Thermomechanical and conductivity studies of doped niobium titanates as possible current collector material in the SOFC anode

Lashtabeg, Anna; Irvine, John T. S.; Feighery, A.J.

doi:10.1007/bf02375970

Cited by 11 publications

(13 citation statements)

References 6 publications

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“…In order to identify the possibility of using the material as a hydrogen separation membrane, hydrogen flux measurements were attempted. However, a considerable volume difference (3%,) between TiNb 2 O 7 and TiNb 2 O 6 at, respectively, the sweep and feed side, led to cracks along the edge of the sealing area, which again resulted in a large leakage during the flux measurement.…”

Section: Resultsmentioning

confidence: 99%

Defects and Transport Properties in TiNb₂O₇

Xing

Kalland

et al. 2013

J. Am. Ceram. Soc.

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The electrical conductivity of TiNb2O7 was characterized as a function of temperature, pO2 and pH2O. The total conductivity was independent of pO2 in the low oxygen partial pressure regime, while a dependency of pO2 −1/4 was observed at higher oxygen partial pressures. The conductivity increased with increasing pH2O under oxidizing conditions below 700°C. Mixed electronic and protonic conduction was indicated by H/D isotope exchange and transport number measurements. A defect model based on interstitial type of hydration was established and fitted to the conductivity data allowing for determination of physicochemical parameters of hydration and electron migration.

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Section: Resultsmentioning

confidence: 99%

Defects and Transport Properties in TiNb₂O₇

Xing

Kalland

et al. 2013

J. Am. Ceram. Soc.

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“…The discrepancy in the crystal system as well as the lattice parameters are yet to be known. Whereas Li et al [83] and Lashtabeg et al [84] report conforms to the crystal structure and lattice parameter reported in this work for both Nb2TiO7 and Nb1.33Ti0.67O4. researchers [82][83][84], Nb2TiO7 exhibits high mechanical redox stability at SOFC operating temperature of 800 o C. It has a CTE of 5.46 x 10 -6 K -1 in air between 25-800 o C, which is far less than YSZ.…”

Section: Resultssupporting

confidence: 92%

“…Lashtabeg et al [84] also reported a conductivity of 1.7 x 10 -3 S/cm at 900 o C in air. In forming gas the conductivity of Nb2TiO7 increases to 1.35 S/cm in the temperature range 650-800 o C as seen in Figure 24a.…”

Section: Resultsmentioning

confidence: 93%

“…In the present work, as seen in Figure 24b, Nb1.33Ti0.67O4 exhibits a high electronic conductivity of 85 S/cm at 800 o C in forming gas. Lashtabeg et al [84] reported a conductivity in excess of 120 S/cm at 900 o C in 5% H2/Ar, whereas Li et al [83] reported a conductivity as low as 49 S/cm at 800 o C in 5% H2/Ar for Nb1.33Ti0.67O4. The discrepancy in the value of conductivities may be due to the initial purity of the precursors, difference in relative density of the test sample and also due to different grain size and grain boundary defects.…”

Section: Resultsmentioning

confidence: 99%

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Redox Stable Anode Materials for SOFC Application

