Evaluation of commercial nickel oxide powders for components in solid oxide fuel cells

Tietz, Frank; Dias, F. J.; Simwonis, D.; Stöver, D.

doi:10.1016/s0955-2219(99)00271-x

Cited by 80 publications

(65 citation statements)

References 17 publications

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“…22 However, both samples showed larger values of electrical conductivity at lower Ni concentrations than data usually reported for this cermet. 8,23,24 In addition, the cermet with 28 vol % Ni ͑former v = 40 vol % NiO͒ had smaller electrical resistivity values, attributed to both the higher electrical conductivity of the precursor composite and to the lower porosity after reduction of samples with lower volume fraction of NiO. These results confirmed that the control of the microstructural properties of the precursor composite is an important factor to produce cermets with high electrical conductivity at low Ni contents.…”

Section: Resultsmentioning

confidence: 58%

Mixed Ionic–Electronic YSZ/Ni Composite for SOFC Anodes with High Electrical Conductivity

Fonseca

Florio

Esposito

et al. 2006

J. Electrochem. Soc.

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The preparation of the ZrO 2 :8 mol % Y 2 O 3 /NiO ͑YSZ/NiO͒ composites by a modified liquid mixture technique is reported. Nanometric NiO particles dispersed over the yttria-stabilized zirconia ͑YSZ͒ were prepared, resulting in dense sintered specimens with no solid solution formation between the oxides. Such a feature allowed for the electrical characterization of the composites in a wide range of relative volume fraction, temperature, and oxygen partial pressure. The main results indicate that the composites have high electrical conductivity, and the transport properties in these mixed ionic-electronic ͑MIEC͒ composites are strongly dependent on the relative volume fraction of the phases, microstructure, and temperature. These parameters should hence be taken into consideration for the optimized design of MIEC composites for electrochemical applications. In this context, the composite was reduced under H 2 for the preparation of high-conductivity YSZ/Ni cermets for use as solid oxide fuel cell anode material with relatively low metal content. Mixed ionic-electronic conductors ͑MIECs͒ have attracted a great deal of attention due to the variety of possible applications and interesting electrical properties.1-3 These materials are thought to be used in high-temperature electrochemical devices such as gas separation membranes and solid oxide fuel cell ͑SOFC͒ electrodes. 2,3The mixed conduction can be either an intrinsic property of singlephase materials ͑like cerium oxide and some rare-earth manganites͒ or a result of the mixture of ionic and electronic conductors ͑MIEC composite͒.3 The main advantage of the MIEC composite is the possibility for tailoring the properties according to optimized parameters for a specific application.3 In this context, the SOFC anode is the cermet ZrO 2 :Y 2 O 3 /Ni ͑YSZ/Ni͒, produced by the reduction of the precursor composite ZrO 2 :Y 2 O 3 /NiO ͑YSZ/NiO͒.4 Both the cermet and the oxide precursor are MIEC composites and must fulfill several requirements for a high-performance SOFC. An important issue regarding this anode material is the reduction of the Ni volume fraction for better matching of the thermal expansion coefficient with the electrolyte, while both high electric conductivity and catalytic activity must be preserved. 4 In fact, the final properties of the anode cermet are strongly dependent on the precursor composite, and various studies deal with the fabrication of the YSZ/NiO composite aiming for the production of SOFC anodes, but rather few papers report a more detailed microstructural and electrical characterization of the precursor composite.5-7 The usually high temperatures ͑ജ1500°C͒ reported for the densification of the composite promote the YSZ destabilization or solid solution formation due to the reaction with NiO, resulting in a considerable reduction of the electrical conductivity. [8][9][10] It is well known that the electrical properties of composites depend not only on the electrical properties of each phase but also are strongly influenced by microstructu...

