In-situ diagnosis and assessment of longitudinal current variation by electrode-segmentation method in anode-supported microtubular solid oxide fuel cells

Aydın, Özgür; Koshiyama, Takahiro; Nakajima, Hironori

doi:10.1016/j.jpowsour.2014.12.156

Cited by 29 publications

(36 citation statements)

References 17 publications

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“…However, we are aware of the fact that the Nernst-loss in the realistic fuel flow conditions is significant. 12 Therefore, we will analyze the impacts of both temperature variations and Nernst-loss on the current variations under the realistic conditions in the following. Fig.…”

Section: Resultsmentioning

confidence: 99%

“…By analyzing the longitudinal variation of these local properties, we can elaborate the concerning physical and electrochemical processes, such as ionic conductivity, kinetic limitations, and mass transport limitation, etc. 12,13 We call this spatial characterization method "segmentation". Especially in polymer electrode membrane fuel cells, the segmentation is usually realized on the gas distribution plates due to practical restrictions.…”

Section: Methodsmentioning

confidence: 99%

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Processes Involving in the Temperature Variations in Solid Oxide Fuel Cells In-Situ Analyzed through Electrode-Segmentation Method

Aydın

Nakajima

2015

J. Electrochem. Soc.

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We aim to mitigate the spatial temperature variations contributing to the thermal stresses in solid oxide fuel cells. We thus analyze the involving processes through spatial temperature, current, and impedance variations in-situ measured by the electrode-segmentation method in a microtubular solid oxide. We find that, despite the preheating, the excess air flow commonly supplied in the practical applications for the convective cooling is the prevailing factor on the temperature variations causing a significant temperature gradient in the air inlet region, that poses a high risk of mechanical failure. In terms of the flow configuration, counter-flow shows larger temperature and current variations. The impedance variations clarify the impact of the temperature distribution on the current variations. Namely, high temperature in the fuel upstream accompanied with the high hydrogen concentration boosts the local current density, thus, results in larger Nernst-loss in the downstream wherein temperature is lower as well. We conclude that the excess air flow indirectly contributes to the thermal stresses and thus we recommend the reduction of the excess flow. The thermal stresses are accounted for the mechanical failure of solid oxide fuel cells (SOFC).1-3 To resist the thermal stresses at maximum achievable electrochemical performance, SOFCs are designed in various forms, for instance flat-tubular, tubular, and planar, etc. For in-situ investigating the properties spatially varying regardless of the SOFC form, microtubular SOFCs (mt-SOFCs) are quite practical owing to the simple form. Besides, a mt-SOFC with a small diameter can represent a unit gas flow channel in other forms. We thus elaborate the temperature, current, and concentration variations in mt-SOFCs.A mt-SOFC fundamentally consists of three main components, anode, electrolyte, and cathode. The cell fabrication requires sequential high temperature heat-treatment processes (1473-1673 K) for each component, thus, the induction of the residual stresses to the cell is inevitable.1,2,4,5 Because the components are made of distinct ceramicbased materials, they possess diverse intrinsic coefficients of thermal expansion (CTE). Selimovic et al. reports the CTEs of Ni/YSZ, 8YSZ, and LSM as 13 × 10 −6 , 10 × 10 −6 , 11 × 10 −6 1/K, respectively. The CTE and temperature are the main parameters determining the thermal strain of materials as Eq. 1 stateswhere ε th is the thermal strain, α (1/K) the CTE, T (K) temperature, and T ref (K) the stress-free reference temperature. According to Eq. 1, even a small difference among the CTEs of the components can result in thermal stresses due to the high operation temperature of mtSOFCs. 1,2,4,6,7 The cell components are hence required to be made of materials featuring similar CTEs. Even if the materials exhibit similar CTEs, longitudinal temperature variations over the cell surface induce thermal stresses.1-4,6-9 While a cell is operating with hydrogen and -excess air-, due to the electrochemical hydrogen oxidation reaction (HOR...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Processes Involving in the Temperature Variations in Solid Oxide Fuel Cells In-Situ Analyzed through Electrode-Segmentation Method

Aydın

Nakajima

2015

J. Electrochem. Soc.

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“…As a result, the Nernst loss, based on Eq. (4), included in the concentration loss develops toward the downstream and this causes a remarkable performance deterioration [22,23]. On the other hand, a continuous consumption of the product H 2 O along the anode flow channel by the MSR reaction could increase the H 2 partial pressure in the downstream and thus lead to a more homogeneous current distribution.…”

Section: Introductionmentioning

confidence: 99%

“…With the electrode-segmentation method, local currents along mt-SOFCs can be in-situ measured [22,25]. Relying on the relation between the local currents and H 2 partial pressures on the regarding parts of the cell, the fuel distribution during the DIR can be evaluated by the longitudinal current variations.…”

Section: Introductionmentioning

confidence: 99%

Current and temperature distributions in-situ acquired by electrode-segmentation along a microtubular solid oxide fuel cell operating with syngas

Aydın

Nakajima

Kitahara

2015

Journal of Power Sources

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“…When the SOFC stack operates at high hydrogen utilization, the current density and/or cell voltage becomes lower at the downstream of the flow direction because the hydrogen fuel is in short supply (Aydın et al, 2015;Tseronis et al, 2008;Iwata et al, 2000). In addition, oxidation of the Ni particles in the anode cermet may occur due to oxide ions passing through the electrolyte when the fuel supply is not sufficient (Sarantaridis and Atkinson, 2007;Hatae et al, 2008;Laurencin et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Power generation characteristics of a SOFC with a Ni/YSZ anode incorporating a SrZr0.95Y0.05O3-α proton conductor

Nagasawa

Hanamura

2015

JTST

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In order to improve the performance and stability of anodes for solid oxide fuel cells (SOFCs) under low hydrogen concentration conditions, SrZr 0.95 Y 0.05 O 3-α (SZY) proton conductor particles were incorporated into the conventional Ni/YSZ anode. Power generation experiments were conducted using the electrolyte-supported single cells with conventional Ni/YSZ and Ni/YSZ-5%SZY anodes. Enhanced output power density under low hydrogen partial pressure conditions was achieved with the modified anode. This enhancement is ascribed to a decline in the anode overpotential of the Ni/YSZ-5%SZY anode, estimated from impedance spectra, compared to that of the conventional Ni/YSZ anode. In addition, the amount of hydrogen adsorption on Ni, YSZ, and SZY was measured using thermal desorption spectroscopy (TDS). This revealed that the proton conductor SZY could adsorb a large amount of hydrogen compared with YSZ. Consequently, the SZY proton conductor may play an important role in the supply/storage of adsorbed hydrogen, or in increasing the oxidation resistance of Ni under low hydrogen concentration conditions.

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In-situ diagnosis and assessment of longitudinal current variation by electrode-segmentation method in anode-supported microtubular solid oxide fuel cells

Cited by 29 publications

References 17 publications

Processes Involving in the Temperature Variations in Solid Oxide Fuel Cells In-Situ Analyzed through Electrode-Segmentation Method

Processes Involving in the Temperature Variations in Solid Oxide Fuel Cells In-Situ Analyzed through Electrode-Segmentation Method

Current and temperature distributions in-situ acquired by electrode-segmentation along a microtubular solid oxide fuel cell operating with syngas

Power generation characteristics of a SOFC with a Ni/YSZ anode incorporating a SrZr<sub>0.95</sub>Y<sub>0.05</sub>O<sub>3-α</sub> proton conductor

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