Fuel cells, including solid-oxide fuel cells (SOFC) are highly efficient electrochemical devices that directly convert the chemical energy of a fuel into electricity. Conventional Ni/YSZ SOFC anodes work well with hydrogen but require modification to tolerate other fuels and not accumulate carbon, which degrades cell performance and eventually damages the anode microstructure. Our group has studied the carbon formation on Ni/YSZ anodes under a variety of conditions with different temperatures, current densities, fuels, humidification levels and cell configurations. Our understanding has been enhanced by a variety of characterization and analysis techniques including in situ Raman spectroscopy. Through this technique we have confirmed that H2O is the best compound (compared to O2 or CO2) to use to regenerate a coked anode in terms of removal efficiency and minimal NiO formation. We have also shown that barium oxide (BaO) reduces carbon accumulation on Ni/YSZ anodes operated with methane but is less beneficial with reformate fuels. Traditional methods of preparing these anodes (in particular, impregnation) are not ideal because the Ba diffuses into the YSZ structure over time causing a morphological change and volume expansion of YSZ, which is problematic in this solid device. We have developed an alternative method using microwave irradiation to selectively deposit BaO onto Ni. The role of BaO has been debated. Our experiments suggest that BaO blocks sites on the Ni, preventing the formation of coke, and also enhances carbon removal, possibly by providing additional sites for H2O adsorption. The formation, characterization, removal, and avoidance of carbon accumulation on Ni/YSZ solid-oxide fuel cells will be discussed in this presentation.

Formation, characterization, removal, and avoidance of carbon on Ni/YSZ solid-oxide fuel cells

247th National Meeting (2014)

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