Intermediate Temperature Solid Oxide Fuel Cells Research Articles

Cu-Content La1−XSrxNi1−YCuyO3−Δ Perovskites As Cobalt-Free Cathode Materials for High-Performance It-SOFCs

Solid Oxide Fuel Cells (SOFCs) are one of the most attractive energy conversion and storage devices, which can be applied for decentralized energy applications. However, the high operating temperature making SOFCs still unmarketable, which indicates that lowering the working temperature of SOFCs while still maintaining a high-power output is very crucial. For Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs), new cathode materials with high electrocatalytic activity and stability are necessary to provide a stable and high performance of cells. Perovskite-structured oxide (ABO3−δ) is one group of the most interesting material candidates for IT-SOFCs, presenting great potential in chemical composition modifications, yielding the design and gain of desired physicochemical and electrochemical properties [1]. The simple perovskite LaCuO3 is one of the well-studied Cu-content oxides with a high conductivity (106 S·cm−1), but it can be hardly obtained and suffers with stability issues in air [1, 2]. To stabilize the perovskite structure and to improve electrochemical properties of Cu-content oxides A-site and B-site modification strategy can be applied. It has been noted that Cu- and Ni-containing LaNi0.5Cu0.5O3−δ simple perovskite possesses low cathodic polarization of 0.056 Ω·cm2 at 800 °C, and a high power output of 870 mW·cm−2 at 900 °C [1, 3]. The generation of oxygen vacancies by strontium doping contributes to the increase of ionic conductivity component, and the Sr dopant can reduce the oxygen vacancy formation energy and increase the ionic conductivity of La1−xSrxMO3−δ (M = Fe, Mn) perovskites [1,4]. Therefore, in this work, Cu-content La1−xSrxNi1−yCuyO3−δ oxides with strontium doping at the A-site were evaluated as very promising Co-free cathode material candidates for IT-SOFCs.In this work, all La1−xSrxNi1−yCuyO3−δ compounds have been successfully obtained using soft chemistry. The room-temperature crystal structure of all oxides was assigned to the R-3c trigonal system. The substitution of La with Sr lowers the phase transition temperature from the R-3c space group to Pm-3m simple perovskite while increases the oxygen non-stoichiometry and the thermal expansion coefficient of studied materials. All investigated materials are chemically compatible with GDC-10, while unstable in contact with LSGM and 8YSZ. The manufactured anode-supported IT-SOFC with the La0.95Sr0.05Ni0.5Cu0.5O3−δ cathode presents an excellent power density of 445 mW·cm−2 at 650 °C in humidified H2. The results confirmed that La1−xSrxNi1−yCuyO3−δ perovskites can be potentially qualified as promising cathode candidates for IT-SOFCs, yielding promising electrochemical performance in the intermediate-temperature range [1].

Enhancing the Cathodic Performance of LSM Via Nanostructured Surface Decoration with Infiltrated Sm0.5Sr0.5CoO3-Δ

The Solid Oxide Fuel Cell (SOFC) is getting attention from next-generation electrochemical energy conversion devices with high efficiency and low pollutant emission. But the high operating temperature in SOFC can lead to problems like high cost, difficult sealing, and fast degradation. To alleviate this problem, Intermediate temperature SOFC (IT-SOFC) has become an adequate alternative. But, as the operating temperature decreased, the Oxygen reduction reaction (ORR) also decreased, contributing to performance degradation and efficiency loss. The infiltration method, effectively improving the performance of the SOFC electrode, is one of the most effective ways. However, this method has been limited due to the multi-step process and instability of long-term operation. In this study, we suggest a new process that combines the infiltration and spray method with co-sintering to diminish the multi-step. We fabricated a cathode in which the LSM and Sm0.5Sr0.5CoO3-δ infiltration solvent coated simultaneously by the spray process and co-sintered. And we measured the cell performance and stability. Consequently, when applied as electrolyte-supported cells at 1073K, performance is measured by exhibiting a maximum power density of 0.986W cm-2 in fuel cell mode and electrolysis performance of 0.878A cm-2 at 1.3V. The result of this study was 0.724W higher than that of the bare LSM electrode. Figure 1

