High power density solid oxide electrolyte fuel cells using Ru/Y2O3 stabilized zirconia cermet anodes

doi:10.1016/0167-2738(93)90260-A

Solid State Ionics

Volume 62, Issues 1–2, July 1993, Pages 125-130

https://doi.org/10.1016/0167-2738(93)90260-A Get rights and content

Abstract

Ru/YSZ cermet SOFC anodes were fabricated using the EVD method. Ru has high sintering resistivity compared with Ni. During the power generation tests at 1273 K the Ru/YSZ cermet anode showed high activity for hydrogen oxidation compared with conventional Ni/YSZ cermet anodes. Especially in the high current density of a maximum of 3200 mA/cm² the ac polarization value was reduced to approximately 200 mV. Tubular type SOFCs were made by depositing 10 micro m thick 10 mol% yttriastabilized zirconia (YSZ) electrolyte films on porous La(Sr)MnO_x cathode tubes using the EVD process and then making a Ru/YSZ cermet anode on YSZ. The cells had the highest power generation density with a maximum density of 1550 mW/cm². After the power generation test of approximately one week including several thermal cycles, the anode polarization was unchanged and there was no change in the Ru metal grain size.

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However, the Co/YSZ cathode would face the challenge of high cost [15]. Compared to Co/YSZ, the Ru/ZrO2 electrode shows much more advantages, such as high melting point, high activity, stable performance in SOEC operating temperature; however, Ru is much more expensive than Co element [16]. Active cermet Ni-Fe mixed with LSFM (Ni-Fe-LSFM) has been recently reported, which has demonstrated large current density (2.32 A cm−2) with coking resistance for CO2 electrolysis at 1.6 V and 1073 K [2].
To reduce greenhouse effects, reduction of CO₂ in solid oxide electrolyser has attracted considerable attentions. Herein, a series of metallic nickel cathodes with in situ grown Cr₂O_3-δ nano-islands are developed for CO₂ electrolysis at high temperature. Enhanced CO₂ chemisorption is observed with distributed Cr₂O_3-δ nanoparticles on porous nickel backbone while the adsorption mechanism is discussed. The optimal current density of 2.07 A cm⁻² is harvested when using Ni/12.20% Cr₂O_3-δ as cathode in CO₂/CO atmosphere at 800 °C and 1.6 V. Long-term stability is achieved for either CO₂/CO or pure CO₂ electrolysis even after high-temperature operation of 50 h, indicating that the Ni/Cr₂O_3-δ would be an attractive cathode for CO₂ electrolysis at high temperature.
Effects of zinc nitrate as a sintering aid on the electrochemical characteristics of Sr<inf>0.92</inf>Y<inf>0.08</inf>TiO<inf>3–δ</inf> and Sr<inf>0.92</inf>Y<inf>0.08</inf>Ti<inf>0.6</inf>Fe<inf>0.4</inf>O<inf>3–δ</inf> anodes
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Alternative anode materials for SOFCs must meet several requirements [10,11]: (i) electrocatalytic activity for hydrocarbon oxidation, (ii) suitable ionic and electronic conductivity under SOFC operating conditions, (iii) physical and chemical stability at high temperatures, (iv) compatibility with electrolytes, and (v) sulfur tolerance and carbon-coking resistance. Recently, many efforts have been devoted to developing Ni-free alternative anodes for the direct utilization of practical hydrocarbon fuels [12–18]. Although many metal-based anodes, including Cu, Co, W, Ru, and Pt, show good performance as alternative anodes, they are not appropriate for a practical utilization of commercial hydrocarbon fuels because the metal phase is easily sintered at high temperatures after long-term operation.
Although Sr_0.92Y_0.08TiO_3–δ (SYT) and Sr_0.92Y_0.08Ti_0.6Fe_0.4O_3–δ (SYTF) have been widely considered as promising materials for solid oxide fuel cell anodes, the poor densification restricts their commercial applications. As a sintering aid, zinc nitrate successfully stimulates the sintering process and improves densification. An investigation of linear shrinkage and scanning electron microscopy images indicated that the sinterability of SYT and SYTF materials was effectively improved by impregnating the green body with 5 mol% of Zn. It was found that the modification with zinc lowered the activation energy of the electrical conduction process and significantly improved the electrical conductivities of SYT and SYTF at all atmospheric conditions. The maximum power densities of the SYT and SYTF anodes were improved from 19.7 and 34.1 mW cm^–2 to 56.9 and 92.3 mW cm^–2 in H₂ and from 10.2 and 19.4 mW cm^–2 to 47.5 and 61.9 mW cm^–2 in CH₄, respectively.
