Wet H2 Research Articles

Cerium and ruthenium co-doped La0.7Sr0.3FeO3–δ as a high-efficiency electrode for symmetrical solid oxide fuel cell

Symmetrical solid oxide fuel cells (SSOFCs) could be alternative energy conversion devices due to their simple fabrication process and low cost. Herein, perovskite La0.6Ce0.1Sr0.3Fe0.95Ru0.05O3–δ (LCSFR) was synthesized and evaluated as a high-performance electrode for SSOFCs based on the electrolyte of La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM). LCSFR retains their stable perovskite crystal structure in both reducing and oxidizing atmospheres, though a minor amount of LaSrFeO4 phase is present under reducing conditions. Morphology investigation shows that homogeneously dispersed Ru metallic nanoparticles are exsolved on the surface of LCSFR after being reduced. The polarization resistance (Rp) of LCSFR-CGO (Ce0.9Gd0.1O2–δ) is about 0.11 Ω⋅cm2 at 800 °C in air, while the value of Rp for LCSFR-CGO in wet H2 (3% H2O) increases up to 0.32 Ω⋅cm2. The symmetrical LCSFR-CGO|LSGM|LCSFR-CGO cell demonstrates a performance with an open circuit potential (OCV) of 1.07 V and a maximum peak power density of 904 mW/cm2 at 800 °C using wet H2 as the fuel. This high performance indicates that LCSFR is a candidate electrode for SSOFCs.

Stability and activity controls of Cu nanoparticles for high-performance solid oxide fuel cells

Cu-based electrodes could advance solid oxide fuel cells (SOFC) technology due to good electric conductivity and relatively high electrochemical activity among transition metals. However, one of the main challenges for designing anode materials is thermal stability in SOFC operation condition. Herein, a promising anode material decorated with Cu nanoparticles (NPs) was synthesized via in-situ exsolution from La0.43Sr0.37Cu0.12Ti0.88O3-δ (LSCuT) perovskite. Compared to infiltration process, Cu NPs prepared by in-situ exsolution displayed homogeneous nano size distribution on the substrate and excellent thermal stability at 600 °C in H2 atmosphere, for ∼50 h. In addition, we employed electrochemical reduction (ER) at 2.3 V for a few seconds to demonstrate that NPs can be rapidly grown, and the substrate reduced. A single cell with LSCuT anode (10 μm)||ScSZ electrolyte (90 μm) ||LSM-ScSZ cathode (20 μm) exhibits maximum power density of 1.38 Wcm−2 at 900 °C under wet H2. The present study provides possibility of a broad application of thermally stable Cu-based electrodes.

Increasing the thermal expansion of proton conducting Y-doped BaZrO3 by Sr and Ce substitution

Proton conducting oxide electrolytes find potential application in proton ceramic fuel cells and electrolyzers operating at intermediate temperatures, e.g. 400–600 °C. However, state-of-the-art proton conducting ceramics based on Y-doped BaZrO3 (BZY) have lower thermal expansion coefficient (TEC) than most commonly applied or conceived supporting electrode structures, making the assembly vulnerable to degradation due to cracks or spallation. We have increased the TEC of 20 mol% Y-doped BZY (BZY20) by partially substituting Ba and Zr with Sr and Ce, respectively, to levels which still maintain the cubic structure and sufficiently minor n-type conduction; (Ba0.85Sr0.15)(Zr0.7Ce0.1Y0.2)O2.9 (BSZCY151020). High temperature XRD shows that this material has a cubic structure (space group Pm3¯m) in the temperature range of 25–1150 °C and a linear TEC of ~10 × 10−6 K−1, as compared to the ~8 × 10−6 K−1 for BZY. It exhibited a DC conductivity of ~5 mS cm−1 at 600 °C in wet H2. This electrolyte with increased TEC may find application in proton ceramic electrochemical cells in general and metal supported ones in particular.

