Solid Oxide Fuel Cell Materials Research Articles

Achieving exceptional activity and durability toward oxygen reduction based on a cobalt-free perovskite for solid oxide fuel cells

In response to the shortcomings of cobalt-rich cathodes, iron-based perovskite oxides appear as promising alternatives for solid oxide fuel cells (SOFCs). However, their inferior electrochemical performance at reduced temperatures (<700 °C) becomes a major bottleneck for future progress. Here, a novel cobalt-free perovskite Ba0.75Sr0.25Fe0.875Ga0.125O3−δ (BSFG) is developed as an efficient oxygen reduction electrode for SOFCs, featuring cubic-symmetry structure, large oxygen vacancy concentration and fast oxygen transport. Benefiting from these merits, cells incorporated with BSFG achieve exceptionally high electrochemical performance, as evidenced by a low polarization area-specific resistance of 0.074 Ω cm2 and a high peak power density of 1145 mW cm−2 at 600 °C. Meanwhile, a robust short-term performance stability of BSFG cathode can be ascribed to the stable crystalline structure and favorable thermal expansion behavior. First-principles computations are also conducted to understanding the superior activity and durability toward oxygen reduction reaction. These pave the way for rationally developing highly active and robust cobalt-free perovskite-type cathode materials for reduced-temperature SOFCs.

Anodic properties of Ni-Fe bimetallic nanofiber for solid oxide fuel cell using LaGaO3 electrolyte

Solid oxide fuel cells (SOFCs) are attracting much attention as alternative energy conversion devices owing to their high energy conversion efficiency and fuel flexibility. Currently, Ni-based cermets or Ni-based bimetal are often being used as anode materials for SOFCs. However, in anode materials, metallic spherical particles generally agglomerate, which affects the electrode reaction under reduction conditions at high temperature. Furthermore, such agglomeration affects both microstructure of the electrode and the cell stability. To overcome this problem, in this study, we designed a bimetallic anode and fabricate it by electrospinning. This Ni-Fe fiber anode exhibits enhanced anodic activity and tolerance to coarsening of metallic particle compared to the Ni-Fe spherical powder. The ohmic and polarization resistance of Ni-Fe fiber anode is lower than Ni-Fe powder anode at all operation temperature. In addition, the single cell using Ni-Fe fiber anode shows higher maximum power densities of 0.40, 0.80, and 1.64 W/cm2 at 973, 1073, and 1173 K, respectively. Such enhanced power generation properties and lower resistance originated from continuous pathways for excellent charge transport pathways generated by electrospinning and the enhanced gas-diffusion properties of the nanofibers. These results demonstrate that the introduction of Ni-Fe fiber anode in SOFCs is an effective approach to enhance their power generation properties and stability.

Undoped Sr2MMoO6 Double Perovskite Molybdates (M = Ni, Mg, Fe) as Promising Anode Materials for Solid Oxide Fuel Cells.

The chemical design of new functional materials for solid oxide fuel cells (SOFCs) is of great interest as a means for overcoming the disadvantages of traditional materials. Redox stability, carbon deposition and sulfur poisoning of the anodes are positioned as the main processes that result in the degradation of SOFC performance. In this regard, double perovskite molybdates are possible alternatives to conventional Ni-based cermets. The present review provides the fundamental properties of four members: Sr2NiMoO6-δ, Sr2MgMoO6-δ, Sr2FeMoO6-δ and Sr2Fe1.5Mo0.5O6-δ. These properties vary greatly depending on the type and concentration of the 3d-element occupying the B-position of A2BB’O6. The main emphasis is devoted to: (i) the synthesis features of undoped double molybdates, (ii) their electrical conductivity and thermal behaviors in both oxidizing and reducing atmospheres, as well as (iii) their chemical compatibility with respect to other functional SOFC materials and components of gas atmospheres. The information provided can serve as the basis for the design of efficient fuel electrodes prepared from complex oxides with layered structures.

A Parameter Sensitivity Study of Solid Oxide Fuel Cells Based on One-dimensional Model

Solid oxide fuel cells (SOFCs) are promising and efficient energy conversion devices. The modeling method was widely used to study characteristics of SOFCs due to limitation of experiments. Values of material properties such as porosity, tortuosity and pore radius are required information in modeling. Current modeling works usually employ material properties used in the literature, which are not exactly measured and the values vary in wide ranges. However, inappropriate selection of material properties can result in incorrect modeling results of SOFCs. In this study, a one-dimensional model of SOFCs was established to analyze the effects of different material parameters on the modeling results. A parameter sensitivity analysis was also conducted to determine the most influential parameters on the polarization curve. The results provide a reference for selection values of SOFC material parameters. This work can also be used as a guideline to fit the experimental polarization curve in numerical simulations by adjusting appropriate material parameters.

