Ni SDC Research Articles

Improved power generation performance of solid oxide fuel cells using doped LaGaO3 electrolyte films prepared by screen printing method II. Optimization of Ni–Ce0.8Sm0.2O1.9 cermet anode support

A Ni and Sm-doped ceria (Ce0.8Sm0.2O1.9, SDC) cermet anode as a porous support of doped LaGaO3 film prepared by a wet coating and co-firing process was investigated. Different preparation methods and compositions were used to improve the power density of intermediate temperature solid oxide fuel cells. NiO–SDC precursor powder with fine particles and a porous microstructure with high surface area was synthesized by a modified impregnation method and compared with that synthesized by a ball milling method. In addition, an open circuit voltage, which is almost equal to the theoretical value of 1.1 V, and maximum power densities of 835, 277, and 67 mW cm−2 at 700, 600, and 500 °C, respectively, were achieved on a single cell supported by a 75 wt% Ni–SDC cermet anode when a 60 μm thick Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was used. The improved power density was explained by the enlarged reaction area for the anode as a result of the low polarization resistance of the anode by high porosity and uniform distribution of Ni and SDC particles. Although a small amount of Ni diffused to the interface between the La-doped ceria (LDC) buffer layer and the LSGM electrolyte film, an adverse reaction that deteriorates cell performance seemed to be suppressed, and thus, reasonably high power density was achieved on the cell using the LSGM film prepared by the screen printing method with optimization of the anode substrate structure and composition.

Characteristics of the Hydrogen Electrode in High Temperature Steam Electrolysis Process

YSZ-electrolyte supported solid oxide electrolyzer cells (SOECs) using LSM-YSZ oxygen electrode but with three types of hydrogen electrode, Ni–SDC, Ni–YSZ and LSCM–YSZ have been fabricated and characterized under different steam contents in the feeding gas at 850°C. Electrochemical impedance spectra results show that cell resistances increase with the increase in steam concentrations under both open circuit voltage and electrolysis conditions, suggesting that electrolysis reaction becomes more difficult in high steam content. Pt reference electrode was applied to evaluate the contributions of the hydrogen electrode and oxygen electrode in the electrolysis process. Electrochemical impedance spectra and over potential of both electrodes were measured under the same testing conditions. Experimental results show that steam contents mainly affect the behavior of the hydrogen electrode but have little influence on the oxygen electrode. Further, contribution from the hydrogen electrode is dominant in the electrolysis process for Ni–based SOECs, but this contribution decreases for LSCM–based SOECs.

Electro-catalytic activity of Dy2O3 as a solid oxide fuel cell anode material

Cermet anodes composed of Ni and Dy2O3 have been applied as anode for intermediate-temperature solid oxide fuel cells. Although the oxide ion conductivity of Dy2O3 is negligible compared to that of doped ceria (DCO), Ni–Dy2O3 cermet anodes have displayed very high performance comparable to that of the commonly used Ni–SDC cermet anode. Temperature programmed reduction study suggests that the catalytic activity of the Ni–Dy2O3 cermet might be originated from the hydrogen adsorption ability on the Dy2O3 surface, promoting hydrogen spillover process, and consequently enhancing the electrochemical oxidation of the fuel. Further, the electrochemical catalytic activity of Au-based cermet anode confirms that hydrogen adsorption capability is as important as oxygen-ion conductivity for the ceramic component in a cermet anode.

Direct-methane solid oxide fuel cells with Cu 1.3Mn 1.7O 4 spinel internal reforming layer

Cu 1.3Mn 1.7O 4 spinel oxide has been synthesized and characterized as anode internal reforming layer for Ni–SDC anode-supported solid oxide fuel cells (SOFCs) directly operating on methane fuel. XRD and Cu mapping image results of Cu 1.3Mn 1.7O 4 oxide after in-situ reduction by methane show that a highly dispersed nano-Cu metal network has been obtained. By adopting Cu 1.3Mn 1.7O 4 as an internal reforming layer, the cell demonstrated maximum power densities of 242 and 311 mW cm −2 at 650 and 700 °C, respectively using methane as fuel and ambient air as oxidant. More importantly, Cu 1.3Mn 1.7O 4 internal reforming layer has significantly improved the cell performance stability. The cell with the Cu 1.3Mn 1.7O 4 internal reforming layer has demonstrated reasonably stable performance while the cell without it degraded very rapidly.