High Cu content LaNi1-xCuxO3-δ perovskites as candidate air electrode materials for Reversible Solid Oxide Cells

High Cu content perovskite-type LaNi1-xCuxO3-δ oxides are evaluated as alternative air electrode materials for Solid Oxide Cells. Auto-combustion synthesis allowed to obtain fine oxide powders up to a Cu content of x = 0.75 under ambient pressure. Investigations of the crystal structure, oxygen deficiency, chemical and thermal stability, as well as transport properties reveal satisfactory characteristics, with high total electrical conductivity and high concentration of oxygen vacancies at elevated temperatures. LaNi1-xCuxO3-δ-based electrode layers show low polarization resistance values in La0.8Sr0.2Ga0.8Mg0.2O3-δ-based symmetrical cells. The lowest values for Cu-rich compositions at 800 °C are 0.056 Ω cm−2 for LaNi 0.5Cu0.5O3-δ and 0.054 Ω cm−2 for LaNi0.25Cu0.75O3-δ with La0.2Ce0.8O3-δ buffer layer. For the reversible cell with LaNi0.5Cu0.5O3-δ air electrode, approx. 870 mW cm−2 power density output at 900 °C is obtained when fueled with wet H2, as well as over 3 A cm−2 current density at 2 V in the electrolysis mode.

Improved electrochemical performance of Bi doped La0.8Sr0.2FeO3-δ nanofiber cathode for IT-SOFCs via electrospinning

In this study, perovskite La0.8-xBixSr0.2FeO3-δ (LBSF, x = 0.0–0.5) nanofibers with great crystallinity were prepared by electrospinning method and used as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). The symmetric cells of nanofiber-based LBSF electrode on Sm0.2Ce0.8O1.9 (SDC) electrolyte show excellent electrochemical performance. The La0.4Bi0.4Sr0.2FeO3-δ (LBSF4) cathode has the best performance with a polarization resistance (RP) of 0.126 Ω cm2 at 650 °C. The anode-supported single cell with LBSF4 as the cathode film and Ni-SDC as the anode has a maximum power density of 448 mW cm-2 at 650 °C using wet H2 as the fuel. In addition, the LBSF4 cathode with fibrous structure exhibits outstanding electrochemical behavior. The catalytic activity of the cathode was improved due to the incorporation of the Bi element, indicating that LBSF4 is promising as a cathode material in the field of IT-SOFCs.

Characterization of nio-bczy as composite anode prepared by a one-step sol-gel method

A high polarization resistance (Rp) at intermediate temperature (500–800°C) operation has become one of the major challenges in the development of proton-conducting fuel cells (PCFCs). Rp is the resistance of the cell that contributes by the electrodes parts which are anode and cathode as well as their interfacial components. The present study focused on the NiO-Ba(Ce0.6Zr0.4)0.9Y0.1O3-δ (NiO-BCZY) composite anode and its interfacial parts where the oxidation process takes place. The NiO-BCZY with a ratio of 50:50 was prepared by a sol-gel method and characterized by X-Ray Diffractometer (XRD), Field Emission Scanning Electron Microscopy/Energy Dispersive X-ray (FESEM/EDX), and Electrochemical Impedance Spectroscopy (EIS). At calcination temperature of 1100°C, NiO and BCZY oxides can preserve their phases to form composite anode as proven by XRD analysis. Morphology of the composite anode as observed by FESEM was spherical with particle size in the range of 30-70 nm. XRD analysis showed the formation of Ni-BCZY after undergoing reduction process under wet H2:N2 (10%:90%). As confirmed by the EIS data, the increased conductivity of the composite anode in wet H2:N2 (10%:90%) indicates that the NiO in the composite anode was reduced to Ni metal. The fabricated NiO-BCZY composite anode has shown a good potential to be a promising anode in PCFC application.

Construction of Multifunctional Nanoarchitectures in One Step on a Composite Fuel Catalyst through In Situ Exsolution of La0.5Sr0.5Fe0.8Ni0.1Nb0.1O3-δ.

Multifunctional nanoarchitecture (MNA) on catalysts has attracted great attention because of its capability to improve the performance, durability, and resistance to unwanted side reactions. Such structures, however, are conventionally prepared by deposition methods, which inherently suffer from costly and time-consuming drawbacks. Here, we report a simple one-step process to successfully construct a novel MNA with core-shell nanoparticles anchored at the heterointerface of dual-phase oxide substrates through a phase transition and in situ exsolution of perovskite La0.5Sr0.5Fe0.8Ni0.1Nb0.1O3-δ (LSFNNb0.1) in wet H2 (3% H2O) at 800 °C. The core-shell nanoparticles are composed of a Ni-Fe alloy core and a SrLaFeO4-type layered perovskite oxide shell (RP-Ruddlesden-Popper-layered perovskites), which synergistically improves the electrochemical activity and effectively suppresses aggregation and coarsening of the metallic core. The RP phase also covers the surface of perovskite bulk (SP-single perovskite), forming the heterointerface and preventing further decomposition of the SP phase. The RP/SP heterointerface may improve the kinetics of surface exchange of oxygen species, resulting in the enhancement of performance and durability of the reduced LSFNNb0.1 as an anode for solid oxide fuel cells (SOFCs). A doped zirconia electrolyte-supported single cell with the anode achieves the maximum power density (MPD) of 0.83 W cm-2 at 800 °C in wet H2, and the corresponding polarization resistance is as low as 0.15 Ω cm2. This work reveals the formation mechanism of the MNA by investigating the evolution of the crystal structure, composition and morphology of LSFNNb0.1, when changing reducing temperature and time in wet H2 and 5% H2-Ar. The oxygen vacancies and phase transitions are found to play important roles in the formation of the MNA. The construction of MNAs in one step opens a new opportunity to design and prepare high-performance and stable catalysts for applications in energy conversion and storage.

