The internal reforming of methane on Ni/CGO and Ni/YSZ anodes was investigated with single cells operated at steam to carbon ratios from 0 to 3 and at temperatures of 800 °C and 950 °C. The incorporation of gas extraction ports allowed the measurement of the local gas composition in the anode gas compartment by gas chromatography. The methane conversion is presented as a function of feed gas composition, temperature, gas flow velocity, and electrical load. The impact of the anode material on the reforming reaction and on cell performance is shown. Methane conversion along the Ni/CGO anode was calculated with a one‐dimensional model; the required kinetic parameters were obtained by data fitting.
The influence of hydrocarbon-containing fuel gases on cell performance and coke formation is investigated in this work, wherein acetylene is applied as a model compound for the coke formation. The dependence of coke yield on acetylene amount ͑volume fraction of 0.05-0.50%͒ and gas composition is analyzed. Further parameters which are varied are temperature ͑650-850°C͒ and operation time. It is shown that the mass of coke that is formed on the cell depends strongly on acetylene volume fraction and temperature. As a consequence, acetylene has a severe influence on the electrical cell performance, and acetylene concentration and temperature can be correlated to degradation effects.
Anodes for stationary SOFC systems are most likely to be operated with natural gas at temperatures above 800 °C, whereas mobile SOFC applications such as APUs (auxiliary power units) operated below 800 °C use (liquid) hydrocarbons. The fuel (gasoline or diesel) cannot be converted by 100% in the reformer and so a reformate containing higher hydrocarbons has to be converted at the anode. In operation with hydrocarbons, at high fuel utilization or at sequential redox cycles, the nickel catalyst is subject to various degradation processes. The dominating process depends on the anodic oxygen partial pressure applied and possibly deteriorates the electrochemical performance of the anode.
Sequential cyclic reduction and oxidation (redox) can quickly lead to an aging of the anode or even a complete failure of the cell (fracture of the thin film electrolyte). In operation with hydrocarbons, i.e., at low oxygen partial pressures, degradation ranging from (i) reversible damage by occupancy of the Ni catalyst surface with various deposits to (ii) irreversible damage to the Ni catalyst by carbon whisker growth occurs.
Moreover, the kinetics of methane conversion under various operating conditions, the carbon formation in the presence of higher hydrocarbons (acetylene), and the analysis of electro‐oxidation and gas diffusion in stable operation with hydrogen or biomass‐derived gas are also treated in this article.
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