Effect of Mo-Doping on the Proton-Conducting BaCe0.9-xMoxY0.1O3-δ Electrolyte at Intermediate Temperature SOFCs

Perovskites have been attracting much attention because of their many potential applications as solid electrolytes in solid oxide fuel cells (SOFC). Among various kinds of perovskite materials, the Y2+ doped BaCe0.9Y0.1O3-δ (BCY) have been investigated extensively. It is noted that the doped BCY have good stability and relatively high protonic conductivity. However, the sintering temperature of BCY is very high above 1600 °C to achieve the required densification. High sintering temperature leads to evaporation of barium and the subsequent segregation of doped elements. As a result of this, the electrochemical properties of BaCe0.7Zr0.1Y0.2O3-δ electrolyte are reduced. At high temperatures, it’s difficult to maintain the porous structure of electrodes and causes the formation of impurity phases. So, in order to overcome this issue, we doped Mo- to BCY and reduce the sintering temperature of the electrolyte without comprising its performance. The sol-gel method was followed for the preparation of Ba1Ce0.9-xMoxY0.1O3-δ (BCMY, x=0.025%-0.2%) powder. The precursor's Ba(NO3)2, Ce(NO3)3.6H2O, Y(NO3)3.6H2O, and (NH4)6Mo7O24.4H2O in the stoichiometric ratio were dissolved in a mixture of water, citric acid, and glycine used as chelating agents in the molar ratio of 1:2:1. The solution was heated at 100 °C and was constantly stirred till it becomes a gel. The dried precursor was then heated at 350 °C for 2 hrs to remove the organic residues through combustion. Afterward, it was calcined at a temperature of 1100 °C for 10 hrs and finally, a white powder of BCMY was obtained. The synthesized BCMY electrolytes were sintered at 900, 1000, and 1100 °C to observe the effects of low sintering temperature on the structural, morphological, and electrical properties of BCMY. All BCMY electrolyte materials exhibited a crystalline perovskite structure and were found to be thermally stable as shown in XRD (Fig. 1 (a, b)). The morphology and element distribution of the BCY and BCMY electrolyte were observed by the scanning electron microscope (SEM, (Fig. 1c)) and energy-dispersive x-ray spectroscopy (EDX). SEM images show that BaCe0.9Y0.1O3-δ electrolyte sinterability and densifications are significantly improved. Fully dense pellets are sintered by using 0.025-0.2 mole% Mo. Energy dispersive spectroscopy shows that sintering aids are uniformly distributed throughout the structure. This study demonstrates BCMY as a dense proton-conducting electrolyte for intermediate-temperature solid oxide fuel cells. The BCMY with Mo-doping appears to be a potential candidate for sintering at low temperatures. Sintering facilitates addition from oxygen vaccines, which ease ionic conduction through the electrolyte, result in a low activation energy of at moderate temperatures. Fully dense pellets are sintered by using 0.025-0.2 mole% Mo. This method of decreasing the BCMY sintering temperature is useful in improving the SOFC performance.

Investigation of an Intermediate Temperature SOFC Operation in Series with a CPOx Reformer