Coking resistant Ni–La0.8Sr0.2FeO3 composite anode improves the stability of syngas-fueled SOFC

An improved SOFC anode with excellent stability against carbon deposition with syngas as fuel is reported. The anode material is Ni–La0.8Sr0.2FeO3 (LSF) composite synthesized by anhydrous impregnation. After reduction in wet H2 (3% H2O), the material partially decomposes to SrLaFeO4 and exsolved Fe. The exsolved Fe forms Ni–Fe alloy with impregnated Ni. The particle size of Ni–Fe alloy is about 20–50 nm. The Ni–Fe alloy nanoparticles disperse on the surface of the La0.8Sr0.2FeO3 and SrLaFeO4 oxides. The increase of Ni content promotes the exsolution of Fe and increases the reaction sites of Ni–Fe alloy. With the increase of the Ni content, the electrical conductivity and catalytic activity are enhanced, which improves the electrochemical performance of the single cell. The cell with 10 mol.% Ni impregnated Ni-LSF as anode achieves a maximum power density of 550 mW cm−2 at 700 °C fueled with syngas. The strong interaction of the nano-sized Ni–Fe alloy with the LaxSryFeOz (La0.8Sr0.2FeO3 or SrLaFeO4) oxide substrate efficiently suppresses carbon deposition with high graphitization degree. Besides, the SrLaFeO4 phase which can accommodate interstitial oxygen facilitates the removal of the deposited carbon.

In-situ exsolved FeRu alloy nanoparticles on Ruddlesden-Popper oxides for direct hydrocarbon fuel solid oxide fuel cells

FeRu alloy (FRA) nanoparticles surface decorated Ruddlesden-Popper type layer perovskite PrSrFe1-xRuxO4+δ (RP-PSFeRu) was prepared by in-situ reduction of the cubic (Pr0.5Sr0.5)0.9Fe0.9Ru0.1O3-δ (P–PSFeRu) in H2 at 800 °C. When used as the SOFC anode material, it has excellent catalytic activity for H2 and hydrocarbon fuels. The La0.8Sr0.2Ga0.83Mg0.17O3-δ electrolyte supported SOFC single cell with RP-PSFeRu-FRA-GDC composite anode can deliver a maximum power density of 0.75 and 0.50 W cm−2 in wet H2 and C3H8 at 800 °C, respectively. Furthermore, the single cell shows a stability outputs at a constant current load of 0.5 A cm−2 in wet H2 and 0.15 A cm−2 in wet C3H8 fuels, indicating an exceptional stability and cooking resistance.

Highly stable La0.5Sr0.5Fe0.9Mo0.1O3-δ electrode for reversible symmetric solid oxide cells

Reversible solid oxide cells (RSOCs) using identical material as both fuel electrode and air electrode have received extensive attentions due to their simplified fabrication process, increased compatibility between electrolyte and electrode. In this work, Molybdenum doped La0.5Sr0.5Fe0.9Mo0.1O3-δ (LSFMo) symmetric electrode based on RSOCs is firstly designed and synthesized via sol-gel method. The effect of Molybdenum substitution at Fe-site on crystal structure, chemical stability, conductivity and electrochemical performance of La0.5Sr0.5FeO3-δ oxide is thoroughly investigated. The structural stability of La0.5Sr0.5FeO3-δ (LSF) in reducing condition is significantly enhanced after the incorporation of Mo5+/6+ and the conductivity in 5% H2 for LSFMo is ~7 times higher than that of undoped LSF. In addition, the polarization resistance value at 850 °C based on LSFMo/LSGM/LSFMo is 0.08 and 0.09 Ω cm2 in air and wet H2, respectively. At 850 °C and 20%H2O–H2, a peak power density of 640 mW cm−2 is obtained in fuel cell mode, while a current density of −1000 mA cm−2 is attained at 1.3 V in electrolysis mode. Finally, the symmetric cell exhibits an excellent cycling reversible operation in both SOFCs mode and SOECs mode without detectable degradation.

