Methane Pulse Study on Nickel Impregnated Gadolinium Doped Ceria

Thursday, 27 July 2017: 17:20
Grand Ballroom West (The Diplomat Beach Resort)
M. Ouyang, P. Boldrin, and N. P. Brandon (Imperial College London)
Nickel/gadolinium doped ceria (Ni/CGO) has been a popular SOFC anode material for decades for its superior mix conductivity and excellent oxygen storage capacity. However, the study of Ni/CGO in a realistic working condition is still lacking. Also, not much research has linked the chemical properties of CGO with the carbon resistance which is essential when using hydrocarbon as fuels.

In this research, Ni/CGO powder was prepared via impregnation-calcination method. A novel pulse experiment has been conducted on impregnated powder. We did certain pulses of a fixed amount of methane into the sample at 600℃.The outlet gas composition was monitored by a quadrupole mass spectrometer.

The product gas was composed of several species including hydrogen, steam, carbon monoxide, carbon dioxide, and methane that was not participated to the reaction.

The major reaction was the partial oxidation of methane that produced carbon monoxide and hydrogen. With the increase of pulsing numbers, the product and shape of product peaks changed a lot. Also, we observed a “tail” after each carbon monoxide production peak which extend with the number of pulsing. This was deduced to be caused by the self-oxidation of carbon by the bulk migrated oxygen. These changes revealed the changing of CGO during methane oxidation.

After detailed quantitative analysis of the shape and integrated intensity of the peaks and tails. We confirmed that the majority of methane partial oxidation reaction on Ni/CGO follows a deposition-oxidation route rather than direct oxidation of methane. Also we were able to evaluate the ability of carbon self-oxidation with different ceria oxidation state. Consequently, a model was proposed to elucidate the relation between carbon self-oxidation rate, surface oxygen concentration and bulk oxygen migration rate of CGO, in forms of partial differential equation.

In-situ Raman spectroscopy was performed during the pulse experiment to give a direct parallel evidence. We observed the change of CGO surface oxygen stoichiometry and deposited carbon. Thus we can confirm the conclusion deduced by pulse experiments to prove its validation, and directly relate the carbon self-oxidation rate with bulk oxygen migration rate of CGO.

The results provided a novel yet facile method to evaluate the oxygen storage properties of materials and gave an insight into the design and modification of ceria based SOFC anode materials.