Electrode Properties of the Ruddlesden–Popper Series, Lan+1NinO3n+1 (n=1, 2, and 3), as Intermediate‐Temperature Solid Oxide Fuel Cells

The Ruddlesden–Popper phases, Lan+1NinO3n+1 (n=1, 2, and 3), were synthesized by a solid‐state reaction for use as cathodes in an intermediate‐temperature (500°–700°C) solid oxide fuel cell. The samples crystallized into an orthorhombic layered perovskite structure. The overall electrical conductivity increased with the increase of n in the intermediate temperature range. Single test‐cells, which consisted of samarium‐oxide‐doped ceria (SDC; Sm0.2Ce0.8Ox) as an electrolyte, Ni–SDC cermet (Ni–SDC) as an anode, and Lan+1NinO3n+1 as a cathode, were fabricated for measurements of cell performance at 500°–700°C. Current interruption measurements revealed that both the ohmic and overpotential losses at 700°C decreased with the increase of n. La4Ni3O10 was found to exhibit the best cathode characteristics in the Lan+1NinO3n+1 series. Maximum test‐cell power densities with La4Ni3O10 (n=3) were 10.2, 36.5, and 88.2 mW/cm2 at 500°, 600°, and 700°C, respectively.

Fabrication and performance of anode-supported solid oxide fuel cells via slurry spin coating

Ce 0.8Sm 0.2O 1.9 (SDC) dense electrolyte thin film, La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF) porous cathode layer and Ni–SDC anode functional layer for anode-supported SOFCs are fabricated by a slurry spin coating technique. The optimum conditions for preparing the single cell with a uniform microstructure as well as excellent performance have been investigated. A dense electrolyte thin film with a crack-free microstructure can be obtained by using the SDC powders pre-calcined at 900 °C. The power density of the cells increases with the increasing weight content of corn starch (corn starch wt.%), which is mainly ascribed to the decrease of the concentration loss in the anode. However, the trade-off between the single cell performance and mechanical strength results in the optimum composition being obtained for the Ni–SDC anode containing 15 wt.% corn starch (15-Ni–SDC). In contrast to the data in the literatures, the relatively large ohmic resistance ( R ohm) values in the present study are obtained for the 15-Ni–SDC cell. In order to further improve the cell performance, an anode functional layer is introduced. The power density of the resulting single cell is evidently increased, exhibiting the excellent maximum power densities of 685, 472 and 275 mW cm −2 at 600, 550 and 500 °C, respectively.

High-performance PrBaCo 2O 5+ δ–Ce 0.8Sm 0.2O 1.9 composite cathodes for intermediate temperature solid oxide fuel cell

PrBaCo 2O 5+ δ –Ce 0.8Sm 0.2O 1.9 (PBCO–SDC) composite material are prepared and characterized as cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction result proves that there are no obvious reaction between the PBCO and SDC after calcination at 1100 °C for 3 h. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures shows that the addition of SDC to PBCO improved remarkably the electrochemical performance of a PBCO cathode, and that a PBCO–30SDC cathode exhibits the best electrochemical performance in the PBCO– xSDC system. The total interfacial resistances R p is the smallest when the content of SDC is 30 wt%, where the value is 0.035 Ω cm 2 at 750 °C, 0.072 Ω cm 2 at 700 °C, and 0.148 Ω cm 2 at 650 °C, much lower than the corresponding interfacial resistance for pure PBCO. The maximum power density of an anode-supported single cell with PBCO–30SDC cathode, Ni–SDC anode, and dense thin SDC/LSGM (La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ )/SDC tri-layer electrolyte are 364, 521 and 741 mW cm −2 at 700, 750 and 800 °C, respectively.