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.

On the equation of electrical conductivity relaxation method to measure kinetic parameters of solid oxide fuel cell materials with a three-dimensional rectangular geometry

The electrical conductivity relaxation method has been widely used to measure kinetic properties of species transport process in solid oxide fuel cell materials using rectangular dense samples. It is found that the equation of ECR used in some studies is flawed. An improved equation is presented in this communication.

Development of nickel based cermet anode materials in solid oxide fuel cells – Now and future

High temperature solid oxide fuel cell (SOFC) is the most efficient and clean energy conversion technology to electrochemically convert the chemical energy of fuels such as hydrogen, natural gas and hydrocarbons to electricity, and also the most viable alternative to the traditional thermal power plants. However, the power output of a SOFC critically depends on the characteristics and performance of its key components: anode, electrolyte and cathode. Due to the highly reducing environment and strict requirements in electrical conductivity and catalytic activity, there are limited choices in the anode materials of SOFCs, particularly for operation in the intermediate temperature range of 500–800 ​°C. Among them, Ni-based cermets are the most common and popular anode materials of SOFCs. The objective of this paper is to review the development of Ni-based anode materials in SOFC from the viewpoints of materials microstructure, performance and industrial scalability associated with the fabrication and optimization processes. The latest advancement in nano-structure architecture, contaminant tolerance and interface optimization of Ni-based cermet anodes is presented. And at the end of this paper, we propose and appeal for the collaborative work of scientists from different disciplines that enable the inter-fusion research of fabrication, microanalysis and modelling, aiming at the challenges in the development of Ni-based cermet anodes for commercially viable intermediate temperature SOFC or IT-SOFC technologies.

(Invited) Brief Overview of Current French Hydrogen Research Activities, Focus on SOFC Materials Development

Twenty years ago, the French scientific community working in the field of hydrogen, started to federate under the leadership of the CNRS. It took the form of successive Research Grouping (GdR) bringing together experts in solid oxide fuel cell (SOFC), proton exchange polymer membrane (PEMFC) fuel cells, hydrogen storage and systems mainly from CNRS but also from CEA. These GdRs promoted and structured an interdisciplinary field of research with excellent results.Since January 1st of 2020, the CNRS community has formed the Research network on Hydrogen energy (FRH2) based on the active nucleus of the former GDR laboratories (28 laboratories) with about 90 full-time equivalent positions including researchers and professors, without including technical staff, students, doctoral students and post-docs. A new organization, "from material to system", more visible from industries has been set up around four main technical axes, the production of hydrogen, its storage, and its conversion into electricity for mobile and stationary applications and around 2 transversal axes, education and technological platforms. The first part of the presentation will give a brief overview of this french CNRS research network on hydrogen energy including some highligts for each axes.The second part will be dedicated to the development of materials used in solid oxide fuel cells (SOFC) and more precisely to the ceramic electrolyte. Electrochemical properties of the materials used in SOFC are governed by the defects within the material and limited by the microstructure and the transport mechanisms of charge carrier at the interfaces. Thus, the optimization of the microstructure of the material via accurate monitoring of the synthesis and temperature treatment steps could enhance the conduction properties of existing materials. The usual objective for electrolyte material is to reach a total conductivity level above 10-2 S/cm for operating temperatures below 600°C. Actually, working at low temperature would prevent premature aging of SOFC performance.BCZY type proton conducting electrolyte such as BaCe0.8Zr0.1Y0.1O3-δ has gained a great attention as one of the most promising candidate for intermediate temperature solid oxide fuel cells, due to the combination of a high bulk conductivity associated to a chemical stability [1]. However, some of challenges to manufacture a dense BCZY ceramic are the high sintering temperature typically 1500 to 1600°[2], and the long processing duration in conventional method which can damage the material and cause barium evaporation resulting in a decrease of electrochemical properties.Part of this talk is focused on BaCe0.8Zr0.1Y0.1O3-δ showing properties which are a compromise between the high proton conductivity of BCY and the stability of BZY. The limiting factors are the high sintering temperature (≈1600°C) and intrinsic grain boundaries resistance.The cold sintering process (CSP) is used to reduce the sintering temperature. In this technic, derived from the hydrothermal method, BCZY powder mixed with a small volume of liquid phase (3-30 wt%), is simultaneously pressed (at 50 to 500 MPa) and heat treated during a short time period (1-60 min) at low temperatures (100-200°C), leading to dense pellets.This study deals with the influence of synthesis conditions using the auto combustion and CSP on the microstructure and conductivity. With a calcination temperature of 1000°C and an optimized CSP treatment, a relative density above 93% can be obtained at only 1200°C. We will show also the influence of the cold sintering process (CSP) on the conductivity. Compared to conventional sintering process at about 1600°C, high conductivity level of 10-2 S/cm is obtained at 400°C (figure 1) using CSP process combined with a 1200°C annealing step.[1] K. Thabet, M. Devisse, E. Quarez, O. Joubert, et A. Le Gal La Salle, "Influence of the autocombustion synthesis conditions and the calcination temperature on the microstructure and electrochemical properties of BaCe0.8Zr0.1Y0.1O3−δ electrolyte material", Solid State Ionics, vol. 325, 2018, p. 48-56,[2] F. Iguchi, T. Yamada, N. Sata, T. Tsurui, et H. Yugami, "The influence of grain structures on the electrical conductivity of a BaZr0.95Y0.05O3 proton conductor", Solid State Ionics, vol. 177, no 26, 2006, p. 2381-2384 Figure 1