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Section: Resultsmentioning

confidence: 58%

Mixed Ionic–Electronic YSZ/Ni Composite for SOFC Anodes with High Electrical Conductivity

Fonseca

Florio

Esposito

et al. 2006

J. Electrochem. Soc.

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“…Thus the YSZ/NiO size ratio and the YSZ coarse/ fine ratio affect the conductivity of the cermet [4]. A typical range of conductivity for an anode support (50 wt.-% Ni, ∼40% porosity) operating at 1,000°C is 300-400 S cm -1 [8].…”

Section: State Of the Art Anodes And Anode Substratesmentioning

confidence: 99%

Redox Cycling of Ni‐Based Solid Oxide Fuel Cell Anodes: A Review

2007

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The published literature relating to damage to SOFCs caused by redox cycling of Ni‐based anodes is reviewed. The review covers the kinetics of Ni oxidation and NiO reduction (as single phases and as constituents of composites with yttria‐stabilised zirconia, YSZ), the dimensional changes associated with redox cycling and the effect of this on the mechanical integrity and electrical performance of cells and stacks. A critical parameter is the expansion strain that is caused by oxidation. Several studies report that the first complete oxidation of a Ni/YSZ composite causes a linear expansion of the order of 1%, but the actual values vary substantially between different investigations. The oxidation strain is the result of microstructural irreversibility during the redox process and leads to strain accumulation over several redox cycles. This can cause mechanical disruption to an anode, anode support or other cell components attached to the anode.A simplified mechanical model of the stress and damage that are likely to be caused by anode expansion is proposed and applied to anode‐supported, electrolyte‐supported and inert substrate‐supported cell configurations. This allows the maximum oxidation strain to avoid damage in each configuration to be estimated.

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“…In these devices, the microstructure of the sintered NiO/YSZ cermet anode strongly affects the solid oxide fuel cell performance [3][4][5]. Specific attempts at controlling NiO/YSZ cermet microstructure have focused on starting catalyst powder particle sizes [6], the ratio between NiO and YSZ content [7,8], and processing techniques including mechanical alloying through milling [9][10][11][12]. Nonetheless, there remain challenges to achieving an ideal anode structure, especially in the area of controlling grain growth and densification of the NiO component during high temperature sintering (> 1000 ℃).…”

Section: Introductionmentioning

confidence: 99%

The effect of milling additives on powder properties and sintered body microstructure of NiO

2015

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The evolution of powder particle size, crystal structure, and surface chemistry was evaluated for micron scale NiO powders subjected to impact milling with commonly employed milling additives: methanol, Vertrel XF, and amorphous carbon. The effect of the different comminution protocols on sintered body microstructure was evaluated for high temperature sintering in inert atmosphere (N 2 ). X-ray photoelectron spectroscopy showed that NiO powder surface chemistry is surprisingly sensitive to milling additive choice. In particular, the proportion of powder surface defect sites varied with additive, and methanol left an alcohol or alkoxy residue even after drying. Upon sintering to intermediate temperatures (1100 ℃), scanning electron microscopy (SEM) showed that slurry milled NiO powders exhibit hindered sintering behaviors. This effect was amplified for NiO milled with methanol, in which sub-500 nm grain sizes dominated even after sintering to 1100 ℃. Upon heating to high temperatures (1500 ℃), simultaneous differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) showed that the powders containing carbon residues undergo carbothermal reduction, resulting in a melting transition between 1425 and 1454 ℃. Taken together, the results demonstrated that when processing metal oxide powders for advanced ceramics, the choice of milling additive is crucial as it exerts significant control over sintered body microstructure.

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Evaluation of commercial nickel oxide powders for components in solid oxide fuel cells

Cited by 80 publications

References 17 publications

Mixed Ionic–Electronic YSZ/Ni Composite for SOFC Anodes with High Electrical Conductivity

Mixed Ionic–Electronic YSZ/Ni Composite for SOFC Anodes with High Electrical Conductivity

Redox Cycling of Ni‐Based Solid Oxide Fuel Cell Anodes: A Review

The effect of milling additives on powder properties and sintered body microstructure of NiO

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