Solid oxide fuel cells are known for their fuel flexibility which makes them a great candidate for decentralized power generation and off-grid applications. Depending on the target application, there have been different system configurations such as steam reforming vs. CPOx reforming, external reforming vs. internal reforming, anode recirculation vs. single pass. The CPOx reforming in series with SOFC with single pass configuration opens up the intermittent power source market, due to its unique benefit of low cost, short startup time and easy maintenance. In this scheme fuel cell electrochemical performance is directly related to the syngas composition, i.e. H2 and CO fractions in the fuel stream, as well as any unreformed methane.In this study a computational fluid dynamics (CFD) model has been developed to study the dynamic and steady state behavior of a commercial intermediate temperature SOFC stack operating in series with a CPOx reformer. The CFD model of the SOFC accounts for the charge, species, momentum and energy balances, whereas a reduced order model for the CPOx incorporates equilibrium thermodynamics. CPOx is an exothermic catalytic reaction with an overall balance of:CH4+1/2O2 → 2H2+CO (1)which is defined in stoichiometric ratios. In practice the air flow is regulated to control the reactor temperature and syngas yield. Hence, along with temperature and pressure the ratio of oxygen to carbon (O-C ratio) in the left hand side of Eq. 1 is a critical parameter for determining the overall performance and efficiency of the system. Moreover, the CPOx operation typically has different routes to achieve desired products which constitutes a system with various reaction equilibria [i]. However, apart from Eq.(1) the dominant reaction paths can be summarized as [ii]:Reformation CH4+CO2 ↔ 2H2+2CO (2)Water gas shift CO+H2O ↔ H2+CO2 (3)Boudouard CO2 + C ↔ 2CO (4)CH4 Combustion CH4+2O2 → 2H2O+CO2 (5)CO Combustion 2CO+O2 → 2CO2 (6)H2 Combustion 2H2+O2 → 2H2O (7)Of these, combustion reactions can be practically considered as irreversible. Overall system equilibrium is a result of these reactions and is a function of temperature, pressure and O/C ratio. Any changes in these parameters shift the reaction equilibrium, hence the conversion efficiency and syngas yield. As a result, SOFC performance will be directly dependent on these parameters.In this study different operating regimes of CPOX and SOFC have been investigated. The model is validated experimentally with polarization data and gas chromatography analysis. The model predictions show good agreement with the GC data for both the CPOX and SOFC outlet gas compositions.Performance of the SOFC running on syngas obtained as a result of different CPOx equilibria is compared and a fuel cell efficiency map as a function of temperature and O-C ratio has been constructed. Also, dynamic response of SOFC to the changes in CPOx operating parameters is estimated with the transient simulations. Moreover, selectivity of SOFC toward H2 and CO has been investigated by outlining the different energy conversion paths inside the fuel cell electrode. It is found that SOFC at intermediate temperatures has an overall tendency for CO conversion due to enhanced WGSR reaction inside the electrodes although the standalone CO oxidation overvoltage is higher than that of H2 oxidation. Finally, SOFC performance is analyzed for injecting various amounts of unreformed CH4 into the syngas stream.[i] Bjørn Christian Enger, Rune Lødeng, Anders Holmen, A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts, Applied Catalysis A: General 346 (2008) 1–27.[ii] Ruoshui Ma, Bang Xu, Xiao Zhang, Catalytic partial oxidation (CPOX) of natural gas and renewable hydrocarbons/oxygenated hydrocarbons—A review, Catalysis Today 338 (2019) 18–30. Figure 1

Elevated sintering capability and electrical conductivity of Fe2O3-doped Ce0.8Sm0.1Nd0.1O2-δ as an electrolyte in IT-SOFCs

Ce0.8Sm0.1Nd0.1O2-δ (SNDC) is one of the most promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, the adverse effect on the preparation of the electrolyte due to the high sintering temperature of SNDC limits the application of SNDC as an electrolyte material in IT-SOFCs. In this work, x mol % (x = 0, 0.5, 1.0, 1.5, 2.0, 2.5) Fe-doped SNDC (xFe-SNDC) powders were firstly fabricated by sol-gel synthesis, and then the corresponding bulks were prepared by cold-pressing and sintering at 1200∼1400 °C. The effects of Fe-doping on the sintering capability and electrical conductivity of SNDC were investigated. The results showed that Fe-doping leads to significant improvements in both the relative density and the electrical conductivity of SNDC. Doping Fe reduced the sintering temperature of SNDC from 1400 °C to 1200 °C and the relative density of 0.5Fe-SNDC sintered at 1200 °C reached 95.85%. Moreover, 0.5Fe-SNDC possessed the maximum conductivity of 0.0674 S cm−1 at 750 °C, which was attributed to the highest density and the highest conductivity of grain plus grain boundary.