Optimization of Material Contrast for Efficient FIB‐SEM Tomography of Solid Oxide Fuel Cells

AbstractFocused ion beam (FIB) – scanning electron microscopy (SEM) serial sectioning tomography has become an important tool for three‐dimensional microstructure reconstruction of solid oxide fuel cells (SOFC) to obtain an understanding of fabrication‐related effects and SOFC performance. By sequential FIB milling and SEM imaging a stack of cross‐section images across all functional SOFC layers was generated covering a large volume of 3.5·104 μm3. One crucial step is image segmentation where regions with different image intensities are assigned to different material phases within the SOFC. To analyze all relevant SOFC materials, it was up to now mandatory to acquire several images by scanning the same region with different imaging parameters because sufficient material contrast could otherwise not be achieved. In this work we obtained high‐contast SEM images from a single scan to reconstract all functional SOFC layers consisting of a Ni/Y2O3‐doped ZrO2 (YDZ) cermet anode, YDZ electrolyte and (La,Sr)MnO3/YDZ cathode. This was possible by using different, simultaneous read‐out detectors installed in a state‐of‐the‐art scanning electron microscope. In addition, we used a deterministic approach for the optimization of imaging parameters by employing Monte Carlo simulations rather than trial‐and‐error tests. We also studied the effect of detection geometry, detecting angle range and detector type.

Computational approaches to the exsolution phenomenon in perovskite oxides with a view to design highly durable and active anodes for solid oxide fuel cells

Computational approaches have been used effectively in material design for solid oxide fuel cells (SOFCs). As a way to improve the performance and stability of anode materials in SOFCs, the exsolution phenomenon has been extensively taken advantage of. In the exsolution process, highly active and stable nanoparticles (NPs) are formed uniformly over the surface of the host oxide due to the anchoring effects of exsolved NPs in the host’s structure. In this review, we particularly focus on how computational approaches such as density functional theory calculation, phase field modeling, and analytic methods can be used to understand the exsolution phenomenon; this knowledge can then be exploited to design enhanced anode materials for SOFCs. We first review the nature of exsolution and then look into catalytic applications of exsolved NPs. From this point, we investigate how to engineer exsolved nanoparticles to maximize their catalytic activity with a view that any enhanced performance will aid future applications.

Effects of P-N and N-N heterostructures and band alignment on the performance of low-temperature solid oxide fuel cells

Reducing the operating temperature of solid oxide fuel cells (SOFCs) has attracted worldwide attention in recent years. This has prompted massive efforts in developing new electrolyte materials for low-temperature SOFCs, typically including heterostructure materials consisting of semiconductors and ionic conductors. In this study, a p-n heterostructure (LiZnO–SnO2) and an n-n heterostructure (ZnO–SnO2) are proposed and evaluated in SOFCs to tap further the potential of a heterostructure for low-temperature electrolyte use. The results show that the developed LiZnO–SnO2 and ZnO–SnO2 both capably play competent electrolyte roles in SOFCs with high ionic conductivities and promising fuel cell performance, achieving peak power outputs of 376 and 255 mW cm−2 at 530 °C, respectively. To interpret the good performance of the two heterostructure electrolytes, energy band alignment mechanisms based on p-n hetero-junction and n-n heterostructure are employed to illustrate the ionic enhancement and electronic suppression processes of the materials. These findings reveal new insight into developing heterostructure electrolytes for low-temperature SOFCs.