Characteristics of Sr <inf>0.92</inf> Y <inf>0.08</inf> Ti <inf>1-y</inf> Ni <inf>y</inf> O <inf>3-δ</inf> anode and Ni-infiltrated Sr <inf>0.92</inf> Y <inf>0.08</inf> TiO <inf>3-δ</inf> anode using CH <inf>4</inf> fuel in solid oxide fuel cells
2018, Applied Surface Science
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Alternative anode materials for SOFCs must meet several requirements [1,12,13]; they must be (i) electro-catalytically active for oxidation of the hydrocarbon fuels, (ii) have good ionic and electronic conductivity under reducing conditions at high temperature, (iii) exhibit physical and chemical stability under the operating conditions of the SOFC, (iv) be chemically compatible with the electrolyte, and (v) be tolerant to carbon deposition and sulfur poisoning. One method of avoiding carbon deposition is by replacing Ni with other metals (Cu, Co, Pd, Ru, etc.,) that have poor catalytic activity for carbon formation [14–18,19]. Metal-based anodes, however, are still not appropriate for practical utilization with commercial hydrocarbon fuels, even though they have demonstrated excellent performance as alternative anodes.
Strontium titanium oxide co-doped with yttrium and nickel (Sr_xY_1-xTi_yNi_1-yO_3-δ; hereafter, SYTN), was investigated as an alternative anode material for solid oxide fuel cells. To improve the ionic conductivity of the Sr_0.92Y_0.08TiO_3-δ (SYT) anode, Ni²⁺ was substituted into the B-site (initially occupied by Ti⁴⁺), thereby forming oxygen vacancies. To analyze the effects of Ni-doping in the SYT anode, the electrochemical properties of the SYTN anode were compared with those of the Ni-infiltrated SYT(Ni@SYT) using H₂ and CH₄ as fuels. The electrochemical reactions at the SYTN anode in the presence of both H₂ and CH₄ were limited by relatively slow reactions, such as non-charged processes including oxygen surface exchange and solid surface diffusion. The high electrical conductivity and excellent catalytic activity of the Ni nanoparticles in the Ni@SYT anode led to improved cell performance. CH₄ decomposition at the Ni@SYT anode occurred via thermal pyrolysis of CH₄ rather than by steam methane reforming, resulting in carbon deposition. In comparison, the poor inherent catalytic activity for CH₄ oxidation exhibited by the SYTN anode minimized carbon deposition on the anode surface.
Ru-based SOFC anodes: Preparation, performance, and durability
2017, International Journal of Hydrogen Energy
Citation Excerpt :
Based on these fundamental technological considerations, the aim of this study is to consider the possibility of using an alternative Ru-based anode to replace Ni. Ruthenium-based anodes already have a significant precedent in the literature [16–30]. In the early stages of SOFC development, Ippommatsu and his colleagues [16] developed high-performance Ru-based anodes prepared via a thin film preparation technique.
Ru-based solid oxide fuel cell (SOFC) cermet anodes are presented. The preparation conditions of the Ru-based anodes are adjusted by preventing the sublimation of Ru-oxides at elevated temperatures by using an oxidizing atmosphere. SOFC single cells with zirconia-electrolyte and cathode are prepared, and the electrochemical performance is examined using realistic fuels containing low concentrations of higher hydrocarbons and trace sulfur impurities. The degradation rate is relatively high under simulated high fuel utilization operating conditions. However, under the operational condition near the fuel inlet of SOFC systems, the Ru-based anode satisfies 5000-h durability by using hydrocarbon-containing fuels. While a much higher durability is needed for stationary applications, the cells with the Ru-based anode may be applicable to e.g. automobile applications with hydrocarbon-containing fuels as high internal reforming activity, carbon deposition tolerance, and sulfur impurity tolerance have been verified.
