Low-temperature Solid Oxide Fuel Cells Research Articles

Wet-Chemical Synthesis and Physico / Electro-Chemical Performance Characteristics of Novel Perovskite Cathode Materials for Low-Temperature Solid Oxide Fuel Cells

Different perovskite-based materials are proposed as cathode materials for solid oxide fuel cells (SOFCs) working at low temperatures (~600 oC). In this research work, a set of perovskite cathode materials, such as Sm1-xCexCoO3-δ, Sm1-xCexMnO3-δ, Gd1-xCexCoO3-δ andGd1-xCexMnO3-δ (x = 0.1–0.2)were prepared for SOFC applications by co-precipitation method with sodium hydroxide solution as the precipitating agent. The precipitated hydroxides were calcined at 300, 600, 750, 900, and 1100 oC /2 hours in the air using a thermolyne furnace. The calcined powder particles were characterized by XRD, FT-IR, Particle Size, SEM, and EDAX techniques. XRD patterns revealed the presence of orthorhombic primitive phases in the samples. Crystallite sizes of the materials were also determined with XRD method. The presence of M-O bond was confirmed by FT-IR spectroscopy. Particle size analysis proved the presence of samples in the range of 247-976 nm. However, the SEM images revealed the presence of nano-sized particles. The atomic percentage of elements present in the materials was measured by EDAX. Pellets of cathode samples were made and sintered at high temperatures. The conductivity values of the specimens were measured with electrochemical impedance spectroscopy at different temperatures. The cathode specimen, Gd1-xCexCoO3-δ (x=0.1 and 0.2) exhibited better electronic conductivity than other samples. It was found that the prepared cathode samples are stable at moderate temperatures and suitable for Low-Temperature Solid Oxide Fuel Cell (LTSOFC) application.

Progress in proton‐conducting oxides as electrolytes for low‐temperature solid oxide fuel cells: From materials to devices

AbstractAmong various types of alternative energy devices, solid oxide fuel cells (SOFCs) operating at low temperatures (300‐600°C) show the advantages for both stationary and mobile electricity production. Proton‐conducting oxides as electrolyte materials play a critical role in the low‐temperature SOFCs (LT‐SOFCs). This review summarizes progress in proton‐conducting solid oxide electrolytes for LT‐SOFCs from materials to devices, with emphases on (1) strategies that have been proposed to tune the structures and properties of proton‐conducting oxides and ceramics, (2) techniques that have been employed for improving the performance of the protonic ceramic‐based SOFCs (known as PCFCs), and (3) challenges and opportunities in the development of proton‐conducting electrolyte‐based PCFCs.

Progress in Material Development for Low-Temperature Solid Oxide Fuel Cells: A Review

Solid oxide fuel cells (SOFCs) have been considered as promising candidates to tackle the need for sustainable and efficient energy conversion devices. However, the current operating temperature of SOFCs poses critical challenges relating to the costs of fabrication and materials selection. To overcome these issues, many attempts have been made by the SOFC research and manufacturing communities for lowering the operating temperature to intermediate ranges (600–800 °C) and even lower temperatures (below 600 °C). Despite the interesting success and technical advantages obtained with the low-temperature SOFC, on the other hand, the cell operation at low temperature could noticeably increase the electrolyte ohmic loss and the polarization losses of the electrode that cause a decrease in the overall cell performance and energy conversion efficiency. In addition, the electrolyte ionic conductivity exponentially decreases with a decrease in operating temperature based on the Arrhenius conduction equation for semiconductors. To address these challenges, a variety of materials and fabrication methods have been developed in the past few years which are the subject of this critical review. Therefore, this paper focuses on the recent advances in the development of new low-temperature SOFCs materials, especially low-temperature electrolytes and electrodes with improved electrochemical properties, as well as summarizing the matching current collectors and sealants for the low-temperature region. Different strategies for improving the cell efficiency, the impact of operating variables on the performance of SOFCs, and the available choice of stack designs, as well as the costing factors, operational limits, and performance prospects, have been briefly summarized in this work.

