Anode Material For Solid Oxide Fuel Cells Research Articles

Use of La 0.75Sr 0.25Cr 0.5Mn 0.5O 3 materials in composite anodes for direct ethanol solid oxide fuel cells

The perovskite system La 1− x Sr x Cr 1− y M y O 3− δ (M, Mn, Fe and V) has recently attracted much attention as a candidate material for the fabrication of solid oxide fuel cells (SOFCs) due to its stability in both H 2 and CH 4 atmospheres at temperatures up to 1000 °C. In this paper, we report the synthesis of La 0.75Sr 0.25Cr 0.5Mn 0.5O 3 (LSCM) by solid-state reaction and its employment as an alternative anode material for anode-supported SOFCs. Because LSCM shows a greatly decreased electronic conductivity in a reducing atmosphere compared to that in air, we have fabricated Cu-LSCM-ScSZ (scandia-stabilized zirconia) composite anodes by tape-casting and a wet-impregnation method. Additionally, a composite structure (support anode, functional anode and electrolyte) structure with a layer of Cu-LSCM-YSZ (yttria-stabilized zirconia) on the supported anode surface has been manufactured by tape-casting and screen-printing. Single cells with these two kinds of anodes have been fabricated, and their performance characteristics using hydrogen and ethanol have been measured. In the operation period, no obvious carbon deposition was observed when these cells were operated on ethanol. These results demonstrate the stability of LSCM in an ethanol atmosphere and its potential utilization in anode-supported SOFCs.

Evaluation of Sr- and Mn-substituted LaAlO 3 as potential SOFC anode materials

Lanthanum–aluminate-based oxides, (La 0.8Sr 0.2) 1− y Al 1− x Mn x O 3− δ ( x = 0, 0.3, 0.5; y = 0 or 0.06) (LSAM), were synthesized and evaluated in detail as potential anode materials for solid oxide fuel cells (SOFCs). The electrical conductivity of LSAM (Mn ≥ 30 mol%) is dominated by p-type electronic conduction and can be treated as a diluted system of lanthanum manganites, (La,Sr)MnO 3. At 810 °C, the electrical conductivity of (La 0.8Sr 0.2) 0.94Al 0.5Mn 0.5O 3− δ (LSAM8255b) reaches 12 S/cm in air and 2.7 S/cm in humidified Ar/4% H 2 ( p(O 2) ≈ 10 − 18 bar). The thermal expansion coefficients of LSAM8255a and LSAM8255b match YSZ very well and no chemical reaction was observed between these two perovskite materials and YSZ up to at least 1400 °C. Fairly good electrochemical performance was observed for an LSAM8255b–YSZ composite anode. At 850 °C, the polarization resistances are only 0.34 and 0.50 Ω cm 2 in wet (∼3% H 2O) Ar/20% H 2 and wet Ar/20% CH 4, respectively. In addition, an exposure to Ar/20% CH 4/3% H 2O for 35 h did not cause any apparent carbon deposition on the electrode. However, the chemical stability of LSAM8255a and LSAM8255b in a typical anode environment under open circuit conditions does not seem sufficient, leading to performance degradation with time in wet Ar/20% H 2 or wet Ar/20% CH 4. Furthermore, relatively large chemical expansion (0.3–0.5%) was observed when the atmosphere was switched from air to wet Ar/4% H 2, which might cause intolerable stress on the thin film electrolyte layer for a large-area anode-supported planar SOFC, but which might be tolerable for small geometries or electrolyte-supported SOFCs.

Reduction and Reoxidation Processes of NiO∕YSZ Composite for Solid Oxide Fuel Cell Anodes

Solid oxide fuel cells (SOFCs) are an emerging technology in hydrogen-based energy production, thanks to their high performance, high power density, high efficiency, and reduced emissions over conventional power generation technologies. For these reasons, a great attention has been addressed in these years to SOFCs materials and technologies. An important issue related to the utilization of SOFCs as power generators is the capability of SOFCs materials to resist to thermal cycles in different atmospheres. The present work proposes an experimental investigation on the reduction process of NiO∕YSZ anode into Ni∕YSZ cermet, which is the best candidate for anode material in SOFCs, its reoxidation into NiO∕YSZ and the following rereduction into Ni∕YSZ. Anodes with different NiO∕YSZ ratios were analyzed through different physical and chemical techniques, such as scanning electron microscopy (SEM) and porosity measurements. The reduction, reoxidation and rereduction behaviors were studied by thermogravimetric analysis (TGA) in a unique long experiment, at different temperatures in the range of 700–800°C. The kinetics of the processes was studied and thermodynamic parameters such as activation energy were also calculated and correlated to the compositions and microstructure of the materials. The study clears up the effect of anode composition and microstructure on the reduction, reoxidation, and rereduction processes.

