Biosyngas Utilization in Solid Oxide Fuel Cells With Ni∕GDC Anodes

Electrochem. Solid-State Lett.

Ouweltjes

Woudstra

et al. 2008

Self Cite

The impact of biomass-derived contaminants on solid-oxide fuel cells ͑SOFCs͒ with Ni/gadolinia-doped ceria ͑GDC͒ anodes was investigated using electrochemical impedance analysis. Measurements were carried out with symmetric test cells under a singlegas atmosphere. The impact of H 2 S, HCl, and naphthalene in the gas stream on the performance of Ni/GDC anodes are presented. No significant impact has been observed up to 9 ppm H 2 S and HCl and 110 ppm naphthalene. © 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2820452͔ All rights reserved. Gasification is the conversion of biomass to a gaseous fuel by heating in a gasification medium such as air, oxygen, or steam. Biosyngas from gasification consists of a mixture of carbon monoxide, carbon dioxide, methane, hydrogen, water vapor, and impurities. These impurities are mainly ͑i͒ particulate matter, ͑ii͒ tar, ͑iii͒ alkali metal compounds and other halides, ͑iv͒ sulfur compounds, and ͑v͒ nitrogen-containing compounds, especially ammonia. Once the biosyngas is cleaned to remove the contaminants to a level sufficient for solid oxide fuel cells ͑SOFCs͒, it can probably be used as an SOFC fuel.1,2 As the biomass is a sustainable primary energy source and is essentially CO 2 neutral, such systems offer the potential for sustainable high-efficiency energy systems for the future.Feeding SOFCs with biosyngas draws attention to many important issues. Because the fuel gets oxidized at the SOFC anode, chemical and physical interactions between the anode and the gas components are of critical significance. Different types of anodes have different kinds of interactions with these contaminants, and hence their tolerance levels for these contaminants may vary considerably. This, in turn, alters the choices for the required gascleaning devices when SOFCs with such anodes are connected to biomass gasifiers. Because these different types of anodes may have varying effectiveness in the conversion of the fuel, proper selection of the SOFCs with suitable anodes and gas-cleaning systems and appropriate operation parameters for them is of critical significance in the development of feasible and efficient designs of biomass gasifier-SOFC systems.Conventional SOFC anodes contain substantial amounts of nickel. Nickel is widely considered as an attractive material for SOFC anodes because it is a good electronic conductor and catalytically active for the electrochemical oxidation of hydrogen. In order to increase the mechanical properties, nickel is mixed with an ionconducting material, most commonly yttria-stabilized zirconia ͑YSZ͒. Doped ceria, such as gadolinia-or samaria-doped ceria, is a mixed conductor under reducing conditions. It offers increased surface area for electrochemical reactions, unlike materials offering mainly ionic conductivity and low electronic conductivity, which limit the reactions to fuel/electrode/electrolyte boundaries. They are also expected to give better performance with fuels containing hydrocarbons.3 For this reason, anodes comprising gadolinia-doped ceria ͑...

Section: B26supporting

confidence: 82%

Impact of Biomass-Derived Contaminants on SOFCs with Ni/Gadolinia-Doped Ceria Anodes

Electrochem. Solid-State Lett.

Ouweltjes

Woudstra

et al. 2008

Self Cite

“…[1][2][3][4][5][6][7][8][9] The objective of the work reported in this paper is to evaluate the impedance spectra recorded on symmetrical test cells with nickel/ gadolinia-doped ceria ͑Ni/GDC͒ electrodes to understand the influence of gas-phase processes on electrode performance. It is intended that once the arcs due to gas-phase processes in the spectra are identified, the rest of the spectra can be analyzed to study the influence of fuel gas composition or contaminants present in it on the electrode.…”

mentioning

confidence: 99%

Diffusion Impedance on Nickel/Gadolinia-Doped Ceria Anodes for Solid Oxide Fuel Cells