Microstructure of a solid oxide fuel cell by microbeam X-ray diffraction

Microbeam X-ray diffraction (µ-XRD) using synchrotron radiation at BL33XU (Toyota beamline) in SPring-8 produces a small beam size (1 µm × 1 µm) that allows detecting changes in the lattice parameter and crystal phase of samples. This feature renders this technique suitable for the structural investigation of solid oxide fuel cells (SOFC) having a layered structure of various components in a micrometer order. In this study, using the µ-XRD technique, the refinement of the lattice parameters of SOFC materials and the assignment of secondary phases (e.g., a solid solution of CeO2–ZrO2 and SrZrO3) formed by interdiffusion between layers at the interface with micrometer intervals are achieved in the cell cross section, which had not been accomplished using conventional XRD methods.

High-temperature electrocatalysis and key materials in solid oxide electrolysis cells

Abstract Solid oxide electrolysis cells (SOECs) can convert electricity to chemicals with high efficiency at ~600–900 °C, and have attracted widespread attention in renewable energy conversion and storage. SOECs operate in the inverse mode of solid oxide fuel cells (SOFCs) and therefore inherit most of the advantages of SOFC materials and energy conversion processes. However, the external bias that drives the electrochemical process will strongly change the chemical environments in both in the cathode and anode, therefore necessitating careful reconsideration of key materials and electrocatalysis processes. More importantly, SOECs provide a unique advantage of electrothermal catalysis, especially in converting stable low-carbon alkanes such as methane to ethylene with high selectivity. Here, we review the state-of-the-art of SOEC research progress in electrothermal catalysis and key materials and provide a future perspective.

Demonstrating the dual functionalities of CeO2–CuO composites in solid oxide fuel cells

Nowadays, lowering the operating temperature of solid oxide fuel cells (SOFCs) is a major challenge towards their widespread application. This has triggered extensive material studies involving the research for new electrolytes and electrodes. Among these works, it has been shown that CeO2 is not only a promising basis of solid oxide electrolytes, but also capable of serving as a catalytic assistant in anode. In the present work, to develop new electrolytes and electrodes for SOFCs based on these features of CeO2, a new type of functional composite is developed by introducing semiconductor CuO into CeO2. The prepared composites with mole ratios of 7:3 (7CeO2–3CuO) and 3:7 (3CeO2–7CuO) are assessed as electrolyte and anode in fuel cells, respectively. The cell based on 7CeO2–3CuO electrolyte reaches a power outputs of 845 mW cm−2 at 550 °C, superior to that of pure CeO2 electrolyte fuel cell, while an Ce0.8Sm0.2O2-δ electrolyte SOFC with 3CeO2–7CuO anode achieves high power density along with open circuit voltage of 1.05 V at 550 °C. In terms of polarization curve and AC impedance analysis, our investigation manifests the developed 7CeO2–3CuO composite has good electrolyte capability with a hybrid H+/O2− conductivity of 0.1–0.137 S cm−1 at 500–550 °C, while the 3CeO2–7CuO composite plays a competent anode role with considerable catalytic activity, indicative of the dual-functionalities of CeO2–CuO in fuel cell. Furthermore, a bulk heterojunction effect based on CeO2/CuO pn junction is proposed to interpret the suppressed electrons in 7CeO2–3CuO electrolyte. Our study thus reveals the great potential of CeO2–CuO to develop functional materials for SOFCs to enable low-temperature operation.