Structure and conductivity investigations of alkaline earth substituted uranium oxide, U 1 − xM xO 2 ± δ (M = Mg, Ca, Sr) for solid oxide fuel cell applications

Alkaline earth substituted UO 2 (U 1 − x M x O 2 ± δ ; M = Mg, Ca, Sr; 0.1 ≤ x ≤ 0.525) with fluorite structure was synthesized in reducing atmosphere. Structure and conductivity properties of U 1 − x M x O 2 ± δ fluorites were investigated for possible application in solid oxide fuel cells (SOFC). At room temperature and ambient atmosphere the materials are stable; however they decompose at an oxygen partial pressure p O 2 > 10 − 4 atm and temperatures higher than 600 °C. The total conductivity measured for the best conducting U 1 − x M x O 2 ± δ material with M = Ca and x = 0.177 is as high as 3 S/cm at p O 2 < 10 − 4 atm at 600 °C. The relatively low ionic transference number ( t i∼0.02) is disadvantageous for potential use as electrolyte material for SOFC applications. The high conductivity and possible depolarization effects suggest potential use as anode materials in SOFC.

Phases in copper-stabilized zirconia solid oxide fuel cells anode material

Solid oxide fuel cells (SOFC) are emerging as an alternate source of energy. Anodes form one of the components of the fuel cells. Ni/Yttrium stabilized zirconia is a classic anode material for SOFC when hydrogen is used as the fuel source, but it is not that effective when methane is used as fuel source due to carbon deposition on the anode. Recently, copper stabilized zirconia has been investigated as anode material for SOFC for its self-cleaning properties. We have tried to investigate phases in copper stabilized zirconia for better understanding of its properties. Copper stabilized zirconia (CSZ) with different CuO loading was prepared by the solid-state reaction method. X-ray diffraction studies on these samples reveal only monoclinic zirconia phase in those samples loaded with less than 5 mol% of CuO. Traces of monoclinic CuO along with monoclinic ZrO 2 is observed in the samples when loading of CuO is between 5 and 20 mol%. Orthorhombic copper zirconium oxide and monoclinic zirconia phases were observed when CuO loading was greater than 20 mol%. Scanning and back-scattered electron micrographs reveal a clear two-phase structure only in the samples with greater than 20 mol% of CuO loading. Atomic force microscopy carried out on 33 mol% loaded zirconia shows a three-phase structure with flattened seven-fold-coordination of Zr 4+ with oxygen.

Chemical, electrical, and thermal properties of strontium doped lanthanum vanadate

Strontium doped lanthanum vanadates, La 1− x Sr x VO 3 (denoted LSV with x = 0, 0.3, 0.5, 0.7 and 1.0), were synthesized using a solid-state reaction method. The oxidation and reduction behaviors of LSV were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The chemical stability of LSV in a reducing atmosphere containing H 2S up to 10 vol.% at 950 °C was investigated and their electrical conductivity at 500–1000 °C in reducing atmospheres measured with a 4-electrode technique. The coefficient of thermal expansion (CTE) was determined by dilatometry. The electrochemical catalytic activity of LSV as anodes in solid oxide fuel cells (SOFCs) was characterized using impedance spectroscopy. It was found that the La 1− x Sr x VO 3 materials with x in the range of 0.3–0.7 exhibit good resistance to H 2S, high electrical conductivity and acceptable catalytic activity at elevated temperatures in reducing atmosphere. However, the volume change associated with oxidation/reduction cycle may limit their tolerance to re-oxidation when used as anode materials for SOFCs.

Development of Ni/Y2 O3 – ZrO2 cermet anodes for solid oxide fuel cells

Ni/Y2 O3 – ZrO2 (Ni/YSZ) cermets are the most common anode materials for high temperature solid oxide fuel cells (SOFC). Electrode performance of Ni/YSZ cermets is critically dependent on the microstructure and distribution of Ni and YSZ phases in the cermets. This in turn is closely related to the characteristics of the NiO and YSZ powders, and the fabrication process. The objective of this paper is to discuss some important issues associated with the fabrication and development of Ni/Y2 O3 – ZrO2 anode materials for SOFC from the viewpoint of materials science and technology. Results indicate that the optimisation of Ni/YSZ cermet anodes is a complicated process and understanding of the H2 oxidation reaction is also very important in the development of high performance Ni/YSZ cermet anodes.