Electrochemical Study of the Versatility of a Solid Cell Working both as Fuel Cell and Electrolysis Modes

AbstractA Ni/Yttria‐stabilized zirconia (YSZ) cell with a (La0.60Sr0.40)0.95Co0.20Fe0.80O3–δ cathode is tested both in fuel cell and electrolysis modes. In fuel cell mode under dry air and wet H2, the cell is operated between the open circuit voltage (OCV) and 0.4 V and reaches 330 mW cm−2 at 850 °C for 157 mL min−1 H2 supply. The influence of temperature and air or hydrogen flow rate is studied, and impedance measurements show that below 0.8 V the electrolyte becomes the more resistive part of the cell. Nevertheless, fuel utilization yields are higher under oxygen or hydrogen depletion. If it is possible at 750 °C to work at low voltage during several hours in the entire voltage range, the voltage decrease must be limited at 850 °C. The cell can also be operated under wet air. The same cell can be operated in electrolysis mode, and a power density of 340 mW cm−2 can be obtained at 0.3 V/OCV under 100 mL min−1 wet (3% H2O) 5% H2–95% Ar mixture on the fuel side and dry or wet 100 mL min−1 air flow on the air side. Nevertheless, bubbling air providing the air electrode in saltwater has an irreversible detrimental effect on the cell.

Cobalt and Titanium substituted SrFeO3 based perovskite as efficient symmetrical electrode for solid oxide fuel cell

One of the key tasks in solid oxide fuel cell research is to develop cost-competitive electrodes that work efficiently in wide range of air and fuel utilizations. Herein, we promote our study to a series of Cobalt and Titanium substituted La0.4Sr0.6Fe0.7Ti0.3-xCoxO3-δ (LSFTC, x = 0, 0.05, 0.1, 0.2) perovskite oxides. It is shown that Cobalt doping effectively improves the electrical conductivity and oxygen electrochemical reduction activity, yielding decreased cathode polarization resistance and lower dependence of pO2 change. For example, σ600°C = 81 S/cm and Rp,C750°C = 0.1 Ω cm2 for LSFTC-5 are obtained in pO2=0.21atm. In anode conditions of wet H2, the LSFTC cubic perovskites are partially reduced to hybrid structure of ABO3-A2BO4-metal with Cobalt doping amount less than 10% and are fully decomposed to A2BO4-metal with 20% doping. The higher Cobalt substitution generates more nano particles exsolution, which promotes anode processes at low temperatures. However, the generated AO-rich compositions are shown detrimental to anode performance in both conducting property and anode catalytic activity under low H2 partial pressures. In current study, the electrodes are evaluated under practical working conditions with broad pO2 and pH2, which provides guidelines for industrial-applicable SrFeO3 based symmetrical electrode development.

Hydrogen Sensing Performance of ZnO Schottky Diodes in Humid Ambient Conditions with PMMA Membrane Layer.

Enhanced hydrogen sensing performance of Pt Schottky diodes on ZnO single crystal wafers in humid ambient conditions is reported using a polymethylmethacrylate (PMMA) membrane layer. ZnO diode sensors showed little change in forward current when switching to wet ambient H2 conditions with 100% relative humidity. This sensitivity drop in the presence of water vapor can be attributed to surface coverage of hydroxyl groups on the Pt surface in humid ambient conditions. The hydrogen sensitivity of PMMA-coated diode sensors recovered up to 805% in wet H2 ambient conditions at room temperature. The PMMA layer can selectively filter water vapor and allow H2 molecules to pass through the membrane layer. It is clear that the PMMA layer can effectively serve as a moisture barrier because of low water vapor permeability and its hydrophobicity. In both dry and wet conditions, ZnO diodes exhibited relatively fast and stable on/off switching in each cycle with good repeatability.