Performances of LnBaCo 2O 5+ x–Ce 0.8Sm 0.2O 1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskite oxides, LnBaCo 2O 5+ x (LnBCO) (Ln = Pr, Nd, Sm, and Gd), are prepared using a solid-state reaction as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performances of LnBCO–Ce 0.8Sm 0.2O 1.9 (SDC) composite cathodes were investigated for IT-SOFCs on La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM) electrolyte. The thermal expansion coefficient can be effectively reduced in the case of the composite cathodes. No chemical reactions between LnBCO cathodes and SDC electrolyte, and LnBCO and LSGM are found. The electrochemical performances of LnBCO cathodes and LnBCO–SDC composite cathodes decrease with decreasing Ln 3+ ionic radii, which is closely related to the decrease of the electrical conductivity and fast oxygen diffusion property. The area specific resistances of the LnBCO cathodes and LnBCO–SDC composite cathodes on LSGM electrolyte are all lower than 0.13 Ω cm 2 and 0.15 Ω cm 2 at 700 °C, respectively. The maximum power densities of single-cell consisted of LnBCO–SDC composite cathodes, LSGM electrolyte, and Ni–SDC anode achieve 758–608 mW cm −2 at 800 °C with the change from Ln = Pr to Gd, respectively. These results indicate that LnBCO–SDC composite oxides are candidates as a promising cathode material for IT-SOFCs.

Self-rising synthesis of Ni–SDC cermets as anodes for solid oxide fuel cells

Ni–SDC cermets have been obtained using a self-rising approach by two different ways, one-step direct synthesis (OS) and ball milling the separately prepared NiO and SDC powders (BM). The results showed that self-rising approach was an efficient way for the synthesis of porous materials composed of evenly distributed uniform size nanocrystals. The as-synthesized powders have been applied as anodes for solid oxide fuel cells, whose electrochemical properties have been systematically studied. Cells with anodes from the BM method showed better performance compared with those of the OS method, achieving a maximum power density of 400 mW cm −2 at 600 °C.

Microstructural Characteristics of SDC Electrolyte Film Supported by Ni–SDC Cermet Anode

As a promising electrolyte material for intermediate-temperature solid oxide fuel cells operated at a temperature of , a (SDC) film supported by a Ni–SDC cermet anode was prepared through electrophoretic deposition. Detailed microstructural features of the electrolyte film were studied. In the region away from the interface, the microstructure of the SDC film is similar to that of the SDC bulk sample, containing nanosized domains embedded in a fluorite matrix. However, in the region near the interface, the diffusion of Ni from the cermet anode to the electrolyte film was observed with a depth of about . Furthermore, the reduction in Ce and a high degree of oxygen vacancy ordering can be noticed in the interfacial region at the electrolyte side. It is suggested that these microstructural features could have negative impacts on the ionic conductivity of the electrolyte films.

High performance Ni–Sm2O3 cermet anodes for intermediate-temperature solid oxide fuel cells

Abstract A novel anode consisting of Ni and Sm 2 O 3 with negligible oxygen-ion conductivity was developed for intermediate-temperature solid oxide fuel cells (SOFCs). Its triple phase boundary length is pretty small compared with the conventional Ni-samaria doped ceria (SDC) anode, of which SDC is one of the electrolytes having high oxygen-ion conductivity. Even so, single cells with Ni–Sm 2 O 3 anodes generated peak power density of 542 mW cm −2 at 600 °C, comparable to, if not higher than those with the Ni–SDC anodes when the same cathodes and electrolytes were applied. In addition, Ni–Sm 2 O 3 exhibited lower interfacial polarization resistance than Ni–SDC. The high electrochemical performance, which might be related to the high catalytic activity of Sm 2 O 3 and the unique microstructures of the Ni–Sm 2 O 3 , suggests a viable alternative to the conventional anodes for SOFCs.

