm ^?1 at 750 °C in air. The coefficient of thermal expansion of composite cathode YFC-BZCY is closer to BZCY electrolyte than YFC. The composite cathode represents a relatively low polarization resistance (R_p) of 0.07 Ω cm² at 750 °C in air due to the porous thin sheet-like cathode. The oxygen reduction reaction process and the reaction activation energy of cathode were also analyzed. An anode-supported cell of NiO-BZCY∣BZCY∣YFC-BZCY is fabricated by a simple method of co-pressing. The power density of the cell is 303 mW cm^?2 at 750 °C as the thickness of electrolyte is 400 μm. The results suggest that YFC is a promising cathode candidate for IT-SOFC.     

Perovskite-related intergrowth cathode materials with thin YSZ electrolytes for intermediate temperature solid oxide fuel cells

The electrochemical performances of solid oxide fuel cells with thin yttria-stabilized zirconia (YSZ) electrolytes and YSZ/Ni anodes were studied with two intergrowth oxides cathodes (Sr_2.7La_0.3Fe_1.4Co_0.6O_7−δ and LaSr₃Fe_1.5Co_1.5O_10−δ) and the results compared to a related perovskite cathode (La_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ). It was found that cells produced with LaSr₃Fe_1.5Co_1.5O_10−δ exhibited peak power densities close to 0.75 W cm⁻², despite the relatively modest electrical conductivity of this compound. In contrast, cells produced with Sr_2.7La_0.3Fe_1.4Co_0.6O_7−δ and La_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathodes both exhibited peak power densities of less than 0.4 W cm⁻². The greater performance for the cells produced with LaSr₃Fe_1.5Co_1.5O_10−δ may be attributed to a higher catalytic activity for this compound or to an improved adhesion of the cathode to the interlayer/electrolyte.