Methods to increase electrochemical activity of lanthanum nickelate-ferrite electrodes for intermediate and low temperature SOFCs

In this study the methods to increase electrochemical activity and stability of air electrodes based on LaNi0·6Fe0·4O3-δ (LNF) and Сe0.8Sm0.2O1.9 (SDC) with different collector layers has been developed. The influence of the electrode layers’ composition and sintering conditions on the electrode performance in contact with the SDC electrolyte is considered. The polarization resistance of the electrodes with the LNF collector containing a combined Bi–Cu additive is in a range of 0.60–0.67 Ωcm2 at 600 °C. Appearance of low-melting liquid phases during the collector formation gives rise to both additional sintering and electrochemical activation of the functional layers. The optimized electrodes exhibit a low degradation (13–15%) preserving a polarization resistance level of 0.15–0.21 Ω cm2 at 700 °C after long-term testing for 600 h. To elucidate reasons of the electrode ageing, changes in the electrode performance and microstructure are analyzed using DRT technique and autocorrelation function analysis of SEM images.

Low-temperature solid oxide fuel cells based on Tm-doped SrCeO2-δ semiconductor electrolytes

Low-temperature solid oxide fuel cells (LT-SOFCs) are a promising fuel cell technology but often suffer from low ionic conductivity of the electrolyte. Herein, we develop a solid electrolyte with high ionic conductivity based on thulium (Tm)-doped composite Sr0.1TmxCe0.9-xO2-δ [x = 0.1] having a cubic fluorite structure. The fuel cell using Tm-doped SrCeO2-δ electrolyte achieved the power output of 682 mW/cm2 at 550 °C with an open-circuit voltage (OCV) of 1.03 V, whereas the fuel cell with Sr0·1Ce0·9O2-δ electrolyte produced a power density of 515 mW/cm2 with an OCV of 1.02 V. Doping of 10% Tm into SrCeO2-δ enables the creation of oxygen vacancies in the structure, which enables the enhancement in ionic conductivity and provides the fast transport path. Thus, doping of both Sr and Tm into CeO2 enhances the generation of high content of oxygen vacancies. The calculated ionic conductivity of Tm-doped SrCeO2-δ is 0.13 S/cm which is appreciably higher than that of the pure SrCeO2-δ (0.104 S/cm at 550°C). Moreover, the enhancement of power output can also be ascribed to band bending at the electrolyte-electrode interface, which overall decreases the inherent electronic properties of reduced ceria while increases the ionic conductivity.

Atmospheric pressure plasma jet fabricating of porous silver electrocatalyst as a promising approach to the creation of cathode layers of low temperature solid oxide fuel cells

Abstract Silver (Ag) electrocatalysts as cathode layers for low-temperature solid oxide fuel cells (LT-SOFCs) are prepared using an atmospheric pressure plasma jet (APPJ). The material characteristics of APPJ-coated silver are observed by an X-ray diffractometer and a field-emission scanning electron microscope. The porous cathode films, composed of Ag nanoparticles coated on YSZ electrolytes are observed. The porous Ni anodic layer is also prepared via an APPJ process on the other side of the YSZ. The values of area specific resistance and conductivities of Ag|YSZ are linearly increased with increasing operating temperatures. High conductivities of 139.6 and 143.2 S/cm are obtained at 550 and 600 °C, respectively. The exchange current and power density at 600 °C are 497.9 mA/cm2 and 108.4 mW/cm2, respectively. The AC impedance shows the two oxygen pathways, surface and bulk, of Ag electrocatalysts as reflected by the responses at low and high frequencies, respectively. Furthermore, LT-SOFCs which consist of cathode|electrolyte|anode are fabricated by APPJ technology in a fast-coating process.

