Yongjian Wang

Abstract For hydrogen generation from alkaline sodium borohydride (NaBH 4 ) solution, Co–Fe–B catalysts with different Co/(Co + Fe) molar ratios (χ Co ) were prepared by the chemical reduction of CoCl 2 and FeCl 3 ethanol solution with KBH 4 solution. The X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the as‐prepared Co–Fe–B catalysts were in amorphous form and ultrafine. The hydrogen generation measurements showed that as‐prepared Co–B and Co–Fe–B catalysts exhibited excellent catalytic activity. Co–Fe–B with the Co/(Co + Fe) molar ratio (χ Co ) of 0.85 was the best. Its maximum hydrogen generation rate at 298 K was 4,310 mL min –1 g –1 , while the Co–B was 2,773 mL min –1 g –1 . The enhanced activity could be attributed to large active surface area, electron transfer from B and Fe to active Co sites, and improvement in the dispersion of Co–B with Fe 2 O 3 . The activation energy of Co–Fe–B catalyst with the molar ratio χ Co = 0.85 was decreased to 29.09 kJ mol –1 as compared to 30.85 kJ mol –1 obtained with Co–B.

Polymer coatings in actual use are subject to wear and tear. In this experiment, we look into the dewetting instability of more realistic polymer coatings wherein topographical fluctuations pre-existed. The topographical defects, produced by rubbing the film surface with a piled fabric, could be varied for the density by changing the number of rubbings, N. First, the dewetting mechanism was determined by comparing the dewetting morphology between the unrubbed and rubbed films. Nucleation dewetting was ascribed to samples wherein the characteristic wave vector, q*, of the final dewetted morphology increased with increasing N, whereas spinodal dewetting was ascribed to samples wherein q* was affected little. Second, the evolution of dewetting was compared between the unrubbed and rubbed films. Our result shows that perturbations from rubbing do not produce changes in the free energy of the films that will alter the prevailing dewetting mechanism or the characteristic wave vector in spinodal dewetting. Nonetheless, the rubbing-induced defects do affect the rupturing process, in manners depending on the dominating dewetting mechanisms.