Thomas¹

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The common material design for solid-oxide fuel cells (SOFCs) is based on the cermet (ceramic-metal composite) material group, for example anode compositions like nickel with yttria stabilized zirconia (Ni/YSZ). One of the main limitations of these material groups is that they may undergo unwanted thermal expansion during redox cycles, causing dimensional instability at the anode. The state-of-the-art Ni/YSZ anode experiences a linear expansion of up to 1% when oxidized, causing an irreversible microstructural change, decreasing the electrochemical activity. The problem cumulatively increases if the cell design is anode supported as this puts the electrolyte under tension, causing it to crack and leaking the fuel and oxidant gases. Currently researchers are focusing on the development of new SOFC anodes for internal reforming, lower temperature operation, and poison resistance, but there is a lack of study on the redox stability of these newly developed materials. In this thesis work, the fundamental development of redox stable anode materials has been undertaken. Materials from perovskite, double perovskite, scheelite and double rutile structures has been considered. The material compositions include CeNb1-xWxO4, CeNb1-xMoxO4, Sr2Mg1-xMo1+xO6 (x = 0, 0.1, 0.2), Nb2TiO7 and Nb1.33Ti0.67O4. The thermo mechanical and electrical redox stability of the various novel materials were tested by controlled-atmosphere dilatometry and four-point probe DC electrical conductivity respectively at SOFC operating temperature (800 o C). Based on the thermo mechanical and electrical redox results, several doping strategies were adopted in the material systems to improve their redox stability while maintaining the coefficient of Thermal Expansion (CTE) at a minimum. The qualified material system was subjected to symmetrical and fuel cell tests to analyze the polarization resistance of novel anode material as well as electrochemical activity via in situ EIS. It was found that in CeNbO4 material group, W and Mo doping seized the phase transition of CeNbO4 from monoclinic to tetragonal at elevated temperature. Also the CTE of CeNbO4 in air between 25-800 o C was considerably brought down from 20.77 to 13-14x10-6 K-1 by adopting this doping strategy. Regarding Nb2TiO7 and Nb1.33Ti0.67O4 materials, though these materials exhibit stable phase transformation, Nb2TiO7 as a starting SOFC composition is not ideal due to poor electrical properties (1.35 S/cm in reducing atmosphere at 800 o C). Whereas, though Nb1.33Ti0.67O4 recorded a conductivity of 85 S/cm in reducing condition, the material is mechanically not stable under redox condition at 800 o C. In Sr2Mg1-xMo1+xO6 (x = 0, 0.1, 0.2) material system, the material with Sr2Mg0.9Mo1.1O6-δ composition was made both mechanically and electrical redox stable at 800 o C, with a CTE of 14.5x10-6 K-1 in air between 25-800 o C and electrical conduction of 0.1 S/cm in air and 17.5 S/cm in reducing atmosphere. From symmetrical cell analysis, it was analyzed that Sr2Mg0.9Mo1.1O6-δ had a low polarizat...

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“…In this case, any possible agglomeration of exsolved metallic nanoparticles on the substrate surface can be avoided by periodically exposing the material to oxidising conditions. Fluorite oxide, NbTi 0.5 Ni 0.5 O 4 (NTNO), which is a single-phase rutile-type structure with the tetragonal (P4 2 /mnm) space group, was first reported as a potential anode material for solid oxide fuel cells by Irvine et al2627. Nanoparticles of metallic Ni can be exsolved at the surface of the highly-conducting Nb 1.33 Ti 0.67 O 4 substrate after high-temperature reduction under a reducing gas.…”

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confidence: 99%

In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

Wei

Xie

Zhang

et al. 2014

Sci Rep

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In this paper, we report the in situ growth of NixCu1-x (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the NixCu1-x alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized NixCu1-x/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the NixCu1-x/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies.

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Thermomechanical and conductivity studies of doped niobium titanates as possible current collector material in the SOFC anode

Abstract: Abstract. In the reducing atmosphere of the SOFC anode at operating temperatures of 800 ~ and

Cited by 11 publications

References 6 publications

Defects and Transport Properties in TiNb₂O₇

Defects and Transport Properties in TiNb₂O₇

Redox Stable Anode Materials for SOFC Application

In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

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Thermomechanical and conductivity studies of doped niobium titanates as possible current collector material in the SOFC anode

Abstract: Abstract. In the reducing atmosphere of the SOFC anode at operating temperatures of 800 ~ and

Cited by 11 publications

References 6 publications

Defects and Transport Properties in TiNb2O7

Defects and Transport Properties in TiNb2O7

Redox Stable Anode Materials for SOFC Application

In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

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Defects and Transport Properties in TiNb₂O₇

Defects and Transport Properties in TiNb₂O₇