Nickel agglomeration in solid oxide fuel cells: The influence of temperature

Ni/CG40-cermet anodes with two different ratios of nickel and ceria-gadolinia-oxide were exposed to seven different reduction temperatures between 555 °C and 1140 °C. For each reduction temperature one sample was analysed by scanning electron microscopy. The continuous particle size distributions were determined from the images. Significant nickel particle growth occurred above a reduction temperature of 850 °C for both anodes. The T-dependent nickel particle growth in the range of several initial particle radii could be fitted well with an Arrhenius type equation. However, no clear trend was obtained for the activation energy of the nickel agglomeration as a function of the initial particle sizes and the Ni/CG40 ratio. This lack of systematic trend may indicate competing material transport mechanisms such as diffusion and/or evaporation/condensation.For Ni/CG40 anodes with higher metallic content, nickel agglomeration was more pronounced for reduction temperatures above 950 °C. Besides the nickel, the ceria-gadolinia-oxide showed an increase in particle size at reduction temperatures above 950 °C as well.