Highly conductive proton-conducting electrolyte with a low sintering temperature for electrochemical ammonia synthesis

BaCe0·7Zr0.1Gd0.2O3-δ (BCZG) powder is synthesized by a citrate sol-gel method, and different amounts of Li2CO3 are introduced to lower the sintering temperature. The densification temperature of BCZG ceramic is decreased drastically to 1250 °C by using Li2CO3 as sintering aid. BCZG with 2.5 wt% of Li2CO3 (BCZG-2.5L) can not only remarkably promote the sintering process of BCZG but also enhance its electrical conductivity. The total ionic conductivity of BCZG-2.5L attains to 1.9 × 10−2 S cm−1 at 600 °C in a wet H2 atmosphere. Ammonia synthesis at atmospheric pressure is conducted on (2K, 10Fe)/Ni-BCZG | BCZG-2.5L | Ni-BCZG electrolytic cell with an applied voltage of 0.2–1.6 V at a temperature of 450–600 °C. The highest NH3 formation rate of 1.87 × 10−10 mol s−1 cm−2 and the highest current efficiency of 0.53% is achieved at 500 °C with an applied voltage of 0.8 V.

Structural and electrochemical property evolutions of perovskite SOFC anodes: Role of fuel atmosphere in (La0.4Sr0.6)1-xCo0.2Fe0.7Nb0.1O3-δ

The in-situ precipitated nano metal particle-perovskite anodes show promising application prospects in Solid Oxide Fuel Cells. Previously reports mainly show new exsolved material, but barely focus on their practical application concerns. Herein, the structural and electrochemical properties evolution of (La0.4Sr0.6)1-xCo0.2Fe0.7Nb0.1O3-δ (LSCFN, x = 0, 0.05, 0.1) versus varied anode fuel atmospheres are presented. Results show that perovskite-type LSCFN anodes are fully reduced to K2NiF4 structure in dry H2 at 850 °C, but maintain to be ABO3 structure with minor structure change under water containing H2. The exsolved Co1-xFex phases are observed under both conditions, but with much higher Fe content under dry H2. The Electrochemical Impedance Spectra shows that LSCFN anodes are more sensitive to pH2 change under humidified fuels than dry conditions. Single cells with (La0.4Sr0.6)0.9Co0.2Fe0.7Nb0.1O3-δ anode show promising performance with maximum power densities of 1.2 and 0.95 W/cm2 under dry and wet H2 at 850 °C, respectively.

Stepwise construction of Pt decorated oxygen-deficient mesoporous titania microspheres with core-shell structure and magnetic separability for efficient visible-light photocatalysis

Solid photocatalysts with high specific surface area, superior photoactivity and ease of recycling are highly desired in chemical process, water treatment and so on. In this study, a facile stepwise sol-gel coating approach was utilized to synthesize Pt decorated oxygen-deficient mesoporous titania microspheres with core-shell structure and convenient magnetic separability (denoted as Fe3O4@SiO2@Pt/mTiO2-x). These photocatalysts consist of magnetic Fe3O4 cores, nonporous insulating SiO2 middle layer and mesoporous anatase TiO2-x shell decorated by Pt nanoparticles (∼3.5 nm) through wet impregnation and H2 reduction. As a result of high activity of oxygen-deficiency of black TiO2-x by H2 reduction and efficient inhibition of electron-hole recombination by Pt nanoparticles, the rationally designed core-shell Fe3O4@SiO2@Pt/mTiO2-x photocatalysts exhibit superior photocatalytic performance in rhodamine B (RhB) degradation under visible light irradiation, with more than 98% of RhB degraded within 50 min. These core-shell structured photocatalysts show excellent recyclability under the assistance of magnetic separation with well-retained photocatalytic performance even after running five cycles. This stepwise synthesis method paves the way for the rational design of a high-efficiency recyclable heterogeneous catalyst, including photocatalysts, for various applications.

Promotion on electrochemical performance of Ba‐deficient Ba1 − xBi0.05Co0.8Nb0.15O3 − δcathode for intermediate temperature solid oxide fuel cells

Reducing the operating temperature is the developing trend for solid oxide fuel cells. The key is to develop the cathode with high electrocatalytic activity for oxygen reduction reaction operated at reduced temperatures. Ba-deficient Ba1 − xBi0.05Co0.8Nb0.15O3 − δ (Ba1 − xBCN, 0 ≤ x ≤ 0.10) are synthesized by solid-state reaction method and evaluated as novel cathodes for intermediate-temperature solid oxide fuel cells. Ba1 − xBCN is preserved to primitive cubic perovskite phase and meets the compatibility requirement with gadolinium doped ceria oxide (GDC) electrolyte at 950°C. Though the Ba deficiency distorts the cell symmetry, it improves the charge transfer steps rapidly, ascribing to the improvement of oxygen vacancy concentration. The polarization resistance of Ba0.95BCN is as low as 0.056 Ω cm2 in air at 700°C. The peak power density of the single cell with this cathode is as high as 1.41 W cm−2 at 750°C with wet H2 as fuel and air as oxidant, indicating the great potential for enhanced performance of Co-based cathodes with A-site deficiency.