Design principle and assessing the correlations in Sb-doped Ba0.5Sr0.5FeO3–δ perovskite oxide for enhanced oxygen reduction catalytic performance

Lack of fundamental understanding of the oxygen reduction reaction (ORR) hampers the development of effective metal oxide catalysts and advance low-temperature solid oxide fuel cells (LT-SOFCs). In this study, we report Ba0.5Sr0.5Fe1–xSbxO3–δ (BSFSb, x = 0, 0.05, and 0.1) cathodes designed from both theoretical and experimental aspects to study a good relationship between a material property and enhanced ORR activity. The BSFSb cathode exhibits a very low area-specific resistance (ASR) of 0.20 Ω cm2 and excellent power output of 738 mW cm−2 using the Sm0.2Ce0.8O2 (SDC) electrolyte at 550 °C. The Sb ions doping significantly enhances electrical conductivity and reduces its ORR activation energy. First-principles calculations screen the potential of designed perovskite by showing very low vacancy formation energy and shift in O-p and Fe3-d band centers near to fermi level by replacing Fe with Sb ions. Correspondingly, wide range coverage of distributed orbitals at the fermi level in BSFSb cathode promotes charge transfer with lower energy barrier. These results demonstrate that this design can impact the development of highly functional ORR electrocatalysts for LT-SOFCs and other electrocatalyst applications.

Antimony-doped strontium cobalt oxide as promising cathode for low-temperature solid oxide fuel cell with excellent carbon dioxide tolerance

The cathode destruction by CO2 erosion has emerged as great obstacle to solid oxide fuel cells (SOFCs) application. In this work, replacing 18.75 % cobalt with antimony in SrCoO3-δ demonstrates substantial improvements in CO2 tolerance and perfect performance recovering from 10 vol% CO2 is achieved with symmetrical and single cell test. Both experimental and computational results prove the weakened CO2 adsorption strength. In addition, outstanding oxygen transport properties is obtained with chemical oxygen surface exchange coefficient of 1.97 × 10−3 cm s-1 at 600 °C, two orders of magnitude higher than the state-of-art cathode material La0.6Sr0.4Co0.2Fe0.8O3-δ. The single phase electrode shows brilliant oxygen reduction reaction activity with electrode resistance of 0.185 Ω cm2 at 600 °C, which is attributed to the accelerated charge transfer rate and augmented adsorbed oxygen species. The combination of exceptional electrochemical activity and excellent CO2 tolerance demonstrates its significant advantage for practical applications as promising cathode for low-temperature SOFCs.

Synthesis and Electrical Characterizations of Graphene Oxide Incorporated Nanocomposite Cathode Materials for Low Temperature SOFCs

Synthesis and Electrical Characterizations of Graphene Oxide Incorporated Nanocomposite Cathode Materials for Low Temperature SOFCs

Performance and Stability Enhancement of Ni-Based Cermet Anode Using Atomic Layer Deposited Ruthenium for Direct Methane-Fueled Low-Temperature Solid Oxide Fuel Cell

Nickel (Ni) based cermet, e.g., Ni-doped zirconia(e.g., YSZ) and Ni-doped ceria(e.g., GDC), is the most widely used anode material for solid oxide fuel cell (SOFC). SOFC has been considered as a promising energy converter because of its high efficiency, eco-friendliness, and fuel flexibility. However, recently, SOFC operating below 500°C with more conventional fuels such as hydrocarbon or alcohol are actively studied for overcoming the limitations of high temperature SOFC, e.g., durability, cost, and limited application. Therefore, the necessity of improving the performance and stability of Ni-based anode is aroused because it shows relatively slow hydrocarbon and alcohol oxidation kinetics in the low-temperature regime and vulnerable to carbon deposition. To improve kinetics and stability of Ni-based anode upon hydrocarbon fuel-based operation, various kinds of metal catalysts, e.g., copper, palladium, iron, etc., have been applied using fabrication techniques such as wet synthesis, infiltration, vapor deposition, etc. In this study, ruthenium (Ru) having high catalytic activity and carbon coking toleration is applied to Ni-based cermet anode used in methane-fueled low-temperature SOFC. In particular, atomic layer deposition (ALD), which can deposit nanoparticles conformally on porous structures, is used for depositing Ru nanoparticles on nano-structured Ni-based cermet anode. ALD Ru nanoparticles fabricated in such a way are well-dispersed on the surface of Ni-based cermet anode and effectively improve the performance and stability of the anode when it is operated with methane-fuel. Especially, Ni-based anode with optimal ALD Ru thickness, i.e., 10nm in thickness, shows 40% higher maximum power density than those without ALD Ru overcoating when operated with methane fuel.