Dynamic evaluation of low-temperature metal-supported solid oxide fuel cell oriented to auxiliary power units

A metal-supported solid oxide fuel cell (SOFC) composed of a Ni–Ce 0.8Sm 0.2O 2− δ (Ni–SDC) cermet anode and an SDC electrolyte was fabricated by suspension plasma spraying on a Hastelloy X substrate. The cathode, an Sm 0.5Sr 0.5CoO 3 (SSCo)–SDC composite, was screen-printed and fired in situ. The dynamic behaviour of the cell was measured while subjected to complete fuel shutoff and rapid start-up cycles, as typically encountered in auxiliary power units (APU) applications. A promising performance – with a maximum power density (MPD) of 0.176 W cm −2 at 600 °C – was achieved using humidified hydrogen as fuel and air as the oxidant. The cell also showed excellent resistance to oxidation at 600 °C during fuel shutoff, with only a slight drop in performance after reintroduction of the fuel. The Cr and Mn species in the Hastelloy X alloy appeared to be preferentially oxidized while the oxidation of nickel in the metallic substrate was temporarily alleviated. In rapid start-up cycles with a heating rate of 60 °C min −1, noticeable performance deterioration took place in the first two thermal cycles, and then continued at a much slower rate in subsequent cycles. A postmortem analysis of the cell suggested that the degradation was mainly due to the mismatch of the thermal expansion coefficient across the cathode/electrolyte interface.

Internal shorting and fuel loss of a low temperature solid oxide fuel cell with SDC electrolyte

Abstract A solid oxide fuel cell with Sm0.2Ce0.8O1.9 (SDC) electrolyte of 10 μm in thickness and Ni–SDC anode of 15 μm in thickness on a 0.8 mm thick Ni–YSZ cermet substrate was fabricated by tape casting, screen printing and co-firing. A composite cathode, 75 wt.% Sm0.5Sr0.5CoO3 (SSCo) + 25 wt.% SDC, approximately 50 μm in thickness, was printed on the co-fired half-cell, and sintered at 950 °C. The cell showed a high electrochemical performance at temperatures ranging from 500 to 650 °C. Peak power density of 545 mW cm−2 at 600 °C was obtained. However, the cell exhibited severe internal shorting due to the mixed conductivity of the SDC electrolyte. Both the amount of water collected from the anode outlet and the open circuit voltage (OCV) indicated that the internal shorting current could reach 0.85 A cm−2 or more at 600 °C. Zr content inclusions were found at the surface and in the cross-section of the SDC electrolyte, which could be one of the reasons for reduced OCV and oxygen ionic conductivity. Fuel loss due to internal shorting of the thin SDC electrolyte cell becomes a significant concern when it is used in applications requiring high fuel utilization and electrical efficiency.

Chemical and redox stabilities of a solid oxide fuel cell with BaCe 0.8Y 0.2O 3− α functioning as an electrolyte and as an anode

The operation of a solid oxide fuel cell (SOFC) based on BaCe 0.8Y 0.2O 3− α (BCY20) at 800 °C was studied without using an anode material. A porous, Ce-rich phase with a fluorite structure was formed at a depth of approximately 10 μm from the BCY20 surface by heat treatment at 1700 °C. This was due to the vaporization of BaO from the BCY20 surface. This treatment improved the cell performance and chemical stability to CO 2 because the Ce-rich phase functioned as an electrically conducting and protective layer. The heat-treated BCY20 also had better chemical and redox stabilities over a Ni–Ce 0.8Sm 0.2O 1.9 (SDC) cermet anode attached to the SDC electrolyte. The cell with the heat-treated BCY20 operated well on unhumidified methane, ethane, propane, and butane without carbon deposition, while the cell with the Ni–SDC cermet anode degraded within a few hours. Moreover, the BCY20 showed higher tolerance to 10 ppm H 2S and stability over 20 times redox cycling in comparison to the Ni–SDC cermet anode.

