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

Hydrogen storage and emission from Ni/Ce (0.1:1) composite oxides, prepared by the co-precipitation method at -2 °C, 22 °C and 60 °C using triethylamine as the precipitating agent, are investigated. The as-prepared uncalcined materials exhibit small amounts of H₂ emission even without prior exposure to H₂, with the amount dependent on the synthesis temperature. Examination of the CO, CO₂ and H₂O emission profiles suggest a link between the presence and stability of carbonate species within these composite materials and the H₂ emission. Following activation in pure hydrogen at 250 °C, all samples show increased H₂ emission levels but it is only in the sample synthesised at 60 °C that a simultaneous decrease in the H₂ emission temperature is found. H₂O emission below 250 °C 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 H₂ interaction with these materials. A marked increase of the crystallite size with synthesis temperature, from 1.7 nm at -2 °C to 11.7 nm at 60 °C, is also found. The difference in of H₂ interaction is associated with a change in the nature/morphology of the materials precipitated at the different temperatures.