Yttria-Stabilized Zirconia Capping Layer on Pt Cathode By Atomic Layer Deposition

Atomic layer deposition (ALD) has the advantage of being able to deposit various materials as nanometer-scale thin films at low temperatures, and to precisely control thickness and doping levels. Due to these advantages, ALD has been applied in various fields including solid oxide fuel cells (SOFCs). SOFC is an echo-friendly next-generation energy conversion device that has high efficiency and fuel-flexibility. However, due to the high operating temperature (1000 ℃) of conventional SOFCs, problems such as thermal degradation and material selection occur. In order to solve this problem, low temperature SOFCs (LT-SOFCs) that can be operated below 500 ℃ are being studied. However, as the operating temperature decreases, oxygen reduction reaction (ORR) at cathodes of SOFCs also slows down. Therefore, engineering cathode surface, where ORR takes place, is important to improve the performance of LT-SOFCs.In this study, we deposited an ultra-thin film (~ 5nm) yttria-stabilized zirconia (YSZ) overlayer on the Pt cathode surface of LT-SOFC through ALD. In addition, the effect of doping level on the performance and thermal stability of LT-SOFC was studied by varying the cycle ratio of zirconia and yttria. The doping level of the YSZ overlayer was controlled to be 6, 13, 16 and 23 mol%, which were confirmed through XPS analysis. The performance of the cell with 16 mol% -doped YSZ overlayer at 450 ℃ showed the highest maximum power density, which was 70 % higher than that of cell without the overlayer. In addition, the activation resistance, which is mostly from ORR, was also reduced by 27 %. In addition, in the prolonged operation for 5 hours at 450 ° C, it was found that the performance of the cell without the overlayer was reduced by 80 %, while that of the cell with 16 mol%-doped ALD YSZ overlayer was reduced by 40 %. This result shows that the thermal stability was also improved when the ALD YSZ overlayer was deposited.

Effect of yttrium-stabilized bismuth bilayer electrolyte thickness on the electrochemical performance of anode-supported solid oxide fuel cells

Lowering operating temperature and optimizing electrolyte thickness, while maintaining the same high efficiencies are the main considerations in fabricating solid oxide fuel cells (SOFCs). In this study, the effect of yttrium-stabilized bismuth bilayer electrolyte thickness on the electrical performance was investigated. The yttrium-stabilized bismuth bilayer electrolyte was coated on the nickel–samarium-doped composite anode/samarium-doped ceria electrolyte substrate with varying bilayer electrolyte thicknesses (1.5, 3.5, 5.5, and 7.5 μm) via dip-coating technique. Electrochemical performance analysis revealed that the bilayer electrolyte with 5.5 μm thickness exhibited high open circuit voltage, current and power densities of 1.068 V, 259.5 mA/cm2 and 86 mW/cm2, respectively at 600 °C. Moreover, electrochemical impedance spectroscopy analysis also exhibited low total polarization resistance (4.64 Ωcm2) at 600 °C for the single SOFC with 5.5 μm thick yttrium-stabilized bismuth bilayer electrolyte. These findings confirm that the yttrium-stabilized bismuth bilayer electrolyte contributes to oxygen reduction reaction and successfully blocks electronic conduction in Sm0.2Ce0.8O1.9 electrolyte materials. This study has successfully produced an Y0.25Bi0.75O1.5/Sm0.2Ce0.8O1.9 bilayer system with an extremely low total polarization resistance for low-temperature SOFCs.

Validation of defect association energy on modulating oxygen ionic conductivity in low temperature solid oxide fuel cell