Ouweltjes

Schoonman

2009

J. Electrochem. Soc.

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Electrochemical impedance measurements were carried out on symmetrical nickel/gadolinia-doped ceria test cells. For H 2 , N 2 , and H 2 O mixtures, the diffusion length obtained based on the impedance measurements is on the order of centimeters. This high value of the diffusion length is attributed to the flow field in the reactor. It is suggested that a detailed analysis of the gas flow field inside the test reactor is essential before interpreting the impedance measurements with various solid oxide fuel cell test configurations. Electrochemical impedance spectroscopy ͑EIS͒ for evaluating the performance of solid oxide fuel cell ͑SOFC͒ anodes with different fuels with and without contaminants has been reported before. [1][2][3][4][5][6][7][8][9] The objective of the work reported in this paper is to evaluate the impedance spectra recorded on symmetrical test cells with nickel/ gadolinia-doped ceria ͑Ni/GDC͒ electrodes to understand the influence of gas-phase processes on electrode performance. It is intended that once the arcs due to gas-phase processes in the spectra are identified, the rest of the spectra can be analyzed to study the influence of fuel gas composition or contaminants present in it on the electrode. Studies on gas-phase processes at SOFC anodes have been reported. 1,6,[10][11][12][13] Primdahl and Mogensen studied gas-phase processes with complete cells having reference electrodes mounted in a two-gas atmosphere and symmetrical test cells kept under a single gas atmosphere. For an anode of a test cell consisting of a working electrode, a counter electrode, and a reference electrode, an arc that appeared in the low frequency part of the spectra was ascribed to gas conversion.6 It was also proposed that an arc that appeared at the medium frequency part of the spectra ͑10-100 Hz͒ was due to gas diffusion limitations. Gas conversion impedance was not reported with the measurements on symmetrical cells under a single gas atmosphere. Bessler developed a numerical model for the impedance due to combined gas-flow limitations ͑diffusion, convection, etc.͒ for a similar gas-flow scheme as used by Primdahl ͑for an anode as part of a complete cell with a reference electrode͒ and he concluded that in such a setup, the diffusion, convection, etc., have a combined effect and have to be treated together. 10 Bessler proposed the name "gas concentration impedance" to describe the impedance due to transport processes in the gas phase and suggested using the name "gas diffusion impedance" when the mass transport is only due to diffusion.Gewies et al. used Ni/yttria-stabilized zirconia ͑YSZ͒ symmetrical electrodes and Aravind used Ni/GDC symmetrical electrodes to carry out EIS measurements under a single gas atmosphere.1,9 The observation of an arc at the low frequencies due to diffusion limitations was reported in both cases. Aravind, with a simple diffusion resistance model, and Gewies et al., with detailed kinetic modeling, showed rather high diffusion lengths on the order of centimeters. This paper presents the...

“…No relevant data is available about stack performance using biosyngas. Some reports on cell performance using bio-syngas are available [1,19]. Based on these reports, data necessary for system calculations have been assumed.…”

Section: Solid Oxide Fuel Cell Systemmentioning

confidence: 99%

System Study on Hydrothermal Gasification Combined With a Hybrid Solid Oxide Fuel Cell Gas Turbine

Toonssen

Smit³

et al. 2010

Fuel Cells

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The application of wet biomass in energy conversion systems is challenging, since in most conventional systems the biomass has to be dried. Drying can be very energy intensive especially when the biomass has a moisture content above 50 wt.% on a wet basis. The combination of hydrothermal biomass gasification and a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system could be an efficient way to convert very wet biomass into electricity. Therefore, thermodynamic evaluation of combined systems with hydrothermal gasification units and SOFC–GT hybrid units has been performed. Three hydrothermal gasification cases have been evaluated; one producing mainly methane, a second one producing a mixture of hydrogen and methane and the last one producing mainly hydrogen. These three gasification systems have been coupled to the same SOFC–GT hybrid system. All the integrated systems have electrical exergy efficiencies around 50%, therefore, the combination of supercritical water gasification and SOFC–GT hybrid systems seems promising. The overall system performance depends for a large part on the liquid gas separation. Further research is required for finding out the optimal separation conditions.