In situ XRD and TGA/DTA study of multiphase La- and Nd-substituted Pr2NiO4 under IT-SOFC cathode operating conditions

Promising cathode materials Pr2−x(La/Nd)xNiO4+δ (x = 0, 0.5, 1) for intermediate temperature solid oxide fuel cells (IT-SOFC) were synthesised via a Pechini route. The samples were studied by in situ XRD in the conditions close to operating for IT-SOFC cathode. For all the samples a phase inhomogeneity was determined, manifesting itself in the apparent presence of two phases with the same 1st order Ruddlesden-Popper structure. The two phases had different unit cell parameters and slightly different phase transition (sp.gr. Fmmm ↔ I4/mmm) temperatures. For the as-synthesised PrNdNiO4+δ sample a loss of crystallinity, accompanied by a release of H2, H2O, CO2 and CO gases upon heating in an inert atmosphere, was observed. The crystallinity of the sample was recovered upon subsequent heating in an air atmosphere. La- and Nd- doping increased thermal stability of samples compared to the undoped one in air at 700 °C. In situ XRD experiments were supplemented by TGA/DTA measurements performed in the same conditions.

The Incorporation of Waste Sludge into the Production of High-Temperature-Resistant Adhesive Ceramic Materials

In recent years, the interest of the scientific community has become focused on the integration of circular economy principles by eliminating end-of-life concepts and forming zero-waste strategies. The present paper suggests the possible application of innovative, eco-friendly, cost-effective, and highly efficient ceramic materials with the partial implementation of aluminosilicate-based waste in the form of wastewater sludge in advanced technology solutions. The specific objective was to demonstrate the effective utilization of the investigated waste in the production of refractory adhesives and/or sealants for Intermediate-Temperature Solid-Oxide Fuel Cells (IT-SOFCs). Different physical–mechanical and chemical properties were determined along with the performance of leaching tests, the thermal cycling procedure, and leakage tests in a single cell. Based on the maintenance of mechanical integrity after thermal cycling and satisfying crystal and microstructural stability after high-temperature treatment, it was concluded that the investigated materials may be considered promising candidates for application as heat-resistant adhesives for connecting components in heating systems. However, they were not found to be applicable as sealants for IT-SOFCs in raw form according to the failure of testing in a single cell. Still, requirements for this purpose could be met after certain modifications of the composition and synthesis methodology, which presents the major initiative for our further research in this field.

Interface engineering to improve electrochemical performance of intermediate-temperature solid oxide fuel cells

The interface between the cathode and the electrolyte is critical in the electrochemical performance of intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, the correlation between the structural properties at the interface and the electrochemical performance is investigated with a focus on the ohmic resistance. Electrostatic spray deposition (ESD) is used to optimize the cathode particle size and distribution by controlling the solvent evaporation rate. A mechanical pull-off test is performed to directly assess the structural properties at the interface. Furthermore, electrochemical impedance spectroscopy (EIS) is employed with an equivalent circuit model to establish a quantitative correlation between the contact coverage at the interface and the interfacial resistance. By maximizing contact coverage, a significantly high peak power density of 1.87 W cm−2 is achieved at 600 °C in a Ni-Gd0.1Ce0.9O1.95 (GDC)-based single cell. The findings indicate that the proposed approach effectively achieves the desired structural properties, thereby enhancing the performance of IT-SOFCs with significant implications for the design and optimization.

Thermal plasma synthesis of (La,Sr)CoO3-(La,Sr)2CoO4 composite cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC)

(La,Sr)CoO3 and (La,Sr)2CoO4 dual phase powders were synthesized via thermal plasma to be used as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). This covered pure (La,Sr)CoO3 as well as the composites where the fraction of (La,Sr)2CoO4 was gradually increased reaching the mid-composition. Powders, all synthesized in the same condition, were extremely small in size, especially at mid-composition where they were close to 30 nm in size. Area specific resistance (ASR) determined from the symmetric cell imply improved cathodic performance at the mid-composition. Taking ASR = 0.15 Ω∗cm2 as benchmark, it was found that the (La,Sr)CoO3: (La,Sr)2CoO4 = 0.53:0.47 cathode may be used at temperatures close 750 °C. Measurements taken from several runs however imply that the cathode performance was not stable and ASR values increases with cycling. This was attributed to the powder form of the cathode which would be expected to coarsen rapidly due to accelerated surface diffusion.