Three-Dimensionally Micro-Architected Protonic Ceramic Fuel Cells

The solid oxide fuel cells (SOFCs) have been considered as important alternative energy technology, due to a variety of advantages, such as their high energy conversion efficiency, free noxious emissions, and direct use of a wide range of hydrocarbon fuels. Especially, the reverse operation of SOFCs, which is called solid oxide electrolysis cell (SOEC), is currently one of the most promising technologies for fuel production. However, their high-temperature operation (typically >700°C) leads to the rapid degradation of electrodes and necessitates a high balance of plant costs. To make SOFCs more economically feasible and viable, further reduction of operating temperature is inevitable. To this end, the utilization of proton-conducting oxides, which exhibit relatively high ionic conductivity with the low activation energy (<0.5eV), enables protonic ceramic fuel cells (PCFCs) to operate at an intermediate temperature regime (IT, 400–600°C), where the aforementioned benefits of SOFCs can also be accomplished. Moreover, PCFCs prevents the dilution of the fuel during the operation and provides higher resistance of carbon cocking on hydrocarbon fuels.Although the PCFCs have distinct advantages against traditional oxygen conducting SOFCs, the lower-than-predicted performance of PCFCs and scalability issues caused the considerable skepticism of the successful applicability of PCFCs. Most importantly, unlike traditional SOFCs, the development of mixed oxide ion and electron conductors (MIECs) for oxygen reduction reaction (ORR) at the cathode of PCFCs has shown marginal success due to the absence of protonic conduction and still needs to be improved. At the cathode, the ORR is limited to triple phase boundary (TPB), where the electrolyte, gas, and cathode mutually contact, and its geometrical enhancement at the interface area between cathode and electrolyte layers is crucial to improve the performance of PCFCs. Therefore, electrode-electrolyte interface architecting via micro-patterning is one of the most attractive approaches, since it significantly expands the catalytic active sites of TPB near the interface, where ORR preferentially occur. Moreover, this architecting approach also facilitates the use of currently viable state-of-art cathode materials of SOFCs; Lanthanum Strontium Cobalt Ferrite (LSCF), Barium Strontium Cobalt Ferrite (BSCF). Therefore, patterns with a high aspect ratio, which maximize the interface area, are required for significant enhancement of electrochemical performance.Here, for the first time, we describe a three-dimensionally micro-architecting process for anode-supported PCFCs, demonstrating dramatic performance enhancement from the expanded interface area between cathode and electrolyte. The various patterns with high ratios were exactly transferred from the original PUA (polyurethane acrylate) molds to the thin and dense protonic conducting electrolyte layer. The patterns maintained the same aspect ratios during the sintering process and finally increased the interface area of more than 30%. The morphology of the patterned surface was characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). The AC electrochemical impedance spectroscopy was utilized to examine the electrochemical performances of patterned cells. Our unique patterning method opens the new pathway for further performance enhancement of PCFCs. Figure 1

Boosting the Electrochemical Performance of Fe-Based Layered Double Perovskite Cathodes by Zn2+ Doping for Solid Oxide Fuel Cells.

Mixed oxygen ionic and electronic conduction is a vital function for cathode materials of solid oxide fuel cells (SOFCs), ensuring high efficiency and low-temperature operation. However, Fe-based layered double perovskites, as a classical family of mixed oxygen ionic and electronic conducting (MIEC) oxides, are generally inactive toward the oxygen reduction reaction due to their intrinsic low electronic and oxygen-ion conductivity. Herein, Zn doping is presented as a novel pathway to improve the electrochemical performance of Fe-based layered double perovskite oxides in SOFC applications. The results demonstrate that the incorporation of Zn ions at Fe sites of the PrBaFe2O5+δ (PBF) lattice simultaneously regulates the concentration of holes and oxygen vacancies. Consequently, the oxygen surface exchange coefficient and oxygen-ion bulk diffusion coefficient of Zn-doped PBF are significantly tuned. The enhanced mixed oxygen ionic and electronic conduction is further confirmed by a lower polarization resistance of 0.0615 and 0.231 Ω·cm2 for PrBaFe1.9Zn0.1O5+δ (PBFZ0.1) and PBF, respectively, which is measured using symmetric cells at 750 °C. Moreover, the PBFZ0.1-based single cell demonstrates the highest output performance among the reported Fe-based layered double perovskite cathodes, rendering a peak power density of 1.06 W·cm-2 at 750 °C and outstanding stability over 240 h at 700 °C. The current work provides a highly effective strategy for designing cathode materials for next-generation SOFCs.

A perspective on DRT applications for the analysis of solid oxide cell electrodes

Conventional electrochemical impedance spectroscopy (EIS) is a popular in-situ technique for electrochemical analysis and has been widely applied in solid oxide cells (SOCs), including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), to determine the polarization resistance of electrodes. To interpret the EIS, equivalent circuit models (ECMs) are widely used, however, usually pre-defined without careful evaluation of the electrochemical processes, such as some elemental processes might overlap in frequency domain. On this background, distribution of relaxation times (DRT) converted from impedance spectra has been developed, that can effectively separate the polarization processes with a high resolution. Rational ECMs can be obtained by calculating and analyzing the characteristics of DRT spectra. The DRT method has been successfully used to SOFCs and SOECs, enabling much clearer understandings of the corresponding electrochemical reaction mechanism of the cells. Although the DRT method has been explored in SOFCs and SOECs for more than ten years, while it is still in its infancy and faces some challenges. Here, we present a review for the status of DRT applications in SOFCs and SOECs. On the basis of rational interpretation of DRT spectra, we believed that the DRT analysis can facilitate the design of key materials for SOFCs and SOECs with high efficiency and excellent performance.

