Impact of synthesis temperature on hydrogen storage and emission from Ni/Ce composite oxides

摘要

Hydrogen storage and emission from Ni/Ce (0.1:1) composite oxides, prepared by the co-precipitation method at -2 ℃, 22 ℃ and 60 ℃ using triethylamine as the precipitating agent, are investigated. The as-prepared uncalcined materials exhibit small amounts of H_2 emission even without prior exposure to H_2, with the amount dependent on the synthesis temperature. Examination of the CO, CO_2 and H_2O emission profiles suggest a link between the presence and stability of carbonate species within these composite materials and the H_2 emission. Following activation in pure hydrogen at 250 ℃, all samples show increased H_2 emission levels but it is only in the sample synthesised at 60 ℃ that a simultaneous decrease in the H_2 emission temperature is found. H_2O emission below 250 ℃ in the activated material indicates that this also originates from hydrogen stored in the material. The activation conditions are shown to have a significant impact on the level of H_2 interaction with these materials. A marked increase of the crystallite size with synthesis temperature, from 1.7 nm at -2 ℃ to 11.7 nm at 60 ℃, is also found. The difference in of H_2 interaction is associated with a change in the nature/morphology of the materials precipitated at the different temperatures.