Effect of Calcination Temperature on the Structural and Electrochemical Behaviour of Li-Based Cathode for Intermediate-Temperature SOFC Application

A new strategy to reduce the operating temperature of the solid oxide fuel cell (SOFC) is needed to foster the progress of developing high-performance and stable SOFC as a solution to the thermal stress and degradation of the cell components induced by high-temperature SOFC. The use of lithium (Li) as a cathode can increase the cell’s efficiency, as it allows for faster ion transport and a higher reaction rate. This study presents an attractive approach to using a Li-based cathode by combining Li with cobalt (Co) to form LiCo0.6Sr0.4O2 (LCSO). In this work, a precursor consisting of Li, Co, and strontium (Sr) was prepared via the glycine-nitrate combustion method. The precursor was calcined at two different calcination temperatures (800 and 900 °C) prior to ink formulation and symmetrical cell fabrication in order to study the effect of calcination temperature on the structural and electrochemical behaviour of a Li-based cathode. The precursor LCSO powder was characterised using X-ray crystallography (XRD) to determine the crystal structure and composition of the developed LCSO. The electrochemical performance of the fabricated symmetrical cell was tested using electrochemical impedance spectroscopy (EIS) to obtain the cell’s resistance information, which is related to the cell’s ionic and electronic conductivity. SDC electrolyte with LCSO calcined at 800 °C has a higher crystallinity percentage and a more porous structure compared to LCSO calcined at 900 °C. The porous structure enhanced the electrochemical performance of the cell, where the symmetrical cell has the highest conductivity (0.038 Scm−1) with the lowest activation energy (0.43 eV). The symmetrical cell was also able to achieve 2.89 Ω cm2 of area-specific resistance (ASR) at 800 °C of operating temperature. In conclusion, the SDC electrolyte with LCSO calcined at 800 °C is the promising cathode material for SOFC applications. The result of this study can benefit the SOFC field of research, especially in the development of intermediate temperature-SOFC.

Effects of Bi-doping on structure and properties of YBaCo2O5+δ layered perovskite cathode for intermediate-temperature solid oxide fuel cells

Layered perovskite oxides, Y1–xBixBaCo2O5+δ (YBBCx, x = 0.0–0.2) were investigated as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results indicate the YBBCx could be indexed to a tetragonal phase with trace of 3 × 3 × 1 superstructure configuration. No significant change in thermal expansion coefficients (TECs) was detected with the Bi-doping, and the TECs were 15.7–16.8 × 10−6 K−1 at 100–935 °C in air. Although the Bi-doping results in a decrease in conductivity of the YBBCx, the x = 0.2 sample still shows higher conductivity than that of a standard SOFC cathode (∼100 S cm−1). Additionally, the Bi-doping leads to an enhancement in the electrochemical performance mainly due to improved ion and electron charge transfers. Among the YBBCx compositions, the YBBC0.2 cathode shows the lowest polarization resistance (Rp) of 0.034 Ω cm2 at 700 °C. For a single cell with 300 µm thick La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM) and YBBC0.2 cathode, a peak power density (Pmax) of 537 mW cm−2 at 700 °C was achieved with no significant deterioration in performance after a 100–h testing.

Mechanical, thermophysical and electrochemical properties of dense BaCeO3 ceramics sintered from hydrazine-nitrate combustion products