A solid oxide fuel cell operating on hydrogen sulfide (H2S) and sulfur-containing fuels

Abstract A new class of materials based on La x Sr 1− x VO 3− δ (LSV) has been studied as the anode for solid oxide fuel cells (SOFCs) operating on H 2 S-containing fuels. The LSV-based anodes are chemically and electrochemically stable under SOFC operating conditions. Furthermore, they appear to be active towards the preferential oxidation of H 2 S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements using various H 2 S and H 2 fuel mixtures. A system with configuration LSV/YSZ/LSM–YSZ showed a maximum power density of 90 mW/cm 2 at 220 mA/cm 2 with a 5% H 2 S–95% N 2 fuel mixture at 1273 K. This same cell configuration showed a maximum power density of 135 mW/cm 2 at 280 mA/cm 2 when the fuel was a 5% H 2 S–95% H 2 mixture at 1273 K. Cell performances were stable and showed no significant deterioration during a 48 h period. Impedance measurements showed overall cell resistances decreased with increasing temperature and H 2 S content of the fuel. The results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC anode materials.

Synthesis and Characterization of ( La0.75Sr0.25 ) Cr0.5Mn0.5 O 3 − δ , a Redox-Stable, Efficient Perovskite Anode for SOFCs

Perovskite-related materials, (LSCM), have been synthesised and examined as potential anode materials for solid oxide fuel cells (SOFCs). exhibits a rhombohedral structure. It appears to be chemically compatible with yttria-stabilized zirconia (YSZ) to at least 1300°C. At 900°C, its electrical conductivity is about 38 S/cm in air and 1.5 S/cm in 5% atm). Good performance was achieved using LSCM as anode with a polarization resistance 0.9 and 0.47 Ω cm2 in wet 5% and wet respectively. The anode polarization was further reduced to 0.6 and 0.25 Ω cm2 in wet 5% and wet when a thin layer of (CGO) layer was coated between YSZ and LSCM anode. Stable performance was sustained for at least for 4 h operating in wet methane. By improving the electrode microstructure, the electrode polarization resistance approaches 0.2 Ω cm2 at 900°C in 97% for LSCM containing a small amount of YSZ to improve adherence but without CGO. Very good performance is achieved for methane without using excess steam. Using ambient humidification (i.e., 3% the same performance is achieved with methane at 950°C as for hydrogen at 850°C. The anode is stable in both fuel and air conditions and shows stable electrode performance in methane. Thus, both redox stability and operation in low-steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes. LSCM and other complex perovskites are promising anode materials for SOFCs. © 2004 The Electrochemical Society. All rights reserved.

Sulfur-Tolerant Materials for the Hydrogen Sulfide SOFC

This study examined sulfur tolerant materials for solid oxide fuel cells (SOFCs) operating on H 2 S and H 2 S containing fuels, focusing on the stability and electrochemical performance of perovskite-type materials in a H 2 S atmosphere under SOFC operating conditions (P = 1 atm, T > 800°C). Preliminary results indicate anodes of the general form La x Sr y VO 3 - δ are stable and active toward the electrochemical oxidation of H 2 S. In particular, an SOFC using La 0 . 7 Sr 0 . 3 VO 3 as the anode has shown good performance at H 2 S levels of 10%, over 5000 times greater than the H 2 S tolerance level of contemporary Ni-based systems. The results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC anode materials.

A review on the status of anode materials for solid oxide fuel cells

Present review is aimed at providing a state-of-art development of anode for solid oxide fuel cell (SOFC) with principal emphasis on the materials aspect. The criteria for the anode of SOFC are first presented. The prospects and problems of the currently developed anode materials are elucidated. In particular, the electrochemical properties of the Ni/YSZ cermet anode that is the most commonly employed in the establishment of SOFC stack is described along with various approaches attempted for their improvements. The advantages and disadvantages of other anode materials are compared to offer some insights for the research and development of new generation of anode materials for SOFC.

Synthesis and characterization of copper-stabilized zirconia as an anode material for SOFC

Solid oxide fuel cells (SOFC) are now being seriously considered for alternate energy source because of the environmental hazards associated with the use of fossil fuels and their limited availability. As a part of the development of these fuel cells, we have synthesized a series of CuO–ZrO 2 samples with varying concentration of CuO. In this paper, we present the study of copper-stabilized zirconia as an anode material in SOFC. The role of copper oxide in stabilizing zirconia and the possible reasons for the increase in catalytic activity of the relevant composition have been discussed using the experimental data.