1 research outputs found
Tailor-made preparation of Co–C, Co–B, and Co catalytic thin films using magnetron sputtering: insights into structure–composition and activation effects for catalyzed NaBH4 hydrolysis
The magnetron sputtering (MS) methodology is a powerful tool for tailor-made fabrication of Co-based thin
film catalysts with controlled microstructures and compositions for sodium borohydride (SBH) hydrolysis. In
particular, Co–C catalysts were tested in this reaction and compared to Co–B and Co catalyst coatings. The
microstructural and chemical analyses by X-ray diffraction (XRD), scanning and transmission electron
microscopy (SEM and TEM), Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy
(XPS) were used to characterize a complete library of thin film catalysts. Pure Co materials were
characterized by their nanocrystalline microstructure, and grain refinement was achieved via an increase
in the deposition pressure. The incorporation of boron or carbon via co-deposition results in
amorphization and dispersion of the active metallic Co phase. The composition can be tuned while
keeping a controlled microstructure, and a comparison of activity at 25 C was performed on catalysts
deposited on Ni foam substrates. A comparison of the initial activities showed that the Co–B samples
were more active than the Co–C samples because of electronic effects. However, a strong activation
was found for the Co–C catalysts after the first use. This effect was dependent upon the incorporation
of cobalt boride (CoxB) species on the catalysts' surface, as shown by XPS. After the first several uses, the
activity of the Co–C samples (values up to 2495 mL min 1 gcatalyst
1) were as high as that of fresh Co–B,
and the surface composition of both the catalysts was similar. This activation was not observed for the
pure Co and was very weak for the Co–B catalysts. The use of polymeric (PTFE) substrates (flexible
membranes) illustrated the versatility of the methodology to obtain catalytic membranes and allowed for
a TEM microstructural analysis at the nanoscale. Catalytic activities at 60 C were as high as 16.7 and
20 L min 1 gCo
1 for the Co–C and Co–B membranes, respectively. We determined the optimized
conditions to increase the catalytic activity of Co-based coatings prepared via magnetron sputtering.Peer reviewe