The development of intermediate-temperature solid oxide fuel cells (IT-SOFCs) is currently a focus of research, as it has the potential to improve their operational characteristics, lower their cost, and enhance their stability. However, achieving high-performance functional materials at working temperatures of 600–800 °C poses a significant challenge. Barium cerate (BaCeO3) has been identified as a promising material for the solid electrolyte of IT-SOFCs due to its high proton conductivity among A2+B4+O3-type perovskites. Nevertheless, producing a single-phase and dense ceramic based on BaCeO3 with high conductivity in the intermediate-temperature range remains a challenge. This study employed the hydrazine-nitrate combustion method to obtain BaCeO3 precursor powder, which was then used to produce dense proton-conducting ceramics by isostatic pressing and subsequent isothermal sintering at temperatures of 1100–1500 °C. The resulting samples were characterized using various techniques, including XRD, SEM, Vickers microhardness, TMA, LFA, and impedance spectroscopy. The findings indicate that the proposed hydrazine-nitrate approach was successful in producing ceramic samples with an average crystallite size of 95–220 nm, an average grain size of 4.8–9.9 μm, and a relative density of 70.7–91.2% depending on the sintering conditions. The most densely sintered sample (91.2%) exhibited the highest mechanical and functional properties, with Vickers microhardness values of 3.0 GPa (R T.), a coefficient of thermal expansion of 8.7 × 10–6 (R T.-1000 °C), thermal conductivity of 1.51–1.06 W/m·°C (R.T.-1000 °C), and logarithmic conductivity of −3.37 to −6.35 S/cm (675–980 °C). Thus, the proposed hydrazine-nitrate approach shows promise for producing high-performance conducting ceramic materials for IT-SOFCs.

A fluid-flow approach in oxidation evaluation of SUS 430 steels coated by Fe/Mn-modified MnCo2O4 for solid oxide fuel cell application

The Fe/Mn-modified Mn–Co spinel oxides (MCO) are coated on SUS430 interconnect to protect against oxidation and chromium diffusion by wet spray followed by nitrate solution impregnation for intermediate-temperature solid oxide fuel cell (IT-SOFC) application. 1000 h oxidation tests at 800 °C show that the FeMCO-coated sample have the minimum parabolic rate constant (9.02 × 10−7 mg2cm−4s−1), which is lower than half of the uncoated sample. The area-specific resistance (ASR) of the FeMCO-coated sample is 6.41 mΩcm2 at 800 °C after 1000 h oxidation, which is much lower than the MCO sample (19.38 mΩ cm2) and the uncoated sample (186.84 mΩ cm2). The samples microstructures are examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Based on a novel approach, the dimensionless fluid numbers are related to the high-temperature conductivity of coated interconnects, and the inward diffusion of oxygen is introduced as the limiting factor for oxide-scale growth of coated interconnects.

A medium-entropy perovskite oxide La0.7Sr0.3Co0.25Fe0.25Ni0.25Mn0.25O3-δ as intermediate temperature solid oxide fuel cells cathode material

In this study, we report a novel medium-entropy perovskite oxide of La0.7Sr0.3Co0.25Fe0.25Ni0.25Mn0.25O3-δ (LSCFNM73) with high constitutive entropy (Sconfig) as the cathode material of intermediate temperature solid oxide fuel cells (IT-SOFCs). The intrinsic properties of phase structure, electrical conductivity, thermal expansion and oxygen adsorption capacity of La1-xSrxCo0.25Fe0.25Ni0.25Mn0.25O3-δ (LSCFNM, x = 0, 0.1, 0.2, 0.3) oxides are evaluated in detail. The LSCFNM73 oxide exhibits the maximum electrical conductivity of 464 S cm−1 at 800 °C and a relatively lower thermal expansion coefficient (TEC) of 15.34 × 10−6 K−1, which is selected as the propriate cathode composition. The B-site of LSCFNM73 contains four elements which can increase the configuration entropy. Additionally, NiO-Yttria stabilized zirconia (YSZ) supported fuel cell is fabricated by tape casting, hot pressing-lamination, co-sintering and screen printing technologies. The fuel cell demonstrates a maximum power density of 1088 mW cm2 at 800 °C, and excellent stability at 750 °C under 0.75V in 120 h and 10 times thermal cycling between 750 °C and 400 °C. Therefore, the medium-entropy LSCFNM73 oxide can be applied in IT-SOFCs as a competitive cathode material.