Ni 1− xCu x alloy-based anodes for low-temperature solid oxide fuel cells with biomass-produced gas as fuel

Ni–Cu alloy-based anodes, Ni 1− x Cu x ( x = 0, 0.05, 0.2, 0.3)–Ce 0.8Sm 0.2O 1.9 (SDC), were developed for direct utilization of biomass-produced gas in low-temperature solid oxide fuel cells (LT-SOFCs) with thin film Ce 0.9Gd 0.1O 1.95 electrolytes. The alloys were formed by in situ reduction of Ni 1− x Cu x O y composites synthesized using a glycine-nitrate technique. The electrolyte films were fabricated with a co-pressing and co-firing technique. Electrochemical performance of the Ni 1− x Cu x –SDC anode supported cells was investigated at 600 °C when humidified (3% H 2O) biomass-produced gas (BPG) was used as the fuel and stationary air as the oxidant. With Ni–Cu alloys as anodes, carbon deposition was substantially suppressed and electrochemical performance of the cells was sustained for much longer periods of time. For example, the power export of a Ni–SDC supported cell was only 50% of the initial value (200 mW cm −2 at 0.5 V) after 20 min, while Ni 0.8Cu 0.2–SDC supported cells could maintain 90% of the initial power density (250 mW cm −2 at 0.5 V) over a period of 10 h. The improved performance of the Ni–Cu alloy-based anodes is worth considering in developing SOFCs fueled directly with dilute hydrocarbons such as gases derived from biomass.

Fe xCo 0.5− xNi 0.5–SDC anodes for low-temperature solid oxide fuel cells

Trimetal alloys, Fe x Co 0.5− x Ni 0.5 ( x = 0.1, 0.2, 0.25, 0.3, 0.4), were studied as anodes for low-temperature solid oxide fuel cells (LT–SOFCs) based on GDC (Ce 0.9Gd 0.1O 1.95) electrolytes. The alloys were formed by in situ reduction of Fe x Co 0.5− x Ni 0.5O y composites, which were synthesized using a glycine-nitrate technique. Symmetrical cells consisted of Fe x Co 0.5− x Ni 0.5–SDC electrodes and GDC electrolytes, and single cells consisted of Fe x Co 0.5− x Ni 0.5–SDC (Ce 0.8Sm 0.2O 1.9) anodes, GDC electrolytes, and SSC (Sm 0.5Sr 0.5CoO 3)–SDC cathodes were prepared using a co-pressing and co-firing process. Interfacial polarization resistances and I– V curves of these cells were measured at temperature from 450 to 600 °C. With Fe 0.25Co 0.25Ni 0.5–SDC as anodes, the cells showed the lowest interfacial resistance and highest power density. For example, at 600 °C, the resistance was about 0.11 Ω cm 2 and power density was about 750 mW cm −2 when humidified (3% H 2O) hydrogen was used as fuel and stationary air as oxidant. Further, the cell performance was improved when the molar ratio of Fe:Co:Ni approached 1:1:2, i.e. Fe 0.25Co 0.25Ni 0.5. In addition, higher power density and lower interfacial resistance were obtained for cells with the Fe 0.25Co 0.25Ni 0.5–SDC anodes comparing to that with Ni–SDC anodes, which have been usually used for LT–SOFCs. The promising performance of Fe x Co 0.5− x Ni 0.5 as anodes suggests that trimetallic anodes are worth considering for SOFCs that operate at low-temperature.