An efficient and durable perovskite electrocatalyst for oxygen reduction in solid oxide fuel cells

Achieving superior electrocatalytic activity and thermal/chemical stability of cathode materials is the key to high-performance and durable solid oxide fuel cells (SOFC). Here, we present a barium and praseodymium co-substituted perovskite Bi0.7Pr0.1Ba0.2FeO3-δ (BPBF), a cubic-symmetry oxide phase, as a candidate cathode material for SOFC, with a focus on its crystalline structure, oxygen transport, electrocatalytic activity, as well as structural and chemical stability. The BPBF-based cathode delivers superior electroactivity, with a polarization area-specific-resistance as low as 0.056 Ω cm2 at 700 °C in symmetrical cells. Surprisingly, when exposed to both air and 1 vol% CO2-containing air at 600 °C for 100 h, the electrode activity remains constant. The prominent thermal and chemical (CO2 tolerance) stability can be ascribed to co-substitution of barium and praseodymium and high acidity of bismuth ions. Endowed with favorable electrocatalytic activity and excellent durability, the BPBF-based material can be a promising cathode to facilitate commercialization of SOFC technology.

Electrochemical properties of Sr-doped layered perovskite as a promising anode material for direct hydrocarbon SOFCs

A direct utilization of hydrocarbon fuels in solid-oxide fuel cell (SOFC) has been considered a worthwhile and realizable goal. Admittedly, while great strides have been made toward this development goal, there still remain Ni-based anode materials issues to be resolved. In this regard, this study focuses on Sr effect on electrical and electrochemical behaviors in PrBaMn2O5+?? (PBM) to be employed as an anode in SOFC operation under hydrogen and hydrocarbon fuels. The electrical conductivity of A-site layered PrBa0.8Sr0.2Mn2O5+?? (PBSM) oxide reaches 3.74 S cm???1 at 800 ??C in H2, which is higher than that of PBM due to doping smaller Sr into Ba site and fully meets the requirement to be employed as an anode material. The electrochemical performance is evaluated using La0.9Sr0.1Ga0.8Mg0.2O3????? electrolyte-supported cell based on A-site layered PBSM anode with Co???Fe catalysts, and shows peak power density around 1.38 and 0.68 W cm???2 at 800 ??C in H2 and C3H8, respectively. Considering the electrical and electrochemical properties, A-site layered PBSM might offer the opportunities to discover and explore new high-performance anode material for direct hydrocarbon SOFCs.

Effects of cobalt and iron proportions in Pr0.4Sr0.6Co0.9-xFexNb0.1O3-δ electrode material for symmetric solid oxide fuel cells

Abstract Pr0.4Sr0·6Co0.9-x FexNb0.1O3-δ (PSCFxN) (x = 0, 0.2, 0.4, 0.6 and 0.9) oxides are evaluated as symmetric electrode materials for solid oxide fuel cells (SOFCs). Both the thermal expansion coefficient (TEC) and conductivity decrease with the increasing of Fe amount. With the increase in Fe content, more Fe4+ species are reduced to Fe3+, generating more oxygen vacancies. It effectively promotes the oxygen incorporation kinetics, and lowers the polarization resistance (Rp). As a result, the PSCF0·6N exhibits the lowest polarization resistance of 0.028 and 0.077 Ωm2 at 900 °C in air and hydrogen, respectively, and the highest electrical conductivity of 258.90 Scm−1 at 650 °C among all the prepared PSCFxN materials. Meanwhile, with the doping of Fe, the TEC decreases near to the electrolyte TEC value. As such, the peak power densities of the electrolyte supported PSCF0.6N-based symmetric SOFCs with different electrolyte thicknesses of 500, 400 and 300 μm are 0.642, 0.713 and 0.891 Wcm−2, respectively. Meanwhile, the output voltage of the obtained PSCF0·6N/LSGM/PSCF0·6N symmetric SOFC decreases only 5% in 50 h stability test under a current density of 0.5 Acm−2. These results indicate that the PSCF0·6N material should be a promising electrode material for the symmetric SOFCs.