A p-n heterostructure composite of NaCrO2 and CeO2 for intermediate temperature solid oxide fuel cells

The development of heterostructure electrolytes represents a promising strategy for enhancing the performance of solid oxide fuel cells for the intermediate temperature solid oxide fuel cell (IT-SOFC). In this study, a new p-n semiconductor heterojunction of NaCrO2-CeO2 is proposed as a potential electrolyte for IT-SOFC, which exhibits a high ionic conductivity of 0.173 S·cm−1 and power density of 627.5 mW·cm−2 at 600 °C. A substantial number of oxygen vacancies are revealed in the NaCrO2-CeO2 heterostructure, with protons as the primary charge carriers. Additionally, an apparent P-N rectification effect is observed. Semiconductor band arrangement calculations are performed to elucidate the underlying mechanisms responsible for the exceptional performance of this heterojunction. The results indicate that the heterojunction enhances ion transport, while concurrently inhibiting electron flow, thus significantly contributing to its robust power output and ionic conductivity. This study not only provides a novel perspective on the application of semiconductor theory in ceramic fuel cells, but also advances the scientific understanding of the mechanisms that govern the exceptional performance of heterojunctions in SOFCs.

Ni-free CeO2-ZrO2-Sc2O3 nanostructured fuel electrodes for high performance solid oxide cells

Ni-based state-of-the-art cermet electrodes for SOFC are prone to deactivation when using hydrocarbon-based fuels due to surface carbon deposition. CeO2-based oxides offer major advantages to improve long-term performance of electrodes, such as high oxygen transport properties, carbon deposition resistance and optimum chemical compatibility with intermediate temperature SOFC (IT-SOFC) high performance electrolytes. Ceria-containing electrodes are generally mixed with Ni or other metallic phases to improve electronic percolation. In this work, we present two Ni-free electrodes: Ce0.9Zr0.1O2-δ and Ce0.9Zr0.06Sc0.04O2-δ. These electrodes exhibit a large amount of electrochemical reaction sites due to the nanoscale particle size distribution of the electrode material (Dav=25 nm). We show that, by partially replacing Zr by Sc in the Ce0.9Zr0.1O2 lattice, the polarization resistance of the electrode is significantly improved. The Sc-containing system exhibited a superior performance especially when using CH4 as fuel, thus implying that the incorporation of additional oxygen vacancies in the lattice enhances the electrode activity for fuel oxidation and its resistance towards carbon formation. These results reveal that the Ce0.9Zr0.06Sc0.04O2-δ electrode stands both as a promising Ni-free anode for IT-SOFC/SOEC operation and as a highly active redox support for Ni-based cermets.

Morphological Evolution of La2NiO4 Coatings Synthesized by Reactive Magnetron Sputtering (RMS) at High Pressure as Cathode for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC)

This work focuses on the evolution of the morphology and structure of La2NiO4 (namely, LNO) coatings deposited by reactive magnetron sputtering (RMS) with subsequent annealing processes. The LNO coatings start to crystallize at 600 °C, and the LNO with K2NiF4 structure was formed at 700 °C. A small amount of La3Ni2O7 appeared in the La2NiO4 coatings at 1100 °C. Interestingly, the LNO coatings realize the transformation from dense to different porous morphologies due to the annealing process. The LNO coating with abundant pores was formed after annealing treatment at 1000 °C for 2 h. This porous morphology can be stably maintained after short-term thermal stability experiments at 750 °C for 120 h. The electrochemical impedance spectroscopy (EIS) measurement of the LNO/YSZ/LNO symmetrical half-cells shows that the LNO cathode coating after annealing at 1000 °C for 2 h exhibits lower polarization resistance (Rpol) and activation energy.

Bi0.5Sr0.5FeO3-δ perovskite B-site doped Ln (Nd, Sm) as cathode for high performance Co-free intermediate temperature solid oxide fuel cell

