Experimental Investigation of Carbon Deposition on a Ni/YSZ Anode of Solid Oxide Fuel Cell

Solid Oxide Fuel Cell (SOFC) is a promising energy conversion device with high efficiency and low emissions. Nickel-doped yttria-stabilized zirconia (Ni-YSZ) is the most commonly used material for anode of SOFC. However, a major concern with Ni-based anode is carbon deposition when SOFC is operated by hydrocarbon fuels. The deposited carbons on the surface of catalysts affect the activity of catalysts and the flow of gas through the anode. The carbon formation has to be effectively controlled in the operation of SOFC before the hydrocarbon fuels, such as natural gas, biogas, etc., are widely used in SOFC [1-2].

Methane cracking and CO disproportionation (Boudouard reaction) are the main reactions causing carbon deposition. The methane cracking reaction has been intensely studied by researchers in both kinetic models of simulations and experiments [3-5].There has also been efforts to observe the CO disproportionation reaction at temperatures from 773 to 848K [6]. Mostly, these work are applied to the operating temperatures below 600℃, which are not applicable to the operating conditions of SOFC.

In this work, experiments are carried out to study the carbon deposition from the methane cracking and CO disproportionation reaction over a Ni/YSZ catalyst. The carbon deposition experiments for the anode samples exposed to CH₄+H₂ and CO+CO₂gas mixtures with different gas compositions are conducted separately. The steady-state rates for carbon deposition by methane cracking and CO disproportionation are measured at different temperatures between 873K and 1073K, which is the typical operating temperatures of SOFC. Based on the experimental data, the kinetic models for both methane cracking and CO diaproportionation are established for the operating environments of SOFC. Microstructures of the carbon deposits in the anode samples are examined by a Hitachi 7800F field emission scanning electron microscope (FE-SEM) and an energy dispersive X-ray spectrometer (EDS).

Acknowledgements:

This work is financially supported by Projects from National Nature Science Foundation of China No. 51276145.

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