In Situ Optical Studies of Oxidation Kinetics of Ni/YSZ Cermet Anodes

摘要

Vibrational Raman spectroscopy was used to monitor directly and in situ the kinetics of nickel particle surface oxidation and reduction at 715°C and 550°C. Reduction with hydrogen happens in a matter of seconds, but surface oxidation requires 5-10 minutes to reach an asymptotic limit. Ni oxidation kinetics are explored for samples prepared with three different Ni particle sizes (5-20 nm, 2-3 μm, and 3-7 μm). Data show that initial particle size is not a significant factor in controlling the pseudo-first order oxidation rates. Furthermore, water vapor by itself does not appear to oxidize the Ni particles in contrast to reports. However, humitidity does affect the susceptibility of Ni to subsequent oxidation when the H_2O(g) is replaced with O_2(g). Following exposure to water, Ni oxidation appears to follow two separate 1st order kinetic processes. This effect occurs only for the first oxidation cycle following exposure to water.