dc.description.abstract | Amorphous CoB catalyst was prepared by cobalt acetate using sodium borohydride as the reducing agent in this research. The main reaction was hydrolysis of sodium borohydride solution. Different additives were added into CoB to modify its physical and chemical properties in favor of better hydrogen generation rate. The series of modified CoB catalysts were characterized by X-ray diffraction (XRD), BET (Brunauer-Emmett-Teller), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS).
The catalytic activity of CoB (2230 ml/min•g) was higher than NiB (140 ml/min•g) catalyst. Comparing with a series of NiCoB catalysts, which contained different doping ratio of Co, it was obvious that Co played an important role as an active site in this reaction. With increasing Co content, hydrogen generation rate increased as well. Adding Ni would decrease Co content of CoB causing negative effect.
Modified by Mo and W, not only metallic Co content but also surface area of CoB increased. Both Mo and W transferred partial electron to Co. Oxides of Mo and W provided good dispersion effect, so the probability of aggregation could be reduced. As a result, the activity of MoCoB and WCoB were 5050 ml/min•g and 5464 ml/min•g, respectively, more than double the activity of CoB.
Among different doping ratio of additives, the optimum molar ratio for MoCoB and WCoB was 0.05:1:3 and 1:1:3, respectively. CoB was sensitive for doping of Mo. The activity of MoCoB (0.01:1:3) was closer to the activity of CoB due to its lower Mo content. Increasing Mo content would decrease metallic Co. The decrease in the surface area was observed owing to the cover of active sites by the additive; metallic Co did not significantly increase by adding more W. But the remarkable increase in the surface area observed was due to the smaller particle size of the nanoalloys. However, excess W still covered many active sites, directly caused reduction of activity.
Based on this research, using MoCoB or WCoB as a core catalyst, a continuous hydrogen generator can be designed. This module was sufficient for 15W portable fuel cell.
Key words: Sodium borohydride, hydrogen generation, amorphous catalyst, Co, Mo, W | en_US |