Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies
Solid oxide fuel cells (SOFCs) are environmentally clean, high efficiency devices that operate at >600°C. Present-day SOFCs consist of Ni-based anodes, 8% yttria stabilized zirconia (YSZ) electrolytes, and manganite-based cathodes. The large-scale commercialization of SOFCs is hindered by several...
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University of Calgary
2007
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oai:192.168.1.90:123456789-12142022-03-28T10:19:24Z Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies Keech, Peter George Hydrogen oxidation Solid oxide fuel cells Solid oxide fuel cells (SOFCs) are environmentally clean, high efficiency devices that operate at >600°C. Present-day SOFCs consist of Ni-based anodes, 8% yttria stabilized zirconia (YSZ) electrolytes, and manganite-based cathodes. The large-scale commercialization of SOFCs is hindered by several factors, including anode and cathode performance. This work has focused on the kinetics and mechanism of hydrogen oxidation and water reduction at Ni-based anodes and at Pt, for comparative purposes. The electrochemical methods used to obtain this information were developed first at single phase Pt and Ni, and then applied later to all other electrode materials. Experiments were carried out using a three-electrode half-cell at 750-950°C (typically at 800°C) in 97:3 H2:H2O. Using the low-field, high-field and Allen-Hickling approximations, as well impedance spectroscopy, the exchange current density (io ), the activation energy (130 kJ/mol), and the anodic and cathodic transfer coefficients were determined. In general, the rate determining step of H2 oxidation at Ni was found to be the second electron transfer step, while water reduction is significantly slower, with the first step being the slowest. While the anodic transfer coefficient at Ni is larger than at Pt, the io values cannot be compared as the reactive areas remain unknown. Therefore, Ni point electrodes, pressed against a YSZ disc, were examined to correlate the io values with the known electrode perimeter. Unfortunately, the Ni/YSZ contact region was found to be porous, so that the true area remained unknown. Efforts to use coke deposition as a means of identifying the active anode area also proved to be unsuccessful. In order to increase anode performance, high surface area NiO and YSZ sol¬derived (SD) materials were studied. Compared to ceramic grade, micron-sized NiO and YSZ, deposited using the same methods, the SD materials are very promising, being 40 to 50 times more active. A new method to establish the NiO-YSZ electrode porosity, involving monitoring the Ni2+/3+ oxide redox response in aqueous alkaline solutions was developed. As long as the sweep rate was sufficiently slow, a good correlation between the measured redox charge and the amount of NiO in the composite electrodes was seen. 2007-12-05T02:17:37Z 2007-12-05T02:17:37Z 2006 Thesis http://ir.vnulib.edu.vn/handle/123456789/1214 en_US Doctor of Philosophy application/pdf University of Calgary |
| institution |
Đại học Quốc Gia Hồ Chí Minh |
| collection |
DSpace |
| language |
en_US |
| topic |
Hydrogen oxidation Solid oxide fuel cells |
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Hydrogen oxidation Solid oxide fuel cells Keech, Peter George Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| description |
Solid oxide fuel cells (SOFCs) are environmentally clean, high efficiency devices that operate at >600°C. Present-day SOFCs consist of Ni-based anodes, 8% yttria stabilized zirconia (YSZ) electrolytes, and manganite-based cathodes. The large-scale commercialization of SOFCs is hindered by several factors, including anode and cathode performance. This work has focused on the kinetics and mechanism of hydrogen oxidation and water reduction at Ni-based anodes and at Pt, for comparative purposes.
The electrochemical methods used to obtain this information were developed first at single phase Pt and Ni, and then applied later to all other electrode materials. Experiments were carried out using a three-electrode half-cell at 750-950°C (typically at 800°C) in 97:3 H2:H2O. Using the low-field, high-field and Allen-Hickling approximations, as well impedance spectroscopy, the exchange current density (io ), the activation energy (130 kJ/mol), and the anodic and cathodic transfer coefficients were determined. In general, the rate determining step of H2 oxidation at Ni was found to be the second electron transfer step, while water reduction is significantly slower, with the first step being the slowest.
While the anodic transfer coefficient at Ni is larger than at Pt, the io values cannot be compared as the reactive areas remain unknown. Therefore, Ni point electrodes, pressed against a YSZ disc, were examined to correlate the io values with the known electrode perimeter. Unfortunately, the Ni/YSZ contact region was found to be porous, so that the true area remained unknown. Efforts to use coke deposition as a means of identifying the active anode area also proved to be unsuccessful.
In order to increase anode performance, high surface area NiO and YSZ sol¬derived (SD) materials were studied. Compared to ceramic grade, micron-sized NiO and YSZ, deposited using the same methods, the SD materials are very promising, being 40 to 50 times more active.
A new method to establish the NiO-YSZ electrode porosity, involving monitoring the Ni2+/3+ oxide redox response in aqueous alkaline solutions was developed. As long as the sweep rate was sufficiently slow, a good correlation between the measured redox charge and the amount of NiO in the composite electrodes was seen. |
| format |
Thesis |
| author |
Keech, Peter George |
| author_facet |
Keech, Peter George |
| author_sort |
Keech, Peter George |
| title |
Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| title_short |
Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| title_full |
Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| title_fullStr |
Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| title_full_unstemmed |
Hydrogen oxidation at solid oxide fuel cell anodes: Mechanistic, kinetic and structural studies |
| title_sort |
hydrogen oxidation at solid oxide fuel cell anodes: mechanistic, kinetic and structural studies |
| publisher |
University of Calgary |
| publishDate |
2007 |
| url |
http://ir.vnulib.edu.vn/handle/123456789/1214 |
| work_keys_str_mv |
AT keechpetergeorge hydrogenoxidationatsolidoxidefuelcellanodesmechanistickineticandstructuralstudies |
| _version_ |
1749008523859066880 |