The commercialization of the Co-free solid oxide fuel cell (SOFC) cathode was hindered due to its insufficient oxygen reduction reaction (ORR) activity. In this paper, the ORR activity of the cathode material is effectively increased by doping a small amount of low-valence Ln3+ (Nd3+, Sm3+) ions at the B-site of Fe-based perovskite Bi0.5Sr0.5FeO3-δ (BSF). Nd3+ increases the free volume (Vfree) per unit cell of perovskite due to its larger ionic radius, thus increasing the oxygen vacancy concentration of Bi0.5Sr0.5Fe0.95Nd0.05O3-δ (BSFN). Compared with BSF, BSFN has greatly improved the surface oxygen exchange and volume diffusion rate through the electronic conductivity relaxation (ECR) method. At 700 °C, the area-specific resistance (ASR) of BSFN reached 0.062 Ω cm2, which was 65% lower than that of BSF (0.177 Ω cm2), and the peak power density (PDD) of BSFN-based single cell reached 1.10 W cm−2, which was 1.7 times higher than that of BSF-based single cell (0.64 W cm−2). Through DRT analysis, it is concluded that BSFN can accelerate the adsorption/dissociation process of oxygen due to its higher oxygen vacancy concentration compared with BSF, so that ORR is not limited to the three-phase interface but extends to the entire cathode surface. In addition, in the 80 h long-term stability test at 600 °C, the BSFN-based single cell has better long-term stability because the thermal expansion coefficient of BSFN (14.1 × 10−6 K−1) is lower than that of BSF (14.4 × 10−6 K−1). In general, BSFN is expected to become a Co-free base high-performance intermediate temperature SOFC cathode.

Electrochemical Impedance Spectroscopy of Core‐Shell Nanofiber Cathodes, with Ce0.9Gd0.1O1.95 (Core) and Cu‐Doped La0.6Sr0.4MnO3 (Shell), for Application in Solid Oxide Fuel Cells

AbstractSeveral core‐shell nanofiber electrodes are prepared through electrospinning and tested for application as intermediate‐temperature solid oxide fuel cell (IT‐SOFC) cathodes. The materials investigated are La0.6Sr0.4MnO3 (LSM), La0.6Sr0.4Cu0.1Mn0.9O3‐δ (LSCuM_1), and La0.6Sr0.4Cu0.2Mn0.8O3‐δ (LSCuM_2) perovskites, used at the shell side of the nanofibers. Ce0.9Gd0.1O1.95 (GDC10) fluorite is used as the core material. The electrochemical characterization of the core‐shell nanofiber electrodes is performed through electrochemical impedance spectroscopy (EIS). The EIS results are reported and discussed based on equivalent circuit modeling. The polarization resistance of the GDC10/LSM core‐shell nanofibers electrodes is RP∼4.5 Ω cm2 at 650 °C. Improvement is accomplished with GDC10/LSCuM_1 and GDC10/LSCuM_2 core‐shell nanofibers, with RP∼1.8 Ω cm2 and 1.7 Ω cm2 respectively at 650 °C. Post‐test SEM characterization is carried out, to ascertain possible degradation and identify the most promising shell perovskite.

Solid Oxide Fuel Cells with Magnetron Sputtered Single-Layer SDC and Multilayer SDC/YSZ/SDC Electrolytes.

Samarium-doped ceria (SDC) is considered as an alternative electrolyte material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because its conductivity is higher than that of commonly used yttria-stabilized zirconia (YSZ). The paper compares the properties of anode-supported SOFCs with magnetron sputtered single-layer SDC and multilayer SDC/YSZ/SDC thin-film electrolyte, with the YSZ blocking layer 0.5, 1, and 1.5 μm thick. The thickness of the upper and lower SDC layers of the multilayer electrolyte are constant and amount to 3 and 1 μm, respectively. The thickness of single-layer SDC electrolyte is 5.5 μm. The SOFC performance is studied by measuring current-voltage characteristics and impedance spectra in the range of 500-800 °C. X-ray diffraction and scanning electron microscopy are used to investigate the structure of the deposited electrolyte and other fuel cell layers. SOFCs with the single-layer SDC electrolyte show the best performance at 650 °C. At this temperature, open circuit voltage and maximum power density are 0.8 V and 651 mW/cm2, respectively. The formation of the SDC electrolyte with the YSZ blocking layer improves the open circuit voltage up to 1.1 V and increases the maximum power density at the temperatures over 600 °C. It is shown that the optimal thickness of the YSZ blocking layer is 1 µm. The fuel cell with the multilayer SDC/YSZ/SDC electrolyte, with the layer thicknesses of 3/1/1 µm, has the maximum power density of 2263 and 1132 mW/cm2 at 800 and 650 °C, respectively.