Properties and development of Ni/YSZ as an anode material in solid oxide fuel cell: A review
2014, Renewable and Sustainable Energy Reviews
Citation Excerpt :
Platinum spalled off in service, presumably due to water vapor evolution at the metal–oxide interface. Several metals such as Fe, Co, Ni [2], Pt [3] and Ru [4] have also been studied as anode materials. Among the transition metals, iron corrodes with the formation of an iron oxide when the partial pressures of oxidation products in the anode compartment of an operating cell exceed a critical value.
In recent times, synthesis, development and fabrication of anode component of solid oxide fuel cell (SOFC) have gained a significant importance, especially after the advent of anode supported SOFC. The function of the anode electrode involves the facilitation of fuel gas diffusion, oxidation of the fuel, transport of electrons and transport of by-product of the electrochemical reaction. Although impressive progress has been made in the development of alternative anode materials with mixed conducting properties and few of the other composite cermets, Ni/YSZ continues to be the most sought after anode for high temperature SOFC applications. Despite of its poor carburization and sulfidation capabilities during the operation of SOFC directly on hydrocarbons, Ni/YSZ continues to be the most opted anode electrode material due to its high catalytic activity for hydrogen oxidation, methane reforming, high electronic and ionic conductivity and stability.
Present review focuses on the various aspects pertaining to Ni/YSZ as an anode in SOFC. Various factors that influence the ohmic, activation and the concentration polarization contribution of anode while using Ni/YSZ are discussed. Importance of optimizing the composition, microstructure and porosity to minimize the above mentioned polarizations are discussed extensively. Various synthesis methods that are used in the preparation of optimized NiO/YSZ composite powder and the methods that are adopted to fabricate anode component are provided in detail in the article. Information on Ni/YSZ anode failure and strategies to improve the long term stability are also discussed exhaustively. Parameters that influence the carburization and sulfidation of Ni/YSZ while using hydrocarbons as fuel are elaborated in this article and means to minimize the same are also discussed.
Effect of complex oxide promoters and Pd on activity and stability of Ni/YSZ (ScSZ) cermets as anode materials for IT SOFC
2008, Catalysis Today
Effect of fluorite-like or perovskite-like complex oxide promoters, Pd and Cu on the performance of Ni/8YSZ and Ni/ScCeSZ anode materials in CH₄ steam reforming (SR) or selective oxidation (SO) by O₂ into syngas was studied. The spatial distribution of dopants in composites before and after contact with the reaction feed, features of components mutual interaction and forms of deposited coke were controlled by TEM combined with EDX analysis. The lattice oxygen mobility and reactivity were estimated by CH₄ and H₂ temperature-programmed reduction (TPR), and the amount of deposited carbon after operation in the feed with stoichiometric H₂O/CH₄ ratio was estimated by the temperature-programmed oxidation. Promoters decrease the amount of deposited coke, while doping by Pd or Cu ensures also a good and stable performance at moderate (∼550 °C) temperatures required for the intermediate-temperature solid oxide fuel cells (IT SOFC) operation.

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High power density solid oxide electrolyte fuel cells using Ru/Y2O3 stabilized zirconia cermet anodes

Abstract

J. Electrochem. Soc.

Chetmech.

Denki Kagaku

High power density solid oxide electrolyte fuel cells using Ru/Y₂O₃ stabilized zirconia cermet anodes