Operation of ceria-electrolyte solid oxide fuel cells on iso-octane–air fuel mixtures

Reduced-temperature solid oxide fuel cells (SOFCs) – with thin Ce 0.85Sm 0.15O 1.925 (SDC) electrolytes, thick Ni–SDC anode supports, and composite cathodes containing La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) and SDC – were fabricated and tested with iso-octane/air fuel mixtures. An additional supported catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density (e.g. 0.6 W cm −2 at 590 °C) without anode coking. The Ru-CeO 2 catalyst produced CO 2 and H 2 at temperatures <350 °C, while H 2 and CO became predominant above 500 °C. Power densities were substantially less than for the same cells with H 2 fuel (e.g. 1.0 W cm −2 at 600 °C), due to the dilute (≈20%) hydrogen in the fuel mixture produced by iso-octane partial oxidation. Electrochemical impedance analysis showed a main arc that represented ≈60% of the total resistance, and that increased substantially upon switching from hydrogen to iso-octane/air.

Electrochemical performance of gel-cast NiO–SDC composite anodes in low-temperature SOFCs

NiO–Ce 0.8Sm 0.2O 1.9 (SDC) composites were synthesized using gel-casting technique. The electrochemical performance of the gel-cast (GC) Ni–SDC cermet as anode was investigated contrast with that fabricated from traditional mechanical mixing (MM) technique using fuel cells with about 35 μm-thick SDC electrolyte and Sm 0.5Sr 0.5CoO 3–SDC cathode. Maximum power density of the cell with GC anode achieved 491 mW cm −2 at 600 °C, over 100 mW cm −2 larger than that with MM anode, inferring high catalytic activity of the GC anode. Impedance measurements on the fuel cell at open circuit showed that the anodic interfacial polarization resistance of the GC anode was 0.1 Ω cm 2 lower than that of the MM anode. Long-term stability of the cell with GC anode in hydrogen was also performed, which showed that it can stabilize at least 7 days.

Composite cathode La 0.6Sr 0.4Co 0.2Fe 0.8O 3–Sm 0.1Ce 0.9O 1.95–Ag for intermediate-temperature solid oxide fuel cells

Sm 0.1Ce 0.9O 1.95 (SDC) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) were synthesized by a glycine–nitrate process. A composite LSCF–SDC–Ag cathode was prepared and its structure was analyzed by X-ray diffraction. No chemical reactions among LSCF, SDC, and Ag in the composite cathode were found. The composite cathode was applied onto SDC electrolyte and the microstructure of the electrolyte–electrode interface was examined by SEM. The overpotential of the interface was measured. A single SOFC was prepared by using LSCF–SDC–Ag as cathode, SDC as electrolyte, and Ni–SDC as anode and its performance was measured. Compared to a similar SOFC with LSCF–SDC cathode, it is found that adding Ag in the cathode improved the SOFC performance significantly.

High performance Ni–Sm 0.15Ce 0.85O 2− δ cermet anodes for intermediate temperature solid oxide fuel cells using LaGaO 3 based oxide electrolytes

Effect of the composition and synthesizing approaches on the performance of Ni–15 mol% Sm 3+ doped CeO 2 (Sm 0.15Ce 0.85O 2− δ , SDC) composite anodes were studied. The results showed that the addition of SDC into Ni significantly improved the performance of Ni anode mainly by reducing the ohmic resistance of the cell and the overpotential at anode/electrolyte interface. The introduction of SDC into Ni created more active sites for H 2 oxidation; however, it also increased the activation energy of the process at the same time. Therefore, the anodic overpotential of Ni–SDC composite electrode was higher than pure Ni at low reaction temperatures (873 K), while lower than that of pure Ni at 1073 K. Further experiments showed that the activities of Ni–SDC composite electrodes showed strong dependency on the synthesizing approaches. The electrodes prepared with impregnation methods exhibited a much higher activity compared with the electrodes prepared with solid-state reaction due to the reduced ohmic resistance. The low ohmic resistance of the cells using Ni–SDC anodes prepared with impregnation method is due to the improved distribution of Ni and SDC in the green powder of anode. An equal distribution of Ni and SDC is essential to minimize the reaction between Ni and strontium and magnesium doped lanthanum gallate (LSGM), and decrease the ohmic resistance.