Structural evolution of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite MPEC membrane by in-situ synchrotron XRD analyses

Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered very promising materials for H2 separation at T > 600 °C. Among these, BaCe0.65Zr0.2Y0.15O3-δ-Ce0.85Gd0.15O2-δ (BCZ20Y15-GDC15) composite combine an acceptable H2 flux and good chemical stability under CO2- and H2S-containing atmospheres. However, a clear understanding of its crystal structure, phase stability and mechanical stability under real working conditions could not yet be obtained. In this work, its structural evolution was investigated from room temperature to 800 °C by in-situ synchrotron XRD analyses under dry and wet H2. No chemical interaction between the BCZ20Y15 and GDC15 phases occurred in the composite, thus demontrating its excellent chemical stability under operating conditions. However, some phase transitions were observed for the BCZ20Y15 phase, under both dry and wet H2: i.e., it showed an orthorhombic Imma structure from room temperature to 100 °C, trigonal R-3c up to 700 °C and cubic Pm-3m up to 800 °C. On the other hand, the GDC15 phase did not display any phase transition, remaining in a cubic Fm-3m structure under all tested conditions. Moreover, a synergistic effect of the BCZ20Y15 and GDC15 phases in the volume expansion of the composite was revealed: indeed, BCZ20Y15 and GDC15 lattice expansion rates tend to approach each other in the composite under reducing conditions. This synergistic effect is very important for the mechanical performances of BCZ20Y15-GDC15 composite. The similar expansion rate observed for BCZ20Y15 and GDC15 may reduce the strain and prevent failure of this ceramic membrane under operating conditions.

Ru-doped barium strontium titanates of the cathode for the electrochemical synthesis of ammonia

Ru-doped barium strontium titanate (BSTR) perovskites (Ba0.5Sr0.5Ti1-xRuxO3-δ, x = 0, 0.05, 0.1) (BSTR) were evaluated as cathode materials for the electrochemical synthesis of ammonia from wet H2 and dry N2. Phase crystallinity and the electrochemical properties of BSTR were analyzed. The BSTR structure is stable in low oxygen partial pressure, possibly as a result of its cubic nature. Doping Ru on the B-site of the BST improves its electrochemical properties, because increasing replacement of Ti4+ by Ru4+ causes a decrease in ohmic resistance. Introduction of Ru4+ ions on the B-site of the BST increased catalytic activity for the ammonia synthesis reaction. An electrochemical cell using BSTR as the cathode (Ni/BaCe0.4Zr0.4Y0.2O3 (BCZY)/BCZY/BSTR) exhibits a maximum ammonia formation rate of 1.1 × 10−9 mol s−1 cm−2 and a Faradaic efficiency of 5.9% at 500 °C under an applied voltage of 1.2 V; short-term stability tests showed high stability.

Tailoring Ni and Sr2Mg0.25Ni0.75MoO6−δ Cermet Compositions for Designing the Fuel Electrodes of Solid Oxide Electrochemical Cells

The design of new electrode materials for solid oxide electrochemical cells, which are stable against redox processes as well as exhibiting carbon/sulphur tolerance and high electronic conductivity, is a matter of considerable current interest as a means of overcoming the disadvantages of traditional Ni-containing cermets. In the present work, composite materials having the general formula (1−x)Sr2Mg0.25Ni0.75MoO6−δ + xNiO (where x = 0, 15, 30, 50, 70 and 85 mol.%) were successfully prepared to be utilised in solid oxide fuel cells. A detailed investigation of the thermal, electrical, and microstructural properties of these composites, along with their phase stability in oxidising and reducing atmospheres, was carried out. While possessing low thermal expansion coefficient (TEC) values, the composites having low Ni content (15 mol.%–70 mol.%) did not satisfy the requirement of high electronic conductivity. Conversely, the 15Sr2Mg0.25Ni0.75MoO6−δ + 85NiO samples demonstrated very high electrical conductivity (489 S sm−1 at 850 °C in wet H2) due to well-developed Ni-based networks, and no deterioration of thermal properties (TEC values of 15.4 × 10−6 K−1 in air and 14.5 × 10−6 K−1 in 50%H2/Ar; linear expansion behaviour in both atmospheres). Therefore, this material has potential for use as a component of a fuel cell electrode system.