The defect association modifies the energy barrier for oxygen ion hopping between the vacancies, which is sensitive to the dopant ionic size in the CeO2-δ. Here, the work focuses on the co-dopant strategy of M0.1Sm0.1Ce0.8O2-δ (M = Yb, Gd, Sm, Nd, La) to study the defect association energy, and its subsequent effect on ionic conduction and power density. The electrolyte material with different co-dopants modifies the lattice parameter and bond length of cation–anion, which changes the defect–dopant interactions. Among the tested dopant, Nd0.1Sm0.1Ce0.8O2-δ exhibits the highest ionic conductivity of 34 mS cm−1 at 550 °C, which is nearly 2.3 times higher than the conventional Sm0.2Ce0.8O2-δ. This experimental observation validates the theoretically proposed concept of the balanced defect–dopant interactions at different sites leading to the reduction in defect association enthalpy. The experimental results were rationalized by calculating the defect association enthalpy for the co-doped system using density functional theory via one-cell method. The cell with Nd0.1Sm0.1Ce0.8O2-δ as an electrolyte shows a peak power density of 466 mW cm−2 at 550 °C, which is twice higher than the cell containing standard Sm0.2Ce0.8O2-δ electrolyte (212 mW cm−2). The results confirm that Nd0.1Sm0.1Ce0.8O2-δ is the potential electrolyte for low temperature SOFC operation.

Ultrathin sputtered platinum–gadolinium doped ceria cathodic interlayer for enhanced performance of low temperature solid oxide fuel cells

Improvement of the sluggish oxygen reduction reaction (ORR) is the key to lower the operating temperature of conventional solid oxide fuel cells (SOFCs). Developing a novel nanostructure in the cathodic catalyst layer is one of the efficient ways to reduce the operating temperature while improving fuel cell performance. In this paper, all components of low-temperature SOFCs were prepared on a nanoporous substrate by the sputtering method. For the performance enhancement at low temperature, an ultrathin Pt-Gadolinium Doped Ceria (GDC) cermet interlayer was deposited on the cathode side of electrolyte and demonstrated. A significant improvement in electrochemical performance was observed in the Pt-GDC interlayer fuel cell compared to a reference cell. The peak power density of Pt-GDC cathodic cermet interlayer cell was 334 mW/cm2 at 500 °C, which was 42.7% higher than that of the reference cell. Through additional analysis, we confirmed that the observed performance enhancement was attributed to the ultrathin cathodic cermet interlayer, which increases the triple phase boundary and enhances the reaction kinetics for ORR.

Effects of Microstructure of Ni Anode on Nanotemplate Based Low Temperature Solid Oxide Fuel Cells

For nano-porous anodized aluminum oxide (AAO) template based low temperature solid oxide fuel cells (LT-SOFCs), anode structure has crucial effects on electrochemical characteristics because of triple phase boundary densities and electrical connectivity of metal catalysts on porous AAO substrates. In this study, we investigated effects of fabrication processes of Ni anode for AAO template based LT-SOFCs. Ni anodes were prepared at various deposition pressure, i.e. low pressure, high pressure and low pressure–high pressure, on nano-porous AAO substrates by physical vapor deposition. Surface morphology and cross-sectional structure of various Ni anodes were systematically evaluated. Electrochemical characterizations of LT-SOFCs with various anode structures were successfully conducted at 500 °C. The Ni anode prepared at low pressure showed high electrical conductivity and low catalytic activity. However, Ni anode which was fabricated at high pressure exhibited poor electrical conductivity and good catalytic activity. Bilayer Ni anode which was deposited in sequence at low pressure and high pressure presented both good electrical conductivity and good catalytic activity. The LT-SOFC with the bilayer Ni anode cell achieved the best performance, 201 mW/cm2 at 500 °C. Electrochemical impedance spectroscopy analysis was conducted to reveal detailed behaviors of AAO based LT-SOFCs. Therefore, we successfully optimized the anode structure for high performance AAO template based LT-SOFCs.

Electrical properties of Ni-doped Sm2O3 electrolyte

Nowadays, semiconductor ionic materials have drawn significant attention for developing new electrolytes in low temperature solid oxide fuel cells (LT-SOFCs). Here we investigate the effect of nickel doping on ionic conductivity of Sm2O3 as an electrolyte material for low temperature SOFCs. The amount of Ni ion doping has an intense effect on the electrochemical properties and power generation. An optimized composition of 10 mol% nickel doped samarium oxide (10NSO) as an electrolyte in the fuel cell has a high open circuit voltage (OCV) of 1.09 V and a notable power output of 1080 mW cm−2 at 520 °C. Further investigation revealed that the 10NSO displays a superior ionic conduction up to 0.26 S cm−1 at 520 °C. Moreover, the cell demonstrates high stability up to 80 h. The high electrochemical property and good stability recommend that the NSO is a favorable candidate for symmetrical SOFC electrolyte.

Nano-Ceramic Cathodes via Co-sputtering of Gd–Ce Alloy and Lanthanum Strontium Cobaltite for Low-Temperature Thin-Film Solid Oxide Fuel Cells

We report the electrochemical performance and structural characteristics of porous nanostructured ceramic cathodes for thin-film solid oxide fuel cells (TF-SOFCs) based on yttria-stabilized zirconi...

Application of a negative thermal expansion oxide in SOFC cathode

To improve the performance of solid oxide fuel cells (SOFCs) at intermediate temperature, an idea of adding a negative thermal expansion (NTE) oxide into cathode is proposed. The effects of NdMnO3-δ (NM) NTE oxide addition in Ba0.5Sr0.5FeO3-δ (BSF) cathode on the performance of proton-conducting SOFCs (H-SOFCs) are studied. The 30 wt % NM addition can lead to an ideal thermal matching between BSF-NM cathode and BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte, and improve the electrochemical performance of H-SOFCs significantly. At 500–750 °C, the peak power density (PPD) of H-SOFCs with BSF-NM cathode is 139–941 mW cm−2, which is apparently higher than that (73–661 mW cm−2) with BSF one. In addition, the relative increment of peak power density (PPD) increases from 42.36% at 750 °C to 90.41% at 500 °C, which is seldom obtained by conventional cathode doping. Comprehensive results of electrochemical impedance spectra, electrical conductivities, and SEM observations show that the apparent improvement of PPDs should be mainly associated with the increased three phase boundary length due to the ideal thermal matching between cathodes and electrolytes. In all, it provides a novel idea to develop intermediate and low temperature SOFCs.

Compositing protonic conductor BaZr0.5Y0.5O3 (BZY) with triple conductor BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) as electrolyte for advanced solid oxide fuel cell

BaZr0.5Y0.5O3(BZY) electrolyte exhibited enormous potential for low temperature solid oxide fuel cell (SOFC) due to its proton dominant mobile carriers rather than oxygen ions during the electrochemical process. In order to enhance the ionic conductivity, triple conductor BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) was composited with proton conductor BZY to form semiconductor-ionic conductor composite (SIM), which was applied as electrolyte to fabricate symmetrical fuel cell. The microstructural and electrochemical properties for BZY, BCFZY and BZY-BCFZY composites were studied. After optimizing the weight ratio of composite content, the ionic conductivity and electronic conductivity reached an equilibrium state to obtain the maximum cell performance, namely the highest output of 902.5 mW cm−2 and an open circuit voltage (OCV) of 1.043 V at 550 °C. The BZY-BCFZY cell also presented decent power output at low temperature, a power density of 265.625 mW cm−2 was received even at 500 °C, demonstrating that the BZY-BCFZY composite was a potential electrolyte for low temperature SOFCs.

A triple (e−/O2−/H+) conducting perovskite BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for low temperature solid oxide fuel cell

Low-temperature solid oxide fuel cells (LT-SOFCs) have recently gained enormous attention worldwide with a new research trend focusing on single layer fuel cells (SLFC), which have better cell performance than traditional SOFCs at low operating temperatures. In this study, a triple (e−/O2−/H+) conducting perovskite BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) is used as the intermediate layer material for SLFC. A high current density of 994 mA/cm2 at 0.6 V and a peak power density of 610 mW/cm2 with an OCV of 1.01 V has been achieved with a cell operating temperature of 550 °C, confirming the application feasibility of BCFZY in SLFCs. Furthermore, a typical proton conductor BaZr0.8Y0.2O3-δ (BZY) is introduced into BCFZY to enhance the cell performance. By adjusting the mass ratio of the BCFZY-BZY layer, an optimal power density is obtained, achieving 703 mW/cm2 with an OCV of 1.03 V at 550 °C with an 8BCFZY:2BZY (wt%) ratio. These findings prove that the proposed BCFZY-BZY holds great promise for developing SLFCs to realize low-temperature operation.